final thesis complete with cover page - quteprints.qut.edu.au/16024/1/bradley_siddans_thesis.pdf ·...

Epoxy/Clay Nanocomposites: Effect of Clay and Resin Chemistry on Cure and Properties

Bradley Siddans B. App. Sc. (Chemistry)

A thesis presented to the School of Physical and Chemical Sciences in

partial fulfilment of the requirements for the degree of:

Master of Applied Science

Queensland University of Technology

August 2004

Supervisors:

Associate Professor Ray Frost

Professor Graeme George

Declaration of Authorship

ii

DECLARATION OF AUTHORSHIP

The work contained in this thesis has not been previously submitted for a degree or

diploma at any higher education institution. To the best of my knowledge and belief,

this thesis contains no material previously published or written by another person

except where due reference is made.

Bradley Siddans

31st August 2004

Acknowledgements

iii

ACKNOWLEDGEMENTS

Thank you to my supervisors throughout the duration of this Masters. Associate

Professor Ray Frost, who’s been with me since the start. Dr Mat Celina for his

assistance and enthusiasm. Professor Graeme George for the financial support and

help and guidance he has provided.

Thanks to Mr Tony Raftery for his assistance with XRD and Dr Thor Bostrom for his

assistance with TEM. Their efforts are greatly appreciated.

Thank you to Dr Darren Martin from UQ for helping me with the first sample of

organoclay and telling how to acquire more.

Thank you to my employer, Flexitech Pty Ltd, for allowing me some time off to work

on my Masters.

Thank you to John Colwell and Karina George for their encouragement and their time

proof reading my work.

Thank you to all postgraduate students both past and present who have helped me in

one way or another along the way.

Thank you to my family for all their help and a special thank you to Cassy for the

encouragement and patience while I spent every day and night working.

Abstract

iv

ABSTRACT

Polymer/clay nanocomposites consisting of an epoxy resin matrix filled with

organoclays have been investigated. The main objective of this study was to

determine which combination of components led to the greatest enhancement in

properties of the epoxy resin. Exfoliation of the clay was desired, as exfoliated

nanocomposites are known to exhibit great improvements in mechanical properties [1].

The epoxy resins studied were di-functional DGEBA and tetra-functional TGDDM.

The epoxy resin was cured with three different hardeners, these included: the high

functionality amine hardener, TETA, and two anhydride hardeners, accelerated

MTHPA and pure HHPA. The three organoclays used, contained alkylammonium

cations and were also compared to the unmodified clay.

Morphology was investigated by XRD and TEM, and the flexural properties of the

resulting nanocomposites were studied. The effect that the addition of an organoclay

has on the cure of the epoxy resin was investigated using MDSC. Both the

temperatures required to cure the resin with, and without, the clay, and any changes in

the total heat flow that occurred were studied. The Tg∞ of the cured nanocomposites

was also measured using MDSC.

The heat flow results indicated that the clays added to the epoxy resins act as a

physical barrier, which prevents the resin from reaching full cure. In the higher

functional resin, the addition of clay resulted in a significant decrease in the total heat

flow, suggesting that a large amount of epoxy remains uncured, and, as a result, there

should be a reduction in the amount of cross-linking. The lower cross-link density led

to a significantly lower Tg and the mechanical properties were also poorer.

The reactivity of the hardener towards the resin was found to have the greatest impact

on the cured nanocomposite morphology. Intragallery polymerisation occurring at a

faster rate than the extragallery polymerisation causes exfoliation. In order to achieve

a balance that favours intragallery polymerisation, it was found that the curing

reaction was required to be catalysed by the alkylammonium cation of the organoclay,

and not catalysed by other means. The DGEBA cured with HHPA provided the

Abstract

v

largest layer expansion in the clay structure due to the alkylammonium cation

catalysing the anhydride ring-opening reaction. The effect was not seen with

TGDDM due to the tertiary amine in its structure. The accelerator within the

MTHPA assisted extragallery polymerisation of the resin and the TETA cured readily

without additional catalysis.

List of Abbreviations

vi

LIST OF ABBREVIATIONS

DGEBA Diglycidylether of Bisphenol A

TGDDM Tetraglycidyl -4,4-diamino-diphenylmethane

DDM 4,4-diamino-diphenylmethane

EEW Epoxy Equivalent Weight

TETA Triethylenetetramine

HHPA Hexahydrophthalic Anhydride

MTHPA Methyl Tetrahydrophthalic Anhydride

Tg Glass Transition Temperature

Tc Temperature of Cure

XRD X-ray Diffraction

TEM Transmission Electron Microscopy

DSC Differential Scanning Calorimetry

MDSC Modulated Differential Scanning Calorimetry

Table of Contents

vii

TABLE OF CONTENTS

DECLARATION OF AUTHORSHIP .......................................................................ii

ACKNOWLEDGEMENTS ...................................................................................... iii

ABSTRACT.................................................................................................................iv

LIST OF ABBREVIATIONS ....................................................................................vi

TABLE OF CONTENTS ..........................................................................................vii

LIST OF FIGURES .....................................................................................................x

LIST OF TABLES .....................................................................................................xii

1 INTRODUCTION.............................................................................1

2 BACKGROUND ...............................................................................3

2.1 CLAY STRUCTURE..................................................................................3

2.1.1 Formation of Clays ...............................................................................3

2.1.2 Structure of Clays .................................................................................3

2.1.2.1 Structure of Kaolinite........................................................................5

2.1.2.2 Structure of Smectite.........................................................................6

2.1.2.3 Structure of Mica ..............................................................................7

2.1.2.4 Structure of Talc ...............................................................................7

2.2 EPOXIDES ..................................................................................................9

2.2.1 Structure of Epoxy Resins ....................................................................9

2.2.2 Molecular Weight of Epoxy Resin .....................................................11

2.2.3 Epoxy Equivalent Weight ...................................................................12

2.2.4 Curing of Epoxy Resins ......................................................................13

2.2.4.1 Aliphatic Amine Cure of Epoxy Resins..........................................14

2.2.4.2 Anhydride Cure of Epoxy Resins ...................................................15

2.2.5 Curing Process of Epoxy Resin ..........................................................17

2.2.5.1 Glass Transition Temperature.........................................................19

2.2.6 Properties of Epoxy Resins.................................................................20

2.2.7 Applications of Epoxy Resins.............................................................21

2.3 ORGANIC/INORGANIC COMPOSITES.............................................22

Table of Contents

viii

2.4 ORGANOPHILIC SUBSTITUTION .....................................................22

2.5 MODIFIED CLAY/POLYMER INTERACTION ................................23

2.6 COMPOSITES..........................................................................................24

2.7 NANOFILLERS.........................................................................................24

2.8 NANOCOMPOSITES ...............................................................................25

2.8.1 Structure of Nanocomposites..............................................................26

2.8.2 Nanocomposite production .................................................................28

2.8.2.1 Melt Intercalation............................................................................28

2.8.2.2 Solution Method..............................................................................28

2.8.2.3 In Situ Polymerisation.....................................................................29

2.9 CHARACTERISATION OF EPOXY/CLAY NANOCOMPOSITES .30

2.9.1 Mechanical Behaviour of Epoxy Nanocomposites.............................31

2.9.2 Tg of Epoxy/Clay Mineral Nanocomposites .......................................31

2.9.3 TEM of Epoxy Nanocomposites.........................................................32

3 MATERIALS AND METHODS ....................................................33

3.1 MATERIALS .............................................................................................33

3.2 METHODS .................................................................................................35

3.2.1 Preparation of Samples ........................................................................35

3.2.2 Modulated Differential Scanning Calorimetry ....................................37

3.2.3 X-Ray Diffraction ................................................................................38

3.2.4 Instron Flexural Tests ..........................................................................39

3.2.5 Transmission Electron Microscopy .....................................................39

4 RESULTS AND DISCUSSION ......................................................40

4.1 SAMPLE PRODUCTION.........................................................................40

4.2 MDSC OF NANOCOMPOSITES............................................................41

4.2.1 Heat Flow during Cure of DGEBA & MTHPA Systems ....................44

4.2.2 Heat Flow during Cure of DGEBA & HHPA Systems .......................49

4.2.3 Heat Flow during Cure of DGEBA & TETA Systems........................53

4.2.4 Heat Flow during Cure of TGDDM & MTHPA Systems ...................57

4.2.5 Heat Flow during Cure of TGDDM & HHPA Systems ......................62

Table of Contents

ix

4.2.6 Heat Flow during Cure of TGDDM & TETA Systems.......................66

4.2.7 Heat Flow during Cure of Epoxy Resin Systems ................................69

4.3 GLASS TRANSITION TEMPERATURE..............................................72

4.3.1 Tg of DGEBA & MTHPA Systems .....................................................72

4.3.2 Tg of DGEBA & HHPA Systems ........................................................74

4.3.3 Tg of DGEBA & TETA Systems .........................................................76

4.3.4 Tg of TGDDM & MTHPA Systems ....................................................78

4.3.5 Tg of TGDDM & HHPA Systems .......................................................80

4.3.6 Tg of TGDDM & TETA Systems ........................................................82

4.3.7 Glass Transition Temperature of Epoxy Resin Nanocomposites ........82

4.4 XRD OF NANOCOMPOSITES...............................................................86

4.4.1 XRD of Cloisite® Clay........................................................................86

4.4.2 XRD of Nanocomposites ....................................................................88

4.4.3 XRD of Epoxy Resins.........................................................................91

4.4.4 XRD of DGEBA.................................................................................93

4.4.4.1 XRD of DGEBA and MTHPA .......................................................96

4.4.4.2 XRD of DGEBA and HHPA ..........................................................99

4.4.4.3 XRD of DGEBA and TETA.........................................................102

4.4.5 XRD of TGDDM ..............................................................................104

4.4.5.1 XRD of TGDDM and MTHPA Nanocomposites.........................106

4.4.5.2 XRD of TGDDM and HHPA .......................................................109

4.4.5.3 XRD of TGDDM and TETA ........................................................111

4.4.6 XRD of Clay Layer Expansion in Curing Agents ............................114

4.4.7 XRD of Epoxy Resin Nanocomposites.............................................115

4.5 TEM OF EPOXY NANOCOMPOSITES ............................................119

4.6 MECHANICAL ANALYSIS OF NANOCOMPOSITES ...................122

4.6.1 Young’s Modulus of Elasticity .........................................................122

4.6.2 Flexural Strength of Epoxy Systems.................................................125

5 CONCLUSIONS ...........................................................................126

6 FUTURE RESEARCH.................................................................128

7 REFERENCES..............................................................................129

List of Figures

x

LIST OF FIGURES

Figure 2.1.2 – Crystal Structure.....................................................................................4

Figure 2.5 – Intercalation of Epoxy Resin ...................................................................23

Figure 2.8.1a – Possible Nanocomposite Structures....................................................26

Figure 2.8.1b – Intercalated Nanocomposite ...............................................................27

Figure 2.8.1c – Exfoliated Nanocomposite..................................................................27

Figure 3.2.1 – Epoxy Bar Brass Moulds......................................................................35

Figure 4.2 – Heat Flow during Cure ............................................................................42

Figure 4.2.1a – Heat Flow during Cure for DGEBA/MTHPA Systems .....................43

Figure 4.2.1b – DGEBA/MTHPA Integrated Heat Flow ............................................46

Figure 4.2.2a - Heat Flow during Cure for DGEBA/HHPA Systems .........................48

Figure 4.2.2b – DGEBA/HHPA Integrated Heat Flow ...............................................50

Figure 4.2.3a - Heat Flow during Cure for DGEBA/TETA Systems..........................52

Figure 4.2.3b – DGEBA/TETA Integrated Heat Flow................................................54

Figure 4.2.4a - Heat Flow during Cure for TGDDM/MTHPA Systems .....................56

Figure 4.2.4b – TGDDM/MTHPA Integrated Heat Flow ...........................................59

Figure 4.2.5a - Heat Flow during Cure for TGDDM/HHPA Systems ........................61

Figure 4.2.5b – TGDDM/HHPA Integrated Heat Flow ..............................................63

Figure 4.2.6b – TGDDM/TETA Integrated Heat Flow ...............................................67

Figure 4.3.1 – DGEBA/MTHPA Tg ............................................................................71

Figure 4.3.2 – DGEBA/HHPA Tg................................................................................73

Figure 4.3.3 – DGEBA/TETA Tg ................................................................................75

Figure 4.3.4 – TGDDM/MTHPA Tg............................................................................77

Figure 4.3.5 – TGDDM/HHPA Tg...............................................................................79

Figure 4.3.6 – TGDDM/TETA Tg ...............................................................................81

Figure 4.4.1 – XRD of Cloisite® Clays.......................................................................85

Figure 4.4.2 – XRD Pattern of a Nanocomposite ........................................................88

Figure 4.4.3a – XRD of Cured DGEBA Resins ..........................................................90

Figure 4.4.3b – XRD of Cured TGDDM Resins .........................................................90

Figure 4.4.4a – XRD of Cloisite® Na+ Layer Expansion in DGEBA.........................92

Figure 4.4.4c – XRD of Cloisite® 93A Layer Expansion in DGEBA ........................92

Figure 4.4.4b – XRD of Cloisite® 30B Layer Expansion in DGEBA ........................92

List of Figures

xi

Figure 4.4.4d – XRD of Cloisite® 15A Layer Expansion in DGEBA........................92

Figure 4.4.4.1 – XRD of DGEBA/MTHPA Systems ..................................................95

Figure 4.4.4.2 – XRD of DGEBA/HHPA Systems .....................................................98

Figure 4.4.4.3 – XRD of DGEBA/TETA Systems....................................................101

Figure 4.4.5a – XRD of Cloisite® Na+ Layer Expansion in TGDDM......................103

Figure 4.4.5c – XRD of Cloisite® 93A Layer Expansion in TGDDM .....................103

Figure 4.4.5b – XRD of Cloisite® 30B Layer Expansion in TGDDM .....................103

Figure 4.4.5d – XRD of Cloisite® 15A Layer Expansion in TGDDM.....................103

Figure 4.4.5.1 – XRD of TGDDM/MTHPA Systems ...............................................105

Figure 4.4.5.2 – XRD of TGDDM/HHPA Systems ..................................................108

Figure 4.4.5.3 – XRD of TGDDM/TETA Systems ...................................................110

Figure 4.4.6 – XRD of Cloisite® 30B Layer Separation in Curing Agents ..............113

Figure 4.5 – TEM images of Nanocomposites ..........................................................118

Figure 4.6.1 – Young’s Modulus of Elasticity...........................................................121

Figure 4.6.2 – Flexural Strength of Epoxy Systems ..................................................124

List of Tables

xii

LIST OF TABLES

Table 3.2.1 – Nanocomposites Prepared......................................................................36

Table 4.2.1 – Temperatures of Heat Flow for DGEBA/MTHPA................................44

Table 4.2.2 – Temperatures of Heat Flow for DGEBA/HHPA...................................49

Table 4.2.3 – Temperatures of Heat Flow for DGEBA/TETA....................................53

Table 4.2.4 – Temperatures of Heat Flow for TGDDM/MTHPA...............................57

Table 4.2.5 – Temperatures of Heat Flow for TGDDM/HHPA..................................62

Table 4.2.6 – Temperatures of Heat Flow for TGDDM/TETA...................................66

Table 4.3.1 – Tg of DGEBA/MTHPA systems............................................................72

Table 4.3.2 – Tg of DGEBA/HHPA systems...............................................................74

Table 4.3.3 – Tg of DGEBA/TETA systems................................................................76

Table 4.3.4 – Tg of TGDDM/MTHPA systems...........................................................78

Table 4.3.5 – Tg of TGDDM/HHPA systems ..............................................................80

Table 4.3.1 – Tg of TGDDM/TETA systems...............................................................82

Table 4.4.1 – Layer Spacing of Organoclays...............................................................86

Table 4.4.4 – Clay Separation in DGEBA Epoxy Resin .............................................93

Table 4.4.4.1 – Clay Separation in DGEBA/MTHPA Nanocomposites .....................96

Table 4.4.4.2 – Clay Separation in DGEBA/HHPA Nanocomposites ........................99

Table 4.4.4.3 – Clay Separation in DGEBA/TETA Nanocomposites.......................102

Table 4.4.5 – Clay Separation in TGDDM Epoxy Resin ..........................................104

Table 4.4.5.1 – Clay Separation in TGDDM/MTHPA Nanocomposites ..................106

Table 4.4.5.2 – Clay Separation in TGDDM/HHPA Nanocomposites .....................109

Table 4.4.5.3 – Clay Separation in TGDDM/TETA Nanocomposites ......................111

Table 4.4.6 – Clay Layer Expansion in Curing Agents .............................................114

Table 4.6.1 – Young’s Modulus of Elasticity for Epoxy Systems.............................122

Table 4.6.2 – Flexural Strength of Epoxy Systems ...................................................125

Chapter 1 – Introduction

1

1 INTRODUCTION

In recent years polymer/layered silicate nanocomposites have attracted great interest.

They have been shown to exhibit improvements in the material’s properties when

compared to the polymer matrix alone or to a conventional composite [2]. These

properties include high moduli [3-6], increased strength and heat resistance [7],

decreased gas permeability [8, 9], decreased flammability [10-12] and increased

biodegradability of biodegradable polymers [13].

Polymer/clay mineral nanocomposites have been studied and produced using a wide

range of polymer types. These include vinyl polymers [14-56], condensation

polymers [3-8, 32, 57-99], epoxy resins [2, 15, 85-122] and polyolefins [33, 37, 49, 123-141].

The nanocomposites produced can be classified primarily as either intercalated, where

the polymer matrix has migrated between the clay layers expanding the d-spacing, or

exfoliated/delaminated, where the clay layers have been separated completely by the

polymer matrix. It is generally accepted that exfoliated nanocomposites have the

greatest potential for property enhancements [1]. When the clay layers are separated

completely and evenly within the polymer matrix, the extent of clay/polymer

interaction is maximised. This results in the greatest enhancement of properties for

certain polymers. If, for a given polymer, the maximum property enhancement can be

achieved by an intercalated nanocomposite then the exfoliated nanocomposite of the

same polymer would not be expected to show further enhancements. The type of

nanocomposites produced depends, in part, on the polarity and viscosity of the

polymer matrix [117].

In this work a number of different epoxy resin based nanocomposites are to be

examined. The epoxy resin systems will consist of either the bi-functional

Diglycidylether of Bisphenol A (DGEBA) or the tetra-functional Tetraglycidyl -4,4-

diamino-diphenylmethane (TGDDM), which will be cured with a highly reactive

amine hardener, Triethylenetetramine (TETA), or a heat catalysed anhydride

hardener, accelerated Methyl Tetrahydrophthalic Anhydride (MTHPA) or

unaccelerated Hexahydrophthalic Anhydride (HHPA). The effect, of the relative

Chapter 1 – Introduction

2

reactivity of the hardener and the cross-linking potential of the resin on the structure

of the final nanocomposites, and any changes in the physical properties, will be

evaluated. A selection of different organoclay structures, made by organophilic

substitution of montmorillonite as well as the unmodified montmorillonite will be

used to examine the effect of the organic cation and the difference between

microscale and nanoscale interactions on the physical properties of the epoxy resin.

Nanocomposite materials are expected to be obtained from combining the various

epoxy resins with the organoclays. Furthermore, it is expected that the structure of

the nanocomposite will depend on both the curing agent used and the specific

organoclay employed. The TETA curing agent is capable of producing a greater

cross-linked density network compared to the anhydride curing agents. This is also

the case for the TGDDM compared to the DGEBA. The accelerated MTHPA is

expected to cure more readily than the pure HHPA. The organoclay is a

montmorillonite modified with either a quaternary ammonium cation or a ternary

ammonium cation and for the anhydride cured systems the presence of this cation is

known to have a catalysing effect but the mechanism is unclear [142]. In addition to

the catalysis from the ammonium cation, the clay structure contains free OH groups,

which can open the anhydride ring and start the curing reaction and are also known to

catalyse amine epoxy reactions [103]. The effect of these subtle variations will be

studied.

Chapter 2 – Background

3

2 BACKGROUND

2.1 CLAY STRUCTURE

2.1.1 Formation of Clays

Clays form at the earth’s surface, either in contact with air or with covering water

bodies. The majority of clay formed is through the process of weathering, either

subaerial or subaquatic. Sedimentation and burial changes the clay from one structure

to other structures. Some clay is produced by hydrothermal processes, that is,

water/rock interactions at temperatures of 100-250°C. The high quality clays used in

industrial processes are produced by the hydrothermal method [143].

2.1.2 Structure of Clays

Clay mineral is the broad term given to a group of minerals based on the general

structure formed with the individual particles. Another term often used to describe

the clay mineral family is layered silicate. This name gives an indication of the

overall structure of the clays. Clays consist of a number of layers stacked one upon

the other and within each layer is either two or three sheets. The number of sheets is

dependent on the group of clay minerals the material falls into. The kaolin group

consist of 2 sheets while all other groups consist of 3 sheets. The sheets within the

layers are based primarily on Silicon or Aluminium. The clay family can be divided

into the following groups; kaolin, smectite, mica and talc. The differences between

these groups will be discussed later.


4

All clay materials form a three-dimensional crystal structure, which have a continuous

structure through the octahedral and tetrahedral layers, in the a and b planes. These

are stacked one upon the other in the c plane [144].

ab

c

Figure 2.1.2 – Crystal Structure

The gallery is the term used to describe the stacked array of clay sheets separated by a

regular spacing. A particular feature of the clay structure is that water and other polar

molecules can enter between the unit layers because of the relatively weak forces

between the unit layers, causing the lattice to expand in the c direction [95].


5

2.1.2.1 Structure of Kaolinite

Primary kaolins are those that have formed in situ, usually by the alteration of

crystalline rocks such as granites and rhyolite. The alteration results from surface

weathering, groundwater movement below the surface or from the action of

hydrothermal fluids. Secondary kaolins are sedimentary, which were eroded,

transported and deposited as beds or lenses associated with other sedimentary rocks.

Most kaolin deposits of secondary origin were formed by the deposition of kaolinite,

which had been formed elsewhere. Some secondary deposits are formed from

sediments that were altered during deposition, primarily by groundwater. There are

far more deposits of primary kaolins in the world than secondary kaolin deposits

because special geological conditions are necessary for both the deposition and

preservation of secondary kaolins [143].

Kaolinite has the chemical formula [Al2Si2O5(OH)4]. A single kaolinite layer

contains a siloxane tetrahedral sheet linked via oxygen atoms to an octahedral sheet

containing aluminium, oxygen and hydroxyl-groups. The inner hydroxyl group lies

between the tetrahedral and octahedral sheet, while the three inner surface hydroxyl

groups lie between adjacent kaolinite layers forming hydrogen bonds to the oxygen

atoms of the next siloxane sheet. The hydrogen bonds between sheets of adjacent

layers are what hold the structure together and give kaolinite its layered structure [145].


6

2.1.2.2 Structure of Smectite

The basic coordination units of the smectite group are two tetrahedra and one

octahedron. The octahedral unit is linked via oxygen to two tetrahedrally coordinated

ions and hydroxyls are found in the intermediate layer of the octahedrally coordinated

structural unit. This structural combination of two tetrahedra and one octahedron is

called a dioctahedral 2:1 structure. The octahedral layer is occupied by two cations in

the three possible sites with a total of six positive charges. This forms the basis of the

smectite structure, and different minerals within the smectite group are formed by

substitution of ions into different structural sites. The substitution that occurs can be

of two types: the first retains the overall charge balance of the basic structure and the

second results in an change in the cationic charge [143].

Neutral substitution:

Octahedral e.g. Al3+ → Fe3+

Charged substitution:

Octahedral e.g. Al3+ → Mg2+

Tetrahedral e.g. Si4+ → Al3+

When tri-valent aluminium ions are partially substituted by divalent magnesium ions,

or tetravalent silicon ions are partially substituted by aluminium ions, the individual

layers become anionically charged. Due to this substitution, counter ions such as

sodium, potassium, or calcium are required and are located in the interlayer galleries.

The interlayer substitutions can range from 0.2 to 0.9 charges per unit cell. These

charges allow the galleries to accept polar molecules, which is responsible for the

water swelling of clay minerals [146]. The clay can swell and shrink substantially

depending on the amount of water incorporated and the particular composition of the

clay. Naturally occurring smectite clays consists of a random mixture of unit cells,

and the spacing between the layers can vary from 1.0 nm to 2.1 nm [95].


7

2.1.2.3 Structure of Mica

The structure of the mica group consists of two tetrahedra and one octahedron

forming a dioctahedral 2:1 layered silicate structure like that of the smectite group.

The octahedral unit is linked via oxygen to two tetrahedrally coordinated ions and

hydroxyls are found in the intermediate layer of the octahedrally coordinated

structural unit. The octahedral layer is occupied by two cations in the three possible

sites with a total of six positive charges. Substitution within the layer of mica

minerals is entirely charged substitution e.g. Al3+ → Mg2+, Si4+ → Al3+. The

interlayer substitutions that occur in mica result in high charge substitution (from 0.9

to 1.0) per unit cell. Only potassium is found in the interlayer substitution of the mica

structure and the high charge per unit cell locks the layers together in a tightly bonded

structure. Unlike the smectite group the mica is not capable of swelling due to the

absorption of water [143, 147].

2.1.2.4 Structure of Talc

Talcs are found in metamorphic rocks and also found in soils and weathering profiles.

Talc is again a 2:1 layered silicate; however the occupancy of the octahedrally

coordinated layer is complete. Three ions are normally present, meaning it is classed

as a 2:1 trioctahedral clay mineral group. The basic structure of talc consists of a

neutral structure comprising a full range of Mg-Fe substitutions within the octahedral

sheet all with the same charge of 2+. From this base talc structure, substitution occurs

within the tetrahedral sheets and the octahedral sheet resulting in both neutral and

charged substitutions. The substitution resulting in a charged structure occurs like

that of smectite minerals, resulting in a charge per unit cell of less than 0.9. No

substitutions occur with a high charge per unit cell; therefore, no mica-like talcs can

occur. Like the substitution in the smectite minerals, the low charge per unit cell

allows for water swelling of the talcs.


8

Neutral substitution:

Octahedral e.g. Al3+ → Fe3+

Dioctahedral e.g. 3Mg2+ → 2Al3+

Octahedral-tetrahedral e.g. Mg2+Si4+ → Al3+(oct)Al3+(tet)

Charged substitution:

Tetrahedral e.g. Si4+ → Al3+

Octahedral e.g. Al3+ → Mg2+

Interlayer octahedral vacancy e.g. 6Mg2+→ 5Mg2+

The charged substitutions require the presence of a counter ion in the interlayer

gallery to balance the charges. These counter ions are generally sodium, potassium,

or calcium ions. The possible substitutions that occur in talcs are significantly more

complex than those of the smectite and mica minerals. For the octahedral charge

substitution to occur, the dioctahedral neutral substitution has to have previously

occurred. Because of the complexity of the substitutions, large deposits consist of a

combination of possible structures [143].

Generally, the structure of the talc does not show residual surface charges, as a result,

there are no interlayer cations that could act as bridges between successive layers.

The layers are, therefore, only held bonded together by weak Van der Waals forces,

resulting in a low Moh’s hardness [148, 149].


9

2.2 EPOXIDES

Epoxides are compounds that contain three-membered cyclic, the simplest being

ethylene oxide (C2H4O). The highly strained three membered ring of epoxides makes

them more reactive towards nucleophilic substitution than linear ethers. Acid

catalysis assists epoxide ring opening as it creates a better leaving group at the carbon

undergoing nucleophilic attack. Due to ring strain, epoxides can also undergo base

catalysed ring opening provided that the attacking nucleophile is a strong base [150].

2.2.1 Structure of Epoxy Resins

Simple epoxides are not capable of forming polymers of high strength and durability.

Hence, epoxy resins are made up of large molecules containing two or more epoxide

groups. Epoxy resins are classified as thermosetting resins; they are converted to a

thermoset state by a chemical reaction between the resin and a curing agent.

Depending on the chosen curing reagent, the reaction can take place at room

temperature or require an elevated temperature. The fully cured resins are not soluble

and cannot be melted by heating. The most commonly used epoxy compounds are

based on epichlorohydrin and diphenyl propane (Bisphenol A) and are available in a

range of molecular weights. Pure Diglycidylether of Bisphenol A (DGEBA) is solid

while low molecular weight resins are liquid, and the higher molecular weight resins

are solid at room temperature [142].

Diphenol propane is produced from acetone and phenol with an acid catalyst such as

75% sulphuric acid.

O

CH3 CH3

2 + 50°H2SO4

OHOH

CH3

CH3

C + 2H2OOH


10

From this, the resin is manufactured based on the following reaction [151]:

Cl CH2 CH2CH

O

OHOH

CH3

CH3

C

OH

Cl CH2 CH2CH

OH

OO

CH3

CH3

C ClCH2CH2 CH

2

2NaOH+

+

OO

CH2CHCH2 OO

CH3

CH3

C CH2CH2 CH + 2NaCl + H2O

Another epoxy resin of interest is tetraglycidyl-4,4-diamino-diphenylmethane

(TGDDM). 4,4-diamino-diphenylmethane (DDM) or methylenedianiline (MDA) is

prepared by the condensation of aniline with formaldehyde [142].

NH2

HH

O

NH2NH2

H

H2 + + H2O

The four reactive hydrogens in the MDA can then be reacted with epichlorohydrin to

form the TGDDM resin [142].

CH

CH

CH

H

H

CH2

CH2

CH CH2

N C N

CH2

O

CH2

CH2 CH2

CH2

O

OO

Cl CH2 CH2CH

O

4+H

H

H

H

H

H

N C N

OH

OHOH

OH

Cl

ClCl

Cl CH

CH

CH

H

H

CH2

CH2

CH CH2

N C N

CH2

CH2

CH2 CH2

CH2

NaOH

StoiciometricConcentration

+ 4NaCl + 4H2O

DGEBA and TGDDM epoxy resins form the epoxy component of the

nanocomposites produced in this work.


11

2.2.2 Molecular Weight of Epoxy Resin

In the production of an epoxy resin using epichlorohydrin, a large excess of

epichlorohydrin is required. This excess limits the production of higher molecular

weight products. The newly formed DGEBA can react with the bisphenol A in the

same way as epichlorohydrin leading to a higher molecular weight resin. The general

formula given to a DGEBA resin is [151]:

OCH2

OH

CH2O

CH3

CH3

COCH2CH2

O

CH CH

CH3

CH3

C O CH2 CH2

O

CH

n

The low viscosity commercial resin Epon828 used in this work has an average value

for n of approximately 0.15, where as the pure DGEBA (n=0) is a crystalline solid.

Pure DGEBA has a molecular weight of 340.4 g/mol and the Epon828, where

n = 0.15, has a molecular weight is 383g/mol.

A similar increase in molecular weight can proceed in the synthesis of TGDDM. A

large excess of epichlorohydrin is required to limit the number of reactions that occur

between TGDDM and MDA. The tetra functional TGDDM resin has a more complex

molecular structure in high molecular weight resins. The commercial TGDDM resin

MY721 used in this work has a molecular weight of approximately 464 g/mol where

the pure TGDDM has a molecular weight of 422.5 g/mol.

It should be noted that the reaction between epichlorohydrin and bisphenol A, or

DDM, forms a range of different molecular weight species. The molecular weight of

a resin is based on the average molecular weight of the various oligomers.


12

2.2.3 Epoxy Equivalent Weight

The epoxy equivalent weight (EEW) is the molecular weight of the molecule per

reactive epoxy group and is thus calculated by dividing the average molecular weight

of the molecule by the number of epoxy groups per molecule. For the commercial

DGEBA resin, Epon828, the average molecular weight is 383 g/mol. The DGEBA

molecules contain two reactive epoxy groups so the EEW is calculated to be:

EEW = 2

Mr

= 2

383

= 191.5

The EEW of Epon828 is 191.5 g/mol.

The commercial TGDDM resin, MY721, has an average molecular weight of

464 g/mol and contains four reactive epoxy groups. The EEW is calculated to be:

EEW = 4

Mr

= 4

464

= 116

The EEW of MY721 is 116g/mol.

The epoxy equivalent weight is used to determine stoichiometric proportions of the

curing agent required.


13

2.2.4 Curing of Epoxy Resins

The conversion of an epoxy resin to a hard, infusible thermoset network is done by

the addition of a cross-linking or curing agent. Curing of an epoxy resin can occur in

two ways. Firstly by homopolymerisation, which is initiated by a catalytic curing

agent or heat, and secondly, a polyaddition/copolymerisation reaction with a

multifunctional curing agent. There is a large number of curing agents available some

of which include [142]:

• Amines - Aliphatic

- Cycloaliphatic

- Aromatic

- Dicyandiamide

• Polyamides

• Polyamidoamines

• Phenol and amino-formaldehyde resins

• Carboxylic acid functional polyesters

• Anhydrides

• Polysulphides and polymercaptans

The nanocomposites produced in this work were formed using an aliphatic amine or

an anhydride curing agent.


14

2.2.4.1 Aliphatic Amine Cure of Epoxy Resins

The aliphatic amine curing agents based on ethyleneamine are derived from ethylene

and ammonia and have the general formula H2N(CH2CH2NH)xH where x is an

integer. The cure mechanism is based on the active hydrogens adding to the available

epoxy groups. First the primary amine reacts with an epoxy molecule followed by the

secondary amine reacting with an additional epoxy molecule [142].

H

H

ROCCH

O

CH2+R NH21 2 R1 2O

OH

CH2CHCH2HN R

+H

H

ROCCH

O

CH23

2

CH2

R

CH2

N

O

OH

CH2CH R

O

OH

CH2CH R3

1

The unhindered, polyfunctional nature of ethyleneamine curing agents makes them

highly reactive and allows for room temperature curing. Tightly cross-linked

networks occur due to the small distance between reactive sites. The highly

cross-linked, cured resins have excellent solvent resistance and mechanical strength

but are limited in their flexibility.

The ethyleneamine curing agent used in this work was triethylenetetramine (TETA)

where x in the generic formula is equal to three: H2N(CH2CH2NH)3H.

H

HH

HH

H

NCH2

CH2N

CH2CH2

NCH2

CH2N

The structural formula of TETA, showing the six reactive

hydrogens where epoxy groups can react.


15

2.2.4.2 Anhydride Cure of Epoxy Resins

Reaction of epoxy resins with anhydride curing agents usually requires long periods at

elevated temperatures in order to ensure full cure. The cured epoxy resin provides a

low shrinkage, stress-free system with excellent electrical insulating properties. The

mechanism of anhydride curing of epoxy resins is complex due to several competing

reactions which can occur, especially when accelerators are added to enhance cure

rates. In the absence of added accelerators or catalysts, the anhydride ring is opened

by a hydroxyl group from the backbone of the epoxy resin, forming a half-ester. This

is followed by the half-ester carboxylic acid group initiating reaction with epoxy resin

to form a di-ester-alcohol, which can continue the polymerisation process by

esterification with another anhydride molecule [142].

CO

O

CO

+ OH CH(CH2OR )2

COO CH(CH2OR )2

COOH

+ CH2ORCH

O

CH2

CH2

COO CH(CH2OR )2

COO CH2ORCH

OH

1

1

1

2

2

Accelerators commonly used for the cure of epoxy resins with anhydrides are Lewis

bases such as tertiary amines and imidazoles. These accelerators open the anhydride

rings to form internal salts (betaines), which then act as initiators of cure. The

resulting carboxylate ions react with further anhydride molecules to form carboxylate

anion functional esters [142].


16

These can then react with further epoxide groups and continuation of this alternating

sequence leads to the formation of a polyester.

CO

O

CO

+ NR3

CON+R3

COO-+ CH2ORCH

O

CH22

CON+R3

COO CH2 CH2ORCH(O ) 2-+

CO

O

CO

CH2

CON+R3

COO CH2ORCH

O

COO

CO

2

-

Lewis acids such as BF3-amine complexes and tetra-alkylammonium salts are also

catalysts for the epoxy anhydride reaction, although, no fully satisfactory mechanism

has been proposed [142].

Anhydride curing agents are available in a variety of different structures. Varying the

structure of the anhydride can have the effect of widely differing cured mechanical

properties of the epoxy resin. Dianhydrides provide increasing cross-link density and,

as a result, increased heat, solvent and chemical resistance. The two anhydrides used

in this work were hexahydrophthalic anhydride (HHPA), which is the hydrogenated

derivative of phthalic anhydride, and methyl tetrahydrophthalic anhydride (MTHPA),

which is prepared by Diels-Alder reaction between maleic anhydride and

isopropene [142].

O

O

O

CH3

O

O

O

HHPA MTHPA


17

2.2.5 Curing Process of Epoxy Resin

The curing process involves the resin/curing agent mixture being converted from a

liquid to a solid. There are critical steps that occur in the curing progresses defined as

gelation and the onset of vitrification. Vitrification occurs as the glass transition

temperature, Tg (Section 2.2.5.1), approaches the cure temperature, Tc. As the amount

of unreacted epoxy groups decrease, the Tg increases. Vitrification is when the

difference between Tg and Tc becomes small, and consequently the reaction become

diffusion controlled and proceeds slowly because molecular mobility is rapidly

reduced. Initially, the rate of reaction is chemically controlled. With the formation of

larger, more highly branched molecules the gel point is reached, which is then

followed by the formation of an infinite three dimensional network [142].

Gillham [152] developed a Time Temperature Transformation (TTT) reaction diagram

that can be used to compare the cure and glass transition properties of thermosetting

resins. Figure 2.2.5 shows the TTT diagram. The diagram displays Tg∞, the Tg at

maximum cure, gelTg, the temperature at which gelation and vitrification occur

simultaneously, and Tg0, the glass transition temperature of the reagents. The S-shape

curve between Tg0 and Tg∞ results because the reaction rate increases as the

temperature increases. At a cure temperature between gelTg and Tg∞ the reacting resin

first gels forming a network. Then it vitrifies, and the reaction stops. The postcure

above Tg∞ ensures completion of the reactions.


18

Figure 2.2.5 – Gillham TTT diagram

If the chosen temperature of cure is too low, vitrification may be reached before

gelation, which inhibits further reaction. Due to the exothermic heat of reaction, a

relatively low cure temperature is chosen to avoid excessive exotherms. The slow

rate of cure when Tc is near Tg is overcome by post cure at elevated temperatures to

ensure that all of the epoxy groups are consumed [142].


19

2.2.5.1 Glass Transition Temperature

The glass transition temperature is a second order transition where a high molecular

weight polymer goes from a glassy state to a rubbery state during heating and from a

rubbery state to a glassy state during cooling. In the glassy state, molecular motions

are restricted to vibrations and short range rotational motion. The glass transition

region, during heating, sees the onset of long range coordinated molecular motion,

and in the rubbery region, polymers exhibit long range molecular motion, which

means the polymer can be elongated, perhaps several hundred percent. In the special

case of a lightly cross-linked polymer, an elastomer is formed, which on elongation

under load may snap back to its original length on being released [152].

In the case of curing of an epoxy resin, there is a progressive increase in the cross-link

density, resulting in the formation of a three-dimensional network. The decrease in

molecular mobility with increasing extent of reaction causes the glass transition

temperature, Tg, of the sample to increase. It is with progress of the chemical

reactions that the sample vitrifies. This process will be affected by the cure

temperature and the rate of cure. The rate of cure depends on the reactivity of the

hardener with the resin [142]. The final glass transition temperature is above the

temperature of cure. Therefore, for resin/hardener systems, which require curing at

higher temperatures, products with a higher Tg. will be produced.


20

2.2.6 Properties of Epoxy Resins

Epoxy resins have a range of unique properties that make them ideal for applications

where most other materials fail [151].

• The chemical structure of epoxy resins gives them high chemical resistance

against a wide range of severe corrosive conditions. These properties are

derived from the aromatic nature of the backbone and good chemical stability

of the phenolic ether linkage.

• Epoxy resins have good adhesion to a wide range of materials, including:

metals, wood, concrete, glass, ceramic and many plastics. This is due to the

presence of polar hydroxyl and ether groups in the resin.

• Low shrinkage during curing results in good dimensional accuracy in

construction of structural items and enables manufacture of high-strength

adhesives with a glue line of low residual stress.

• Complicated shapes can be reproduced easily using liquid epoxy resins

systems, which can be cured at room temperature.

• Good physical properties, such as: toughness, flexibility and abrasion

resistance can be obtained.

• Although there are temperature limitations, epoxy resins generally perform

better than most thermoplastics at elevated temperatures.


21

2.2.7 Applications of Epoxy Resins

Epoxy resins are convenient to use in solvent-free liquid form, which sets to a hard

infusible solid after the addition of the curing agent. They are used extensively for

potting, embedding or encapsulating of electrical components, for cable joining to

make water proof joints, and in both high voltage and low voltage applications. Low

shrinkage and good dimensional stability in service are important properties utilized

for the manufacture of foundry patterns, vacuum forming moulds, press tools for

prototype or short runs, drilling jigs, and checking fixtures. Adhesives are used in

many applications in place of soldering, bolts or rivets, particularly in small-parts

assembly and in aircraft construction. Fibreglass-reinforced plastics are manufactured

from epoxy resins for application where chemical resistance and good physical

strength properties are the main requirements. In the civil engineering industry, the

use of epoxy resins has also been established as a standard practice. Epoxy adhesives

cure more rapidly than cement, and good adhesion to new and old cement enables a

more rapid construction and repair of concrete structures [151]. The repair strategy

often employs carbon fibres to add stiffness to the unit being repaired.

The properties of cured epoxy resins have lead to their use, in recent time, in

applications such as coatings for concrete structures on motor ways where the high

concentrations of exhaust gases leads to localised acid condensation and subsequent

attack of concrete overpasses and similar structures. The high acid resistance of

epoxy resins is also employed in sewer refurbishment, where bacterial growth leads to

large build up of sulphur gases, which then react with water vapour to form sulphuric

acid and rapidly degrade the concrete tunnel. This, without repair, can have

catastrophic consequences.

Anhydride-cured epoxy resins are key components of electrical insulators. An

important objective in epoxy resin chemistry is to improve the

toughness/stiffness/strength balance without sacrificing the ability to be processed,

dimensional stability and electrical properties [122].


22

2.3 ORGANIC/INORGANIC COMPOSITES

Raw clay minerals, as they are found in natural deposits, have very little affinity for

organic molecules. Because of this, when combined with an organic polymer they

form composites with virtually no interaction between the inorganic and the organic

molecules. To promote interaction between organic molecules and the inorganic

clays, the clays must first be modified to increase their affinity for organic molecules.

This is done by an ion exchange reaction that replaces the existing counter ions with

organophilic molecules.

2.4 ORGANOPHILIC SUBSTITUTION

Organophilic substitution is not possible in 1:1 layered silicates. Naturally occurring

1:1 layered silicates do not undergo the substitution that would result in a negative

charge within the structure and be balanced by the presence of a cation within the

layers. Hence, there is no potential for substitution of an organophilic cation [143].

The mica crystal structure has a high charge per unit cell, resulting in a rigid network

that ensures the structure is too tightly bound for substitution of the potassium counter

ion with an organophilic molecule. Both talc and smectite clays exhibit relatively low

charge per unit cell and, as a result, the structure is water swellable. This important

characteristic allows for substitution of the commonly found counter ions (K+, Na+,

Ca+, Li+) for much larger organophilic molecules into the structure. Figure 2.4 shows

the process of the organophilic substitution. The naturally occurring clay contains a

free cation between the sheets (1), the addition of water to the clay induces a swelling

of the layers (2), then the original cation can be replaced by an organic cation (3).

Figure 2.4 – Organophilic Substitution of Smectite Clay


23

The naturally occurring substitution of talc is random, resulting in large variation

within a deposit. As a single type of substituted talc is rare in large quantities, the

vast majority of work is carried out on minerals from the smectite group, primarily

montmorillonite [2, 15, 93, 96, 100-106, 108-112, 114-117].

Ion-exchange reactions of Na+ or K+, which naturally occurs, within the mineral clay,

with various organic cations such as alkylammonium cations alters the silicate surface

from hydrophilic to a more readily reactive organophilic [146]. These modifications

depend on the exchange capacity of the clay, polarities of the medium and chemical

nature of the organic compound. Long chain ammonium salts or compounds are

usually used as organic cations, which lie parallel or inclined to the silicate layers,

dependent on the size of the ammonium ions. The organophilic modification,

replacing smaller molecules with larger ones, results in increasing interlayer

distances [93, 95, 96, 153].

2.5 MODIFIED CLAY/POLYMER INTERACTION

By modifying the surface through the use of organic surfactant molecules, clay can be

incorporated into a polymer matrix. The surface modification of the clays increases

the spacings between the layers and lowers the surface energy of the clay, thereby,

increasing the ease of entry of polymer or prepolymer, and serves as a compatibliser

between the hydrophilic clays and the hydrophobic polymer. It then becomes

possible for organic species to migrate between the layers and separate them

further [93, 97, 154]. The modified clay with its organophilic nature and low surface

energy interacts readily with a given polymer matrix. The large polymer molecules,

compared to the size of the interlayer galleries, gradually migrate between the clay

layers causing expansion, further reducing the interactions that occur between the

layers.

Figure 2.5 – Intercalation of Epoxy Resin


24

2.6 COMPOSITES

Synthetic polymers were discovered during the early 1900’s and phenolic resins were

among the first commercially exploited. Since that time, compounding the polymers,

including phenolics, with inorganic fillers and fibres has been developed as a versatile

route leading to novel polymeric materials with improved thermal and mechanical

properties and a significant reduction in cost [153]. The properties of composite

materials are greatly influenced by the compatibility and degree of mixing between

the two phases. In general, the organic polymer and inorganic filler are immiscible,

resulting in a coarsely blended macrocomposite with chemically distinct phases. The

result is poor physical attraction between the organic and inorganic components,

leading to agglomeration of the latter, and therefore, weaker materials. In addition,

the micrometre size particles may act as stress concentrators [154].

Fillers can take a very active part in the micro-mechanical processes occurring during

mechanical failure. The filler shape, particle size, particle size distribution, degree of

dispersion, and interfacial adhesion all have an effect on the mode of failure. The

effectiveness of initiating multiple crazing or multiple plastic deformation of the

polymer matrix should increase with decreasing average filler particle size [153]. If

multiple crazing and plastic deformation is initiated, the failure of the polymer matrix

would begin in a greater number of locations. As a result a larger amount of energy

would be required for the polymer matrix to catastrophically fail.

2.7 NANOFILLERS

The reduction in size of the inert filler to the nanometre level should result in the best

potential for initiating the multiple crazing required to increase the toughness and

strength of a composite. The more individual cracks that form in a polymer network,

the more energy is required for it to catastrophically fracture. However, due to the

very large surface area of nanofillers, strong interparticle interactions are likely to

result in cluster formation or agglomeration. When exposed to mechanical stresses,

cluster formation can cause premature mechanical failure with respect to compounds


25

with uniform nanofiller distribution. The problem of agglomeration can be somewhat

overcome by the addition of a dispersing surfactant. The loss of adhesion or decrease

in cohesive strength of the polymer then tends to be of greater concern than the

agglomeration of the nanofiller.

Potential health hazards related to handling and inhalation of nanofillers are obstacles

for the development of polymeric nanocomposites. As well as being a danger in the

production of nanocomposites, the processing of nanofillers is a health hazard,

resulting in limited commercial availability [153].

2.8 NANOCOMPOSITES

The field of polymer nanocomposites has attracted considerable attention as a method

of enhancing polymer properties and extending their utility. Nanocomposites utilise

molecular or nanoscale reinforcements rather than conventional particle filled

microcomposites [154]. Nanocomposites comprise two or more materials, which

interact on a nanometre scale. This combination is utilized to give nanocomposite

materials physical properties that are superior to the original materials used in their

construction [155]. Nanocomposites have ultrafine phase dimension, typically in the

range of 1-100 nm. The unique phase morphology and the improved interfacial

properties of nanocomposites, imparts better physical and mechanical properties in

comparison to their micro-counterparts [94]. Nanocomposites are a combination of

organic polymers with nanometre sized inorganic particles. The unique nanometre

sized dispersion of the inorganic particles in the polymer matrix, generally renders

these materials with significant improvements in mechanical properties, thermal

stability, barrier performance, flame retardancy etc. compared with the unfilled

polymer at very low loading levels. These materials exhibit behaviour different from

conventional composite materials with microscale structure, due to the small size of

the structural unit and the high surface area to volume ratio [154]. The low loading of

inorganic particles maintains polymeric clarity and cost, and also allows for

conventional polymer processing such as injection moulding and infusion processing

of fibre-reinforced composites [121].


26

2.8.1 Structure of Nanocomposites

Clay minerals modified to be receptive of organic polymer chains interact readily to

accept the polymer molecules into the layers of the clay. The large size of the

polymer molecules, relative to the original layer spacing of the clay, causes further

expansion. The growth of the polymer chains results in the formation of the final

organic/inorganic network. The resulting nanocomposite is then generally referred to

as either intercalated or exfoliated. Intercalated nanocomposites consist of either a

single monomer or extended polymer sandwiched between the host silicate layers.

This results in a well-ordered, multi-layered structure comprising alternating silicate

and polymer layers [2]. In exfoliated or delaminated nanocomposites, further

separation of the clay layers occurs and the original structure of the clay is lost [2].

Exfoliation results in a much less ordered system than the intercalated structure. Two

types of far less common structures, both of which are end tethered, can also occur:

one where the end of the polymer is attached to the outside of the silicate sheet and

the other where the end of the polymer is attached to an exfoliated layer of the

silicate. More than one nanocomposite type may be found in a system, usually with

one as the major component and the other minor [95, 121, 155, 156].

(1) (2) (3) (4)

Figure 2.8.1a – Possible Nanocomposite Structures An intercalated nanocomposite will contain the majority of the clay particles retaining

the initial ordered clay structure with increased layer spacing (1). However, the

system will also contain a small amount of exfoliated clay platelets (2) and some

unchanged clay particles. There is also the potential for some end tethered formation

with the polymer attached to the silicate sheet (3 and 4).


27

Figure 2.8.1b – Intercalated Nanocomposite

An exfoliated nanocomposite will contain a majority of exfoliated silicate layers

randomly dispersed throughout the polymer matrix (2) but some intercalated

nanocomposite is likely to be present (1). In an exfoliated nanocomposite system, a

polymer attached to a delaminated silicate sheet is the most likely end tethered

formed (4).

Figure 2.8.1c – Exfoliated Nanocomposite

The naming of a type of nanocomposite is based on the majority product. A totally

intercalated or exfoliated nanocomposite is difficult to produce, as a small amount of

the other will always be present. End tethered nanocomposites do not occur as a

primary structural type. They are only present as secondary structures with either of

the two primary structures.


28

2.8.2 Nanocomposite production

In order to produce a polymer layered silicate nanocomposite, the hydrophobic clay

first needs to be modified to accept an organic monomer or polymer between the clay

layers. This is achieved by cation exchange of the Na+ or K+ present in the clay with

an alkyl ammonium cation. The organophilic layered silicate can then be combined

with the organic polymer to form a nanocomposite by solvent intercalation, melt

intercalation, or in situ intercalation

2.8.2.1 Melt Intercalation

In melt intercalation, a thermoplastic polymer is mechanically mixed with an

organophilic clay at an elevated temperature. The polymer chains are then

intercalated between the individual silicate layers of the clay. The proposed driving

force of this mechanism is the enthalpic contribution of the polymer/organoclay

interactions. This method is becoming increasingly used, since the resulting

thermoplastic nanocomposites may be processed by conventional methods such as

extrusion and injection moulding [96]. Some shear is necessary to break up large

tactoids and improve dispersion. The dispersion of the clay has an effect on the cure

of the nanocomposite. It has been demonstrated by Dennis et al [75] and

Wang et al [157] that in addition to the chemical modification of the clay, the

processing conditions effects the structure of the nanocomposite produced.

2.8.2.2 Solution Method

In the solution method, the organoclay, as well as the polymer, are dissolved in a

polar organic solvent. The entropy gained by the desorption of solvent molecules

allows the polymer chains to diffuse between the clay layers, compensating for their

decrease in conformational entropy. The solvent is then removed and an intercalated

nanocomposite results. This method can be used to synthesise epoxy-clay

nanocomposites but the large amount of solvent required is a major disadvantage [96].


29

2.8.2.3 In Situ Polymerisation

The in situ polymerisation approach was the first strategy used to synthesise polymer-

clay nanocomposites and is a convenient method for thermoset-clay nanocomposites.

It is similar to the solution method except that the role of the solvent is replaced by a

polar monomer solution. Once the organoclay has been swollen in the monomer, the

curing agent is added. The polymerisation is believed to be the indirect driving force

of the exfoliation. The clay, due to its high surface energy, attracts polar monomer

molecules into the clay galleries until equilibrium is reached. The polymerisation

reactions occurring between the layers lower the polarity of the intercalated molecules

and displace the equilibrium. This allows new polar species to diffuse between the

layers and progressively exfoliate the clay. Therefore, the nature of the curing agent,

as well as the curing conditions, is expected to play a role in the exfoliation process.

The rate of polymerisation needs to be controlled in order to produce the desired

exfoliated nanocomposite. If a rigid polymer network forms around the intercalated

clay particles it makes it difficult for the platelets to separate further. A balance

between the intragallery and extragallery polymerisation rates is, therefore, required

in order to exfoliate the clay in epoxy systems [96].


30

2.9 CHARACTERISATION OF EPOXY/CLAY NANOCOMPOSITES

Epoxy resins combined with clay mineral nanocomposites have been studied using a

variety of curing systems [15, 93, 95, 96, 100-105, 107, 109-112, 114-116]. Yasmin et al [100]

combined DGEBA resin with an anhydride curing agent and an accelerator with an

organoclay, at differing concentrations, to produce exfoliated nanocomposites or

disordered intercalated nanocomposites with an average d-spacing greater than 70Å.

Guo et al [101] produced an exfoliated nanocomposite by combining a commercial

DGEBA resin and a commercial MTHPA hardener and accelerator with an

organo-montmorillonite. They found that with organo-clay content lower than 8% on

epoxy resin, the exfoliated structure was achieved but higher amounts of clay resulted

in agglomeration. Ratna et al [112] produced epoxy clay nanocomposites by combining

the layered silicate with DGEBA resin and a hyperbranched polymer. They claim that

according to the XRD patterns obtained, exfoliated nanocomposites were produced,

but acknowledged that according to TEM images the nanocomposites were actually

intercalated. XRD is very sensitive at low angles 2θ, which is the critical area for

determining the interlayer spacing. Therefore, the absence of peaks does not mean

the clay is completely exfoliated but that they are intercalated to a large spacing.

Kornmann et al [96] reported that when an organo clay is combined with an epoxy

resin, the system quickly forms an intercalated nanocomposite. When the liquid

epoxy/clay nanocomposite is combined with a hardener, the degree of exfoliation is

dependent on the reactivity of the hardener. A hardener with a lower reactivity

produces a greater level of exfoliation. The lower degree of reactivity allows the

intragallery polymerisation to keep up with the extragallery polymerisation. When a

higher temperature of cure is used for the same curing agent a greater extent of

exfoliation is achieved. Increasing the temperature of cure increases the reactivity of

the curing agent so it would be expected that the increase in reactivity would result in

an intercalated nanocomposite. However, when the temperature is raised, the curing

kinetics, as well as the diffusion rate, is increased and a greater degree of exfoliation

occurs.


31

2.9.1 Mechanical Behaviour of Epoxy Nanocomposites

Mechanical behaviour, in particular the elastic modulus, of an epoxy resin system

increases when combined with organo-clay [96, 100, 112, 115]. Yasmin et al [100] found that

elastic modulus increases with increasing clay content; a 1 wt.% of clay results in a

25% increase and a 5 wt.% content has a 50% increase in modulus. The improvement

in elastic modulus is as a result of the good dispersion and exfoliation of the clay

particles. A good dispersion restricts the mobility of the epoxy chains under load and

an increased surface area for good adhesion between the clay particles and the epoxy

matrix both lead to an increased modulus [2]. Ratna et al [112] report an increase in

flexural strength and modulus of epoxy resin when a nanocomposite is produced. Isik

et al [115] found that the elastic modulus increases with increasing clay content but the

tensile strength increases with the addition of up to 1 wt.% clay but decreases

thereafter. Kornmann et al [96] found that the degree of exfoliation has an effect on

the increase in modulus. They found that an exfoliated nanocomposite has a larger

increase in the elastic modulus than an intercalated nanocomposite consisting of the

same wt.% of clay added. Pinnavaia et al [120] found that the flexural strength and

modulus increases more in flexible nanocomposites than in glassy nanocomposites. If

the elastic modulus is recorded above an epoxy nanocomposite’s Tg, the increase in

elastic modulus is larger.

2.9.2 Tg of Epoxy/Clay Mineral Nanocomposites

The effect of clay on the Tg of an epoxy system has been shown to increase and

decrease in different circumstances. Ratna et al [112, 117] and Isik et al [115] found that

the glass transition temperature of an epoxy clay nanocomposite is greater than that of

the neat resin, due to the confinement of the polymer chains. This is a result of

intercalation into the layers of the clay. The mobility of the polymer chains falls due

to the interaction between the clay and the polymer molecules resulting in higher Tg.

In contrast, Xu et al [119] found that the Tg decreases with the addition of organoclays

into the epoxy resin, due to the absence of some cross-linking in the hybrid material

the segmented mobility within the polymer increases.


32

2.9.3 TEM of Epoxy Nanocomposites

TEM can be used to visualise the structure of nanocomposites. TEM images are

commonly used as supporting evidence for either an exfoliated or intercalated

nanocomposite determined by XRD. TEM images of nanocomposites often disagree

with conclusions drawn from XRD. The absence of peaks at low angles 2θ in XRD

patterns is generally claimed as evidence that an exfoliated nanocomposite has been

formed. When a TEM image is taken, it is then revealed that the structure is, in fact,

intercalated with d-spacings up to 200Ǻ [85-88, 93, 96, 110, 118]. A more accurate term for

what is commonly referred to as being exfoliated would be either an ordered

exfoliated nanocomposite or a well intercalated nanocomposite [102, 112].

Chapter 3 – Materials and Methods

33

3 MATERIALS AND METHODS

3.1 MATERIALS

DGEBA resin was supplied by AKZO NOBEL LTD, Brisbane. TGDDM was a

commercial resin MY721 supplied by Ciba Specialty Chemicals. The MTHPA curing

agent was a commercial hardener HY225 obtained from Vantico. The HHPA curing

agent and the TETA curing agent were purchased from Sigma. The clay and

modified clay were obtained from Southern Clay Products, a division of Rockwood

Specialties, Inc via Jim Chambers and associates, Sydney. The variations used were

Cloisite® Na+, Cloisite® 30B, Cloisite® 93A and Cloisite® 15A in order of

increasing surface hydrophobicity [158]. Cloisite® Na+ is a natural montmorillonite

with a layer spacing of d001 =11.7Å and has a weight loss on ignition of 7%.

Cloisite® 30B is a natural montmorillonite (Cloisite® Na+) modified with a

quaternary ammonium salt giving a layer spacing of d001 =18.5Å and has a weight

loss on ignition of 30%. The average molecular weight of the quaternary ammonium

cation is 361.8, giving 8.29 x 10-4 moles of ammonium head group per gram of

Cloisite® 30B.

T

CH2CH2OH

CH2CH2OH

CH3 N+

Where T is Tallow (~65% C18; ~30% C16; ~5% C14)

Anion: Chloride


34

Cloisite® 93A is a natural montmorillonite (Cloisite® Na+) modified with a ternary

ammonium salt giving a layer spacing of d001 =23.6Å and has a weight loss on

ignition of 40%. The average molecular weight of the quaternary ammonium cation

is 515.6, giving 7.76 x 10-4 moles of ammonium head group per gram of

Cloisite® 93A.

HT

HT

H

CH3 N+

Where HT is Hydrogenated Tallow (~65% C18; ~30% C16; ~5% C14)

Anion: HSO4-

Cloisite® 15A is a natural montmorillonite (Cloisite® Na+) modified with a

quaternary ammonium salt giving a layer spacing of d001 =31.5Å and has a weight

loss on ignition of 43%. The average molecular weight of the quaternary ammonium

cation is 529.6, giving 8.11 x 10-4 moles of ammonium head group per gram of

Cloisite® 30B.

HT

HT

CH3

CH3 N+

Where HT is Hydrogenated Tallow (~65% C18; ~30% C16; ~5% C14)

Anion: Chloride

It is expected that the small differences in the number of moles of ammonium head

group per gram of Cloisite® clay would not have a significant effect on the cure and

properties of the nanocomposites produced.


35

3.2 METHODS

3.2.1 Preparation of Samples

Brass moulds were made for the production of the nanocomposite bars. The moulds

were made to be 115mm long by 25mm wide and 10mm deep. The ends of the

moulds were made removable for ease of releasing the sample cast. Epoxy release

agent was applied to the mould for ease of sample removal.

Figure 3.2.1 – Epoxy Bar Brass Moulds

Nanocomposites were prepared by the in situ polymerisation method. First, the clay

was physically dispersed into the epoxy resin and then heated to 80°C, followed by

dispersion with a Heidolph Diax 900 high-speed mechanical mixer. The elevated

temperature was used to lower the viscosity of the epoxy resin, which assisted with

the high shear mixing process. This additionally increased the rate of interaction

between the layered silicate and the resin. The amount of clay added was calculated

to be 5 wt% on the total amount of epoxy and curing agent (i.e. epoxy-anhydride or

epoxy-amine systems). The mixture was then placed in a vacuum oven at 50°C and

the vacuum applied to remove air from within the composite.

After the air was removed, and for the TETA cured systems the temperature reduced

to ambient, the hardener was added using physical mixing. The hardener was added

at a stoichiometric ratio of 1:1, calculated using the epoxy equivalent weight of the

epoxy and the number of sites of reaction on the hardener. The composite systems


36

were then transferred to the brass moulds and cured at the temperatures indicated in

Table 3.2.1. The temperature of cure was chosen to be in the lower region of the heat

flow during cure, section 4.2.

An isothermal cure at the lower end of the heat flow curve ensures that the reaction

does not occur too rapidly. An appropriate post-cure temperature was then chosen to

be above the maximum temperature of the heat flow exotherm. The high post-cure

temperature ensures that the highest possible extent of cure is achieved.

Table 3.2.1 – Nanocomposites Prepared

Epoxy Hardener Cloisite®

Clay

Cure

(4 Hr)

Post Cure

(2 Hr)

1 DGEBA MTHPA - 120°C 180°C

2 DGEBA MTHPA Cloisite® Na+ 120°C 180°C

3 DGEBA MTHPA Cloisite® 30B 120°C 180°C

4 DGEBA MTHPA Cloisite® 93A 120°C 180°C

5 DGEBA MTHPA Cloisite® 15A 120°C 180°C

6 DGEBA HHPA - 140°C 220°C

7 DGEBA HHPA Cloisite® Na+ 140°C 220°C

8 DGEBA HHPA Cloisite® 30B 120°C 180°C

9 DGEBA HHPA Cloisite® 93A 120°C 180°C

10 DGEBA HHPA Cloisite® 15A 120°C 180°C

11 DGEBA TETA - 25°C 120°C

12 DGEBA TETA Cloisite® Na+ 25°C 120°C

13 DGEBA TETA Cloisite® 30B 25°C 120°C

14 DGEBA TETA Cloisite® 93A 25°C 120°C

15 DGEBA TETA Cloisite® 15A 25°C 120°C

16 TGDDM MTHPA - 80°C 150°C

17 TGDDM MTHPA Cloisite® Na+ 80°C 150°C

18 TGDDM MTHPA Cloisite® 30B 80°C 150°C

19 TGDDM MTHPA Cloisite® 93A 80°C 150°C

20 TGDDM MTHPA Cloisite® 15A 80°C 150°C


37

21 TGDDM HHPA - 80°C 150°C

22 TGDDM HHPA Cloisite® Na+ 80°C 150°C

23 TGDDM HHPA Cloisite® 30B 80°C 150°C

24 TGDDM HHPA Cloisite® 93A 80°C 150°C

25 TGDDM HHPA Cloisite® 15A 80°C 150°C

26 TGDDM TETA - 50°C 110°C

27 TGDDM TETA Cloisite® Na+ 50°C 110°C

28 TGDDM TETA Cloisite® 30B 50°C 110°C

29 TGDDM TETA Cloisite® 93A 50°C 110°C

30 TGDDM TETA Cloisite® 15A 50°C 110°C

3.2.2 Modulated Differential Scanning Calorimetry

DSC measures the heat flow to and from the epoxy resin/clay sample during the

curing reaction. This may be performed either isothermally or while ramping the

temperature at a controlled heating rate. The single heating rate method provides a

large amount of information. However, the method is not particularly reliable when

used to predict the reaction over a wide time-temperature range. For thermoset cure

reactions this method consistently overestimates the activation energy and the

frequency factor when compared to isothermal experiments [159]. As a result, the

method is only useful for comparative studies. In this work a comparative study is the

objective so the single heating rate method was utilised.

Modulated differential scanning calorimetry (MDSC) was carried out using a TA

Instruments Q100 with a compressed gas cooling system under a nitrogen atmosphere

(flow rate: 50 ml/min). MDSC was performed on all nanocomposites before and after

curing. The heat flow during cure was recorded using a heating rate of 3°C per

minute with a modulation of ± 1°C every 60 seconds over the range of 10°C to 300°C.

MDSC was also performed on fully cured nanocomposites to determine the Tg. The

procedure was set up to measure Tg∞, which is the maximum Tg that can be achieved.

The samples were first heated at 20°C per minute to above the expected Tg, to ensure


38

complete curing had occurred, and then cooled to below the Tg. A heating rate of 3°C

per minute with a modulation of ± 1°C every 60 seconds over the range of 20°C to

300°C was then used to measure the Tg∞.

3.2.3 X-Ray Diffraction

X-ray diffraction was performed using a PANalytical X’Pert Pro MPD. The patterns

were recorded using a Cu-Kα incident beam at 40kV and 40mA, a 0.4rad soller slit, a

1.4mm anti-scatter slit, a 1/8° fixed divergence slit and a parallel plat collimator.

XRD was performed on all cured systems. A diffraction pattern was recorded on the

clay, as obtained, from Jim Chambers and Associates for reference purposes.

A diffraction pattern was also made after interaction between the epoxy resin and the

clay mineral and the Cloisite® 30B and the curing agents. The samples were

prepared by placing the high sheared epoxy-clay nanocomposite in a silicone mould

40mm long, 30mm wide and 2mm deep. The samples were then placed in a standard

upright freezer at -18°C for one hour to lower the temperature, and as a result increase

the viscosity to a point where the angle change of the sample required in XRD, did

not result in significant movement of the uncured nanocomposite being tested. All

tests were performed in the range of 1-25 degrees 2θ. Measurements recorded at

1-5 degrees 2θ are largely affected by small variations in how the sample is mounted.

If the sample is too high or too low, the intensity of the peak in this region is

dramatically affected. As a result, these peaks can appear far more intense in some

patterns compared to others. The variations in the magnitude of these peaks are,

therefore, due to small experimental error and are not an indication of a variation in

the true diffraction intensity. The presence or absence and location of the peaks is the

significant information from the XRD patterns, rather than the intensity.

The nanocomposites were prepared for XRD by sanding the surface using a NRG

orbital sander with P60 grade sand paper and then polishing with 500 wet and dry

paper.


39

3.2.4 Instron Flexural Tests

Flexural tests were performed using an Instron 5567 tensile testing machine using a

1kN load cell and a ramp of 1.0mm per minute according to ASTM D790-00 –

Standard Test Methods for Flexural Properties of Unreinforced and Reinforced

Plastics and Electrical Insulating Materials. These test methods utilise a three point

loading system applied to a simple supported beam. The tests were performed

following the guidelines for Procedure A, which is designed principally for materials

that break at comparatively small deflections.

The rate of crosshead motion was calculated to be 1.05mm/min, using Equation 1.

R = ZL2

6d (1)

where:

R = rate of crosshead motion, mm/min,

L = support span, mm, (50mm)

d = depth of beam, mm, (4mm)

Z = rate of straining of the outer fibre, mm/mm/min. Z shall be equal to 0.01.

R = 0.01 × 502

6 × 4

3.2.5 Transmission Electron Microscopy

The samples were prepared by cutting 100 ± 20nm slices using a RMC MT-7

Ultramicrotome and a glass knife. The slices were then collected on a 300 mesh

copper grid and coated in carbon using a Cressington carbon coater. TEM images

were recorded using a Phillips CM200 Transmission Electron Microscope.

Chapter 4 – Results and Discussion

40

4 RESULTS AND DISCUSSION

4.1 SAMPLE PRODUCTION

The TGDDM resin, when combined under high shear with the clay mineral,

progressively changed in colour from a reddish colour of the pure resin to a

blue-green colour. This indicated a change in the structure of the TGDDM molecule

as it interacted and intercalated with the clay. The degree of colour change varied

depending on the Cloisite® clay used. The colour change was most rapid with

Cloisite® 93A and more gradual with Cloisite® Na+. The colour change only

occurred with Cloisite® 30B once the HHPA or MTHPA was added. In the case of

the TETA cured TGDDM the colour change that occurred during dispersion of the

Cloisite® 93A and Cloisite® Na+ disappeared when the system cured. The colour

change of TGDDM from red to green may indicate the presence of Wurster’s blue

centres in the resin. This is caused by the formation of a radical cation of the

TGDDM molecule, due to oxidative attack[160].

CH

CH

CH

H

H

CH2

CH2

CH CH2

N C N

CH2

O

CH2

CH2 CH2

CH2

O

OO

+

CH

CH

CH

H

H

CH2

CH2

CH CH2

N C N

CH2

O

CH2

CH2 CH2

CH2

O

OO

+ e-

No colour change was associated with the Cloisite® 15A. This indicates that the type

of cation present between the layers of the clay determines whether the radical cation

can form. The radical cation was formed using the unmodified Cloisite® Na+, which

is not intercalated with the TGDDM (discussed further in Section 4.4.4). This

indicates that the formation of the radical cation is due to interaction between the clay

and the TGDDM and is not an indication of intercalation occurring. However, the

colour development is more rapid with the Cloisite® 93A than the Cloisite® Na+.

This may be due to the organophilic cation allowing intercalation of the TGDDM


41

between the layers of the clay. The intercalation process results in a more rapid

interaction between the cations, producing the Wurster’s Blue.

There was no visible colour change or other indications of interaction occurring

between the DGEBA and the clays tested.

4.2 MDSC OF NANOCOMPOSITES

The epoxy ring-opening reaction is an exothermic reaction and it is assumed that the

measured thermograms can be directly related to the rate and extent of epoxy ring

opening reactions [159]. The integral can be used to calculate the percentage of epoxy

groups reacted at a given temperature, which can be better viewed after integrating the

cure exotherm. The integral of the heat flow curve can better show differences in the

initial and final stages of cure.

Curing parameters were controlled to ensure the initial cure occurred at the low end of

the exotherm. The cure proceeds from a liquid through gelation to a rigid network

structure. Once a rigid network is formed the epoxy must be post cured to ensure

maximum curing. It is desirable to produce epoxy systems with the highest possible

glass transition temperatures. Glass transition temperature increases with the extent

of epoxy cure, so the epoxy is post cured at a temperature above the maximum of the

exotherm.


42

The peak maximum was taken as the maximum value of the curve. The onset and

completion temperatures were determined by the intersection between a line

continuing the baseline and the gradient line at the point of inflection on the curve,

demonstrated in Figure 4.2. This method of determining the onset and completion

ignores any differences that can occur in the initial and final stages of cure. These

differences are better analysed comparing the integrated heat flow curve.

Heat Flow During Cure

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

90 110 130 150 170 190 210

Temperature(°C)

Hea

t Flo

w

Peak Maximum152°C

Peak Onset130°C

Peak Completion176°C

Figure 4.2 – Heat Flow during Cure


43

Figure 4.2.1a – Heat Flow during Cure for DGEBA/MTHPA Systems

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

75 95 115 135 155 175 195 215

Temperature (°C)

Hea

t Flo

w (a

.u.)

15A93A30BNa+Control


44

4.2.1 Heat Flow during Cure of DGEBA & MTHPA Systems

The heat flow versus temperature for the cure reaction of DGEBA with MTHPA

incorporating organoclays is shown in Figure 4.2.1a. There were variations in the

temperatures of the reaction depending on the modification of the clay added.

Table 4.2.1 shows the heat flow, temperature of onset and completion of cure as well

as the peak maximum. If the clay added to the epoxy has no effect on the cure

reaction it is expected that the heat flow during cure would be equal to 95% of the

unfilled resin, to allow for the reduction in the number of possible reactions due to the

addition of 5% clay. This standardised heat flow for the unfilled resin is displayed in

brackets.

Table 4.2.1 – Temperatures of Heat Flow for DGEBA/MTHPA

Onset Peak Completion Range Heat Flow

Control 132.4°C 152.4°C 176.7°C 44.3°C 198 (188) ±20 J/g

Na+ 129.0°C 160.4°C 185.4°C 56.4°C 236 ± 20 J/g

30B 118.6°C 145.8°C 169.7°C 51.1°C 191 ± 20 J/g

93A 122.4°C 147.4°C 173.9°C 51.5°C 227 ± 20 J/g

15A 119.3°C 141.2°C 166.3°C 47.0°C 164 ± 20 J/g

The total heat flow suggests that there is no significant reduction in the percentage of

possible reactions that occur during the full cure when clay is added to the

DGEBA/MTHPA resin. The di-functional DGEBA and the mono-functional

anhydride are not impeded significantly by the clay particles and, as a result no

reduction in the extent of cure is seen. The presence of the clay within the

DGEBA/MTHPA, epoxy/hardener system has an effect on the shape of the exotherm

during cure. Relative to the control reaction, which contained no added clay, the

unmodified Cloisite® Na+ caused a broadening of the temperature range at which the

epoxy reactions occur. There was virtually no effect on the starting temperature but

the broadening was seen in the higher temperatures required to complete the curing.

This indicates that once gelation occurs, the presence of the Cloisite® Na+ impedes

the reaction of the DGEBA with the MTHPA, resulting in higher temperatures being

required to achieve full cure.


45

The Cloisite® 30B, Cloisite® 93A and Cloisite® 15A all produced exotherms

showing a slight broadening effect. This indicates that any clay within the network

impedes the curing reaction. Unlike for the Cloisite® Na+, the onset temperature of

cure for the modified clays decreased. This is particularly evident in the systems

containing Cloisite® 30B and Cloisite® 15A. An acceleration of the cure reaction of

DGEBA with MTHPA is to be expected, as Cloisite® 30B and Cloisite® 15A are

modified with a quaternary ammonium salt, which is a catalyst for the epoxy

anhydride reaction. The Cloisite® 93A has been modified with a ternary ammonium

salt, which acts as a catalyst for the reaction but not to the same extent as the

quaternary ammonium salt.

The increasing surface hydrophobicity of the different clays had no apparent effect on

the exotherm during cure. The effect of the clay on the curing of the DGEBA with

MTHPA is more dependent on the catalysing ability of the modifying cation and not

controlled by the differences in how the organoclays intercalate with the epoxy.


46

Figure 4.2.1b – DGEBA/MTHPA Integrated Heat Flow

0102030405060708090100

9011

013

015

017

019

021

0Te

mpe

ratu

re (°

C)

Percent Cure

15A

93A

30B

Na+

cont

rol


47

The integral of the heat flow curves for the DGEBA/MTHPA systems (Figure 4.2.1b)

shows the curing occurring at lower temperatures for the systems containing the

organoclays and that the unfilled resin and the resin filled with the unmodified

Cloisite® Na+ required higher temperatures. The variation in the temperatures

required for cure of the organoclay epoxy nanocomposites suggests that while the

ternary amine of the Cloisite® 93A and the quaternary amine of the Cloisite® 15A

and Cloisite® 30B all have a catalysing effect on the cure reaction, the rate of

catalysis varies; with the Cloisite® 15A being the most effective, followed by the

Cloisite® 30B and then the Cloisite® 93A. There is very little difference in the

commencement of cure between the control system and the systems containing the

organoclays. The curing reaction then begins to occur more rapidly with the greater

degree of catalysis offered. While the Cloisite® 15A system remains at lower

temperature all the way to completion, the Cloisite® 30B and the Cloisite® 93A slow

down in the final stages to reach completion at approximately the same temperature as

the control system. The cure of the epoxy containing the Cloisite® Na+ required

increasingly higher temperatures as the percentage of epoxy cured increased,

indicated by the lower gradient. The Cloisite® Na+ interferes with the cure reaction

and as the reaction continues, the effect becomes more apparent resulting in a broader

range between onset and completion of cure.


48

Figure 4.2.2a - Heat Flow during Cure for DGEBA/HHPA Systems

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

100 120 140 160 180 200 220 240Temperature (°C)

Hea

t Flo

w (a

.u.)

15A93A30BNa+Control


49

4.2.2 Heat Flow during Cure of DGEBA & HHPA Systems

The heat flow versus temperature for the cure reaction of DGEBA with HHPA

incorporating organoclays is shown in Figure 4.2.2a. The exotherm for the heat flow

during cure of the unfilled resin is a very broad peak requiring high temperatures to

complete the curing. The high temperatures are required because with the

unaccelerated HHPA, the anhydride ring opening is heat controlled. The addition of

clay leads to a reduction in the temperature required to cure the DGEBA resin with

HHPA. The reduction in the temperature was significantly greater when the

organoclays were used. Table 4.2.2 shows the heat flow, temperature of onset and

completion of cure as well as the peak maximum.

Table 4.2.2 – Temperatures of Heat Flow for DGEBA/HHPA


Control 136.7°C 184.0°C 246.9°C 110.2°C 233 (221) ±20 J/g

Na+ 134.1°C 177.6°C 218.1°C 84.0°C 210 ±20 J/g

30B 123.4°C 151.5°C 175.7°C 52.3°C 204 ±20 J/g

93A 127.4°C 157.9°C 181.0°C 53.6°C 209 ±20 J/g

15A 117.4°C 149.1°C 176.0°C 58.6°C 234 ±20 J/g

The heat flow again, shows no reduction in extent of cure, indicating no reduction in

the extent of cure due to the clay. The addition of the clay resulted in a significant

reduction in the curing range of the DGEBA cured with HHPA. The addition of the

unmodified Cloisite® Na+ resulted in a reduction in the peak maximum and the

completion temperature, while the addition of the modified clays resulted in a greater

reduction in the peak maximum and completion and also the onset temperature. The

alkylammonium cations in the organoclays are catalysts for the anhydride curing

reaction, and since no accelerator was used with the HHPA curing agent, the

organoclays are able to catalyse the reaction, hence curing occurs at lower

temperatures.


50

Figure 4.2.2b – DGEBA/HHPA Integrated Heat Flow

0102030405060708090100 10

012

014

016

018

020

022

024

026

0Te

mpe

ratu

re (°

C)

Percent Cure

15A

93A

30B

Na+

cont

rol


51

The integrated heat flow exotherm (Figure 4.2.2b) of DGEBA cured with HHPA

shows the effect the clays have on lowering the temperatures required for cure. When

the clay is added to the resin, the reactions occur more rapidly and at lower

temperatures. The organoclays show an increase in the rate and decrease in

temperature of reaction in addition to that caused by the unmodified clay. The

Cloisite® 15A and Cloisite® 30B, which are modified with a quaternary ammonium

cation, show an increase in the rate and decrease in the temperature of reaction

compared to the Cloisite® 93 A, which is modified with a ternary ammonium cation.

This was seen in the DGEBA cured with MTHPA and suggests that the quaternary

ammonium cations are better catalysts than the ternary ammonium cation for the

anhydride cure of DGEBA.


52

Figure 4.2.3a - Heat Flow during Cure for DGEBA/TETA Systems

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

25 45 65 85 105 125 145 165

Temperature (°C)

Hea

t Flo

w (a

.u.)

15A

93A

30B

Na+

Control


53

4.2.3 Heat Flow during Cure of DGEBA & TETA Systems

The heat flow versus temperature for the cure reaction of DGEBA with TETA

incorporating organoclays is shown in Figure 4.2.3a. There is a small endotherm

before the exotherm commences in the control sample that is not present when the

clays are added to the DGEBA resin. The endotherm suggests that an input of energy

is required for the curing reactions to commence. Table 4.2.3 shows the heat flow,

temperature of onset and completion of cure as well as the peak maximum.

Table 4.2.3 – Temperatures of Heat Flow for DGEBA/TETA


Control 45.8°C 79.0°C 108.8°C 63.0°C 468 (445) ±20 J/g

Na+ 43.2°C 75.5°C 112.3°C 69.1°C 255 ±20 J/g

30B 44.1°C 74.5°C 112.3°C 68.2°C 241 ±20 J/g

93A 44.1°C 77.2°C 113.7°C 69.6°C 288 ±20 J/g

15A 46.1°C 78.5°C 116.7°C 70.6°C 291 ±20 J/g

The hexa-functional TETA has a larger number of reactive sites per mole compared to

the anhydride curing agents. As a result, the total heat released during curing is

expected to be higher. This is seen in the unfilled control sample. However, the clay

filled samples show a significant reduction in the total heat flow. This suggests that

the clay acts as a barrier, and prevents curing reactions from occurring as the resin

forms a more highly cross-linked structure. The unreacted epoxy groups would result

in a reduction in cross-linking, which should be seen as a reduction in the Tg (Section

4.3.3). The presence of the clays within the DGEBA/TETA system had little effect on

the cure temperatures of the resin, with only a slight decrease in the temperature of

peak maximum and a slight increase in the range. The range between onset

temperature and peak maximum is consistent across all the DGEBA/TETA systems,

at approximately 30°C. The broadening of the peaks occurs during the final stages of

cure, between peak maximum and completion temperature, for the epoxy resin

containing the Cloisite® clays but remains constant at approximately 33°C for the

control resin. The broadening of the cure range may be due to interference by the clay

f


54

Figure 4.2.3b – DGEBA/TETA Integrated Heat Flow

0102030405060708090100

2040

6080

100

120

140

Tem

pera

ture

(°C

)

Percent Cure

15A

93A

30B

Na+

Con

trol


55

between reactive epoxy and hardener as the number of unreacted epoxy groups is

diminished. The magnitude of the interference is reduced when TETA is used,

compared to the anhydrides, as the curing agent because the hexa-functional TETA

forms a highly cross-linked structure and the addition of more energy, by raising the

temperature, can not overcome the physical barriers of the clay, and hence the

percentage of polymerization is decreased.

The integrated heat flow curve (Figure 4.2.3b) for the DGEBA/TETA systems shows

that there is very little difference between the temperatures of cure when either

organoclay or unmodified clay is added to the resin. All the composite systems do,

however, commence and reach completion of curing at lower temperature than the

control sample containing no clay. The unmodified Cloisite® Na+ assists the

commencement of cure at the lowest temperature. The cure of the Cloisite® 30B

sample increases more rapidly and, after approximately 30% reacted, cures at the

lowest temperature. This suggests that, in the case of DGEBA cured with TETA, the

presence of clay within the structure assists the cure. The nanoscale interactions that

are possible in the organoclay are not primarily controlling the effect on the cure

reaction as the unmodified Cloisite® Na+, with no nanoscale interactions possible,

produces a similar result.

While Figure 4.2.3b suggests the cure of all systems is similar, the heat flow during

cure suggests that only 60% of the DGEBA/TETA is actually reacted when the 5%

clay is added. This means that the actual reaction rate and subsequent heat released

was significantly lower when the clay was added to the resin.


56

Figure 4.2.4a - Heat Flow during Cure for TGDDM/MTHPA Systems

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

50 70 90 110 130 150 170 190

Temperature (°C)

Hea

t Flo

w (a

.u.)

15A93A30BNa+Control


57

4.2.4 Heat Flow during Cure of TGDDM & MTHPA Systems

The heat flow versus temperature for the cure reaction of TGDDM with MTHPA

incorporating organoclays is shown in Figure 4.2.4a and Table 4.2.4 shows the heat

flow, temperature of onset and completion of cure as well as the peak maximum.

Table 4.2.4 – Temperatures of Heat Flow for TGDDM/MTHPA


Control 84.6°C 107.1°C 127.5°C 42.9°C 405 (385) ±20 J/g

Na+ 74.1°C 105.6°C 124.8°C 50.7°C 280 ±20 J/g

30B 76.0°C 100.4°C 120.6°C 44.6°C 246 ±20 J/g

93A 74.2°C 100.6°C 124.8°C 50.6°C 206 ±20 J/g

15A 76.0°C 103.2°C 127.6°C 51.6°C 240 ±20 J/g

The tetra-functional TGDDM has a larger number of reactive groups per mole than

the DGEBA resin and, as a result, the total heat flow is expected to be higher. This is

only seen with the unfilled control sample. The addition of clay to the

TGDDM/MTHPA leads to a barrier preventing the final reactions from occurring.

When curing TGDDM with MTHPA the heat flow curve shows a broadening effect

when the epoxy is combined with Cloisite® clay, compared to when there is no clay

added. The extent of the broadening is greatest in the unmodified Cloisite® Na+ and

the Cloisite® 93A and the Cloisite® 15A. The Cloisite® 30B showed the smallest

temperature range increase. The increase in the range between onset of cure and

completion of cure is due to the clay particles, which are present in the system,

creating interference between the epoxy and hardener, some of which was overcome

by higher temperatures. As the highly cross-linked network forms, the presence of

the clay makes it more difficult for further reactions to occur, hence the rate of

reaction decreases.

The presence of the clay within the epoxy resin resulted in a lowering of the onset

temperature of cure. This is to be expected in the Cloisite® 15A and Cloisite®30B,

as they have been modified with a quaternary ammonium cation, and Cloisite 93A, as

it has been modified with a ternary ammonium cation, which act as catalysts for the


58

anhydride cure of epoxy resins. The unmodified Cloisite® Na+ also resulted in a

lower onset temperature. The presence of the clay, together with the tertiary amine of

the TGDDM resin provides a catalyst for the cure reaction. The effect of the

unmodified clay is different to the modified clays. The heat flow curve shows that the

cure commences at the same temperature as the modified clays but takes longer to

reach the maximum. This means that the –OH ions of the Cloisite® Na+ has an initial

accelerating effect on the cure, but after the initial stages the cure reaction slows down

to reach a peak at a similar temperature to the control system, without clay. As a

result, the peak for the Cloisite® Na+ has a significantly greater temperature change

between onset and maximum than it does between maximum and completion. The

Cloisite® 30B and the Cloisite® 15A have a similar shape but the effect is not as

large. This is caused by the catalysis reaction proceeding much more easily in the

early stages of the curing process.

The curves for the epoxy/clay nanocomposites have a shoulder that occurs outside the

completion temperature using the described method of calculation (section 4.2). This

shoulder indicates the occurrence of further curing. The interference caused by the

presence of the clay on the epoxy curing, is responsible for the shoulder on the heat

flow exotherm for the Cloisite® Na+, Cloisite® 15A and Cloisite® 93A. This

shoulder extends the cure to higher temperatures in the final stages of cure, means that

a higher post cure temperature is required to react the unreacted curing agent with the

remaining epoxy groups.


59

Figure 4.2.4b – TGDDM/MTHPA Integrated Heat Flow

0102030405060708090100

4060

8010

012

014

016

018

0Te

mpe

ratu

re (°

C)

Percent Cure

15A

93A

30B

Na+

cont

rol


60

The integrated curve of the TGDDM/MTHPA systems (Figure 4.2.4b) shows a better

representation of the differences. There are differences in the curves that are not

analysed by the heat flow curve method of analysis (Section 4.2) and these can be

seen in the integral. The commencement of cure is reached first in the

TGDDM/MTHPA control system, followed by the three organoclay systems and

finally the unmodified clay. The TGDDM/MTHPA epoxy resin containing the clay

then proceeds to cure at a faster rate and at lower temperatures. The system

containing the Cloisite® 30B continues to cure at a faster rate than all other systems

and reaches the completion of cure at the lowest temperature.

The shoulder on the peak of the heat flow curve for the Cloisite® Na+, Cloisite® 15A

and Cloisite® 93A can be seen in the integrated curve where the rate of cure slows.

The completion of cure for theses systems is reached at a temperature close to that of

the control. The Cloisite® Na+ shows a similar result to that of the Cloisite® 15A and

Cloisite® 93A. This suggests that the lowering of the temperature for cure for the

majority of the reactive groups is due to the presence of the clay and not necessarily

any nanoscale interactions that can occur with the organoclays. For the

Cloisite® 30B, its quaternary ammonium cation has a significant effect on the cure.

The cure reactions occur more rapidly and at lower temperatures. This indicates that,

although all of the modifying cations would provide a catalyzing effect on the

anhydride curing agent, the cation in the Cloisite® 30B has a far greater catalysing

effect on both the rate of reaction and subsequent temperature of reaction and also the

curing in the final stages, which is impeded using the other clays. While the

integrated heat flow (figure4.2.4b) suggests that the rate of reaction is faster when the

clay is added, the total heat flow, at 65% compared to the unfilled resin, suggests that

as fewer reactions occur the rate was actually slower.


61

Figure 4.2.5a - Heat Flow during Cure for TGDDM/HHPA Systems

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

50 70 90 110 130 150 170 190Temperature (°C)

Hea

t Flo

w (a

.u,)

15A93A30BNa+Control


62

4.2.5 Heat Flow during Cure of TGDDM & HHPA Systems

The heat flow versus temperature for the cure reaction of TGDDM with HHPA

incorporating organoclays is shown in Figure 4.2.5a. The resin with Cloisite® 15A

and the control sample have a shoulder on the lower temperature side of the peak

maximum. When the curing reaction commences the organoclay filled epoxy and the

control sample cure at a similar rate. The control sample and the Cloisite® 15A

experience a decrease in the rate of reaction before the peak maximum. The rate of

reaction is slower for the epoxy filled with the unmodified Cloisite® Na+. The

reaction up to the peak maximum, proceeds at a similar rate to the control and

Cloisite® 15A filled sample after the peak maximum. Table 4.2.5 shows the heat

flow, temperature of onset and completion of cure as well as the peak maximum.

Table 4.2.5 – Temperatures of Heat Flow for TGDDM/HHPA


Control 95.5°C 125.0°C 138.9°C 43.4°C 370 (350) ±20 J/g

Na+ 96.6°C 139.9°C 157.4°C 60.8°C 325 ±20 J/g

30B 85.7°C 113.9°C 125.5°C 39.8°C 277 ±20 J/g

93A 94.3°C 125.8°C 138.1°C 43.8°C 288 ±20 J/g

15A 92.8°C 120.1°C 134.0°C 41.2°C 247 ±20 J/g

There is, again, a reduction in the total heat flow when clay is added to the TGDDM

resin cured with HHPA, approximately 80% of the possible reaction occur, caused by

the physical barrier provided by the clay. When the TGDDM resin is cured with

HHPA the modified Cloisite® clays only have a small effect on the curing range. The

Cloisite® 93A has virtually no effect, and the Cloisite® 15A and the Cloisite® 30B

produce a slightly narrower range. The presence of Cloisite® Na+ causes a very large

increase in the temperature range. The majority of the increase occurs before the peak

maximum. The presence of the unmodified clay acts as a barrier, which then requires

higher temperatures for the cure reactions to continue. The cure commences at a

similar temperature to the other systems but the completion temperature is higher,

which necessitates a higher post cure temperature.


63

Figure 4.2.5b – TGDDM/HHPA Integrated Heat Flow

0102030405060708090100

6080

100

120

140

160

180

Tem

pera

ture

(°C

)

Percent Cure

15A

93A

30B

Na+

Con

trol


64

The Cloisite® 93A, in relation to onset of cure, peak maximum and completion of

cure has very little variation from the unfilled TGDDM/HHPA. This suggests that the

Cloisite® 93A, which was modified with a ternary ammonium cation, has an effect of

accelerating the rate of cure due to the catalysing effect of the ammonium cation and

an equivalent deceleration due to the inhibiting effect of the clay particles.

The Cloisite® 15A and the Cloisite® 30B are Cloisite® Na+ modified with a

quaternary ammonium cation, which are known to have a strong catalysing potential

on anhydride curing of epoxy resins. As a result the epoxy systems cure over a

narrower range at a lower temperature. The effect is greatest in the Cloisite® 30B,

indicating that the quaternary ammonium cation used in its production has a greater

catalysing effect than the cation used in Cloisite® 15A. The heat flow during cure of

Cloisite® 30B has no shoulder on the exotherm, which would indicate a reduction in

the rate of the reaction prior to the peak maximum. This suggests that the quaternary

ammonium cation used in its production has a stronger catalysing effect, which

overcomes the reduction in reaction rate that usually occurs for TGDDM cured with

HHPA.

The integrated heat flow curve (Figure 4.2.5b) shows a comparison between the

curing with various clays more clearly. For TGDDM cured with HHPA the addition

of unmodified clay, Cloisite® Na+, results in a slowing down of the rate of reaction,

evident by the lower gradient. The reduced rate of reaction means that higher

temperatures are required to reach the same level of cure as the TGDDM/HHPA cure

without any filler added. The addition of the Cloisite® 93A, modified with a ternary

ammonium cation, cures at virtually the same rate as the control system. The

Cloisite® 30B and Cloisite® 15A reduce the temperature required to cure the resin.

The Cloisite® 30B has a greater effect than the Cloisite® 15A, which means that the

type of ammonium cation used has a significant effect on the temperatures required to

cure the TGDDM epoxy resin with HHPA. The use of an organoclay within the

TGDDM/HHPA generally requires a lower temperature to cure than the unfilled

control, while the addition of an unmodified clay results in higher temperatures being

required. The catalysing effect of the ternary or quaternary ammonium cation in the

organoclays has a greater effect of reducing the temperature of cure than the presence

of the clay has of increasing the temperature required.


65

Figure 4.2.6a - Heat Flow during Cure for TGDDM/TETA Systems

0

0.5

1

1.5

2

2.5

20 40 60 80 100 120 140

Temperature (°C)

Hea

t Flo

w (a

.u.)

15A

93A

30B

Na+

Control


66

4.2.6 Heat Flow during Cure of TGDDM & TETA Systems

The heat flow versus temperature for the cure reaction of TGDDM with TETA

incorporating organoclays is shown in Figure 4.2.6a. Table 4.2.6 shows the heat flow,

temperature of onset and completion of cure as well as the peak maximum.

Table 4.2.6 – Temperatures of Heat Flow for TGDDM/TETA


Control 68.1°C 92.2°C 102.6°C 34.5°C 489 (465) ±20 J/g

Na+ 65.1°C 90.4°C 101.2°C 37.1°C 457 ±20 J/g

30B 65.9°C 89.9°C 100.0°C 34.1°C 454 ±20 J/g

93A 67.3°C 90.9°C 99.9°C 32.6°C 464 ±20 J/g

15A 62.3°C 87.0°C 95.9°C 33.6°C 507 ±20 J/g

TGDDM cured with TETA contains the highest combined functionality, and hence

the greatest potential for cross-linking. It would be expected that, based on the other

systems, that there would be a higher total heat flow for the unfilled control resin and

a significant reduction in the heat flow when clay is added. This was not shown in the

results. This suggests that the unfilled resin already experiences difficulty in reaching

full cure, resulting in a number of unreacted amine and epoxy groups. The addition of

the clay does not seem to result in any further reduction in the extent of cure. It

would be expected that, for TGDDM cured with TETA, there would be a smaller

decrease in the Tg due to reduced cross-linking.

When TGDDM is cured with TETA the exotherms produced using DSC show very

little difference between the unfilled resin system and systems filled with the

Cloisite® clays. The temperature range of cure is slightly reduced when the epoxy

system contains the organophilic clays but is increased when the system contains the

unmodified clay. This suggests that the organophilic clays assist in allowing diffusion

controlled reactions, where as the unmodified Cloisite® Na+ slightly inhibits the

reactions after vitrification. The potential for the clay within the system to impede the

reactions occurring is reduced by the fact that the TETA molecule has six reactive

f


67

Figure 4.2.6b – TGDDM/TETA Integrated Heat Flow

0102030405060708090100

3040

5060

7080

9010

011

012

013

0Te

mpe

ratu

re (°

C)

Percent Cure

15A

93A

30B

Na+

Con

trol


68

sites, which means the unreacted TETA molecules do not require higher temperature

to react with the remaining epoxy groups then when no clay is added to the resin.

The integrated heat flow curve (Figure 4.2.6b) shows that the TGDDM systems cured

with TETA commence and complete curing at close to the same temperature. The

commencement and completion temperatures are not controlled or affected by the

presence of any clay within the structure. When clay is incorporated into the

TGDDM/TETA epoxy resin, the commencement of cure occurs at the same

temperature as the control, but as the reaction proceeds, the clay has the effect of

increasing the rate of reaction and a higher percentage cure is reached at the same

temperature of cure. In the final stages of cure the clay provides interference and

decreases the rate of reaction compared to the unfilled TGDDM, and, as a result, the

completion of cure is reached at roughly the same temperature.


69

4.2.7 Heat Flow during Cure of Epoxy Resin Systems

The heat flow during cure of the various epoxy resin/curing agent systems studied

(Section 4.2.1-4.2.6) shows that the effect of the addition of either an unmodified

montmorillonite (Cloisite® Na+) or an organophilic montmorillonite (Cloisite® 30B,

Cloisite® 93A and Cloisite® 15A) varies, depending on the curing agent. The

tetra-functional TGDDM resin reaches a higher percentage of epoxy groups

consumed, than the di-functional DGEBA resin, before a reduction in the rate of

reaction occurs.

The TETA is the most reactive curing agent and, as a result, cures both the TGDDM

and the DGEBA at the lowest temperature. The commercial MTHPA curing agent,

which contains an accelerator, cures at higher temperatures than the TETA and at a

lower temperature than the HHPA, which did not contain an accelerator. This is

expected, as the purpose of the accelerator is to assist the cure, which would then

occur at lower temperatures. When using TETA as the curing agent the DGEBA

cures at a lower temperature than the TGDDM (~75°C compared to ~90°C). For the

anhydride curing agents the TGDDM cures at significantly lower temperatures than

the DGEBA resin (~105°C & ~125°C compared to ~150°C & ~160°C). The

TGDDM molecule contains a tertiary amine, which is a catalyst for the anhydride

cure of epoxy resins. As a result, the TGDDM molecule causes a self-catalysed

reaction and has the effect of significantly reducing the temperatures required to cure

the resin.

When clay is added to the resins cured with TETA there is a reduction in the

temperature required for cure. This occurs for both modified and unmodified clay.

This suggests that the cure reaction is assisted by the presence of the clay and not the

nanoscale interactions that are possible with the modified clays.

For the anhydride cured epoxy resins, the addition of the unmodified Cloisite® Na+,

with the exception of the TGDDM/MTHPA system, resulted in an increase in the

temperature required to cure the resin. This suggests that the clay within the structure

provides a greater barrier to cure, which needs to be overcome for the cure reactions

to proceed. In the case of the TGDDM cured with MTHPA, the self catalysis of the


70

TGDDM and the accelerator present in the commercial MTHPA were able to

overcome the effect of the clay within the structure. The effect of the unmodified clay

is greater when the epoxy is cured with the un-accelerated HHPA compared to the

MTHPA.

The total heat flow during cure suggests that the addition of the clay can have a large

effect on the percent of possible reaction that occur. In low functionality resin and

hardener systems no reduction is seen. The low cross-link density allows for enough

movement, of the polymer chains, to react around the clay. When the functionality

increases, a higher cross-link density occurs preventing the movements required to

cure around the clay. The result is a decrease in extent of cure and the total heat flow.

For the TGDDM/TETA, the large amount of cross-linking prevents the full cure of

the epoxy groups in the unfilled resin. The addition of the clay does not seem to

result in any further reduction in the curing.

The Cloisite® 93A, containing a ternary ammonium cation, and the Cloisite® 30B

and Cloisite® 15A, containing a quaternary ammonium cation decrease the

temperature required to cure the epoxy resins. This is to be expected, as the

ammonium cations used in the modification of the clay are known to be catalysts for

the anhydride cure of epoxy resins [142]. The magnitude of the reduction in

temperature of cure required varies depending on the alkylammonium cation used.

For the anhydride cured DGEBA, the Cloisite® 15A provided the largest reduction in

cure temperature, while for the anhydride cured TGDDM, the Cloisite® 30B provides

the largest reduction. The reduction in the cure temperature, of systems containing

modified clay does not appear to be greatly affected by whether or not the anhydride

hardener contains an accelerator.


71

Figure 4.3.1 – DGEBA/MTHPA Tg

6065

7075

8085

9095

100

105

110

Tem

pera

ture

(°C

)

Reversing Heat Capacity (a.u.)

15A

93A

30B

Na+

Con

trol


72

4.3 GLASS TRANSITION TEMPERATURE

The glass transition temperature is a second order transition where a high molecular

weight polymer goes from a glassy state to a rubbery state during heating. Using

MDSC the Tg can be seen as a step in the reversing heat capacity when the sample is

heated at constant rate over the range of the Tg. The Tg is measured as the inflection

in the step of the reversing heat capacity.

4.3.1 Tg of DGEBA & MTHPA Systems

The Tg of DGEBA cured with MTHPA was found to decrease when clay was added

to the resin. Figure 4.3.1 shows the reversing heat capacity of each of the systems

studied. The Tg for each of the different Cloisite® clays added is shown in

Table 4.3.1.

Table 4.3.1 – Tg of DGEBA/MTHPA systems

Control Na+ 30B 93A 15A

97°C 88°C 78°C 83°C 82°C

The reversing heat capacity showed clear steps indicating a clear transition takes place

between the glassy state at lower temperatures and the rubbery state at higher

temperatures. The addition of clay to the DGEBA resin has the effect of decreasing

the Tg when cured with MTHPA compared to when no clay is added. There is a

further decrease in the Tg with the addition of an organoclay. Benfarhi et al [15]

reported a drop in the Tg for the nanocomposites produced compared to the cross-

linked epoxy. The same was reported by Kornmann et al [161] who saw a decrease in

Tg as the percentage organoclay added increased. This suggests that the clay, when

dispersed within the resin, acts as a barrier and prevents some cross-linking from

occurring, resulting in the decreased Tg. When the organoclays are added, the resin

intercalates between the layers and, as a result, further blocking of cross-linking

occurs. The Cloisite® 30B has the lowest Tg, which suggests a larger number of

DGEBA molecules should be within the layers of the clay compared to the

Cloisite® 93A and Cloisite® 30B (shown to be the case by XRD, Section 4.4.3.1).


73

Figure 4.3.2 – DGEBA/HHPA Tg

100

110

120

130

140

150

Tem

pera

ture

(°C

)

Reversing Heat Flow (a.u.)

15A

93A

30B

Na+

Con

trol


74

4.3.2 Tg of DGEBA & HHPA Systems

The addition of clay to the TGDDM cured with HHPA has a dramatic effect on the

Tg, shown by the reversing heat capacity in Figure 4.3.2. The glass transition region

for the unfilled DGEBA cured with HHPA is broad and has no clear inflexion in the

reversing heat capacity, so the Tg was taken to be the midpoint of the step. This

suggests that the transition from glassy, at lower temperatures, to rubbery, at higher

temperatures, is more gradual due to variations in the cross-linked structure. The

transition is over a narrower temperature range and is clearer when clay is added to

the resin, which suggests the clay promotes a more uniform structure of the composite

system. The Tgs for the DGEBA cured with HHPA systems are shown in Table 4.3.2

Table 4.3.2 – Tg of DGEBA/HHPA systems


125°C 137°C 130°C 131°C 122°C

The Tg of the systems containing added clay cannot easily be compared to the resin

without clay due to the broad, unclear transition of the unfilled resin. The addition of

the unmodified Cloisite® Na+ results in a higher Tg than when a modified clay is

added. The Cloisite® 15A has a lower Tg than the Cloisite® 30B and the

Cloisite® 93A. This suggests that when an organoclay is added, the DGEBA resin

migrates between the layers of the clay results in a barrier which reduces the

cross-linking. It was shown by XRD (Section 4.4.3.2) that the DGEBA resin cured

with HHPA produces a far greater layer spacing of the Cloisite® 30B and the

Cloisite® 93A than it does with the Cloisite® 15A. The layers are separated to an

extent, such that further cross-linking of the resin can occur between the layers of the

clay, which results in a higher Tg for the resin with Cloisite® 30B and Cloisite® 93A

than for the Cloisite® 15A. More cross-linking is possible when the epoxy remains

outside the clay layers, therefore the Cloisite® Na+ has the highest Tg of the systems

containing added clay.


75

Figure 4.3.3 – DGEBA/TETA Tg

5060

7080

9010

011

012

013

014

015

0Te

mpe

ratu

re (°

C)


15A

93A

30B

Na+

Con

trol


76

4.3.3 Tg of DGEBA & TETA Systems

The Tg of DGEBA cured with TETA is drastically reduced when clay is added to the

resin, shown in the reversing heat flow of Figure 4.3.3. The transition range of the

unfilled resin is broader and less defined, but significantly higher than when the clay

is added. The narrower transition range when the clay is added suggests that the

presence of the clay particles promotes a more uniform cross-linked structure

resulting in a sharper transition from a glassy state, at lower temperatures, to a

rubbery state at higher temperatures. The unfilled resin ay have some variations in

the cross-linking, resulting in a less defined transition from glassy to rubbery, The Tg

of the DGEBA cured with TETA after the addition of various clays is shown in

Table 4.3.3.

Table 4.3.3 – Tg of DGEBA/TETA systems


130°C 81°C 88°C 84°C 90°C

The presence of the clay particles within the resin, was shown by the reduction in total

heat flow to provides a barrier, which prevents some reactions from occurring. The

subsequent reduction in cross-linking has the effect of lowering the Tg. When an

organoclay is added to the resin the DGEBA can migrate between the layers and when

the TETA curing agent is added greater degree of cross-linking can occur around the

individual platelets of the clay. The TETA molecule containing six reactive sites, was

able to react with the DGEBA between the layers, where an anhydride curing agent

was not, resulting in a higher Tg than for the unmodified Cloisite® Na+.


77

Figure 4.3.4 – TGDDM/MTHPA Tg

120

130

140

150

160

170

180

190

Tem

pera

ture

(°C

)


15A

93A

30B

Na+

Con

trol


78

4.3.4 Tg of TGDDM & MTHPA Systems

The addition of clay to TGDDM cured with MTHPA results in a slight decrease in the

Tg, shown in Figure 4.3.4. The Tg is sharpest when the unmodified Cloisite® Na+ is

added. The addition of the unmodified clay promotes the formation of a uniform

cross-linked structure with a clear transition from the glassy state, at lower

temperatures, to a rubbery, state at higher temperatures. The TGDDM cured with

MTHPA, without clay added, and with the addition of the organoclays have a clear

Tg, over a larger range. This indicates a slightly less uniformly cross-linked structure

than the system with the Cloisite® Na+. The measured Tg for the TGDDM cured with

MTHPA is in Table 4.3.4.

Table 4.3.4 – Tg of TGDDM/MTHPA systems


163°C 157°C 143°C 155°C 157°C

The reduction in the Tg after the addition of the clay suggests that the presence of the

clay within the structure provides a barrier that prevents some cross-linking from

occurring, supported by the total heat flow (Section 4.2.4). The addition of

Cloisite® 30B, which is shown by XRD (Section 4.4.4.1) to have the largest layer

expansion, has the largest decrease in Tg. This suggests that when the TGDDM

molecule is within the layers of the clay, the epoxy groups become trapped and some

cross-linking cannot occur. The integral of the heat flow during cure (Figure 4.2.4b)

shows that the TGDDM containing Cloisite® 30B cured with MTHPA reaches a

larger percentage epoxy groups reacted before a reduction in the rate of reaction is

seen. The reduced Tg suggests that the apparent larger percentage cured before

reduction in the rate of reaction may be due to the epoxy groups within the layers of

the clay remaining unreacted. Ratna et al [117] reported an increase in Tg with the

addition of 5% organoclay to an epoxy. They claim the effect is due to the

confinement of the polymer chains, as a result of intercalation, into the interlayer

gallery of the clay. The small reduction in the Tg compared to the significant decrease

in the total heat flow suggests that, while the reduced cross-linking would lower the

Tg, the clay provides a confinement of the epoxy to increase the Tg. The net result is a

slightly lower Tg.


79

Figure 4.3.5 – TGDDM/HHPA Tg

120

140

160

180

200

220

240

260

Tem

pera

ure

(°C

)


15A

93A

30B

Na+

Con

trol


80

4.3.5 Tg of TGDDM & HHPA Systems

There is a large variation in the Tg of TGDDM cured with HHPA depending on the

type of clay added, as shown in Figure 4.3.5. The transition region is broad and not

well defined for the unfilled resin and when the organoclay is added. When the

unmodified Cloisite® Na+ is added, the Tg is well defined. This suggests that the

presence of the unmodified clay promotes the formation of a uniformly cross-linked

network. Table 4.3.5 shows the measured Tgs.

Table 4.3.5 – Tg of TGDDM/HHPA systems


230°C 160°C 190°C 211°C 228°C

The addition of Cloisite® Na+ results in a large decrease in the Tg. This is caused by

the presence of the clay being a barrier, which prevents cross-linking. The addition of

the organoclays results in a range of effects. The Cloisite® 15A has a Tg the same as

the neat resin, while the Cloisite® 93A and the Cloisite® 30B show a reduction in the

Tg, with Cloisite® 30B showing the largest reduction. All organoclays have a Tg

higher than the unmodified Cloisite® Na+. This suggests that for the TGDDM cured

with HHPA, more cross-linking can occur when the resin is within the layers of the

clay than when it has to go around the clay. It was shown by XRD (Section 4.4.4.2)

that the Cloisite® 93A and the Cloisite® 30B produced the largest layer spacing in

the final nanocomposite. The lower Tg, compared to the Cloisite® 15A, suggests that

when more resin is within the layers of the clay a reduction in the cross-linking

occurs. The heat flow during cure of TGDDM/HHPA (Figure 4.2.5a) shows that

reduction in the extent of cure was less for TGDDM cured with HHPA than when it

was cured with MTHPA. The balance between the reduction in Tg due to the reduced

cross-linking, and the increased Tg due to the clay confinement of the epoxy, results in

a smaller net reduction in Tg.


81

Figure 4.3.6 – TGDDM/TETA Tg

125

145

165

185

205

225

245

265

Tem

pera

ture

(°C

)


15A

93A

30B

Na+

Con

trol


82

4.3.6 Tg of TGDDM & TETA Systems

The Tg of TGDDM cured with TETA is poorly defined with, and without, the addition

of clay. This suggests that the highly cross-linked network that results from the

curing of tetra-functional TGDDM with hexa-functional TETA undergoes a gradual

transition from a glassy state, at lower temperatures, to a rubbery state, at higher

temperatures. Table 4.3.6 shows the approximate Tg of the TGDDM cured with

TETA. The values are only approximate as no clear inflexion in the reversing heat

capacity is present.

Table 4.3.1 – Tg of TGDDM/TETA systems


240°C 183°C 170°C 161°C 171°C

The addition of clay to the TGDDM resin cured with TETA results in a decrease in

the Tg. The decrease is larger when an organoclay is used. The presence of the clay

within the partially uncured resin promotes longer chains and less cross-linking,

indicated by DSC total heat flow, which reduces the Tg. The reduction in the Tg when

an organoclay is added suggests that when the TGDDM molecules migrate between

the layers of the clay, the epoxy groups become trapped and are unable to react with

the TETA. This results in a reduction in the cross-linking and subsequent Tg. The

lowest Tg was found for the Cloisite® 93A composite, which was shown by XRD

(Section 4.4.4.3) to have the largest layer spacing, suggesting it has the largest

number of unreacted epoxy groups of all the TGDDM/TETA systems.

4.3.7 Glass Transition Temperature of Epoxy Resin Nanocomposites

The Tg was found to be considerably higher for the TGDDM resin than for the

DGEBA resin. This was to be expected as the TGDDM has four epoxy groups per

molecule compared to the DGEBA with two epoxy groups. The larger number of

epoxy groups per molecule results in a more cross-linked structure and a higher Tg.


83

In all systems studied the addition of clay to the resin resulted in a decrease in the Tg.

This agrees with Xu et al [119] who found that Tg decreases with the addition of

organoclays into the epoxy resin. The reduction is due to the reduction in

cross-linking in the composite resulting in increased polymer segmented mobility.

This disagrees with Ratna et al [112, 117] and Isik et al [115] who found that the glass

transition temperature of an epoxy clay nanocomposite is greater than that of the neat

resin due to the confinement of the polymer chains as a result of intercalation into the

layers of the clay. They suggested that mobility of the polymer chains falls due to the

interaction between the clay and the polymer molecules, resulting in higher Tg. The

difference may have been due to the additional sonification step employed by

Ratna et al [112, 117], which may have resulted in improved dispersion. They also used

organoclay from a different source, which may also explain the difference in results.

The organoclays, Cloisite® 30B, Cloisite® 93A and Cloisite® 15A generally resulted

in a Tg lower than when the unmodified Cloisite® Na+ was added to the resins. The

exception was the TGDDM/HHPA system, which had significantly higher Tg’s with

organoclays than unmodified clay. When the highly reactive TETA was used as the

curing agent the variation in the Tg, depending on the clay used, was minimal while

the largest variations were seen in the un-accelerated HHPA cured systems. This

suggests that the more readily the resin can react with the curing agent the less likely

the modification of the clay is going to have an effect on the Tg. The largest drop in

the Tg was seen when the TETA was used as the hardener. The highly cross-linked

structure of the TETA cured epoxy experiences the largest interference from the clay

present within the structure. The small relative distances between reactive sites make

it more difficult for the epoxy/TETA resin to form a highly cross-linked structure

around the clay particles.

When the epoxy resin was combined with the organoclays, a higher Tg was seen with

a smaller d-spacing of the clay. This suggests that when the epoxy molecule migrates

between the layers of the clay the epoxy groups are unable to react with the curing

agent to contribute to the cross-linking. With small increases in the d-spacing, the Tg

decreased, indicating that more epoxy groups were left unreacted within the clay

layers. When the clay layers were expanded dramatically, the reduction in Tg

decreased. This is because when there is large separation the hardener is able to


84

migrate between the layers and react with the epoxy groups resulting in a more highly

cross-linked network results.


85

Figure 4.4.1 – XRD of Cloisite® Clays

0

5000

1000

0

1500

0

2000

0

2500

0

16

1116

21D

egre

es 2θ

Counts (a.u.)

15A

93A

30B

Na+


86

4.4 XRD OF NANOCOMPOSITES

4.4.1 XRD of Cloisite® Clay

XRD is a technique that can be used to accurately determine the spacing between clay

layers and was used to determine any change that occurred when the clays were

incorporated into an epoxy polymer matrix. Figure 4.4.1 shows an analysis that was

prepared on the clays as received to provide accurate reference layer spacings.

The peak at the lower end of the diffraction pattern shows the layer spacing of the

modified clays. There is a slight variation in the figure measured and that reported by

the manufacturer [158]. This is not considered to be a significant variation. Table 4.4.1

shows the comparison between the measured value and the value given by the

manufacturer, where the d spacing in angstroms (Å) is calculated from the angle of

incidence, θ, using the Bragg Equation.

nλ = 2d sin θ

where n = an integer

λ = wavelength of incident X-ray

θ = angle of incidence

Table 4.4.1 – Layer Spacing of Organoclays

Experimental Reported [158]

Cloisite® Na+ 12.3Å 11.7 Å

Cloisite® 30B 18.2Å 18.5Å

Cloisite® 93A 24.0Å 23.6Å

Cloisite® 15A 35.1Å 31.5Å

The shoulder on the Cloisite® 15A peak at 20.7Å indicates that not all the clay is

modified to have the same structure. This is not reported by the company that

produces the nanoclays [158], but the smaller spacing may be due to a different

orientation of the organic cation. The small peak at 6.1 degrees 2θ corresponds to the


87

peak in the Cloisite® Na+. This indicates that not all the clay was successfully

converted to an organoclay. There is an additional peak at 19.8 degrees 2θ (4.5Å)

present in all variations of the clay. This peak shows the spacing of the repeating

crystal structure of the clay in the a and b directions. The magnitude of this spacing is

consistent among all clays of the same source, and, as a result, is not altered by the

organophilic modification of natural Cloisite® Na+ to any of the organoclays

Cloisite® 30B, Cloisite® 93A or Cloisite® 15A. It is therefore expected, in all x-ray

diffraction patterns of nanocomposites containing Cloisite® clays, that the peak at

19.8 degrees 2θ will be present. If the peaks at low angles are not present, the peak at

19.8 degrees 2θ is proof of an exfoliated nanocomposite. Ratna et al [112] reported that

this peak can be difficult to determine. However, without this peak being present, an

XRD pattern of a nanocomposite that does not show any peaks at lower angles 2θ

could be indicating an absence of clay and not an exfoliated nanocomposite.


88

4.4.2 XRD of Nanocomposites

The d-spacing of the clay when combined with either epoxy resin (TGDDM or

DGEBA) produces a very strong XRD signal. Figure 4.4.2 shows a typical XRD

pattern of a clay/epoxy nanocomposite.

XRD of Typical Nanocomposite

0

2000

4000

6000

8000

10000

12000

14000

16000

1 2 3 4 5 6 7 8 9 10 11Degrees 2θ

Cou

nts

(a.u

.)

001(37.6Å)

002(2 x 18.3Å)

003(3 x 12.2Å)

004(4 x 9.2Å)

Figure 4.4.2 – XRD Pattern of a Nanocomposite

The four peaks all indicate the same d-spacing with 37.6Å being the actual layer

spacing. The second peak indicates half the spacing, the third indicates one third the

spacing and the forth indicates one quarter of the layer spacing. Each peak can be

used to calculate the d-spacing by changing the value of n in the Bragg equation.

The additional peaks in the XRD pattern do not provide any additional information.

They can, however, be used to provide a more accurate layer spacing. There is a

greater potential for error in the peaks at lower degrees 2θ. This is because, in this

region, there is a larger change in the measured distance per change in degree 2θ. For

the example shown in Figure 4.3.2a the 001 peak indicates a layer spacing of 37.6Å,

whereas the 002 and 003 peaks suggest that the spacing is 36.6Å. The fourth peak is

less defined so the potential for error is again increased. Becker et al [105] report the

presence and of the 002 peak to measure d-spacing when the large spacing prevents a

clear 001 peak. The 002 peak can be used to determine the d-spacing when the 001

peak is at low angles 2θ. For XRD patterns where well defined 001 and 02 peaks are


89

present these peaks provide the most accurate information for measurement of the

layer spacing and when available were used to calculate d-spacings in this study.

The epoxy resins, when combined with the organoclays, produces a uniform cured

product so the XRD pattern is the same whether taken from the top of the sample or

the bottom. The Cloisite® Na+, however, settles to the bottom of the epoxy resin.

The settling is more evident when the epoxy is cured with an anhydride. When the

temperature is raised to allow for the anhydride cure reaction to occur, the viscosity is

reduced. The reduction in viscosity allows the Cloisite® Na+, which has no affinity

for the epoxy resin, to settle to the bottom. The settling is not as evident in the TETA

cured resins, as the same temperature increase is not required. The organophilic

modification of the Cloisite® 30B, Cloisite® 93A and Cloisite® 15A kept them

suspended, even in low viscosity resin. An XRD pattern is recorded for both the top

and the bottom of the samples containing Cloisite® Na+, generally, with stronger clay

peaks from the bottom and weaker clay peaks from the top. The non-intercalated

Cloisite® Na+ act as larger particles with a smaller surface area in contact with the

resin compared to the intercalated clay and, as a result, more readily settle to the

bottom of the resin when not agitated.

halla

Acrobat has difficulties displaying Figures 4.4.3a and 4.4.3b online. To view please consult the hardcopy thesis available from the QUT Library


91

4.4.3 XRD of Epoxy Resins

The XRD pattern of the epoxy resins is a broad peak indicating an amorphous

structure. The XRD patterns of the DGEBA and TGDDM epoxy resins cured with

the three different hardeners are shown in Figure 4.4.3a and Figure 4.4.3b,

respectively. When epoxy resins cure, they form a random network structure without

a distinct repeating unit. This is signified by the broadness of the peaks in the XRD

patterns. The epoxy resins do however form a consistent XRD pattern. The location

of the main peak in the XRD pattern can be used as an indicator of the epoxy resin

used, as the broad peak varies depending on the epoxy. For the DGEBA, resin the

peak centred around 18.0 degrees 2θ and for TGDDM the peak is centred at 16.8

degrees 2θ. Different anhydride curing agents have no effect on the XRD pattern of

the epoxy resins but there is a change in the location of the smaller peak at lower

angles when the TETA curing agent is used. This may be due to the TETA

containing six reactive groups for epoxy cure and, as a result, it has the potential to

form a more cross-linked polymer matrix and a different polymer structure.

The broad epoxy peaks are expected to be present in all the XRD patterns of the

nanocomposites, as only the layer spacings of the clay is expected to vary.


92

Figure 4.4.4a – XRD of Cloisite® Na+

Layer Expansion in DGEBA

0

1000

2000

3000

4000

5000

6000

7000

8000

1 6 11 16 21

Degrees 2θ

Cou

nts

(a.u

.)

DGEBA Na+ 6hrs @ 80 degreesDGEBA Na+ 0hrs @ 80 degreesCloisite® Na+

Figure 4.4.4c – XRD of Cloisite® 93A


0

5000

10000

15000

20000

1 6 11 16 21

Degrees 2θ

Cou

nts

(a.u

.)

DGEBA 93A 6hrs @ 80 degreesDGEBA 93A 0hrs @ 80 degreesCloisite® 93A

Figure 4.4.4b – XRD of Cloisite® 30B


0

5000

10000

15000

20000

25000

30000

1 6 11 16 21

Degrees 2θ

Cou

nts

(a.u

.)

DGEBA 30B 6hrs @ 80 degreesDGEBA 30B 0hrs @ 80 degreesCloisite® 30B

Figure 4.4.4d – XRD of Cloisite® 15A


0

5000

10000

15000

20000

25000

30000

1 6 11 16 21Degrees 2θ

Cou

nts

(a.u

.)

DGEBA 15A 6hrs @ 80 degreesDGEBA 15A 0hrs @ 80 degreesCloisite® 15A


93

4.4.4 XRD of DGEBA

XRD was performed on the DGEBA after the addition of the Cloisite® clays but

before the addition of any curing agent. The XRD was performed immediately

following the combination of the resin and the clay and also after six hours at 80°C.

This was to show the layer separation that occurred between initial mixing and after

being left at elevated temperature. It was initially intended to record a series of XRD

patterns between zero minutes and six hours; however, the layers reached close to the

maximum separation during the mixing process. This can be seen in the comparison

between time equals zero and time equals six hours in Figures 4.4.4a-d. The broad

peak of the epoxy resin is present in all epoxy clay mixtures, as expected, as well as

the peak generated by the repeating unit of the clay in the b and c directions (010 and

100). There is a dramatic change in the layer spacing of the clays in the initial stages

of the dispersing process. While the increase in the layer spacing upon mixing is

largely due to the incorporation of the DGEBA resin into the layers of the clay, the

force applied by the high shear mixer, could result in a slight distortion of the silicate

galleries. Table 4.4.4 shows the changes that occur from the clay to the epoxy/clay

uncured nanocomposite.

Table 4.4.4 – Clay Separation in DGEBA Epoxy Resin

Clay 0 Hours 6 Hours @ 80°C

Cloisite® Na+ 12.3Å 12.3Å 13.5Å

Cloisite® 30B 18.2Å 36.0Å 36.1Å

Cloisite® 93A 24.0Å 36.1Å 36.0Å

Cloisite® 15A 35.1Å 36.6Å 36.4Å

There was only a slight change in the d-spacing of the Cloisite® Na+ when it was

combined with the DGEBA resin. The location of the peak defining the layer spacing

was difficult to accurately determine for the Cloisite® Na+ as it became hidden within

the broad, amorphous epoxy peak. The location does suggest no significant layer

expansion has occurred. There was a dramatic change in the d-spacing for both the

Cloisite® 30B and the Cloisite® 93A and only a slight increase in the d-spacing of

the Cloisite® 15A, as it has a larger initial layer spacing. There was an insignificant

increase in d-spacing between the completion of mixing and after six hours at 80°C.


94

This demonstrates the degree of acceptance the clay has for the organic molecules.

The ammonium cation substituted into the clay to replace the Na+ ions promotes the

incorporation of the DGEBA molecule between the layers of the clay and increased

the layer distance to approximately 36Å. Kornmann et al [93] reported a layer spacing

of 34Å when dispersing a similar alkylammonium modified clay with a DGEBA

resin. The hydrophilic nature of the alkylammonium modified clays allows the epoxy

molecules to migrate between the layers. It is suggested that the alkylammonium ions

reorientate from the lateral bilayer in the dry state to a perpendicular orientation in

order to accommodate the DGEBA resin. The perpendicular orientation is thought to

optimise the solvation interaction between the alkyl groups and the DGEBA

molecules. The uniformity of the d-spacing across the organoclays when combined

with the DGEBA resin, suggests that the DGEBA resin requires a layer spacing of

36Å to fit between the layers of the clay, regardless of the structure of the alkyl

ammonium cation. The unmodified clay shows no indication of an interaction with

the epoxy resin compared to the modified clays, which shows the benefit of the

organophilic substitution prior to incorporating the epoxy.


95

Figure 4.4.4.1 – XRD of DGEBA/MTHPA Systems

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

1 6 11 16 21Temperature (°C)

Cou

nts

(a.u

.)

15A93A30BNa+ TopNa+ BottomControl


96

4.4.4.1 XRD of DGEBA and MTHPA

The XRD pattern of the nanocomposites produced from DGEBA cured with MTHPA

show that Cloisite® 30B, Cloisite® 93A and Cloisite® 15A successfully produced a

cured, intercalated nanocomposite. Observation of the DGEBA and MTHPA with

Cloisite Na+ did not show any separation within the structure. In composites

involving Cloisite® Na+, a separation could be seen; therefore; an XRD pattern was

recorded for both the top and the bottom of the Cloisite® Na+ sample and the top of

the other clays (Figure 4.4.4.1). The XRD pattern of the Cloisite® Na+ bottom shows

a greater similarity to that of the clay (Figure 4.4.1) on its own and the pattern for the

top shows almost only the epoxy resin broad peaks. This supports the hypothesis that

a phase separation has occurred. Table 4.4.4.1 shows the final layer separation of the

clay in the nanocomposites produced.

Table 4.4.4.1 – Clay Separation in DGEBA/MTHPA Nanocomposites

Clay Clay/Resin Nanocomposite


Cloisite® 30B 18.2Å 36.1Å 41.8Å

Cloisite® 93A 24.0Å 36.0Å 37.0Å

Cloisite® 15A 35.1Å 36.4Å 36.1Å

The Cloisite® Na+ had a small separation in the layer spacing compared to before the

hardener was added. This was evident in the pattern from the bottom of the sample.

This means there was no interaction between the inorganic clay particles and the

organic epoxy resin but the hardener did force some expansion. However, the settling

of the clay to the bottom of the samples indicates that there was virtually no

interaction between the clay and the organic epoxy resin. As a result, the final

product is only a poor epoxy/clay composite and not a nanocomposite.

A nanocomposite was successfully produced using the three modified clays. Only the

Cloisite® 30B showed any significant increase in d-spacing after addition of the

MTHPA curing agent. This indicated, for the Cloisite® 93A and the Cloisite® 15A,

that no additional organic molecules, neither epoxy resin nor curing agent, were

incorporated into the layers, suggesting that the epoxy resin between the layers of


97

the clay remains uncured. All modified clays produced an intercalated nanocomposite

with the XRD patterns suggesting that only the Cloisite® 30B expanded after the

addition of the curing agent.

Tolle et al [104] reported that the structure of the organoclay has an effect on the layer

separation. They claim this is due to the different amounts of organic groups on the

silicate surface, and different amounts lead to different ratios between the organic

groups of the cations and the epoxy/hardener mixture between the layers. Differences

were only seen between the Cloisite® clays used after the addition of the curing

agent. This suggests that the organoclay used, has a variable effect on the curing

agent used, not the epoxy.

No indication of the further layer expansion of the Cloisite® 30B is seen in the heat

flow during cure (Figure 4.2.1). The Tg for the DGEBA cured with MTHPA

(Figure 4.3.1) shows that the Cloisite® 30B nanocomposite has the lowest Tg. This

suggests that the additional layer expansion is due to further intercalating of epoxy

groups that, both, remain uncured and do not contribute to the cross-linking of the

nanocomposite. The reduction in the Tg for Cloisite® 93A and Cloisite® 15A is not

as large as there are fewer epoxy groups within the layers of the clay so a larger

amount of cross-linking can occur in the resin, outside or around the clay.


98

Figure 4.4.4.2 – XRD of DGEBA/HHPA Systems

0

5000

10000

15000

20000

25000

30000

1 6 11 16 21

Degrees 2θ

Cou

nts

(a.u

.)



99

4.4.4.2 XRD of DGEBA and HHPA

For DGEBA cured with HHPA, the XRD pattern of the nanocomposites produced

show that Cloisite® 30B and Cloisite® 93A successfully produced a cured

nanocomposite with large layer spacings. The Cloisite® 15A produces a

nanocomposite, but the layer spacing was not as large. Due to evidence of separation,

an XRD pattern was recorded for both the top and the bottom of the Cloisite® Na+

sample and the top of the other clays (Figure 4.4.4.2). The XRD pattern of the

Cloisite® Na+ bottom shows a greater similarity to that of the clay (Figure 4.4.1) on

its own and the pattern for the top shows only the epoxy resin amorphous peaks.

Table 4.4.4.2 shows the final layer separation of the clay in the nanocomposites

produced.

Table 4.4.4.2 – Clay Separation in DGEBA/HHPA Nanocomposites



Cloisite® 30B 18.2Å 36.1Å ~66Å

Cloisite® 93A 24.0Å 36.0Å >80Å

Cloisite® 15A 35.1Å 36.4Å 34.0Å

The low viscosity, caused by the elevated temperatures required for anhydride cure of

DGEBA, means the Cloisite® Na+ with low surface area in contact with the resin

settles to the bottom to form a non-uniform composite. Nanocomposites were

successfully produced using the three modified clays. The Cloisite® 15A showed no

further layer spacing increase when the HHPA hardener was added. This indicates

that the hardener was unable to migrate between the layers. As a result the epoxy

molecules that were between the layers would have remained unreacted, supported by

the Tg (Figure 4.3.2), which is the lowest of the DGEBA/HHPA systems. A very

large layer expansion occurred for the systems using Cloisite® 30B and

Cloisite® 93A. The exact location of the peak is difficult to determine, due to the

very low angle, and the second phase peak is obstructed by the first peak so it too is

difficult to determine accurately. The large expansion of the layer indicates that the

curing agent migrated between the layers and reacted with the epoxy groups within.

The presence of the clay (001) peaks indicates that the clay layers still possess a


100

degree of organisation, meaning that they should technically be classed as intercalated

nanocomposites. If the layers were expanded further, difficulty in recording

information at such low angles means that, the XRD pattern would show no peaks at

low angle but the peak at 19.8 degrees 2θ would still remain. The XRD pattern, in

that case, would suggest that a delaminated nanocomposite was produced.

The increasing layer spacing, while retaining the ordered structure suggests that the

mechanism for insertion of organic epoxy and hardener molecules is uniform from all

directions. The uniform interaction between the inorganic clay and the organic

DGEBA/HHPA resin causes the layers to move apart in an ordered manner, not slide

or fall apart in an unordered manner. With such large layer spacings it would be

anticipated that any property changes would be similar to those of a fully delaminated

nanocomposite.

The large increase in layer spacing of the Cloisite® 93A and the Cloisite® 30B

compared to the Cloisite® 15A and a comparison between the Tg (Figure 4.3.2)

suggests that the layer expansion results in more epoxy groups reacting. The larger

number of reacted epoxy groups means more cross-linking has occurred, leading to

the higher Tg.


101

Figure 4.4.4.3 – XRD of DGEBA/TETA Systems

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

1 6 11 16 21

Degrees 2θ

Cou

nts

(a.u

.)



102

4.4.4.3 XRD of DGEBA and TETA

The XRD pattern of the nanocomposites produced show that the organoclays

successfully produced a cured nanocomposite. Observation of the DGEBA and

TETA with Cloisite Na+ did not show any separation within the structure. However,

an XRD pattern was recorded for both the top and the bottom of the Cloisite® Na+

sample and the top of the other clays, shown in Figure 4.4.4.3. The comparison

between the XRD pattern of the Cloisite® Na+ bottom and top shows greater

similarity than for anhydride cured DGEBA, indicating that low temperature cure

does not give the same reduction in viscosity, which allows the separation. The peak

at 19.8 degrees 2θ is also strong in the XRD pattern of the top. This suggests that in

the DGEBA and TETA systems separation does not occur. Table 4.4.4.3 shows the

final layer separation of the clay in the nanocomposites produced.

Table 4.4.4.3 – Clay Separation in DGEBA/TETA Nanocomposites



Cloisite® 30B 18.2Å 36.1Å 44.0Å

Cloisite® 93A 24.0Å 36.0Å 38.4Å

Cloisite® 15A 35.1Å 36.4Å 35.9Å

There is a small increase in the d-spacing of the Cloisite® Na+. The extent of the

layer expansion is not large enough to be intercalating of the epoxy resin. It is most

likely caused by an intercalation of the TETA curing agent between the layers. This

is supported by the increase only occurring after the hardener has been added. Of the

nanocomposites produced, only the Cloisite® 30B showed any increase in d-spacing

after addition of the TETA curing agent. This indicates that, for the Cloisite® 93A

and the Cloisite® 15A, no curing agent was incorporated into the layers, suggesting

that the epoxy resin between the layers of the clay remains uncured. All modified

clays produced an intercalated nanocomposite. For DGEBA cured with TETA, the

additional layer expansion, after the curing agent is added, for Cloisite® 30B has no

significant effect on the Tg (Figure 4.3.3). This suggests that the curing agent that is

intercalated between the layers of the clay does not lead to a significant reduction in

the amount of cross-linking within the resin.


103

Figure 4.4.5a – XRD of Cloisite® Na+

Layer Expansion in TGDDM

0

1000

2000

3000

4000

5000

6000

7000

1 6 11 16 21

Degrees 2θ

Cou

nts

(a.u

.)

TGDDM Na+ 6hrs @ 80 degreesTGDDM Na+ 0hrs @ 80 degreesCloisite® Na+

Figure 4.4.5c – XRD of Cloisite® 93A


0

2000

4000

6000

8000

10000

12000

14000

16000

1 6 11 16 21

Degrees 2θ

Cou

nts

(a.u

.)

TGDDM 93A 6hrs @ 80 degreesTGDDM 93A 0hrs @ 80 degreesCloisite® 93A

Figure 4.4.5b – XRD of Cloisite® 30B


0

5000

10000

15000

20000

25000

1 6 11 16 21

Degrees 2θ

Cou

nts

(a.u

.)

TGDDM 30B 6hrs @ 80 degreesTGDDM 30B 0hrs @ 80 degreesCloisite® 30B

Figure 4.4.5d – XRD of Cloisite® 15A


0

10000

20000

30000

40000

50000

60000

1 6 11 16 21

Degrees 2θ

Cou

nts

(a.u

.)

TGDDM 15A 6hrs @ 80 degreesTGDDM 15A 0hrs @ 80 degreesCloisite® 15A


104

4.4.5 XRD of TGDDM

An XRD pattern was recorded to show the layer expansions that occur when the clays

are combined with the TGDDM resin before the addition of the hardener. An XRD

pattern of the TGDDM resin/clay composites was taken immediately after combining

and after a period of six hours at 80°C. The majority of layer expansion takes place

while mixing, as shown by Figures 4.4.5a-d. The broad peak, due to the amorphous

epoxy resin, is present in all patterns as well as the peak at 19.8 degrees 2θ, which can

be seen when the area is magnified, proving the presence of the clay. Table 4.4.5

shows the changes that occur from the clay to the epoxy/clay uncured nanocomposite.

Table 4.4.5 – Clay Separation in TGDDM Epoxy Resin

Clay 0 Hours 6 Hours @ 80°C


Cloisite® 30B 18.2Å 35.0Å 35.4Å

Cloisite® 93A 24.0Å 35.7Å 38.2Å

Cloisite® 15A 35.1Å 36.6Å 37.4Å

There was virtually no change in the d-spacing of the Cloisite® Na+ when it was

combined with the TGDDM resin. There was a dramatic change in the d-spacing for

both the Cloisite® 30B and the Cloisite® 93A and a slight increase in the d-spacing

of the Cloisite® 15A. There is only a slight increase in d-spacing between the

completion of mixing and after six hours at 80°C. This demonstrates the degree of

acceptance the clay has for the organic molecules. The ammonium cation, substituted

into the clay to replace the Na+ ions promote the incorporation of the TGDDM

molecule between the layers of the clay and increase the layer distance to

approximately 38Å. The layer spacing achieved after the addition of the organoclay

to the TGDDM is similar to that of DGEBA. This indicates that the mechanism of

intercalation reported by Kornmann et al [93] for DGEBA is the same for TGDDM.

The reorientation of the of the alkylammonium cations from lateral bilayer to

perpendicular is what controls the final spacing.


105

Figure 4.4.5.1 – XRD of TGDDM/MTHPA Systems

0

5000

10000

15000

20000

1 6 11 16 21

Degrees 2θ

Cou

nts

(a.u

.)15A93A30BNa+ TopNa+ BottomNo Clay


106

4.4.5.1 XRD of TGDDM and MTHPA Nanocomposites

The XRD pattern of the nanocomposites produced show that Cloisite® 30B,

Cloisite® 93A and Cloisite® 15A successfully produced a cured, intercalated

nanocomposite. Observation of the TGDDM and MTHPA with Cloisite Na+ showed

a large degree of separation within the structure. It was clear that the majority of the

clay was present on the bottom of the sample. For this reason, an XRD pattern was

recorded for both the top and the bottom of the Cloisite® Na+ sample and the top of

the other clays (Figure 4.4.5.1). The XRD pattern of the Cloisite® Na+ bottom shows

a greater similarity to that of the clay (Figure 4.4.1) on its own, and the pattern for the

top shows a greater similarity to the epoxy resin. This supports the observation of a

separation occurring. Table 4.4.5.1 shows the final layer separation of the clay in the

nanocomposites produced.

Table 4.4.5.1 – Clay Separation in TGDDM/MTHPA Nanocomposites



Cloisite® 30B 18.2Å 35.4Å 43.0Å

Cloisite® 93A 24.0Å 38.2Å 39.4Å

Cloisite® 15A 35.1Å 37.4Å 37.4Å

The Cloisite® Na+ showed no evidence of layer separation. This means there was no

interaction between the inorganic clay particles and the organic epoxy resin. There is

no interaction on the nanometre scale and, as a result, the final product is only an

epoxy/clay composite and not a nanocomposite. Nanocomposites were successfully

produced using the three modified clays. Only the Cloisite® 30B showed any

increase in d-spacing after addition of the MTHPA curing agent. This suggests that

for the Cloisite® 93A and the Cloisite® 15A no curing agent was incorporated into

the layers, suggesting that the epoxy resin between the layers of the clay remains

uncured.


107

The additional layer expansion that occurred with the Cloisite® 30B after the

MTHPA curing agent was added was seen as an anomaly in the heat flow during cure

(Figure 4.2.4). The curing reaction reached a larger percentage cured before a

reduction in the rate of reaction was seen and fewer reactions were evident after that

point. The additional layer expansion, together with the decrease in the Tg

(Figure 4.3.4), indicates that further TGDDM molecules are intercalated between the

clay layers. The epoxy groups between the layers then remained uncured, which

means the heat during cure shows the trapped epoxy groups remain uncured, not a

more efficient curing nanocomposite.


108

Figure 4.4.5.2 – XRD of TGDDM/HHPA Systems

0

2000

4000

6000

8000

10000

12000

14000

16000

1 6 11 16 21

Degrees 2θ

Cou

nts

(a.u

.)

15A93A30BNa+ TopNa+ BottomNo Clay


109

4.4.5.2 XRD of TGDDM and HHPA

When TGDDM containing an organoclay is cured with HHPA, an intercalated

nanocomposite results. Figure 4.4.5.2 shows the XRD patterns for the

TGDDM/HHPA systems. Due to the separation that occurs with Cloisite® Na+, an

XRD pattern was recorded for the top and bottom of the sample. Table 4.4.5.2 shows

the layer expansion that occurs in the curing of the nanocomposites.

Table 4.4.5.2 – Clay Separation in TGDDM/HHPA Nanocomposites



Cloisite® 30B 18.2Å 35.4Å 43.2Å

Cloisite® 93A 24.0Å 38.2Å 46.6Å

Cloisite® 15A 35.1Å 37.4Å 37.7Å

No layer expansion occurred with the Cloisite® Na+, and the separation that occurred

resulted in a poorly dispersed composite. The Cloisite® 15A did not separate further

after the addition of the HHPA curing agent. This may be due to the curing reactions

occurring more readily around the clay particles than within the layers. As a result, a

rigid cross-linked network forms around the clay preventing layer separation. The

expansion in the layers of the Cloisite® 30B and the Cloisite® 93A indicates that

some reactions within the layers were able to occur before the infinite network of the

epoxy was formed, preventing further expansion. The Tg for the TGDDM cured with

HHPA (Figure 4.3.5) suggests that the additional layer expansion of the

Cloisite® 30B is due to more epoxy resin intercalating between the layers. The

reduced Tg indicates that the epoxy groups between the layers do not contribute to

cross-linking. The epoxy resin within the layers may either self polymerise, react

with the HHPA, but terminate within the layers, or remain uncured. The Tg for the

Cloisite® 93A is slightly higher than that of the Cloisite® 30B. This suggests that the

larger expansion that occurs in the layers spacing allows some increased cross-linking

between the layers compared to the Cloisite® 30B.


110

Figure 4.4.5.3 – XRD of TGDDM/TETA Systems

0

5000

10000

15000

20000

1 6 11 16 21

Temperature (°C)

Cou

nts

(a.u

.)



111

4.4.5.3 XRD of TGDDM and TETA

An XRD pattern was recorded for both the top and the bottom of the Cloisite® Na+

sample and the top of the other clays, as shown in Figure 4.4.5.3. The comparison

between the XRD pattern of the Cloisite® Na+ bottom and top shows greater

similarity than for anhydride cured TGDDM. The peak at 19.8 degrees 2θ is also

strong in the XRD pattern of the top but the peak at 6.5 degrees 2θ is slightly stronger

for the bottom of the sample. This suggests that, in the TGDDM/TETA systems, only

slight separation occurs. This is because the curing reaction occurs at lower

temperatures and, as a result, the systems proceeds to the gel point without sitting at

low viscosity for an extended period of time, similarly to high temperature cure

TGDDM systems. Table 4.4.5.3 shows the final layer separation of the clay in the

nanocomposites produced.

Table 4.4.5.3 – Clay Separation in TGDDM/TETA Nanocomposites



Cloisite® 30B 18.2Å 35.4Å 39.4Å

Cloisite® 93A 24.0Å 38.2Å 42.3Å

Cloisite® 15A 35.1Å 37.4Å 37.9Å

There is a slight increase in the d-spacing of the Cloisite® Na+. The extent of the

layer expansion is not large enough to be intercalation of the epoxy resin. It is

possibly caused by a small amount of intercalation of the TETA curing agent between

the layers. This is supported by the increase only occurring after the hardener has

been added. Of the nanocomposites produced, only the Cloisite® 30B and

Cloisite® 93A showed any increase in d spacing after addition of the TETA curing

agent. This indicates that, for the Cloisite® 15A, no curing agent was incorporated

into the layers, suggesting that the epoxy resin between the layers of the clay remains

uncured or undergoes self polymerisation. The Cloisite® 93A, which has the largest

layer spacing, has the lowest Tg (Figure 4.3.6). This indicates that a larger number of

epoxy groups are within the layers and remain unreacted, or the polymerisation

terminates within the layers preventing cross-linking. The Cloisite® 30B also shows

some layer expansion after the addition of the TETA curing agent. The Tg of the


112

Cloisite® 30B system is higher than that of the Cloisite® 93A, suggesting that fewer

epoxy groups remain unreacted between the layers.


113

Figure 4.4.6 – XRD of Cloisite® 30B Layer Separation in Curing Agents

0

5000

10000

15000

20000

1 6 11 16 21Degrees 2θ

Cou

nts

(a.u

.)

TETAHHPAMTHPACloisite 30B


114

4.4.6 XRD of Clay Layer Expansion in Curing Agents

An XRD pattern was recorded to show the layer expansion that may occur when the

clay and the aliphatic amine or anhydride curing agent are able to interact without the

epoxy resin being present. Cloisite® 30B was used, as it had consistently shown the

greatest potential to expand. The layer expansion that occurred is shown in Figure

4.4.6. Table 4.4.6 shows the d-spacing recorded. The variations in the intensity of

the peaks were caused by the positioning of the sample for analysis, which is

particularly difficult to control with liquid samples. As a result only the location is

important not the intensity of the peaks.

Table 4.4.6 – Clay Layer Expansion in Curing Agents

Cloisite® 30B MTHPA HHPA TETA

18.2Ǻ 38.9Ǻ 57.7Ǻ 44.4Ǻ

The clay within the TETA had a tendency to separate and fall to the bottom of the

sample, caused by low viscosity of the TETA curing agent. In comparison the

anhydride curing agents were more viscous, which prevented separation. As a result,

the XRD pattern of the TETA shows the expansion of the clay but does not show the

expected peak at 19.8 degrees 2θ. Adding the clay to the curing agent resulted, for

MTHPA and TETA, in a layer expansion similar to what was achieved when the clay

was added to the epoxy resin prior to addition of the hardener. The peak for the clay

within MTHPA is broad in comparison to the HHPA and TETA. This suggests a

wider range of layer spacings is present. The large d-spacing achieved when the clay

was added to HHPA compared to MTHPA suggests that the un-accelerated curing

agent (HHPA) has a greater affinity for the quaternary ammonium cation. When the

curing agent is added to the organoclay without any epoxy resin being present, the

interactions between the clay and organic hardener, are not impeded by the formation

of longer polymer chains and a network structure. The HHPA curing agent promotes

an exfoliated structure. When the clay is added to the epoxy resin before the addition

of the hardener, the curing reactions that occur most readily are where the quaternary

ammonium cations catalyse the anhydride curing reaction inside the organoclay

layers. The reactions occurring in, and around, the clay layers result in a rigid

network encapsulating the clay, which then prevents exfoliation.


115

4.4.7 XRD of Epoxy Resin Nanocomposites

The addition of unmodified Cloisite® Na+ to the epoxy resin systems resulted in a

composite being produced. There was no interaction on a nanoscale level and when

the epoxy was cured with the anhydride hardeners, the elevated temperatures caused a

reduction in viscosity that resulted in a settling of the clay to the bottom. The addition

of the modified clays resulted in the production of intercalated nanocomposites. The

Cloisite® 15A showed no further layer expansion after addition of the curing agent

while the Cloisite® 30B and Cloisite® 93A expanded by different amounts depending

on the hardener used. A small increase in the layer spacing when the hardener was

added resulted in a reduction in the Tg. The reduction in Tg suggests that the

expansion is due to more epoxy resin being intercalated and, as a result, more epoxy

groups do not contribute to cross-linking. The exception was DGEBA cured with

HHPA, which had a large layer expansion, meaning the epoxy resin between the

layers was able to contribute to cross-linking.

The structure of the clay had very little effect on the layer separation when added to

the epoxy resin. This suggests that the structure of the organophilic cation has no

effect on the intercalation of the Cloisite® with the epoxy resin. However, an

organophilic cation is required for intercalation, as no layer expansion was seen with

the unmodified Cloisite® Na+. The layer expansion varied within an epoxy/curing

agent system depending on the modified clay used. As a result it can be concluded

that the structure of the organophilic cation has an effect on the layer expansion

during cure. The Cloisite® 30B and Cloisite® 15A have the same reactive groups

(quaternary amine) to influence the cure. The differences in their structure are due to

variations in the inert carbon chains. Cloisite® 93A contains a ternary amine which

can react differently with the epoxy/curing agent systems. The effect of this

difference varies from system to system according to the degree of catalysis provided

by the clay for the epoxy cure reaction. As a result the difference in the ability of the

organic cations to assist in the layer expansion is limited due to the physical size and

chemical structure of the molecules and varies between Cloisite® 30B, Cloisite® 93A

and Cloisite® 15A.


116

Becker et al [105] reported that larger expansion of the layers is achieved with lower

functionality resins. This effect was only seen with the HHPA curing agent. The

results showed that the final layer spacings of the nanocomposites were similar for

both MTHPA and TETA regardless of whether the epoxy was the di-functional

DGEBA or the tetra-functional TGDDM. The final layer expansion that was

achieved was determined by the rate at which the curing reactions reach gelation. The

highly cross-linked network that forms at gelation prevents the layers from expanding

any further. While the DGEBA cured with HHPA had a larger layer expansion than

the TGDDM cured with HHPA, the difference is more likely due to the differences in

the relative reactivity between the epoxy and the curing agent than the functionality of

the resin. Kornmann et al [96] reported that the exfoliation of the organophilic clay in

the epoxy systems is controlled by the relative difference in the reaction rates between

the intragallery and extragallery polymerisation. They claim that a lower reactivity of

the curing agent will lead to a larger extent of exfoliation. The hexa-functional TETA

and the accelerated MTHPA readily react with the epoxy resin independent of the

clay and, as a result, the rate of intragallery polymerisation is not able to proceed at a

faster enough rate compared to the extragallery polymerisation to allow significant

separation of the layers. For TGDDM cured with HHPA, the self catalysis of the

tertiary amine in the TGDDM promotes extragallery polymerisation, which forms a

highly cross-linked network and prevents exfoliation of the layers. When the

DGEBA is cured with HHPA, alkylammonium cations of the modified clay provide

the catalyst for the curing reactions and, as a result, the intragallery polymerisation

occurs more readily than the extragallery polymerisation resulting in the larger layer

expansion.

Chen et al [116] proposed a three stage exfoliation mechanism for an epoxy resin

nanocomposite. In the first stage, the interlayer expansion induced by intragallery

polymerisation must overcome any polymer chains that bridge the silicate layers. The

interlayer expansion cannot proceed beyond the first stage if the number of bridging

units becomes too great. The second stage involves a steady and linear increase in

interlayer spacing and accounts for the majority of the total expansion. They found

that the activation energy associated with interlayer expansion was less than the

activation energy associated with curing. The third stage is the completion of

expansion, which occurs when the modulus of the extragallery polymer becomes


117

equal to, or exceeds, the modulus of the intragallery polymer. For systems that

showed no further layer expansion after the addition of the curing agent, the

extragallery polymer became equal to, or exceeded, the intragallery polymer very

early in the curing process. In these systems, the curing reactions proceed more easily

outside the clay layers than between them. The layer expansion achieved within each

system would be controlled by the expansion that can occur before the modulus of the

extragallery polymer exceeds that of the intragallery polymer. For more reactive

curing agents this point would be reached faster resulting in a smaller d-spacing. A

more reactive catalyst, provided by the alkylammonium cation, would promote a

larger layer expansion.


118

Figure 4.5 – TEM images of Nanocomposites

TEM images of Cloisite® 30B in TGDDM/HHPA

TEM images of Cloisite® 30B in TGDDM/HHPA


119

4.5 TEM OF EPOXY NANOCOMPOSITES

XRD showed that the structure of the nanocomposites formed was generally an

intercalated nanocomposite with a clay interlayer spacing of approximately 40Ǻ. The

spacing produced clear peaks in the XRD patterns. TEM images, Figure 4.5, were

taken to verify that the interlayer spacings were at the distances indicated by XRD.

The sample of TGDDM/MTHPA with Cloisite® 30B was chosen to be a

representative sample of the intercalated nanocomposites. In the case of

DGEBA/HHPA with Cloisite® 30B and Cloisite® 93A, the layer spacing increased

dramatically and could not be accurately recorded using XRD. TEM images were

taken of the DGEBA/HHPA with Cloisite® 93A to show the large interlayer spacing

of the organoclay. In both cases the clay retained the stacked layer pattern. The

TGDDM/MTHPA with Cloisite® 30B showed smaller layer spacing than the

DGEBA/HHPA with Cloisite® 93A, which supports the results of XRD. The clay

layers within the DGEBA/HHPA, while generally retaining the stacked layer

structure, showed more variation in the layers than the nanocomposite with the

smaller spacing. Had the spacing been within a recordable region of XRD, a broader

peak would be expected. The TEM images support that, in the nanocomposites with

layer spacings of approximately 40Å, an intercalated nanocomposite was produced.

Becker et al [102, 112] reported the formation of nanocomposites with a layer spacing of

approximately 100Å, which was measured by TEM after XRD indicated an exfoliated

nanocomposite. A more accurate description of the morphology was described by

them as well intercalated or an ordered exfoliated nanocomposite. Kornmann et al [96]

reported that if the spacing between the layers is small, so that they could obtain a

basal (001) reflection on the diffraction pattern, the nanocomposite is termed

intercalated. If the spacing is large, X-rays can not detect the (001) reflection, the

nanocomposite was then termed exfoliated. This method ignores that exfoliation

implies a complete separation and random orientation of the clay layers. This was

seen for the Cloisite® 30B and Cloisite® 93A when dispersed in DGEBA and cured

with HHPA and the TEM images suggest the morphology is best described as a well

intercalated nanocomposite.


120

In Figure 4.5d it may be seen that the exfoliation of the layers, which had begun to

occur as the d-spacing increased in the DGEBA/HHPA with Cloisite® 30B and

Cloisite® 93A, appeared to have been halted by the formation of a rigid network

structure around the layers of the clay. Thus, the HHPA hardener promotes the

formation of an exfoliated nanocomposite. The quaternary ammonium cation

catalysed curing reactions that occur around the clay prevent proper exfoliation from

occurring.


121

Figure 4.6.1 – Young’s Modulus of Elasticity


122

4.6 MECHANICAL ANALYSIS OF NANOCOMPOSITES

4.6.1 Young’s Modulus of Elasticity

Mechanical analysis was performed on all nanocomposites, composites and control

samples to determine the effect of the nanoscale interaction between the clay and the

epoxy resin. According to the literature [93, 96, 100, 112, 115, 120] it is expected that the

nanocomposites would have a greater Young’s modulus of elasticity than the

composite with the Cloisite® Na+ and the unfilled epoxy sample. Table 4.6.1 and

Figure 4.6.1 show the measured Young’s modulus for the epoxy systems studied.

Table 4.6.1 – Young’s Modulus of Elasticity for Epoxy Systems

No Clay Cloisite® Na+

Cloisite® 30B

Cloisite® 93A

Cloisite® 15A

DGEBA MTHPA

4.0 ± 0.5 GPa

4.7 ± 0.5 GPa

4.0 ± 0.5 GPa

4.4 ± 0.5 GPa

3.5 ± 0.5 GPa

DGEBA HHPA

3.0 ± 1 GPa

4.9 ± 1 GPa

3.0 ± 1 GPa

3.3 ± 1 GPa

2.5 ± 1 GPa

DGEBA TETA

1.2 ± 0.7 GPa

2.4 ± 0.7 GPa

3.0 ± 0.7 GPa

2.4 ± 0.7 GPa

2.6 ± 0.7 GPa

TGDDM MTHPA

1.2 ± 0.1 GPa

1.3 ± 0.1 GPa

1.2 ± 0.1 GPa

1.2 ± 0.1 GPa

1.1 ± 0.1 GPa

TGDDM HHPA

1.14 ± 0.1 GPa

1.29 ± 0.1 GPa

1.30 ± 0.1 GPa

1.26 ± 0.1 GPa

1.25 ± 0.1 GPa

TGDDM TETA

2.38 ± 0.4 GPa

2.42 ± 0.4 GPa

2.80 ± 0.4 GPa

4.12 ± 0.4 GPa

4.03 ± 0.4 GPa

The change in the Young’s modulus with the addition of clay, both modified and

unmodified, shows that whether any increase or decrease is seen is related to the

hardener used. This indicates that the effect the clay has on strengthening the epoxy

is dependent on the rate of reaction and/or the potential for cross-linking provided by

the hardener. The amine (TETA) cured epoxy systems resulted in an increase with

the addition of the Cloisite® Na+ and a greater increase with the addition of the

organophilic clays. These results agree with those obtained by Ratna et al [112], Isik et

al [115] and Kornmann et al [96] that the nanocomposites produced have a greater elastic

modulus than the resin on its own.


123

The epoxy systems cured with MTHPA resulted in only a small change in the elastic

modulus. The TGDDM/MTHPA showed a general decrease in the modulus with the

modified clays and the DGEBA/MTHPA had a slight decrease with the

Cloisite® 30B and Cloisite® 15A and a slight increase with the Cloisite® 93A. The

largest increase in modulus was seen with the unmodified Cloisite® Na+. The epoxy

systems cured with the HHPA generally increased slightly with the addition of clay.

The increase with Cloisite® Na+ was equivalent with the TGDDM epoxy resin and

significantly greater with the DGEBA epoxy resin than the modified clays. The

nanocomposites closest to exfoliated in structure, shown by XRD, DGEBA/HHPA

with Cloisite® 30B and Cloisite® 93A, showed very little increase in the elastic

modulus compared to the unfilled epoxy resin. This disagrees with the results

obtained by Pinnavaia et al [120], who claimed that the elastic modulus increased with

increasing degree of exfoliation. Yasmin et al[100] reported that the

DGEBA/anhydride cured system has an increase in elastic modulus with the addition

of a modified clay. The anhydride cured systems show a greater increase in elastic

modulus when combined with unmodified clay. This suggests that if the procedure

was repeated by Yasmin et al [100] using an unmodified clay their results for elastic

modulus would show a greater increase. For anhydride cured epoxy resins, the

interactions between the inorganic clay and the organic resin that lead to an increase

in the elastic modulus can be achieved with microscale interaction of unmodified

clay. While nanoscale interactions of nanocomposites are not detrimental to the resin

they do not offer the same increases in modulus that can be achieved with unmodified

clay.


124

Figure 4.6.2 – Flexural Strength of Epoxy Systems


125

4.6.2 Flexural Strength of Epoxy Systems

The flexural strengths measured for the epoxy systems studied, shown in Figure 4.6.2,

generally decreased with the addition of clay compared to the unfilled resins, with

only the TGDDM cured with HHPA showing an increase. Table 4.6.2 shows the

flexural strengths measured.

Table 4.6.2 – Flexural Strength of Epoxy Systems

No Clay Cloisite® Na+

Cloisite® 30B

Cloisite® 93A

Cloisite® 15A

DGEBA MTHPA

79 ± 10 MPa

68 ± 10 MPa

41 ± 10 MPa

54 ± 10 MPa

47 ± 10 MPa

DGEBA HHPA

81 ± 10 MPa

52 ± 10 MPa

48 ± 10 MPa

74 ± 10 MPa

41 ± 10 MPa

DGEBA TETA

69 ± 10 MPa

73 ± 10 MPa

48 ± 10 MPa

74 ± 10 MPa

42 ± 10 MPa

TGDDM MTHPA

72 ± 5 MPa

78 ± 5 MPa

65 ± 5 MPa

73 ± 5 MPa

44 ± 5 MPa

TGDDM HHPA

42 ± 10 MPa

79 ± 10 MPa

77 ± 10 MPa

67 ± 10 MPa

64 ± 10 MPa

TGDDM TETA

67 ± 10 MPa

56 ± 10 MPa

34 ± 10 MPa

40 ± 10 MPa

51 ± 10 MPa

Isik et al [115] found that addition of organoclay results in a decrease in strength of the

nanocomposite compared to the unfilled resin. They claim that the clay particles form

agglomerates. These act as stress concentrators, which decrease the strength. The

flexural strength of the epoxy/clay composite produced using the unmodified

Cloisite® Na+ resulted in a higher flexural strength than when the organoclays were

added. The interaction of the clay with epoxy resin may act as a point of weakness.

For the organoclays when the layers are more evenly dispersed, the distance between

layers, the points of weakness, is reduced. The shorter distances between the points

of weakness within the epoxy nanocomposite result in a decrease in the flexural

strength. The reduced cross-linking that occurs with the addition of the clay to the

epoxy system would also contribute to a decrease in the flexural strength.

Chapter 5 – Conclusions

126

5 CONCLUSIONS

When a DEGBA or TGDDM resin is combined with an organoclay modified with

either a quaternary ammonium cation or a ternary ammonium cation, an intercalated

nanocomposite is produced. When the unmodified clay is used there is no interaction

on the nanoscale level and, as a result, a composite is the product. The high

temperature of cure required for the anhydride hardeners results in settling of the

unmodified clay to the bottom of the sample, while the organophilic cations in the

organoclays hold the clay suspended evenly throughout the epoxy resin. The epoxy

resins readily intercalate with the organoclay during the mixing process but the effect

of the hardener varies depending on the system. Of the organoclays studied the

Cloisite® 30B expands, beyond the initial expansion of mixing, most readily.

Expansion is also seen in the Cloisite® 93A but not in Cloisite® 15A. This suggests

the type of organic cation in the clay has a large effect on how the resin cures

surrounding the clay particles.

DGEBA cured with HHPA, when combined with Cloisite® 93A and Cloisite® 30B

provided the largest layer expansion, with d-spacings exceeding 60Å. The HHPA,

unlike the MTHPA, contains no accelerator and the DGEBA resin does not have the

catalysing structure of the tertiary amine in the TGDDM. There is no other source of

catalysis, so the curing reaction of DGEBA with HHPA is controlled by the

ammonium cations within the layers of the clay. The catalysing effect of the

ammonium cations within the clay means that the clay particles are the sites of the

curing reactions at lower temperatures, and the dependency of the resin on the cations

forces the layers further apart.

The extent of the intercalation has a significant effect on the Tg of the final

nanocomposite. When there is only a small increase in the d-spacing following the

addition of the curing agent, there is a decrease in the Tg. The small layer expansion

means that the epoxy groups between the layers of the clay remain unreacted due to

the difficulty in the curing agent getting between the layers. This may be caused by

the resin forming a relatively rigid structure around the clay which then holds the

layers of the clay, at the expansion achieved following the mixing of the epoxy and

Chapter 5 – Conclusions

127

the clay, in place. In the case of DGEBA cured with HHPA it is easier for the resin to

cure within the layers where the catalysing cations are present than it is around the

clay.

The addition of clay, either modified or unmodified, had very little effect on the

curing temperatures of the DGEBA and TGDDM cured with TETA. The addition of

the organoclay to the DGEBA and TGDDM cured with the anhydride curing agents

resulted in a decrease in the temperatures of cure. The reduction in temperature was

greater for the unaccelerated HHPA. The quaternary and ternary ammonium cations

used in the modification of the clay act as a catalyst for the anhydride curing reaction

and, as a result, the temperatures required are lower. The unaccelerated HHPA curing

agent is more dependent on the catalysts within the clay compared to the accelerated

MTHPA, so the reduction in cure temperature is larger. The cure of the TGDDM

does not require an additional catalyst because the TGDDM is a tertiary amine and, as

a result, is a catalyst. The DGEBA, however, has no catalysing potential so the

unaccelerated anhydride cure required high temperatures. When DGEBA is cured

with an unaccelerated curing agent the quaternary or ternary ammonium cation in an

organoclay acts as a catalyst and negates the need for an accelerator. This system has

the most potential to form an exfoliated nanocomposite.

The addition of clay to an epoxy resin acts as a physical barrier, which prevents some

of the potential reactions from occurring. The decrease in the number of reactions

means a reduction in the cross-linking. The result was a lower Tg and a weakening of

the mechanical properties. The production of a nanocomposite when compared to a

traditional composite without nanoscale interactions does not produce a greater

Young’s Modulus or Flexural Strength. The modulus was greater when the

unmodified clay was added than when the organoclays were used. Nanoscale

interactions do not lead to an increased Young’s modulus of elasticity when compared

to microscale interactions. The unreacted epoxy groups trapped within the layers of

the clay could provide a weakness within the epoxy resin.

Chapter 6 – Future Research

128

6 FUTURE RESEARCH

The graphics of heat flow during cure suggest that the epoxy/clay nanocomposites

cure at lower temperatures than the unfilled resin. An isothermal study of the curing

of the epoxy nanocomposites would show whether lower cure temperatures could be

used to cure the nanocomposites, resulting in an energy saving.

The tendency of an epoxy system to form an exfoliated nanocomposite was found to

be determined by the rate of cure in, and around, the clay layers. Changing reaction

parameters to allow further layer separation before the formation of a rigid network

would lead to a more exfoliated nanocomposite than what has been achieved. This

could be achieved by altering the stoichiometric ratio of epoxy to curing agent,

changing the accelerator within the anhydride curing agent or using an organoclay

containing a different organic cation.

It was found that the clay readily intercalates with the curing agents, specifically the

un-accelerated anhydride. Work involving addition of the organoclay to the curing

agent prior to addition of the epoxy would show if an exfoliated nanocomposite

would be more readily achieved by that method.

The nanocomposites produced did not show a dramatic increase in physical

properties. The mechanical properties varied considerably and the Tg of the

nanocomposites compared to the unfilled resin was generally significantly lower. An

aging study would show whether the addition of an organoclay reduces degradation of

the epoxy resin, which would lead to a longer lifetime of subsequent products.

Chapter 7 – References

129

7 REFERENCES

1. Massam, J and Pinnavaia, TJ, Clay nanolayer reinforcement of a glassy epoxy

polymer. Mater. Res. Soc. Symp. Proc., 1998. 520(anostructured Powders and Their Industrial Applications): p. 223-232.

2. Sinha Ray S and Okamoto M, Polymer/Layered silicate nanocomposites: a review from preparation to processing. Progress in Polymer Science, 2003. 28: p. 1539-1641.

3. Vaia, RA, Price, G, Ruth, PN, Nguyen, HT, and Lichtenhan, J, Polymer/layered silicate nanocomposites as high performance ablative materials. Appl. Clay Sci., 1999. 15(1-2): p. 67-92.

4. LeBaron, PC, Wang, Z, and Pinnavaia, TJ, Polymer-layered silicate nanocomposites: an overview. Appl. Clay Sci., 1999. 15(1-2): p. 11-29.

5. Giannelis, EP, Polymer layered silicate nanocomposites. Adv. Mater., 1996. 8(1): p. 29-35.

6. Giannelis, EP, Krishnamoorti, R, and Manias, E, Polymer-silicate nanocomposites: model systems for confined polymers and polymer brushes. Adv. Polym. Sci., 1999. 138(Polymers in Confined Environments): p. 107-147.

7. Giannelis, EP, Polymer-layered silicate nanocomposites: synthesis, properties and applications. Appl. Organomet. Chem., 1998. 12(10/11): p. 675-680.

8. Bharadwaj, R, Modeling the barrier properties of polymer-layered silicate nanocomposites. Macromolecules, 2001. 34: p. 337-339.

9. Messersmith, P and Giannelis, E, Synthesis and barrier properties of poly(?(epsalon)-caprolactone)-layered silicate nanocomposites. J Polym Sci, Part A: Polym Chem, 1995. 33: p. 1047-1057.

10. Gilman, JW, Kashiwagi, T, Brown, JET, Lomakin, S, Giannelis, EP, and Manias, E, Flammability studies of polymer layered silicate nanocomposites. Int. SAMPE Symp. Exhib., 1998. 43(Materials and Process Affordability--Keys to the Future, Book 1): p. 1053-1066.

11. Gilman, JW, Jackson, CL, Morgan, AB, Harris, R, Jr., Manias, E, Giannelis, EP, Wuthenow, M, Hilton, D, and Phillips, SH, Flammability properties of polymer-layered silicate nanocomposites. Polypropylene and polystyrene nanocomposites. Chem. Mater., 2000. 12(7): p. 1866-1873.

12. Gilman, JW, Flammability and thermal stability studies of polymer layered-silicate nanocomposites. Appl. Clay Sci., 1999. 15: p. 31-49.

13. Sinha Ray, S, Yamada, K, Okamoto, M, and Ueda, K, New polylactide/layered silicate nanocomposite: a novel biodegradable material. Nano Lett, 2002. 2: p. 1093-1096.

14. Alexandre, M and Dubois, P, Polymer-layered silicate nanocomposites: preparation, properties and uses of a new class of materials. Materials Science and Engineering: R: Reports, 2000. 28(1-2): p. 1-63.

15. Benfarhi, S, Decker, C, Keller, L, and Zahouily, K, Synthesis of clay nanocomposite materials by light-induced crosslinking polymerization. European Polymer Journal, 2004. 40(3): p. 493-501.


130

16. Chen, H-W, Lin, T-P, and Chang, F-C, Ionic conductivity enhancement of the plasticized PMMA/LiClO4 polymer nanocomposite electrolyte containing clay. Polymer, 2002. 43(19): p. 5281-5288.

17. Choi, YS, Xu, M, and Chung, IJ, Synthesis of exfoliated poly(styrene-co-acrylonitrile) copolymer/silicate nanocomposite by emulsion polymerization; monomer composition effect on morphology. Polymer, 2003. 44(22): p. 6989-6994.

18. Chu, L-L, Anderson, SK, Harris, JD, Beach, MW, and Morgan, AB, Styrene-acrylonitrile (SAN) layered silicate nanocomposites prepared by melt compounding. Polymer, 2004. 45(12): p. 4051-4061.

19. Du, J, Zhu, J, Wilkie, CA, and Wang, J, An XPS investigation of thermal degradation and charring on PMMA clay nanocomposites. Polymer Degradation and Stability, 2002. 77(3): p. 377-381.

20. Du, J, Wang, D, Wilkie, CA, and Wang, J, An XPS investigation of thermal degradation and charring on poly(vinyl chloride)-clay nanocomposites. Polymer Degradation and Stability, 2003. 79(2): p. 319-324.

21. Du, J, Wang, J, Su, S, and Wilkie, CA, Additional XPS studies on the degradation of poly(methyl methacrylate) and polystyrene nanocomposites. Polymer Degradation and Stability, 2004. 83(1): p. 29-34.

22. Fu, X and Qutubuddin, S, Synthesis of polystyrene-clay nanocomposites. Materials Letters, 2000. 42(1-2): p. 12-15.

23. Fu, X and Qutubuddin, S, Polymer-clay nanocomposites: exfoliation of organophilic montmorillonite nanolayers in polystyrene. Polymer, 2001. 42(2): p. 807-813.

24. Gong, F, Feng, M, Zhao, C, Zhang, S, and Yang, M, Thermal properties of poly(vinyl chloride)/montmorillonite nanocomposites. Polymer Degradation and Stability, 2004. 84(2): p. 289-294.

25. Hull, TR, Price, D, Liu, Y, Wills, CL, and Brady, J, An investigation into the decomposition and burning behaviour of Ethylene-vinyl acetate copolymer nanocomposite materials. Polymer Degradation and Stability, 2003. 82(2): p. 365-371.

26. Lepoittevin, B, Pantoustier, N, Devalckenaere, M, Alexandre, M, Calberg, C, Jerome, R, Henrist, C, Rulmont, A, and Dubois, P, Polymer/layered silicate nanocomposites by combined intercalative polymerization and melt intercalation: a masterbatch process. Polymer, 2003. 44(7): p. 2033-2040.

27. Moet, AS and Akelah, A, Polymer-clay nanocomposites: polystyrene grafted onto montmorillonite interlayers. Materials Letters, 1993. 18(1-2): p. 97-102.

28. Okamoto, M, Morita, S, Taguchi, H, Kim, YH, Kotaka, T, and Tateyama, H, Synthesis and structure of smectic clay/poly(methyl methacrylate) and clay/polystyrene nanocomposites via in situ intercalative polymerization. Polymer, 2000. 41(10): p. 3887-3890.

29. Okamoto, M, Morita, S, and Kotaka, T, Dispersed structure and ionic conductivity of smectic clay/polymer nanocomposites. Polymer, 2001. 42(6): p. 2685-2688.

30. Okamoto, M, Morita, S, Kim, YH, Kotaka, T, and Tateyama, H, Dispersed structure change of smectic clay/poly(methyl methacrylate) nanocomposites by copolymerization with polar comonomers. Polymer, 2001. 42(3): p. 1201-1206.


131

31. Park, CI, Kim, MH, and Ok Park, O, Effect of heat treatment on the microstructural change of syndiotactic polystyrene/poly(styrene-co-vinyloxazolin)/clay nanocomposite. Polymer, 2004. 45(4): p. 1267-1273.

32. Pramoda, KP, Liu, T, Liu, Z, He, C, and Sue, H-J, Thermal degradation behavior of polyamide 6/clay nanocomposites. Polymer Degradation and Stability, 2003. 81(1): p. 47-56.

33. Shin, S-YA, Simon, LC, Soares, JBP, and Scholz, G, Polyethylene-clay hybrid nanocomposites: in situ polymerization using bifunctional organic modifiers. Polymer, 2003. 44(18): p. 5317-5321.

34. Su, S, Jiang, DD, and Wilkie, CA, Study on the thermal stability of polystyryl surfactants and their modified clay nanocomposites. Polymer Degradation and Stability, 2004. 84(2): p. 269-277.

35. Su, S, Jiang, DD, and Wilkie, CA, Polybutadiene-modified clay and its nanocomposites. Polymer Degradation and Stability, 2004. 84(2): p. 279-288.

36. Su, S, Jiang, DD, and Wilkie, CA, Poly(methyl methacrylate), polypropylene and polyethylene nanocomposite formation by melt blending using novel polymerically-modified clays. Polymer Degradation and Stability, 2004. 83(2): p. 321-331.

37. Su, S and Wilkie, CA, The thermal degradation of nanocomposites that contain an oligomeric ammonium cation on the clay. Polymer Degradation and Stability, 2004. 83(2): p. 347-362.

38. Tang, Y, Hu, Y, Wang, S, Gui, Z, Chen, Z, and Fan, W, Preparation and flammability of ethylene-vinyl acetate copolymer/montmorillonite nanocomposites. Polymer Degradation and Stability, 2002. 78(3): p. 555-559.

39. Wang, S, Hu, Y, Song, L, Wang, Z, Chen, Z, and Fan, W, Preparation and thermal properties of ABS/montmorillonite nanocomposite. Polymer Degradation and Stability, 2002. 77(3): p. 423-426.

40. Wang, S, Hu, Y, Wang, Z, Yong, T, Chen, Z, and Fan, W, Synthesis and characterization of polycarbonate/ABS/montmorillonite nanocomposites. Polymer Degradation and Stability, 2003. 80(1): p. 157-161.

41. Wang, S, Hu, Y, Zong, R, Tang, Y, Chen, Z, and Fan, W, Preparation and characterization of flame retardant ABS/montmorillonite nanocomposite. Applied Clay Science, 2004. 25(1-2): p. 49-55.

42. Wei'an, Z, Xiaofeng, S, Yu, L, and Yue'e, F, Synthesis and characterization of poly(methyl methacrylate)/OMMT nanocomposites by [gamma]-ray irradiation polymerization. Radiation Physics and Chemistry, 2003. 67(5): p. 651-656.

43. Wei'an Zhang, Yu Li, Luo Wei, and Yue'e Fang, In situ intercalative polymerization of poly(methyl methacrylate)/clay nanocomposites by [gamma]-ray irradiation. Materials Letters, 2003. 57(22-23): p. 3366-3370.

44. Xu, M, Choi, YS, Kim, YK, Wang, KH, and Chung, IJ, Synthesis and characterization of exfoliated poly(styrene-co-methyl methacrylate)/clay nanocomposites via emulsion polymerization with AMPS. Polymer, 2003. 44(20): p. 6387-6395.

45. Xu, Y, Brittain, WJ, Xue, C, and Eby, RK, Effect of clay type on morphology and thermal stability of PMMA-clay nanocomposites prepared by heterocoagulation method. Polymer, 2004. 45(11): p. 3735-3746.

46. Yu, Y-H, Lin, C-Y, Yeh, J-M, and Lin, W-H, Preparation and properties of poly(vinyl alcohol)-clay nanocomposite materials. Polymer, 2003. 44(12): p. 3553-3560.


132

47. Zanetti, M, Camino, G, Thomann, R, and Mulhaupt, R, Synthesis and thermal behaviour of layered silicate-EVA nanocomposites. Polymer, 2001. 42(10): p. 4501-4507.

48. Zanetti, M, Camino, G, and Mulhaupt, R, Combustion behaviour of EVA/fluorohectorite nanocomposites. Polymer Degradation and Stability, 2001. 74(3): p. 413-417.

49. Zanetti, M, Bracco, P, and Costa, L, Thermal degradation behaviour of PE/clay nanocomposites. Polymer Degradation and Stability, 2004. 85(1): p. 657-665.

50. Zhang, W, Chen, D, Zhao, Q, and Fang, Y, Effects of different kinds of clay and different vinyl acetate content on the morphology and properties of EVA/clay nanocomposites. Polymer, 2003. 44(26): p. 7953-7961.

51. Zhang, J and Wilkie, CA, A carbocation substituted clay and its styrene nanocomposite. Polymer Degradation and Stability, 2004. 83(2): p. 301-307.

52. Zhao, H, Farrell, BP, and Shipp, DA, Nanopatterns of poly(styrene-block-butyl acrylate) block copolymer brushes on the surfaces of exfoliated and intercalated clay layers. Polymer, 2004. 45(13): p. 4473-4481.

53. Zheng, X and Wilkie, CA, Flame retardancy of polystyrene nanocomposites based on an oligomeric organically-modified clay containing phosphate. Polymer Degradation and Stability, 2003. 81(3): p. 539-550.

54. Zheng, X and Wilkie, CA, Nanocomposites based on poly ([epsi]-caprolactone) (PCL)/clay hybrid: polystyrene, high impact polystyrene, ABS, polypropylene and polyethylene. Polymer Degradation and Stability, 2003. 82(3): p. 441-450.

55. Zhu, J, Start, P, Mauritz, KA, and Wilkie, CA, Thermal stability and flame retardancy of poly(methyl methacrylate)-clay nanocomposites. Polymer Degradation and Stability, 2002. 77(2): p. 253-258.

56. Zong, R, Hu, Y, Wang, S, and Song, L, Thermogravimetric evaluation of PC/ABS/montmorillonite nanocomposite. Polymer Degradation and Stability, 2004. 83(3): p. 423-428.

57. Kim, J and Creasy, TS, Selective laser sintering characteristics of nylon 6/clay-reinforced nanocomposite. Polymer Testing, 2004. 23(6): p. 629-636.

58. Hu, X and Zhao, X, Effects of annealing (solid and melt) on the time evolution of polymorphic structure of PA6/silicate nanocomposites. Polymer, 2004. 45(11): p. 3819-3825.

59. Kashiwagi, T, Harris, J, Richard H., Zhang, X, Briber, RM, Cipriano, BH, Raghavan, SR, Awad, WH, and Shields, JR, Flame retardant mechanism of polyamide 6-clay nanocomposites. Polymer, 2004. 45(3): p. 881-891.

60. Tang, Y, Hu, Y, Zhang, R, Gui, Z, Wang, Z, Chen, Z, and Fan, W, Investigation on polypropylene and polyamide-6 alloys/montmorillonite nanocomposites. Polymer, 2004. 45(15): p. 5317-5326.

61. Chow, WS, Mohd Ishak, ZA, Karger-Kocsis, J, Apostolov, AA, and Ishiaku, US, Compatibilizing effect of maleated polypropylene on the mechanical properties and morphology of injection molded polyamide 6/polypropylene/organoclay nanocomposites. Polymer, 2003. 44(24): p. 7427-7440.

62. Qin, H, Su, Q, Zhang, S, Zhao, B, and Yang, M, Thermal stability and flammability of polyamide 66/montmorillonite nanocomposites. Polymer, 2003. 44(24): p. 7533-7538.


133

63. Fornes, TD, Yoon, PJ, and Paul, DR, Polymer matrix degradation and color formation in melt processed nylon 6/clay nanocomposites. Polymer, 2003. 44(24): p. 7545-7556.

64. Fermeglia, M, Ferrone, M, and Pricl, S, Computer simulation of nylon-6/organoclay nanocomposites: prediction of the binding energy. Fluid Phase Equilibria, 2003. 212(1-2): p. 315-329.

65. Uribe-Arocha, P, Mehler, C, Puskas, JE, and Altstadt, V, Effect of sample thickness on the mechanical properties of injection-molded polyamide-6 and polyamide-6 clay nanocomposites. Polymer, 2003. 44(8): p. 2441-2446.

66. McNally, T, Raymond Murphy, W, Lew, CY, Turner, RJ, and Brennan, GP, Polyamide-12 layered silicate nanocomposites by melt blending. Polymer, 2003. 44(9): p. 2761-2772.

67. Liu, TX, Liu, ZH, Ma, KX, Shen, L, Zeng, KY, and He, CB, Morphology, thermal and mechanical behavior of polyamide 6/layered-silicate nanocomposites. Composites Science and Technology, 2003. 63(3-4): p. 331-337.

68. Davis, RD, Gilman, JW, and VanderHart, DL, Processing degradation of polyamide 6/montmorillonite clay nanocomposites and clay organic modifier. Polymer Degradation and Stability, 2003. 79(1): p. 111-121.

69. Liu, X, Wu, Q, and Berglund, LA, Polymorphism in polyamide 66/clay nanocomposites. Polymer, 2002. 43(18): p. 4967-4972.

70. Liu, X and Wu, Q, Non-isothermal crystallization behaviors of polyamide 6/clay nanocomposites. European Polymer Journal, 2002. 38(7): p. 1383-1389.

71. Ranade, A, D'Souza, NA, and Gnade, B, Exfoliated and intercalated polyamide-imide nanocomposites with montmorillonite. Polymer, 2002. 43(13): p. 3759-3766.

72. Bourbigot, S, Devaux, E, and Flambard, X, Flammability of polyamide-6/clay hybrid nanocomposite textiles. Polymer Degradation and Stability, 2002. 75(2): p. 397-402.

73. Fornes, TD, Yoon, PJ, Hunter, DL, Keskkula, H, and Paul, DR, Effect of organoclay structure on nylon 6 nanocomposite morphology and properties. Polymer, 2002. 43(22): p. 5915-5933.

74. Fornes, TD, Yoon, PJ, Keskkula, H, and Paul, DR, Nylon 6 nanocomposites: the effect of matrix molecular weight. Polymer, 2001. 42(25): p. 09929-09940.

75. Dennis, HR, Hunter, DL, Chang, D, Kim, S, White, JL, Cho, JW, and Paul, DR, Effect of melt processing conditions on the extent of exfoliation in organoclay-based nanocomposites. Polymer, 2001. 42(23): p. 9513-9522.

76. Liu, X, Wu, Q, Berglund, LA, Fan, J, and Qi, Z, Polyamide 6-clay nanocomposites/polypropylene-grafted-maleic anhydride alloys. Polymer, 2001. 42(19): p. 8235-8239.

77. Wu, S-H, Wang, F-Y, Ma, C-CM, Chang, W-C, Kuo, C-T, Kuan, H-C, and Chen, W-J, Mechanical, thermal and morphological properties of glass fiber and carbon fiber reinforced polyamide-6 and polyamide-6/clay nanocomposites. Materials Letters, 2001. 49(6): p. 327-333.

78. Kim, G-M, Lee, D-H, Hoffmann, B, Kressler, J, and Stoppelmann, G, Influence of nanofillers on the deformation process in layered silicate/polyamide-12 nanocomposites. Polymer, 2001. 42(3): p. 1095-1100.

79. Okada, A and Usuki, A, The chemistry of polymer-clay hybrids. Mater. Sci. Eng., C, 1995. C3(2): p. 109-15.


134

80. Alexandre, M and Dubois, P, Polymer-layered silicate nanocomposites: preparation, properties and uses of a new class of materials. Mater. Sci. Eng., R, 2000. R28(1-2): p. 1-63.

81. Shelley, JS, Mather, PT, and DeVries, KL, Reinforcement and Environmental Degradation of Nylon-6/clay nanocomposites. Polymer, 2001. 42: p. 5849-5858.

82. Messersmith, PB and Giannelis, EP, Polymer-layered silicate nanocomposites: in situ intercalative polymerization of .epsilon.-caprolactone in layered silicates. Chem. Mater., 1993. 5(8): p. 1064-6.

83. Krishnamoorti, R and Giannelis, EP, Rheology of End-Tethered Polymer Layered Silicate Nanocomposites. Macromolecules, 1997. 30(14): p. 4097-4102.

84. Chen, W, Xu, Q, and Yuan, RZ, Modification of poly(ethylene oxide) with polymethylmethacrylate in polymer-layered silicate nanocomposites. J. Mater. Sci. Lett., 1999. 18(9): p. 711-713.

85. Messersmith, PB and Giannelis, EP, Synthesis and Characterization of Layered Silicate-Epoxy Nanocomposites. Chem. Mater., 1994. 6(10): p. 1719-25.

86. Wang, MS and Pinnavaia, TJ, Clay-Polymer Nanocomposites Formed from Acidic Derivatives of Montmorillonite and an Epoxy Resin. Chem. Mater., 1994. 6(4): p. 468-74.

87. Lan, T and Pinnavaia, TJ, Clay-Reinforced Epoxy Nanocomposites. Chem. Mater., 1994. 6(12): p. 2216-19.

88. Lan, T, Kaviratna, PD, and Pinnavaia, TJ, Mechanism of Clay Tactoid Exfoliation in Epoxy-Clay Nanocomposites. Chem. Mater., 1995. 7(11): p. 2144-50.

89. Wang, Z, Lan, T, and Pinnavaia, TJ, Hybrid organic-inorganic nanocomposites formed from an epoxy polymer and a layered silicic acid (magadiite). Chem. Mater., 1996. 8(9): p. 2200-2204.

90. Shi, H, Lan, T, and Pinnavaia, TJ, Interfacial Effects on the Reinforcement Properties of Polymer-Organoclay Nanocomposites. Chem. Mater., 1996. 8(8): p. 1584-1587.

91. Wang, Z and Pinnavaia, TJ, Hybrid Organic-Inorganic Nanocomposites: Exfoliation of Magadiite Nanolayers in an Elastomeric Epoxy Polymer. Chem. Mater., 1998. 10(7): p. 1820-1826.

92. Zilg, C, Muelhaupt, R, and Finter, J, Morphology and toughness/stiffness balance of nanocomposites based upon anhydride-cured epoxy resins and layered silicates. Macromol. Chem. Phys., 1999. 200(3): p. 661-670.

93. Kornmann, X, Lindberg, H, and Berglund, LA, Synthesis of epoxy-clay nanocomposites: influence of the nature of the clay on structure. Polymer, 2000. 42(4): p. 1303-1310.

94. Jiankun, L, Yucai, K, Zongneng, Q, and Xiao-Su, Y, Study on intercalation and exfoliation behavior of organoclays in epoxy resin. J. Polym. Sci., Part B: Polym. Phys., 2000. 39(1): p. 115-120.

95. Chin, IJ, Thurn-Albrecht, T, Kim, HC, Russell, TP, and Wang, J, On exfoliation of montmorillonite in epoxy. Polymer, 2001. 42(13): p. 5947-5952.

96. Kornmann, X, Lindberg, H, and Berglund, LA, Synthesis of epoxy-clay nanocomposites. Influence of the nature of the curing agent on structure. Polymer, 2001. 42(10): p. 4493-4499.


135

97. Zerda, AS and Lesser, AJ, Intercalated clay nanocomposites: morphology, mechanics, and fracture behavior. J. Polym. Sci., Part B: Polym. Phys., 2001. 39(11): p. 1137-1146.

98. Park, S-J, Kwak, G-H, Sumita, M, and Lee, J-R, Cure and reaction kinetics of an anhydride-cured epoxy resin catalyzed by N-benzylpyrazinium salts using near-infrared spectroscopy. Polym. Eng. Sci., 2000. 40(12): p. 2569-2576.

99. Morgan, AB, Gilman, JW, and Jackson, CL, Characterization of the Dispersion of Clay in a Polyetherimide Nanocomposite. Macromolecules, 2001. 34(8): p. 2735-2738.

100. Yasmin A, Abot JL, and Daniel IM, Processing of clay/epoxy nanocomposites by shear mixing. Scripta Materialia, 2003. 49(1): p. 81-86.

101. Gua B, Jia D, and Cai C, Effects of organo-montmorillonite dispersion on the thermal stability of epoxy layered silicate nanocomposites. European Polymer Journal, 2004. 40(8): p. 1743-1748.

102. Becker O, Varley RJ, and Simon GP, Thermal stability and water uptake of high performance epoxy layered silicate nanocomposites. European Polymer Journal, 2004. 40(1): p. 187-195.

103. Lan T, Kaviratna PD, and Pinnavaia TJ, Epoxy self-polymerization in smectite clays. Journal of Physics and Chemistry of Solids, 1996. 57(6-8): p. 1005-1010.

104. Tolle TB and Anderson DP, Morphology development in layered silicate thermoset nanocoposites. Composites Science and Technology, 2002. 62(7-8): p. 1033-1041.

105. Becker O, Varley RJ, and Simon GP, Morphology, thermal relaxations and mechanical properties of layered silicate nanocomposites based upon high-functionality epoxy resin. Polymer, 2002. 43(61): p. 4365-4373.

106. Kanapitas A, Pissis P, and Kotsilkova R, Dielectric studies of molecular mobility and phase morphology in polymer-layered silicate nanocomposites. Journal of Non-Crystalline Solids, 2002. 305(1-3): p. 204-211.

107. Park JH and Jana SC, The relationship between nano- and micro-structures and mechanical properties in PMMA-epoxy-nanoclay composites. Polymer, 2003. 44(7): p. 2091-2100.

108. Gu A and Liang G, Thermal degredation behaviour and kinetic analysis of epoxy/montmorillonite nanocomposites. Polymer Degredation and Stability, 2003. 80(2): p. 383-391.

109. Weibing X, Pingsheng H, and Dazhu C, Cure behaviour of epoxy rein/montmorillonite/imidazole nanocomposite by dynamic torsional vibration method. European Polymer Journal, 2003. 39(3): p. 617-625.

110. Chen C, Khobaib M, and Curliss D, Epoxy layered-silicate nanocomposites. Progress in Organic Coatings, 2003. 47(3-4): p. 376-383.

111. Lee JY and Lee HK, Characterisation of organobentonite used for polymer nanocomposites. Materials Chemistry and Physics, 2004. 85(2): p. 410-415.

112. Ratna D, Becker O, Krishnamurthy R, Simon GP, and Varley RJ, Nanocomposites based on a combination of epoxy resin, hyperbranched epoxy and a layered silicate. Polymer, 2003. 44(24): p. 7449-7457.

113. Wetzel B, Haubert F, and Zhang MQ, Epoxy nanocomposites with high mechanical and tribological performance. Composites Science and Technology, 2003. 63(4): p. 2055-2067.


136

114. Luo J and DanielI M, Characterisation and modeling of mechanical behavior of polymer/clay nanocoposites. Composites Science and Technology, 2003. 63(11): p. 1607-1616.

115. Isik I, Yilmazer U, and Bayram G, Impact modified epoxy/montmorillonite nanocomposites: sythesis and characterisation. Polymer, 2003. 44(20): p. 6371-6377.

116. Chen J, Poliks MD, Ober CK, Zhang Y, and Weisner U, Study of the interlayer expansion mechanim and thermal-mechanical properties of surface-initiated epoxy nanocomposites. Polymer, 2002. 43(18): p. 4895-4904.

117. Ratna, D, Manoj, N, Varley, R, Singh Raman, R, and Simon GP, Clay-reinforced epoxy nanocomposites. Polymer International, 2003. 52(9): p. 1403-1407.

118. Lan, T, Kaviratna, PD, and Pinnavaia, TJ, Synthesis, characterization and mechanical properties of epoxy-clay nanocomposites. Polym. Mater. Sci. Eng., 1994. 71: p. 527-8.

119. Xu, W-B, Bao, S-P, and He, P-S, Intercalation and exfoliation behavior of epoxy resin/curing agent/montmorillonite nanocomposite. Journal of Applied Polymer Science, 2002. 84(4): p. 842-849.

120. Pinnavaia, TJ and Lan, T. Nanolayer reinforcement in polymer-clay nanocomposites. in Proc. Am. Soc. Compos., Tech. Conf. 1996.

121. Chen, C and Curliss, D, Organoclay-aerospace epoxy nanocomposites. Int. SAMPE Symp. Exhib., 2001. 46(2001: A Materials and Processes Odyssey, Book 1): p. 362-374.

122. Zilg, C, Thomann, R, Finter, J, and Mulhaupt, R, The influence of silicate modification and compatibilizers on mechanical properties and morphology of anhydride-cured epoxy nanocomposites. Macromol. Mater. Eng., 2000. 280(281): p. 41-46.

123. Alexandre, M, Dubois, P, Sun, T, Garces, JM, and Jerome, R, Polyethylene-layered silicate nanocomposites prepared by the polymerization-filling technique: synthesis and mechanical properties. Polymer, 2002. 43(8): p. 2123-2132.

124. Garcia-Lopez, D, Picazo, O, Merino, JC, and Pastor, JM, Polypropylene-clay nanocomposites: effect of compatibilizing agents on clay dispersion. European Polymer Journal, 2003. 39(5): p. 945-950.

125. Gopakumar, TG, Lee, JA, Kontopoulou, M, and Parent, JS, Influence of clay exfoliation on the physical properties of montmorillonite/polyethylene composites. Polymer, 2002. 43(20): p. 5483-5491.

126. Gorrasi, G, Tortora, M, Vittoria, V, Kaempfer, D, and Mulhaupt, R, Transport properties of organic vapors in nanocomposites of organophilic layered silicate and syndiotactic polypropylene. Polymer, 2003. 44(13): p. 3679-3685.

127. Kaempfer, D, Thomann, R, and Mulhaupt, R, Melt compounding of syndiotactic polypropylene nanocomposites containing organophilic layered silicates and in situ formed core/shell nanoparticles. Polymer, 2002. 43(10): p. 2909-2916.

128. Krishnamoorti, R and Yurekli, K, Rheology of polymer layered silicate nanocomposites. Current Opinion in Colloid & Interface Science, 2001. 6(5-6): p. 464-470.

129. Kuo, S-W, Huang, W-J, Huang, S-B, Kao, H-C, and Chang, F-C, Syntheses and characterizations of in situ blended metallocence polyethylene/clay nanocomposites. Polymer, 2003. 44(25): p. 7709-7719.


137

130. Li, J, Zhou, C, and Gang, W, Study on nonisothermal crystallization of maleic anhydride grafted polypropylene/montmorillonite nanocomposite. Polymer Testing, 2003. 22(2): p. 217-223.

131. Lin-Gibson, S, Kim, H, Schmidt, G, Han, CC, and Hobbie, EK, Shear-induced structure in polymer-clay nanocomposite solutions. Journal of Colloid and Interface Science, 2004. 274(2): p. 515-525.

132. Morgan, AB and Harris, JD, Effects of organoclay Soxhlet extraction on mechanical properties, flammability properties and organoclay dispersion of polypropylene nanocomposites. Polymer, 2003. 44(8): p. 2313-2320.

133. Nam, PH, Maiti, P, Okamoto, M, Kotaka, T, Hasegawa, N, and Usuki, A, A hierarchical structure and properties of intercalated polypropylene/clay nanocomposites. Polymer, 2001. 42(23): p. 9633-9640.

134. Nowacki, R, Monasse, B, Piorkowska, E, Galeski, A, and Haudin, JM, Spherulite nucleation in isotactic polypropylene based nanocomposites with montmorillonite under shear. Polymer, 2004. 45(14): p. 4877-4892.

135. Pozsgay, A, Frater, T, Szazdi, L, Muller, P, Sajo, I, and Pukanszky, B, Gallery structure and exfoliation of organophilized montmorillonite: effect on composite properties. European Polymer Journal, 2004. 40(1): p. 27-36.

136. Tang, Y, Hu, Y, Song, L, Zong, R, Gui, Z, Chen, Z, and Fan, W, Preparation and thermal stability of polypropylene/montmorillonite nanocomposites. Polymer Degradation and Stability, 2003. 82(1): p. 127-131.

137. Wang, D and Wilkie, CA, In-situ reactive blending to prepare polystyrene-clay and polypropylene-clay nanocomposites. Polymer Degradation and Stability, 2003. 80(1): p. 171-182.

138. Wang, KH, Choi, MH, Koo, CM, Choi, YS, and Chung, IJ, Synthesis and characterization of maleated polyethylene/clay nanocomposites. Polymer, 2001. 42(24): p. 9819-9826.

139. Xu, W, Liang, G, Zhai, H, Tang, S, Hang, G, and Pan, W-P, Preparation and crystallization behaviour of PP/PP-g-MAH/Org-MMT nanocomposite. European Polymer Journal, 2003. 39(7): p. 1467-1474.

140. Zanetti, M and Costa, L, Preparation and combustion behaviour of polymer/layered silicate nanocomposites based upon PE and EVA. Polymer, 2004. 45(13): p. 4367-4373.

141. Zhang, J and Wilkie, CA, Preparation and flammability properties of polyethylene-clay nanocomposites. Polymer Degradation and Stability, 2003. 80(1): p. 163-169.

142. Ellis, B, Chemistry and Technology of Epoxy Resins, ed. E. B. 1993, London: Chapman and Hall. 1-90.

143. Velde, B, introduction to Clay Minerals. 1992: Chapman and Hall. 198. 144. Willard, HH, Merritt, LLJ, Dean, JA, and Settle, FAJ, Instrumental Methods

of Analysis. 7th ed, ed. J. Carey. 1988: Wadsworth, Inc. 895. 145. Kim, W, Zhang, QW, and Saito, F, Syntheses of zeolite-A and X from kaolinite

activated by mechanochemical treatment. Journal of Chemical Engineering of Japan, 2000. 33(2): p. 217-222.

146. Hsiao, S-H, Liou, G-S, and Chang, L-M, Synthesis and properties of organosoluble polyimide/clay hybrids. J. Appl. Polym. Sci., 2001. 80(11): p. 2067-2072.

147. Ishii, M, Nakahira, M, and Takeda, H. Far Infrared Absorption Spectra of Micas. in International Clay Conference. 1969.


138

148. Aglietti, EF, The effect of dry grinding on the structure of talc. Applied Clay Science, 1994. 9(2): p. 139-147.

149. Aglietti, EF and Porto Lopez, JM, Physicochemical and thermal properties of mechanochemically activated talc. Mater. Res. Bull., 1992. 27(10): p. 1205-16.

150. Solomons, TW, Organic Chemistry. 6th ed. 1996. 151. Adomenas, A, Curran, K, and Falconer-Flint, M, Surface Coatings. 3rd ed.

Vol. 1. 1993: New South Wales University Press. 179-192. 152. Sperling, L, Introduction to Physical Polymer Science. 3rd ed. 2001: John

Wiley & Sons, Inc. 295-362. 153. Zilg, C, Dietsche, F, Hoffmann, B, Dietrich, C, and Mulhaupt, R, Nanofillers

based upon organophilic layered silicates. Macromol. Symp., 2001. 169(Fillers and Filled Polymers): p. 65-77.

154. Ishida, H, Campbell, S, and Blackwell, J, General Approach to Nanocomposite Preparation. Chem. Mater., 2000. 12(5): p. 1260-1267.

155. Porter, D, Metcalfe, E, and Thomas, MJK, Nanocomposite fire retardants - a review. Fire Mater., 2000. 24(1): p. 45-52.

156. Gloaguen, JM and Lefebvre, JM, Plastic deformation behavior of thermoplastic/clay nanocomposites. Polymer, 2001. 42(13): p. 5841-5847.

157. Wang, K, Liang, S, Du, R, Zhang, Q, and Fu, Q, The interplay of thermodynamics and shear on the dispersion of polymer nanocomposites. Polymer, 2004. 45: p. 7953-7960.

158. Rockwood(R), Nanoclay.com. 159. Turi, E, Thermal characterisation of polymeric materials. 2nd ed. Vol. 2.

1981: Acedemic Press, Inc. 1380-1744. 160. Fulton, M, Pomery, P, St. John, N, and George, G, Colour development and

luminescence phenomena in epoxy glasses. Polymers for Advanced Technologies, 1998. 9: p. 75-83.

161. Kornmann, X, Thomann, R, Mulhaupt, R, Finter, J, and Berglund, L, High performance epoxy-layered silicate nanocomposites. Polymer Engineering and Science, 2002. 42(9): p. 1815-1826.

final thesis complete with cover page - quteprints.qut.edu.au/16024/1/bradley_siddans_thesis.pdf ·...

Documents