effect of nanoclay dispersion on the processing of polyester nano composites (2)
TRANSCRIPT
Effect of nanoclay dispersion on the processing of polyester nanocomposites
By:
Muhammad Ali Bashir
August 2008
Department of Mechanical Engineering
McGill University, Montreal, QC, Canada, H3A 2K6
A thesis submitted to
McGill University
In partial fulfillment of the requirements for the degree of
Master of Engineering
ii
RÉSUMÉ Le procédé d’injection sur renfort (RTM) est de plus en plus utilisé en industrie
automobile pour produire de grands volumes de carrosseries à faible coût. Cependant, les
paramètres du procédé peuvent avoir un effet négatif sur les propriétés mécaniques et le
fini de surface de la pièce produite. Une résine polyester insaturé (UP) mixée à des nano-
charges organiques confère de meilleurs paramètres de production, ce qui est une
préoccupation majeure pour le fini de surface des pièces RTM. Les nano-charges sont des
particules faites de couches de silicate traitées pour assurer leur compatibilité avec
différentes résines. Plusieurs techniques pour synthétiser les nanocomposites sont
possibles avec les systèmes UP. Trois techniques de mixage ont été étudiées : mixage
séquentiel, mixage avec solvant et mixage simultané. La méthode la plus efficace a
ensuite été sélectionnée et utilisée pour fabriquer des échantillons. Deux types de mixage,
un moulin à trois cylindres et l’ultrasonification, ont été introduits pour mixer un système
UP/agent anti-retrait (LPA)/styrène avec nano-charges. L’effet de ces deux approches sur
la dispersion des nano-charges a été observé par la diffraction à rayons X. Suite à ces
résultats et des mesures de viscosité, l’ultrasonification a été choisie comme étant la
méthode optimale de mixage (OMM) pour le système étudié. Un des principaux facteurs
qui a influencé ce choix était l’évaporation non-contrôlée de styrène durant la méthode
TRM. 0% à 5% de nano-charges a ensuite été ajouté à la résine en utilisant la méthode
OMM. L’effet de l’ajout des charges sur la viscosité, la cinétique de réaction, le module
de conservation et la température de transition vitreuse (Tg) a été investigué. Il a été
observé que l’ajout des nano-charges augmente le module de conservation et la viscosité,
mais diminue légèrement la température de transition vitreuse et l’activité de
polymérisation. Des tests de rétrécissement de la résine ont montré une faible réduction
du retrait comparé au système sans nano-charges, mais le typique mécanisme de contrôle
du retrait n’a pas été observé.
i
ABSTRACT The automotive industry is increasingly using resin transfer moulding (RTM) to produce
composite body panels at high volumes and low costs. However, the processing
parameters affect the physical and mechanical properties of the final finished part, which
may have negative impact on the desired mechanical properties and surface finish.
Unsaturated polyester (UP) mixed with organo nanoclay provides improved processing
parameters which is a major concern for surface finish in RTM parts. Organo clays are
silicate layers treated suitable to make them organophilic in order to be compatible with
resin systems. UP systems give rise to numerous possible approaches in synthesizing
nanocomposites. Three different techniques to synthesize nanocomposite systems,
sequential mixing, solvent mixing and simultaneous mixing were studied and a suitable
synthesizing technique was selected and used to make the nanocomposite systems. Two
mixing approaches, three roll mill (TRM) machine and ultrasonication, were introduced
to mix a pre-promoted UP resin/Low Profile Additive (LPA)/St system with organoclay.
The effect of using these two approaches on the dispersion of the clays within the resin
mix was studied using X-ray diffraction. Based on the results obtained from the X-ray
analysis and viscosity measurements, ultrasonication was chosen as the optimum mixing
method (OMM) for this system. One of the factors that influenced these results was the
uncontrolled evaporation of styrene during the application of TRM. 0-5 wt% of Cloisite
20A was then added to the resin and mixed using optimum mixing method (OMM). The
effect of adding clays on the viscosity, cure kinetics, storage modulus and glass transition
temperature (Tg) was investigated. It was seen that the addition of clays increased the
storage modulus of the resin samples, increased the viscosity, reduced the glass transition
temperature very slightly and reduced the cure activity of the resin-clay system.
Shrinkage tests on these resin-clay systems showed some reduction in shrinkage,
however the typical shrinkage control mechanism was not observed.
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ACKNOWLEDGEMENTS I would like to acknowledge Professor Pascal Hubert who accepted me as a member of
the Composite Materials and Structures Laboratory. His help and support throughout my
research were greatly appreciated and guided me towards a challenging career within the
same field. Auto21, Network of Centers of Excellence, and Ford Motor Company are
acknowledged as well for their financial support.
The following people are also sincerely thanked for various reasons (in no particular
order):
• Everybody from the Composite Materials Lab for their help and a wonderful time
during my master’s program.
• Jonathan Laliberté for his endless patience and technical help/input.
• Genevieve Palardy and Loleï Khoun for their support throughout the
understanding of their previous work.
• Catherine Billotte and Isabelle Ortega for their valuable support in using the
equipments at École Polytechnique.
• AOC chemicals and Southern clay products for their generous supply of material
samples.
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TABLE OF CONTENTS RÉSUMÉ ............................................................................................................................ ii
ABSTRACT......................................................................................................................... i
ACKNOWLEDGEMENTS................................................................................................ ii
TABLE OF CONTENTS................................................................................................... iii
LIST OF FIGURES ........................................................................................................... vi
LIST OF TABLES.............................................................................................................. x
LIST OF SYMBOLS AND ACRYNOMS........................................................................ xi
1. Introduction................................................................................................................. 1
1.1. Composites in the Auto Industry ........................................................................ 1
1.2. Resin Transfer Moulding (RTM)........................................................................ 2
1.3. Motivation........................................................................................................... 5
1.4. Objectives and Thesis Outline ............................................................................ 6
2. Literature Review........................................................................................................ 8
2.1. Nanocomposites.................................................................................................. 8
2.2. Processing of nanoclays.................................................................................... 10
2.2.1. Characterization methods for dispersion of clays..................................... 11
2.2.2. Synthesizes of nanocomposites................................................................. 13
2.2.3. Mixing methods ........................................................................................ 17
2.2.4. Parameters effecting dispersion ................................................................ 19
2.2.5. Morphology............................................................................................... 20
2.3. Physical and mechanical properties .................................................................. 23
2.3.1. Rheological properties .............................................................................. 23
2.3.2. Material strength ....................................................................................... 25
2.3.3. Glass transition temperature ..................................................................... 27
2.3.4. Volumetric shrinkage................................................................................ 29
2.3.5. Cure Kinetics ............................................................................................ 32
2.4. Literature review summary ............................................................................... 34
2.5. Research Objectives and Approach .................................................................. 35
3. Experimental Procedures .......................................................................................... 38
iv
3.1. Materials Used .................................................................................................. 38
3.2. Resin Characterization ...................................................................................... 39
3.2.1. Sample Preparation to develop optimum mixing method (OMM)........... 39
3.2.2. X-ray diffraction ....................................................................................... 42
3.2.3. Sample preparation for to characterize the effects of nanoclays .............. 43
3.2.4. Cure kinetics ............................................................................................. 43
3.2.5. Rheology and volumetric shrinkage measurements ................................. 44
3.2.6. Dynamic mechanical analyzer (DMA) ..................................................... 46
4. Results and discussions............................................................................................. 48
4.1. X-ray diffraction ............................................................................................... 48
4.1.1. Effect of TRM roller distance ................................................................... 49
4.1.2. Effect of mixing time ................................................................................ 50
4.2. Rheological behaviour during mixing process ................................................. 53
4.3. Rheological behaviour on addition of nanoclays.............................................. 56
4.3.1. Rheological characterization of pre-promoted unsaturated polyester ...... 56
4.3.2. Effect of adding nanoclays on viscosity ................................................... 57
4.3.3. Effect of nanoclays on the gel point ......................................................... 59
4.4. Storage modulus................................................................................................ 60
4.4.1. Determining the LVR (linear viscoelastic region).................................... 60
4.4.2. Effect of post cure..................................................................................... 61
4.4.3. Effect of nanoclays on storage and loss modulus ..................................... 63
4.5. Glass transition temperature ............................................................................. 66
4.5.1. Establishing evaluation criteria for the glass transition temperature (Tg). 66
4.5.2. Effect of nanoclays ................................................................................... 69
4.6. Cure Kinetics .................................................................................................... 71
4.7. Volumetric Shrinkage ....................................................................................... 75
4.7.1. Effect of nanoclays on pre-formulated and pre-promoted resin ............... 75
4.7.2. Effect of LPA and styrene on shrinkage control of the base resin............ 76
5. Conclusion ................................................................................................................ 79
5.1. Future Work ...................................................................................................... 80
6. References................................................................................................................. 82
v
APPENDIX A................................................................................................................... 93
APPENDIX B ................................................................................................................... 98
vi
LIST OF FIGURES Figure 1-1: The Kaiser-Darrin made its apparition in 1952, but only got into production
in 1954 [8]-[10]................................................................................................................... 2
Figure 1-2: The Resin Transfer Moulding (RTM) process................................................. 3
Figure 2-1: Scheme of composite structures arising from the interaction of layered
silicates and polymers [17]. ................................................................................................ 9
Figure 2-2 2θ deviation, the phase shift causes constructive (left figure) or destructive
(right figure) interferences ................................................................................................ 12
Figure 2-3: XRD of 4 wt% Cloisite 10A dispersed in unsaturated polyester at varying
shear mixing speeds [17]. ................................................................................................. 13
Figure 2-4: Curing mechanism of UP: (a) styrene-UP solution before curing; and (b)
after curing [41]. Long curves represents long polymer chains; short solid lines represent
styrene and solid dots represent free radicals. .................................................................. 16
Figure 2-5: High magnification TEM micrographs revealing different morphologies for
DER................................................................................................................................... 23
Figure 2-6 : Viscosity of alkyd/24 wt% I.28MC organo-clay nanocomposite, prepared by
mechanical mixing at high shear levels/high temperature for several durations. Samples
tested at 80°C [33]. ........................................................................................................... 25
Figure 2-7: Storage modulus as a function of temperature; (a) pure epoxy resin; (b)
nanocomposite with 5 wt% of silica; (c) nanocomposite with 10 wt% silica [ 56].......... 26
Figure 2-8: Glass transition temperature of Cloisite 10A and CaCO3 for loadings
between 0 and 10 wt% [17]. ............................................................................................. 28
Figure 2-9: LPA mechanism initiation reaction, (2) micro-gelling, (3) intra and inter-
particle reactions experienced during the polymerisation process, (4) the role of the
micro-void formation ........................................................................................................ 30
Figure 2-10: Volume change profile of UP/St/LPA system with different Cloisite 20A
content cured at 35 8C (0.5% cobalt octoate, 1.5% MEKP, 300 ppm BQ, and 3.5% LPA)
[43]. ................................................................................................................................... 32
Figure 2-11: Heat flow for various nanoclay content as obtained from DSC runs by
Hussain [69] ...................................................................................................................... 33
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Figure 3-1: The three roll milling machine with all its major features and components
[93]. ................................................................................................................................... 40
Figure 3-2: The mould used to cure samples used for X-ray analysis and DMA testing. 42
Figure 3-3: Parallel plate setup on the rheometer ............................................................. 45
Figure 4-1: Effect of the roller spacing on dispersion of the resin with 4 wt% Cloisite 20A
........................................................................................................................................... 50
Figure 4-2: XRD patterns showing the effect of time (ultrasonication) and number of
passes (TRM) for 4 wt% Cloisite 20 A............................................................................. 52
Figure 4-3: XRD Pattern comparing ultrasonication and TRM methods – 4 wt% Cloisite
20A.................................................................................................................................... 53
Figure 4-4: Viscosity as a function of shear rate for different mixing techniques at 25°C
........................................................................................................................................... 54
Figure 4-5: Schematic of the variration in viscosity as a result of the mixing process. This
schematic summarizes the different effects that changes the viscosities. Green line is neat
resin; pink is ultrasonication for 60 minutes; blue is TRM 1 pass; black is TRM 3 pass. 54
Figure 4-6: Characteristic Newtonian behaviour of the as received R580-ZPE-14 resin
system. Tests were carried out at 25°C............................................................................. 57
Figure 4-7: Viscosity as a function of shear rate for different clay content at 25°C using
ultrasonication for 60 minutes at 50°C. ............................................................................ 58
Figure 4-8: Viscosity as a function of curing time until the gel point. Tests were carried
out under oscillation mode at 40°C................................................................................... 60
Figure 4-9: Storage modulus as function of amplitude at 25C. The sample contains 3 w%
of Cloisite 20A prepared using ultrasonication for 60 minutes at 50°C. .......................... 61
Figure 4-10: Effect of post curing on storage modulus and loss modulus for samples
made with 3 wt% Cloisite 20A. The tests were carried out at 25°C................................. 62
Figure 4-11: Storage modulus as a function of temperature with the addition of Cloisite
20A. Samples were prepared by using ultrasonication for 60 minutes at 50°C. .............. 64
Figure 4-12: Loss modulus as a function of temperature with the addition of Cloisite 20A.
Samples were prepared by using ultrasonication for 60 minutes at 50°C. ....................... 64
Figure 4-13: Increasing trend of the storage modulus with increase in clay content
measured at 30°C .............................................................................................................. 65
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Figure 4-14: Evaluation of glass transition temperature using storage modulus and loss
modulus. The sample contains 0 wt% Cloisite 20A prepared using ultrasonication for 60
minutes at 50°C................................................................................................................. 67
Figure 4-15: Tan delta curve for 0 wt% Cloisite 20A prepared using Ultrasonication for
60 minutes at 50°C............................................................................................................ 68
Figure 4-16: Glass transition temperature as a function of clay content at 30°C. The onset
of loss in storage modulus is used as the evaluation criteria ............................................ 71
Figure 4-17: Total heat of reaction as a function of clay content when using
ultrasonication for 60 minutes at 50°C. ............................................................................ 73
Figure 4-18: Cure rate as a function of degree of cure for various clay content mixed
using ultrasonication for 60 minutes at 50°C.................................................................... 74
Figure 4-19: Heat flow curves for nanocomposites synthesized using ultrasonication for
60 minutes at 50°C............................................................................................................ 74
Figure 4-20: Volumetric shrinkage (shown as positive) for the R580 resin system and
modified R580 system with 4 wt% Cloisite 20A at 40°C ................................................ 77
Figure 4-21: Effect of LPA on shrinkage control of T580-63 (base resin for R580-ZPE-
14) at 80°C ........................................................................................................................ 78
Figure 4-22: Effect of styrene on shrinkage of T580-63 (base resin for R580-ZPE-14) at
80°C .................................................................................................................................. 78
Figure B 1: Dynamic DSC scan at 10°C/min for T580-63 with 3% cobalt 1% and MEKP
catalyst .............................................................................................................................. 99
Figure B 2: Dynamic DSC scan at 3°C/min for T580-63 with 3% cobalt 1% and MEKP
catalyst ............................................................................................................................ 100
Figure B 3: Dynamic DSC scan at 3°C/min for T580-63 with 1.5% cobalt 1% and MEKP
catalyst ............................................................................................................................ 102
Figure B 4: Dynamic DSC scan at 3°C/min for T580-63 with 1.5% cobalt 1% and
MIBKP catalyst..................................................................Error! Bookmark not defined.
Figure B 5: Isothermal scan at 75C for T580-63 resin + 1.5% cobalt 3% + 1.5% MIBKP
......................................................................................................................................... 103
ix
Figure B 6: Volumetric Shrinkage results as a function of DOC for T580-63 resin with
1.5% Coblat 3% and MIBKP at 75°C,............................................................................ 104
x
LIST OF TABLES Table 3-1: Materials used for research.............................................................................. 38
Table 3-2: Summary of mixing techniques and parameters tested on resin mix with 4
wt% of Cloisite 20A.......................................................................................................... 41
Table 4-1: XRD analysis showing the d-spacing for different samples ........................... 52
Table 4-2: Percentage increase in the storage modulus at 30°C with addition of Cloisite
20A.................................................................................................................................... 65
Table 4-3: Glass transition temperature as measured from three different criteria .......... 70
Table 4-4: Glass transition values measured using the half length criteria of the storage
modulus............................................................................................................................. 71
xi
LIST OF SYMBOLS AND ACRYNOMS Acronyms
CTE Coefficient of thermal expansion
DMA Dynamic mechanical analyzer
DSC Differential scanning calorimetry
LPA Low profile additive
PE Polyethylene
PMMA Poly(methylmetacrylate)
PS Polystyrene
PU Polyurethane
PVAc Poly(vinyl acetate)
RTM Resin transfer moulding
SMC Sheet moulding compound
TMA Thermo-mechanical analyzer
UP Unsaturated polyester
OMM Optical mixing method
MMT montmorillonite
O-MMT Organic montmorillonite
TRM Three roll milling
Latin Symbols
CTE Coefficient of thermal expansion
Fz Normal force
h Gap between the parallel plates of the rheometer at a given time
h0 Initial gap between the parallel plates of the rheometer
HR Total heat of reaction of a resin sample
ΔH Heat of reaction generated during the first TMA cycle
n Number of panels
xii
|* n| Norm of the viscosity
t Time
T Temperature or thermocouple (if followed by a number)
Tg Glass transition temperature
ΔT Temperature difference
V0 Initial volume of a resin sample
V Volume of a resin sample at any time
ΔV Volume shrinkage
dV/dt Rate of volume change
dT/dt Rate of temperature change
Greek symbols
α Degree of cure
α0 Initial degree of cure of the samples
∆C Cure dimensional changes
∆Thermal Thermal dimensional changes
∆Total Total dimensional changes
∆v Volumetric cure shrinkage
ν Poisson’s ratio
1
1. Introduction The automotive industry is well known to consistently look for methods to improve
design by reducing weight and costs. Today, these costs include the environmental
concerns as well as the consumer satisfaction. Lightweight materials, such as composites,
are well-suited to reduce the total mass of cars. A lower mass implies lower fuel
consumption and therefore, an improvement in fuel efficiency. A brief overview of the
composites and processes used in the car industry will be presented in section 1.1. A
description of the resin transfer moulding (RTM) process as well as its problems and
solutions will be given in sections 1.2 and the motivation behind this research will be
presented in section 1.3. The general work objectives and thesis outline will be discussed
in section 1.4.
1.1. Composites in the Auto Industry
The automotive sector is one of the major consumers of plastics and consumes over 8%
of total domestic/engineering plastics manufactured in the world. The first true step
toward the use of fibre-reinforced materials was in 1953 with the famous Corvette from
General Motors. Practically at the same time, Kaiser-Frazer introduced a sports car, the
Kaiser-Darrin, with a body made of polyester/fibreglass (Figure 1-1).
Composite materials showed promises for the car industry. They were light, strong,
resistant to rust, ideal for low production runs and could be moulded into different shapes
more easily than metals. In the automobile industry today, composite materials are used
in applications as varied as car body panels (doors, roofs) [87], semi-structural parts
(front bumpers) [88], and engine parts (cylinder-head covers) [87, 88]. The use of
thermoplastic composite materials in the automotive industry, already used for under-the-
hood components (radiator-tanks, heater-fan housings, cooling fans) [89], has recently
witnessed a strong growth, with new applications such as intake manifolds, rocker
covers, and engine thermostat parts [89]. Structural parts for front-ends and tailgate
frames, mainly molded through the injection compression or other injection technology,
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have also benefited from the advantages provided by composites. Most of the composites
used for these applications are based on polyamide or polypropylene.
Figure 1-1: The Kaiser-Darrin made its apparition in 1952, but only got into production in 1954 [8]-
[10].
More recent examples of composite uses in the automotive industry include front ends
(Peugeot 405, Audi A4, Volkswagen Golf/Polo, Ford Focus), front fenders (Lincoln
Continental, GM Camaro/Firebird/Thunderbird), tail doors (Citroen, Fiat, Renault,
Mercedes A Class), side doors (GM Corvette, Mazda, Saturn) and even transmission
mounts and clutch for the Porsche Carrera [89]. However, most of those parts are made
by sheet moulding compound (SMC) and few developments were made with resin
transfer moulding (RTM). A notable exception is the most recent Aston Martin DB9,
which exhibits UP/fibreglass body panels manufactured by RTM [90].
1.2. Resin Transfer Moulding (RTM)
The Resin Transfer Molding Process has been in use for decades. It is one of the best
methods for making composite parts with thermoset materials, and is uniquely capable of
satisfying the low-cost/high-volume parts per year of the automotive industry as well as
the higher performance/lower volume parts per year of the aerospace industry. In short:
Resin Transfer Molding is excellent for producing complex composite parts with short
cycle times.
3
The automotive industry has used resin transfer molding (RTM) for decades. The resin
transfer molding process is fairly simple and is described in Figure 1-2 below: A two-
part, matched-metal mold (or tool) is made. A preform is placed into the mould (step 1),
and the mold is closed (step 2). The resin is then pumped under pressure through
injection ports into the mould (step 3) and follows predesigned paths through the
preform. When the mould is completely filled, the excess resin flows through the vent
port. Both the mould and resin can be heated as needed for the application (step 4). Heat
is applied to the resin system in accordance to the cure cycle in order to cure the resin. At
the end of the cure cycle the mould is opened and the composite part is de-moulded (step
5). A more detailed description of the process is explained in the following paragraph.
Figure 1-2: The Resin Transfer Moulding (RTM) process
The above is a simplified model of the RTM production machine. The first step in the
Resin Transfer Molding technique is creating the preform. The preform is the matrix,
already in the shape of the finished product, which the resin will be injected into. There
are a few steps in making a preform. These are:
4
• Selecting the type of fibre. There are several different types of fibre available for use
with composites.
Random Mats.
Two Dimensional Woven Fabrics
Unidirectional Fabric
Other fibre forms: Knit fibres, other 2 dimensional weaves and 3
dimensional weaves
• After selecting the fibre type, the fibre must be preformed into the shape of the
finished product. There are several methods of performing. Some of these are listed
below:
Cut and place preforming: In this method, nearly any 2 dimensional
woven fabric and some 3 dimensional ones may be used. Individual layers
of the preform are separately cut, placed into the female mold cavity by
hand, and then contact preformed within the tool.
Directed fibre preforming: This method uses a 'sprayer' to fire chopped
fibres at a perforated screen shaped like the finished product.
• The mould is then closed and heated up to the appropriate cure temperature
• The resin is injected into the cavity through an injection port.
• When the mould is completely filled, the excess resin flows through the vent port
positioned at the other end.
There are several benefits to using the resin transfer molding process over the alternative
processes available. One of the most prominent benefits is the separation of the actual
molding process from the design of the fibre shape. Having the fibre preform stage occur
at a different time than the injection and curing stages allows the manufacturer a much
greater amount of flexibility and precision when designing a piece. The advantages can
be summarized below:
• The cost of the equipment is low;
• It is a closed-mould process, so the volatile emissions are limited and it is easier the
control the part thickness;
5
• Components have a good surface finish on all sides (For instance, in SMC, the surface
of the parts can suffer from small defects such as pinholes. Rework is often needed to
obtain a Class A surface finish);
• Parts with complex, large and/or hollow shapes can be moulded;
• The fibre volume fraction can reach 60%; the parts produced therefore have superior
mechanical properties.
1.3. Motivation
Many factors are to be considered in the manufacturing of composite automotive parts.
Cost remains a major obstacle to a wider usage of composites for automotive
applications. Car companies that developed a worldwide market throughout all social
classes require a large volume of production. Moreover, the manufactured parts also need
to satisfy a surface quality standard, commonly referred to as Class A in the automotive
industry. There is no precise definition for this standard, but mathematically-speaking, a
Class A surface should possess curvature continuity between surfaces sharing the same
boundary [92]. The surface should be flat, smooth, and exempt of undesirable waviness
and have an optical appearance identical to an adjacent steel panel [91, 92].
The automotive industry has increasingly used RTM to produce composite parts. It
possesses interesting advantages over the other processes, but so far, only companies with
a low volume of production, such as Aston Martin, have successfully developed it
according to Class A surface finish. The main issue is related to the control of the surface
quality, which is influenced by the resin volumetric changes, the fibres
orientation/distribution, the flow distribution, the painting process (glass transition
temperature might be play a role here) and the surface finish of the mould. The
volumetric changes however have the strongest effect on the surface quality as they
include two phenomena: cure shrinkage and thermal expansion/contraction. The cure
shrinkage of the resin, being more significant than its thermal expansion, leads to surface
defects such as ripples, sink marks, fabric print through, and dimensional inaccuracy.
Previously [44, 45], it was found that adding Low Profile Additives (LPA) resulted in
6
improved surface finish. Recently, it is seen that adding silica nanoclays to the resin/LPA
system shows further improvement in shrinkage control and has an effect on the glass
transition temperature. The glass transition temperature is important to ensure greater
thermal stability in post cure painting process in order to ensure that there is no
degradation in the surface finish. Therefore, synthesises of these nanocomposites is
becoming of large interest to researchers and industries alike. Thus, in order to
completely understand the physical and mechanical behaviour of the nanocomposites, it
is necessary to develop a good understanding of the different techniques available to
synthesis a nanocomposite, as well as the constraints, advantages and disadvantages of
these techniques. Furthermore, there is a need to study the compatibility of the materials,
different mixing methods available to disperse the clays and the various parameters that
are involved with these mixing methods as they have a significant effect on the
crystallographic structure of the nanocomposite which is known to be crucial towards the
final performance of the composite. Ultimately, an understanding of these parameters and
constraints will help us develop processes and techniques to manufacture nanocomposite
systems that will achieve the desired properties in terms of strength, volumetric shrinkage
and glass transition temperature.
1.4. Objectives and Thesis Outline
The general goal of this work is to understand the various parameters involved in the
synthesis and processing of a nanoclay modified unsaturated polyester resin. The idea is
to understand the relationship between the processing parameters and the final physical
and mechanical properties. In this research, two most common mixing method, shear
mixing and ultrasonication will be studied using a pre-formulated unsaturated polyester
resin.
Chapter 2 contains the literature review where the nanocomposites are described. The
different synthesizing methods and mixing techniques are reviewed and their effect of the
dispersion is also included. Chapter 2 also tries to correlate the various properties to the
synthesizing and mixing techniques and compare the effects of these different mixing
techniques. Chapter 3 describes the materials and experimental procedures used in this
7
research: x-ray diffraction, differential scanning calorimetry, rheology and dynamic
mechanical analysis. The results of dispersion, viscosity, volumetric cure shrinkage, glass
transition and storage modulus are shown in Chapter 4. Finally, the conclusion as well as
appropriate future work related to this topic, is given in Chapter 5.
8
2. Literature Review The literature review contains topics that were judged to be the most pertinent for this
research. LPA and their expansion mechanism are described extensively. The various
synthesizing methods for nanocomposites (section 2.2.2), mixing processes (section
2.2.3) and influence of various operational parameters like speed, time and temperature
(section 2.2.4) are reviewed. The influence of adding nanoclay to epoxy and unsaturated
polyester on rheological properties (section 2.3.1), the mechanical properties (section
2.3.2) the glass transition temperature (section 2.3.3), most importantly the volumetric
shrinkage (section 2.3.4) and cure kinetic (section 2.3.5),and has been reviewed in this
chapter. A particular attention is given to the synthesizing and mixing techniques as they
are known to affect the nanocomposite performance.
2.1. Nanocomposites
Nanocomposites systems, in which the filler has a dimension in the nano meter range in
at least one spatial direction, may be divided into two categories: intercalated systems and
exfoliated systems. Intercalated nanocomposites are formed when the polymer penetrates
into the silicate layers resulting in their finite expansion. Exfoliated systems consist of
individual nano meter-thick silicate layers distributed in the polymer matrix (see Figure
2-1 ). In more details, immiscible, mica-type silicate tactoids exist in their original
aggregated state with no intercalation of the polymer matrix into the galleries. For this
case, the particles act as micro-scale fillers. Intercalated nanocomposites have the
polymer matrix intercalated between the silicate layers and the expanded silicate layers
are still in order. Exfoliated nanocomposites, in which the individual 1 nm thick silicate
layers are completely dispersed in a polymer matrix and the gallery structures, are
completely destroyed [17]. Both intercalated and exfoliated nanocomposites exhibit
significantly enhanced properties when compared to the neat polymers or conventional
composites.
The formation of nanocomposites is dependent upon the matrix and its ability to
penetrate the silicate layers. Nanocomposites developed from thermoset polymers can be
9
prepared via in situ, intercalative polymerization [9, 16] with phenol, epoxy and polyester
resins all included in this category. Many nanocomposite systems have been investigated
to date utilizing variety of inorganic silicates or other nano-elements and a number of
thermoplastic and thermosetting resins. This involves swelling the organophilic clay with
a compatible monomer followed by a cross-linking reaction. During swelling, the
monomer diffuses from the bulk monomer into the galleries between the silicate layers.
The final morphology depends on the degree of penetration of the monomer into the
organo layered silicate structure [9]. More on different synthesizing methods will be
discussed in section 2.2.2.
It is believed that the high aspect ratio (10–2000) of the nano-scaled layered silicate and
their dispersion in the resin plays a key role in the improvement of the properties of
nanocomposites [11]. Improvements in mechanical properties [12, 13], thermal stability
[14] and dielectic properties [15] have been widely documented. Notably, low
concentrations of silicate (1–5 wt%) result in the aforementioned improvements.
Figure 2-1: Scheme of composite structures arising from the interaction of layered silicates and
polymers [17].
Most common thermoset polymers that are studied are epoxies and styrenated
unsaturated polyesters (UP). However, whereas epoxy based nanocomposites have been
10
extensively investigated [25, 26, 27, 28] there are only a few studies on UP based ones.
UP resins are bi-component systems comprising of an UP pre-polymer (alkyd) that is
usually dissolved in styrene monomer. In the presence of a peroxide catalyst, the system
cures to an insoluble, infusible, cross-linked matrix resin.
A large portion of nanocomposite research utilizes minerals of the 2:1 layered silicates,
very often smectite and specifically montmorillonite. Smectites are noted in the literature
as being unique in their ability to expand or contract while maintaining their 2-D
crystallographic structure and for their high cation exchange capabilities [75]. These
properties are key elements that attribute to their selection as a nanoclay especially when
the goal is to achieve exfoliation of individual silica layers within a polymer (known to
improve mechanical properties). Interestingly, it is seen in the literature that when
different clays are mixed under identical conditions, different results are observed for
dispersion. This is due to the fact that the organic treatments performed on the naturally
hydrophilic minerals make them organophilic (to be able to be compatible with polymers
to assist inter-gallery absorption) and introduce cations which also play an essential role
in the resulting morphology, as the size of initial gallery spacing of the silicates is
affected by the size of cations used as well as the cation exchange capability of the
silicate. In the same way, when different resin systems are used different results are
obtained as the compatibility is affected. Therefore, it is widely agreed upon that the
dispersion of nanoclays depend heavily on the resin-clay interactions. This in turn means
that the mechanical properties and shrinkage control of the nanocomposite is controlled
by these interactions.
2.2. Processing of nanoclays
This section will look into the dispersion characterization and various parameters
involved in preparing the samples involving the nanocomposites. As seen from the
previous sections, these parameters play an important role in determining the level of
intercalation and hence the property changes of the sample.
11
2.2.1. Characterization methods for dispersion of clays
It is well known that dispersion of nanoclays in the resin is a pre-requisite to the required
improvement in properties [9-37]. Therefore, it is important to be able to characterize the
dispersion of these cays. Most researches have used X-ray diffraction as means to
characterize dispersion. However, it is essential that the clay particles have a distinct
reflection and the samples are thin. For this purpose, some researchers have suggested to
progressively remove layers of a sample and carry out the diffraction tests to check for
dispersion through the thickness [17,29].
X-ray scattering techniques are a family of non-destructive analytical techniques which
reveal information about the crystallographic structure, chemical composition, and
physical properties of various materials. These techniques are based on observing the
scattered intensity of an x-ray beam hitting a sample as a function of incident and
scattered angle, polarization, and wavelength or energy. Bragg’s law is then used to
compute the crystallographic spacing. Bragg’s law is as follows:
θλ sin2dn = (Eq. 2-1)
n is an integer determined by the order given,
λ is the wavelength of x-rays
d is the spacing between the planes in the atomic lattice, and
θ is the angle between the incident ray and the scattering planes
12
Figure 2-2 2θ deviation, the phase shift causes constructive (left figure) or destructive (right figure)
interferences
Two main types of scattering techniques have been found in the literature [13-25, 1340-
42]. Small angle X-ray scattering (SAXS) probes structure in the nanometer to
micrometer range by measuring scattering intensity at scattering angles 2θ close to 0°.
Wide angle X-ray diffraction (WAXD) is a technique concentrating on scattering angles
2θ larger than 5°. The type of scattering technique used depends on the typical properties
of clays that are being studied. Most clay under consideration had typical peaks anywhere
between 2θ equal to 3 and 2θ equal to 5. Hence most of the studies conducted for the
dispersion of these nanoclays consisted of small angle X-ray scattering. Although some
papers [69] can be found making use of the WAXD methodology due to availability of
the technique or a larger reflection angle of the clays. Typical range for scanning samples
is between 2θ equal to 2 and 2θ equal to 10.
Figure 2-3 represents a typical result obtained from several XRD tests on samples with
different mixing speed (one of the parameters involved in the mechanical mixing method
used by the Rudd [17]). The results obtained are analyzed using Bragg’s law (Eq. 2-1) to
calculate the d-spacing. As seen above a reflection peak is a clay property. As these clays
are dispersed into the resin, the reflection peak typically shifts to a lower angle and
reduces in intensity. The lower the angle and the intensity peak, the greater the d-spacing
and hence greater inter-gallery spacing of the silicates. As discussed earlier, the
improvement in thermal, mechanical and shrinkage properties is dependent on the
amount of intercalation and exfoliation reached. The increase gallery spacing is a direct
indication of an increase in intercalation or exfoliation.
13
Figure 2-3: XRD of 4 wt% Cloisite 10A dispersed in unsaturated polyester at varying shear mixing
speeds [17].
Although many researchers observe the shift in peak relative to the initial peak there are
some that have quantified exfoliation and intercalation [8]. The extreme limit or idealized
state of exfoliation is defined by individual silicate layers separated as fully as
geometrically possible based on their volume fraction within the polymer. Although Tolle
[8] has defined exfoliation as spacing between the silicate layers greater than 10 nm,
there are no details found as to the process of assigning specific spacing as a starting
point of exfoliation. However, as seen in most other papers, relative analysis of the peak
and their intensity gives sufficient information to the degree of dispersion of these
nanoclays within the resin.
2.2.2. Synthesizes of nanocomposites
There are essentially three different approaches to synthesise polymer–clay
nanocomposites: melt intercalation, solution and in situ polymerisation. The melt
intercalation process was invented relatively recently by Vaia et al. [80]. A thermoplastic
14
polymer is mechanically mixed with organophilic clay at 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 popular since the
resulting thermoplastic nanocomposites may be processed by conventional methods such
as extrusion and injection moulding.
In the solution method, the organoclay, as well as the polymer, are dissolved in a polar
organic solvent [79]. 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 [79]. After evaporation of the solvent, an intercalated
nanocomposite was obtained. This strategy can be used to synthesise epoxy–clay
nanocomposites [82] but the large amount of solvent required is a major disadvantage.
The in situ polymerization approach was the first strategy used to synthesise polymer–
clay nanocomposites and is a convenient method for thermoset-clay nanocomposites
[83]. 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 and complete exfoliation occurs in favourable cases. According to a
previous study [84], 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 in
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. Phenol resins,
epoxy resins and UP resins can all be prepared using this method.
Preparation ways involved with epoxy resin and UP resin can differ depending on the
curing mechanism and the constraints involved with the synthesizing techniques. Where
as the constraints and parameters involved with various mixing techniques will be
15
discussed in the following section, this section will look into more details on using the in
situ and melt intercalation for unsaturated polyester (UP) resin.
Unsaturated polyesters (UP) can be dissolved in a polymerizable monomer such as
styrene. A UP is a long-chain linear polymer containing a number of reactive double
bonds. The styrene monomer, which also contains C and C reactive double bonds, acts as
a curing agent by bridging adjacent polyester molecules at their unsaturation points.
During the styrene–unsaturated polyester cross linking copolymerization, the initiator
decomposes and creates free radicals in the system. The free radicals grow and form
long-chain molecules by connecting styrene monomers and unsaturated polyester
molecules by both inter- and intra-molecular reactions. A schematic of the growth of free
radicals is shown in Figure 2-4 [41]. Due to the typical curing mechanism of unsaturated
polyester, the styrene monomer, unsaturated polyester linear chain and organophilic-
treated MMT exist together in the nanocomposite formation system. Consequently, the
behaviours of each component in the nanocomposite formation system are very
important. Such multi-component UP systems gives rise to the possibility of numerous
approaches in synthesizing UP nanocomposites. As seen before the nanocomposites of
thermoset polymer can be prepared by the in situ intercalative polymerization method
(simultaneous) and melt intercalation (sequential mixing). During the simultaneous
mixing method these thermosetting nanocomposite materials are prepared by first
swelling the various organo-modified montmorillonite (MMT) with the proper
polymerizable monomers (like styrene), followed by crosslinking reactions. During
swelling, the monomer diffuses from the bulk monomer into the galleries between the
silicate layers. Depending on the degree of penetration of the monomer into the organo-
layered silicate (OLS) structure, different types of nanocomposites can be obtained
ranging from intercalated to exfoliated or delaminated. This first method, simultaneous
mixing, is similar to the method used for preparing conventional UP/filler composites,
which was also used by others [30, 31, 32]. The second method is the sequential mixing.
In the first step, pre-intercalates of the unsaturated polyester (UP) resin and
montmorillonite (MMT) clay are generated, i.e., mixtures of the resin and the
organophilic treated MMT are prepared. The second step is the addition of styrene to the
16
resin/MMT pre-intercalates. The addition of styrene after adding the clays creates yet
another parameter in synthesis and performance evaluation of the nanocomposites. Many
studies have already been conducted on the effects of styrene on UP/LPA composites [4-
6]. It can be seen from these studies that styrene play a critical role in UP/St/LPA
polyester systems during the phase separation and micro cracking process, which is
considered the driving mechanism for shrinkage control. This second step is then
followed by curing of the system by adding the appropriate catalyst.
Figure 2-4: Curing mechanism of UP: (a) styrene-UP solution before curing; and (b) after curing [41]. Long curves represent long polymer chains; short solid lines represent styrene and solid dots
represent free radicals.
Suh et al. [29] compared the two different ways of mixing organically modified clay with
UP. They suggest that a more homogeneous network (i.e., homogeneous cross linking
reaction inside and outside of the silicate layers) was obtained for nanocomposites
prepared via sequential mixing. The reason being UP chains, styrene monomers and
organic organophilic MMTs (O-MMTs) coexist in the mixing medium. The styrene
monomers diffuse into the gallery of the O-MMTs much faster than the UP chains
(because of the size and the functionality of the UP polymer chains). If the curing
reaction starts in these conditions, the styrene homo-polymer is produced primarily in the
interlayer of the O-MMT and the crosslinking density decreases inside and outside of the
O-MMT, because the styrene monomers are concentrated on the interlayer and styrene
monomers are insufficient for the crosslinking the reactive double bonds of the
unsaturated polyester. Therefore, by taking advantage of the multi component UP
17
systems, the silicate layers can initially be penetrated by UP polymer chain and then by
styrene in additional steps as defined by the sequential mixing techniques.
2.2.3. Mixing methods
Methodological approach to study the effects of various mixing processes, applied
shearing levels, organo-clay contents and mixing temperatures were developed in various
literature [29, 30, 31, 32]. These methodological approaches provides basis for
understanding the structuring processes involved in the formation of resin/organo-clay
nanocomposites and establishing materials-processing-structure interrelations. The three
main categories for mixing techniques are: ultrasonication, mechanical or shear mixing
and static mixing
Ultrasonication generates alternating low-pressure and high-pressure waves in liquids,
leading to the formation and violent collapse of small vacuum bubbles. This phenomenon
is termed cavitation and causes high speed impinging liquid jets and strong
hydrodynamic shear-forces. These effects are used for the deagglomeration of
nanometre-size materials. In this aspect, ultrasonication is an alternative to high-speed
mixers and agitator bead mills. Ultrasonic provides more energy to the polymer chains
and the silicate layers, so that the polymer chains would enter more easily into the
galleries between the silicate layers. Also, an ultrasonic bath promotes exfoliation and
prevents formation of agglomerates.
Mechanical mixing or shear mixing is a very broad term that can be applied to
mechanical blades, rollers or manual hand mixing used for mixing clays with the resin.
This technique involves the use of a mechanical device to disperse the nano-particles into
the resin. Different techniques and a wide range of parameter are seen in the literature
when it comes to the applying mechanical or shear fixing [9-33, 70-72]
The mixing processes either mechanical or ultrasonication illustrates the increase in the
different clay basal spacing (characterized by X-ray diffraction, TEM or SEM). All
organo-clays show some increase in the gallery spacing when mixed using the techniques
18
described above. Narkis [37] studied the intercalation of various organo-clays and
showed different clays had different intercalation. This has been attributed to the amount
of organophilic treatment of the clay [33-37]. Interestingly, the lower amount of
organophilic treatment gives rise to higher degrees of intercalation, resulting in higher
increase in basal spacing [37]. However, Suh and Park [38] observed opposite trends for
poly99-vinyle carbazole (PVK)/stearlamine treated MMT system, where lower amounts
of treatment have led to lower intercalation levels. Therefore, the relation between
amount of organophilic treatment and intercalation levels depends on the characterization
technique and initial basal spacing as supplied by the manufacturer. Narkis [37] reported
that although the basal spacing varies with the amount of treatment, the end d-spacing for
the organo-clay remains the same.
Three different mixing techniques were investigated by researchers to determine the
effect on basal spacing and intercalation levels: static heating (annealing), mechanical
mixing and ultrasonication. However, no conclusive information or results are available
to impose superiority of one method over the other. Results seen in the literature suggests
that no direct correlation can be established between mixing technique and the
intercalation levels as these results are influenced by other parameters like type of resin
used and the types of clay and their treatment, as well as the resin-clay interaction. For
example, Yasmin et all [70] suggested that nanocomposites with higher clay content
could not be mixed using ultrasonication process due to increased viscosity of the
mixture. In the same way, as indicated by several researchers regarding polymer/clay
system [36-41], intercalation maybe achieved just by static heating. None the less, these
intercalation processes maybe facilitated by dynamic processes such as mechanical
mixing and ultrasonication. It is interesting to mention here that shear mixing has been
reported to reduce the aspect ratio of clay particles [70] especially when using the milling
process. This is because the milling process breaks the clay platelet during mixing as
observed in microscopic imaging used. The high aspect ratio of the clays is known to
play an important role in improvement of the mechanical properties and therefore the
mixing process may have an influence on the nanocomposite properties.
19
2.2.4. Parameters effecting dispersion
Mixing time in the preparation of resin/clay mixtures is one of the parameters that need to
be determined for optimal results. Most researchers [29-33] agreed that a one hour period
of mixing using ultrasonication and mechanical mixing shows sufficient intercalation for
both epoxies and polyesters. Nevertheless, further mixing may lead to better dispersion of
the already intercalated clay or to delamination [38]. X-ray analysis of the samples
(Figure 2-3) clearly indicated that extent of intercalation increased due to increase in
mixing speed using the shear mixing technique (and in case of a three-roll mill with a
decrease in roller spacing [70]). Samples with varying clay content and varying shear
speed have been tested. Results from these samples clearly supported the suggestion that
the extent of intercalation increased with mixing speed and decrease in clay content.
Although not many studies have been found that evaluate the effect of the amplitude
applied during the ultrasonication process, it is believed that an increase in the amplitude
will have similar effect as to increasing the speed in shear mixing. Others have also
shown that high shear promotes the exfoliation of the silicate layers [43]. Adversely,
large amounts of clay may also result in aggregation of clay in the polymer matrix [43],
which may inhibit further intercalation and exfoliation, resulting in the observed two co-
existing intercalated-clay populations. Moreover, it is also possible that the amount of
polymer in a system containing very high clay content (more than 10% wt) is insufficient
to intercalate all the clay to the larger extent (a “starved” condition), resulting in the two
intercalated-clay populations’ structure. In other studies [21] resin was mixed between
different rpm ranges by an air driven shear mixer, subsequently polymerised and then
analysed using X-ray diffraction (XRD). Generally, the results found in the literature
agree when reporting the affect of shear and amount of nanoclays on the intercalation
level.
Generally, increasing the mixing temperature results in reducing the polymer viscosity,
affecting both the shear level exerted during the mixing process and the mobility of the
polymer chains and segments. Low matrix viscosity imparts low shear stresses on the
clay agglomerates, which may skew the stack of platelets rather than separate them [44],
20
and might also facilitate the aggregation of clay, hindering the penetration process of
polymer chains and segments into the clay layers. At the same time, increases polymer
mobility is expected to facilitate intercalation of clay at shorter times. Narkis [37] and
Huang et al [45] studied the effect of mixing temperature by preparing the
nanocomposites at higher temperatures. Narkis [37] found that mixing at higher
temperature (130°C as compared to 180°C) does not result in a large intercalation extent.
These results are contrary to the ones reported by Huang [42] who found that melt-
mixing, static melt-intercalation and solution intercalation of low viscosity polymer
appear to be advantageous in achieving disruption of the silicate structures or high level
of intercalation at short processing times. However, the reason for reduced or no effect
of temperature [33] could be due to the fact the lowered matrix viscosity, causing
decreased shearing during mixing, hinders the intercalation and exfoliation processes and
has a stronger effect on structuring than the increased chain mobility.
Mixing time is yet another important parameter during the preparation of
nanocomposites. Many researchers [83-88, 24-33, 38-41] have studied the effect of
varying the time using different mixing method (mechanical mixing, ultrasonication and
three-roll mill). In case of a three roll mill, the number of passes have been set equivalent
to the time during which the shearing is applied. All results in the literature agree that
increasing the time has increased intercalation (measured by XRD) as more and more
layered silicates are penetrated by the resin.
2.2.5. Morphology
Understanding of the development of morphology for various nanocomposites has been
under investigation over the past decade. Morphological studies have been used in the
past to establish an understanding of how curing [8, 10-13] and processing [17-33, 70-74]
of these nanocomposites effect the morphology and dispersion and as a result effect the
over all performance of the nanocomposites. Although this understanding is certainly
necessary to enable effective material development, it is of critical importance for
tailoring morphology-sensitive properties such as toughness and permeability. This is of
specific importance for thermosetting resins like epoxies and polyesters, for these
21
properties provide the limitations for their use in automotive and aerospace industries.
Furthermore, the sensitivity of morphological development to the processing conditions
has been well documented in polymer literature and also proposed in nanocomposite
literature [73(a)-74].
Most of the researchers use microscopic imaging techniques to verify and confirm results
that are obtained by the x-ray scattering method. Microscopic imaging provides a visual
interpretation of the XRD results and allows us to understand and confirm these results.
The three most common types of imaging techniques found in the literature are discussed
here.
The scanning electron microscope (SEM) is a type of electron microscope that images the
sample surface by scanning it with a high-energy beam of electrons. The electrons
interact with the atoms that make up the sample producing signals that contain
information about the sample's surface topography, composition and other properties
such as electrical conductivity. SEM micrographs have a very large depth of focus
yielding a characteristic three-dimensional appearance useful for understanding the
surface structure of a sample. This great depth of field and the wide range of
magnifications (commonly from about 25 times to 250,000 times) are available in the
most common imaging mode for specimens in the SEM, This particular type of
microscope is exceedingly useful and is seen in the literature the most.
Transmission electron microscopy (TEM) is a microscopy technique whereby a beam of
electrons is transmitted through an ultra thin specimen, interacting with the specimen as it
passes through it. An image is formed from the electrons transmitted through the
specimen, magnified and focused by an objective lens and appears on an imaging screen.
There are a number of drawbacks to the TEM technique. Many materials require
extensive sample preparation to produce a sample thin enough to be electron transparent,
which makes TEM analysis a relatively time consuming process with a low throughput of
samples. The structure of the sample may also be changed during the preparation process.
Also the field of view is relatively small, raising the possibility that the region analysed
22
may not be characteristic of the whole sample. There is potential that the sample may be
damaged by the electron beam.
The optical microscope, often referred to as the "light microscope", is a type of
microscope which uses visible light and a system of lenses to magnify images of small
samples. Optical microscopes are the oldest and simplest of the microscopes. The
objective lens is a cylinder containing one or more lenses to collect light from the sample.
At the lower end of the microscope tube one or more objective lenses are screwed into a
circular nose piece which may be rotated to select the required objective lens. Typical
magnification values of objective lenses are 4x, 5x, 10x, 20x, 40x, 80x and 100x. Some
high performance objective lenses may require matched eyepieces to deliver the best
optical performance. However, other non-optical microscopes like scanning electron
microscope (SEM) and transmission electron microscope (TEM) can magnify
exponentially greater than the optical microscope.
The choice of the methodology to capture images is dependent on the particle size and
type. It is generally seen that optical microscopy does not give a very accurate picture of
the nanocomposite structure as the particles involved are nano-sized therefore requiring
much higher magnification. Therefore many researchers prefer either SEM or TEM in
order to observe morphological development in nanocomposites.
23
Figure 2-5: High magnification TEM micrographs revealing different morphologies for DER
331 epoxy (Dow Chemical) and 5 wt% of Cloisite 30B [60].
2.3. Physical and mechanical properties
2.3.1. Rheological properties
The rheological properties of particulate suspensions are sensitive to their structure,
particle size and shape, and surface characteristics of the dispersed phase. Thus rheology
potentially offers a means to asses the state of dispersion in nanocomposites while still in
the melt state, and may offer a tool complimentary to traditional methods of material
characterization such as X-ray scattering etc.[42].
The viscosity of all nano clay composites (based both on epoxies and on polyester)
increases due to addition of the clays [29-33, 42]. The increase of viscosity was in
agreement to the amount of intercalation achieved in the mixture. Higher intercalation of
a particular clay in the mixture displayed larger increase in viscosity [17, 33, 42]. The
viscosity measurements were done mostly by using a conventional rheometer [42- 45] or
24
Rheometrics dynamic analyzer (RDA) [17, 59] using parallel plate arrangements.
Viscosity was measured under an isothermal condition where the gel point was defined as
the point where the reduced viscosity ηr = η/ η0 (η is the instantaneous viscosity and η0 is
the initial viscosity) reaches 103.
For all nanocomposites higher mixing time and dynamic processes like mechanical
mixing resulted in larger increase in viscosity [33]. It was also seen that these
nanocomposite system showed shear thinning which has been linked to the reorientation
of silicate layers in the direction of the flow (Figure 2-6). As shown by Huang et al. [42],
relative to static annealing, the application of shear appears to be advantageous in
achieving disruption of the silicate structure and dispersion of the resulting particles. It
was previously suggested by Ishida et al. [46] that increasing the mixing time allows the
formation of both intercalated and exfoliated nanocomposites. The increased viscosity
may be attributed to three simultaneous processes. First, a higher intercalation level that
resulted in higher effective clay content and less polymer segments and chain
participating in the bulk flow process [42, 47]. Second, exfoliation, which results in a
higher exposed clay surface and thus higher interaction levels between the polymer and
clay that may partially arrest segmental movements [35]. Third, higher viscosity values
are also obtained due to better dispersion of the particles [48].
Generally, the interaction of polymer chains with filler particles can alter the chain
kinetics in the region immediately surrounding the particle. The interaction, physical or
chemical, between the polymer chains and the filler surface restricts the molecular
mobility of the affected chains, changes the packing density of polymer chains, and
modifies the conformation and orientation of chain segments in the neighbourhood of the
surface. Due to the clay’s extremely high specific surface area, even low filler contents
that are well dispersed in a system provide an enormous amount of interfacial area
through which the bulk properties of the polymer can be altered [49, 50].
25
Figure 2-6 : Viscosity of alkyd/24 wt% I.28MC organo-clay nanocomposite, prepared by mechanical
mixing at high shear levels/high temperature for several durations. Samples tested at 80°C [33].
2.3.2. Material strength
Many variations of the measure of material strength can be found in the literature.
Researchers have tried to use tensile tests [17, 50, 56, 58] (using tensile testing
equipments like Instron testing systems) to determine the Young’s modulus (also known
as tensile modulus), as well as three point bending tests and cantilever beam tests using a
dynamic mechanical analyzer (DMA) to measure the flexural strength and storage
modulus [17, 29, 30, 40, 76]. The young’s modulus is measure of the stiffness of a
material. It is also known as the young’s modulus, modulus of elasticity, elastic modulus
or tensile modulus. The storage and loss modulus in viscoelastic solids measure the
stored energy, representing the elastic portion, and the energy dissipated as heat,
representing the viscous portion (loss modulus).
26
Figure 2-7: Storage modulus as a function of temperature; (a) pure epoxy resin; (b) nanocomposite
with 5 wt% of silica; (c) nanocomposite with 10 wt% silica [ 56]. It is largely reported in the literature that the incorporation of nanoclays into epoxy or UP
[17, 29, 30, 56, 58] resins and of carbon nanotubes into the resin system [60] have
increased the mechanical properties like tensile strength and storage modulus. The
general trend seen is large initial increase of strength with approaching plateau as the clay
content increases. The initial increase in stiffness is linked to the large aspect ratio of the
clay particles that contribute to the reinforcement of the resin as well as increased clay-
resin interaction related to the degree of intercalation and exfoliation [29, 40, 58, 76]. The
decrease in the strength of these nanocomposites with increasing clay content is due to
reduced exfoliation that causes weak adhesion of clays to the resin and therefore a
reduction in the stiffness. Hence, it can be seen that the stiffness of nanocomposites
depends on the mixing method, the compatibility (therefore the treatment) of the
nanoclays with the resin system and the overall curing mechanism of the system under
consideration. Since the increase in stiffness is largely related to the clay-particle
adhesion and interaction, there are some papers that show opposite trends in regards to
the stiffness of nanocomposites. It has been seen that a reduced intercalation and
27
exfoliation has been linked to the reduction of storage modulus [77] and of tensile
modulus [56] of the nanocomposites as the clay-resin adhesion tends to become weaker
with reduced exfoliation.
It is seen that there some discrepancies in observation of the stiffness and tensile strength
of the nanocomposites. However, most researcher’s agree on slight increase in the storage
modulus of the nanocomposites for very low (generally less than 5 wt%) clay content.
2.3.3. Glass transition temperature
The glass transition temperature, Tg is the reversible passage between the rubbery and
solid/glassy states for thermoset resins. For neat UP resins, Tg varies significantly
depending on their composition. It can go from 85°C to almost 200°C for fully cured
samples [50-53]. Tg can be measured by thermo-mechanical analysis (DTMA) [60],
dynamic mechanical analysis (DMA) [29] (the inflection of the storage modulus curve),
differential scanning calorimetry and dielectrometry [17, 69] as found in the literature.
Differential scanning calorimetry measures a change in heat capacity; DMA measures the
change in the mechanical properties of storage or loss modulus (where the Tg is the point
of inflection of the storage modulus or peak of loss modulus or peak of tan δ) and the
dielectrometry measures a change in the permittivity (increase around Tg) and loss factor.
It should be mentioned that the Tg obtained from the dielectric measurement lacked of
consistency. Results in the literature showed that if the frequency of the field is increased,
the glass transition occurs at a higher temperature [69].
The effect of nano clays on the glass transition temperature is an area of debate amongst
researchers. Results shown in Figure 2-8 show an increase in the Tg, but opposite trends
are also observed. As for the effect of LPA, most studies tend to agree: the addition LPA
causes a slight decrease in Tg [53- 55]. Huang and Horng [53] studied the effect of
various LPA on the glass transition temperature.
28
Figure 2-8: Glass transition temperature of Cloisite 10A and CaCO3 for loadings between 0 and 10
wt% [17].
Rudd [17] showed using DSC (Differential scanning calorimeter) by non-isothermal
analysis of the polymerised samples that the glass transition temperature increased (up to
11 °C for 4 wt% clay, see Figure 2-8). However, other related studies [56, 57] have
shown clay to decrease the curing reactivity, which generally results in lower cross-link
density and longer polymer chains among the cross-linking points. This would tend to
decrease the glass transition temperature. As mentioned in section 2.3.5, unsaturated
polyesters containing styrene may show reduced reactivity. This is because the styrene
monomers are concentrated on the interlayer and styrene monomers are insufficient for
the crosslinking the reactive double bonds of the unsaturated polyester. More so, it would
be expected that increased exfoliation levels would result in reduced reactivity due to the
suggested consumption of free radicals by clay particles [58]. On the other hand Suh [29]
tried using the sequential mixing technique to show that the homogenous dispersion of
styrene monomer (which act as a curing agent) with increase in time results in the Tg
29
reaching up to the value of pure UP resin. This supported the hypothesis that an increase
in the crosslink density within the UP resin, causes an increase in the glass transition
temperature. Miyagawa [60] reported that the Tg increased linearly for epoxy resins with
the amount of carbon nanotubes (CNT). Alternatively, Narkis [33] tried to correlate the
intercalation results to understand the effect on the glass transition temperature. He found
that the glass transition temperature decreased after 0.5 hours of mixing followed by an
increase upon further mixing. It is suggested that the decrease was due to the mechanical
degradation. The Tg increase may be the result of slight cross linking reactions or due to
evaporation of degraded low molecular weight fractions. XRD results showed that due to
intercalation of more polymer chains into the organo-clay galleries and exfoliation of
more clay platelets, there was increased interaction between the polymer chains and clay
surfaces. Thus the Tg increases with mixing time.
It can be concluded that the changes in Tg are the result of complicated balance between
the alterations exhibited by the polymer itself and the polymer-clay interactions, affected
by amount of clay, mixing temperature and time. Different characterization techniques
(DMA or DSC) resulted in different results as well. Therefore, it is important to realise
the possibility of difference in the data represented by various researchers.
2.3.4. Volumetric shrinkage
Varied methods to measure the cure shrinkage of resins, without taking the effect of any
additives into consideration, were developed over the past years [60-64]. While some of
those techniques were elaborated for epoxy resins, they are valid nonetheless for all types
of thermoset resins. The most common instrument to measure volumetric shrinkage
remains the dilatometer [61-62], [63, 64]. Being generally slightly modified in most
studies, the principle is always the same: the sample is placed in a cavity of known
dimensions and its thickness variation is monitored at constant temperature. The sample
is sometimes submerged in a different fluid, in which volume variation is recorded during
cure. It is then possible to calculate the final volume of the sample and obtain its
volumetric shrinkage
30
( )0
0
VVV
V−
=Δ (Eq. 2-2)
Where V0 is the initial volume of the sample of the resin and V is the volume at any
given time.
An efficient way to eliminate or reduce the shrinkage is to employ a small amount of
thermoplastic materials, often called low profile additives (LPAs), into the resin system
[17, 33, 43]. LPAs have been found to be very effective in volume shrinkage control of
UP resins cured in high-temperature processes, such as compression moulding of sheet
moulding compounds (SMCs) and injection moulding of bulk moulding compounds
(BMCs). The shrinkage control mechanism has been studied extensively and it is
generally believed that thermal expansion during heating and microvoid formation during
cooling contributes to the shrinkage control [4-6, 44-46]
Figure 2-9: LPA mechanism initiation reaction, (2) micro-gelling, (3) intra and inter-particle
reactions experienced during the polymerisation process, (4) the role of the micro-void formation In the UP/St/LPA system, a reaction-induced phase separation occurs during curing,
resulting in a UP-rich phase and an LPA-rich phase. If microvoids can form in the LPA-
rich phase or at the interface of the two phases, polymerization shrinkage can be reduced
or eliminated without any thermal effect [65-67]. Recently, researchers have found that
microvoid
Intra-particle reaction
Inter-particle reaction
Micro-gel
Precipitated thermoplastic
UP, styrene and thermoplastic
Free radical
31
adding silica based nanoclays to resin systems tend to improve the shrinkage control for
these systems. It was found that the reaction rate of the LPA rich phase is much lower
than that of the UP-rich phase because of the high St/UP ratio (i.e. the St–St reaction is
much slower than the St–UP copolymerization) and the low cobalt promoter level in the
LPA-rich phase (i.e. the cobalt promoter has a higher solubility in the UP-rich phase
during partitioning). Since a liquid LPA phase can release stresses resulting from
polymerization shrinkage of the UP rich phase, the stress-induced local cracking in the
LPA-rich phase or at the interface of the two phases will not occur until after the gelation
of the LPA-rich phase. This local cracking leads to volume expansion of the curing
system, thereby compensating some of the polymerization shrinkage [67].
It has been suggested that increasing the reaction rate in the LPA-rich phase could result
in an earlier microvoid formation/volume expansion in the system for better shrinkage
control [67]. An acid-modified LPA [67] was shown to have the ability to attract more
cobalt promoter to the LPA-rich phase, resulting in a higher reaction rate in the LPA-rich
phase. The dilatometry results demonstrated that acid-modified LPA provided earlier
volume expansion and better shrinkage control. Cao et al. [68] found that the addition of a
secondary monomer such as methyl methacrylate or a co-promoter such as 2,4-
pentanedione can also improve the shrinkage control of the UP/St/LPA systems because
the presence of the co-promoter and co monomer has a more pronounced effect on
increasing the reaction rate in the LPA-rich phase than in the UP-rich phase. Rudd [17]
and Xu [43] showed that addition of nano clays to the resin matrix improves the
volumetric shrinkage control when compared to UP/St/LPA resin systems.
32
Figure 2-10: Volume change profile of UP/St/LPA system with different Cloisite 20A content cured at
35 8C (0.5% cobalt octoate, 1.5% MEKP, 300 ppm BQ, and 3.5% LPA) [43].
Xu and Lee [43] have tried to study the effect of partition of nanoclays on the reaction
kinetics and chemorheology of the LPA rich and UP rich phases. They implemented
temperature induced phase separation method as a qualitative assessment for the
nanoclays selectivity and behaviour of the two important phases. It was observed that
almost all the nanoclay chose the LPA-rich phase during temperature-induced phase
separation and that the conversion of the UP-rich phase when the LPA-rich phase reaches
gelation was lower in samples with nanoclays. In the UP/St/LPA system with nanoclays,
the UP-rich phase was seen as continuing to react after the gelation of the LPA-rich
phase. This polymerization shrinkage may lead to micro-cracking in the system to
compensate some of the volume shrinkage.
2.3.5. Cure Kinetics
33
In this section, the effect of nanoclays on five different characteristics related to the cure
kinetics of UP resins will be discussed: onset of reaction, peak temperature of the
exotherm during cure, total heat of reaction, reaction rate and final degree of cure. A
considerable amount of research was done on each of those subjects. However, results
vary, as will be seen in the following paragraphs.
A differential scanning calorimeter (DSC) is commonly used to characterize the cure
kinetics of resin systems. This technique measures the heat generated during the
polymerization reaction, which is highly exothermal. Before cure, the system contains
styrene, UP molecules and curing agents (i.e. a catalyst and an accelerator). As the
polymerization reaction progresses, UP molecules form polymer chains by linking the
styrene monomers.
Figure 2-11: Heat flow for various nanoclay content as obtained from DSC runs by Hussain [69] Most researchers agree that with the addition of the organoclay to the resin system, the
nanocomposites showed lower curing onset temperature. Moreover, the temperatures in
34
the exothermal heat peak for nanocomposites are shifted to lower temperatures. This
demonstrates the catalytic effect of nanoclay on the cross-linking reaction of the resin
with curing agent [43, 69, 78]. The filled Org-MMT reduces the gelation time and
increases the rate of the curing reaction while reducing the total heat of reaction (Figure
2-11). This is believed mainly due to the fact that montmorillonite acts as a free radical
scavenger, adversely affecting the crosslinking process and decreasing the cross-link
density. Therefore, researchers have linked the reduction in total heat of reaction and the
cure activity to increase in the intercalation of the cure particles into the silicate galleries.
2.4. Literature review summary
The literature review reported effects of various synthesizing methodology, compatibility
of different clays to different resin systems (based on their organic treatment), mixing
techniques on the dispersion of clays in resin systems. Almost all researchers employed
X-ray diffraction analysis to characterize dispersion and study these effects. Three
synthesizing methodologies were seen in the literature. While most researchers
emphasized the compatibility of the materials as a prime factor in the choosing the
method, there were some who were able to show that the sequential mixing techniques
are more suited to styrenated polyester systems when compared to the simultaneous
mixing method. It was seen that mixing techniques (like ultrasonication, shear mixing
and static mixing) involve many parameters like time, temperature, amplitude and
shearing levels that affected the dispersion of the clays. It was seen that increasing the
time and shearing levels generally increased the intercalation levels resulting better
dispersion. However, no direct correlation could be found between the effects of
temperature on the intercalation levels.
There was a considerable amount of discrepancies seen in the literature in regards to the
physical and mechanical properties of the synthesized nanocomposites. Most researchers
reported an increase in viscosity on addition of nanoclays and tried to correlate X-ray
diffraction results (intercalation) to increase in viscosity. Some work was also done to
measure the shrinkage of UP/ St/LPA based nanocomposites and it has been reported that
the addition of clays enhance the shrinkage control of UP. However, when measuring the
35
glass transition temperature, opposite trends were seen amongst various reports. The
increase of glass transition temperature due to incorporation of nanoparticles was
explained by a strong adhesion between polymer and particles. This strong adhesion
restricted the motion near the organic-inorganic interface, which shortened the polymer
chain (increase in thermal stability). In the same way a decrease in Tg was linked to the
weak adhesion between the clay particles, which generally resulted in lower cross-link
density and longer polymer chains which caused a decrease in the Tg. This lower cross
link density was due to the consumption of the free radicals by the clays which tend to
reduce the total heat of reaction during the cure kinetic analysis of nanocomposites which
has been seen by the lower peak of the heat flow curves. Papers have generally agreed
that the addition of clays have a catalytic affect on the cure kinetics of the resin, resulting
in early curing onset temperature and the exothermal peak has been shifted to a lower
temperature. It has been seen that the storage modulus increased with the addition of
nanoclays due to the high aspect ratio and high elastic modulus of the clays. Other
mechanical properties like the young’s modulus and the ultimate tensile strength are a
topic of debate amongst the researchers. However, it can be said with certainty that the
degree of dispersion (degree of intercalation or exfoliation) of clays and the clay-resin
interaction has been linked directly to the behaviour of mechanical properties. To
improve this clay-particle interaction and the dispersion of the clays various parameters
have been studied by researchers. As mentioned earlier, shearing level and applied
amplitude, mixing time and temperature has been in the focus for researchers. These
studies have been conducted on epoxy systems quite extensively. However, the mixing of
UP-clay resin systems cannot be found extensively within the literature. Also the
relatively new sequential mixing method has been said to have great potential for
polyester resin systems and it provides a good potential for some future work.
2.5. Research Objectives and Approach
The long term objective of the research is to obtain better shrinkage control and improved
glass transition temperature by using nano-modified resins or nanocomposites. However,
due to various possibility of synthesizing the nanocomposites, it is necessary to study the
synthesis and mixing techniques involved with making nanocomposite systems.
36
Therefore, this thesis will study the effects and various parameters involved in mixing UP
resin with silicate nanoclays. This will help establish a good understanding of the various
synthesizing technique first and then choose the suitable technique for the pre-formulated
polyester resin. The next step will be to compare different mixing techniques like
ultrasonication and three-roll mill for this polyester resin and study the effect on the clay
dispersion. This will be done using X-ray diffraction and then some basic rheological
tests. These techniques have various parameters that will be needed to be studied. These
parameters are discussed here in brief.
Ultrasonication parameters to be considered:
• Frequency type: Frequency to be used is has to be established. Degassing
(sinusoidal) frequency applies sinusoidal frequency to the sample while
ultrasound (constant frequency) applies constant frequency to the samples in
order to disperse the clays.
• Power (amplitude): The ultrasonication machine available for this research
has fixed amplitude. Hence, variations in amplitude will not be possible.
• Temperature: temperature will be fixed at 50°C to ensure temperature rise due
to ultrasonication does not interact with the results. No variation in the
temperature will be made as research time was a constraint.
• Time: the effects of the sonication time will be studied by in order to establish
an optimum mixing time that would be useful to then compare the dispersion
with the three Roll Mill (TRM)
• Amount of nanoclays: 4 wt% clay will be used to make sure the effects of
clays are clearly visible when comparing it with three roll mill (TRM)
The three roll mill (TRM) parameters to be considered are:
• Speed: speed of rotation is fixed on the TRM available for this research
• Amount of nanoclays: 4 wt% clay will be used to make sure the effects of
clays are clearly visible when comparing it with three roll mill (TRM)
• Distance: the distance between the front roller and the center roll and the back
roller and center roll will be adjusted for various samples. These samples shall
be studied
37
• Temperature: temperature control is not installed on the TRM right now.
However, if the time and the resources permit, it will be installed and the
temperature will be set at 50°C.
• Number of cycle: different number of cycles shall be used to see the effect on
dispersion.
These parameters are going to be adjusted and studied to establish an optimum mixing
method (OMM) using the synthesizing technique chosen earlier. Once the OMM is
established for this particular nanocomposite system, resin characterization tests will used
to study the effects of the clay content. These tests will reveal the cure kinetics,
rheological behaviour, modulus, glass transition temperature and volumetric shrinkage of
nanocomposite system and help us understand the relationship between synthesizing
techniques, material compatibility and material properties.
38
3. Experimental Procedures In this chapter the materials used in this research will be described (Section 3.1). The
experiments carried out to characterize the resin after the application of mixing technique
as well the addition of nanoclays are also discussed in section 3.2.
3.1. Materials Used
Table 3-1: Materials used for research
In this study, the polyester resin was reinforced with montmorillonite (MMT) clay
particles to fabricate UP/LPA/St/Clay composite. The unsaturated polyester system was
obtained from AOC Resin. The system chosen for this study was the R580-ZPE-14.
R580-ZPE-14 is a unique low profile polyester resin system for use in resin transfer
moulding (RTM) and other liquid moulding processes. R580-ZPE-14 offers (as claimed
by the manufacturer) Class A smoothness for low volume application. R580-ZPE-14 is
pre-promoted with cobalt for convenience. The base resin for this pre-formulated, pre-
mixed system is the T580-63 by AOC. Unfortunately, due to proprietary issues, the exact
quantities of the LPA and promoter added to the R580 system are unknown. Organically
treated MMT clay was obtained from Southern Clay Products Inc. Cloisite 20A (basal
spacing 24.9 Å) was used for this study. It consisted of natural MMT modified with a
dimethyl, dehydrogenated tallow (containing ~ 65 wt% C18, ~30 wt% C16, and ~5 wt%
Material Type
Name Description Vendor
Resin
R580-ZPE-14
UP Resin Molecular weight: 800 – 900 g/mol
Pre-promoted with LPA and promoter
AOC
Clay Cloisite 20 A Modified with quaternary ammonium salt
~ 65 wt% C18, ~30 wt% C16, and ~5 wt% C14
Southern Clay Products
Initiator NOROX PULCAT AW
Methyl Isobutyl Ketone Peroxide (MIBKP)
Syrgis
39
C14) quaternary ammonium salt. Cloisite 20A contains about 38 wt% of organic
modifier. The organic treatment modifies the clay surface from hydrophilic to
hydrophobic which could make them compatible to the resin system to assist inter-gallery
absorption (that would enhance properties). To initiate polymerization (curing), 1.5 wt%
of a free radical initiator, MIBKP was added.
3.2. Resin Characterization
3.2.1. Sample Preparation to develop optimum mixing method (OMM)
The sample preparation for section 3.2.2 will be discussed here. The samples are prepared
by adding 4 %wt of Cloisite 20A to the pre-formulated resin R580 in a plastic container
and mixed manually using a metal rod until a homogenous mixture is achieved. The
synthesizing technique used for this type of the resin is only limited to the in situ
(simultaneous mixing method) since the resin is already pre-formulated (i.e. the styrene
and the thermoplastic LPA are already added in quantities not disclosed due to propriety
issues). The reason to use 4%wt is to ensure any effects of adding clays in terms of the
dispersion could be seen. Also, it can be seen that typical quantity of clays used are
between 1 wt% and 10 wt% with majority of the systems showing optimum
improvements around 4wt % or 5 wt% nanoclay [17].
Two mixing methods were used to disperse the nanoclays into the resin system via the
simultaneous synthesizing method. The three roll mill (TRM) used (Figure 3-1) for this
study was obtained from Torrey Hills Technologies, LLC (The model is S2.5”). At the
beginning of the processing, the feed (slow) and the apron (fast) roll were set manually.
One of the parameters involved in this study was the effect of the roller distance on
dispersion. Hence, using the adjustment screws the distances between the apron (fast)
roller and the mid roller and the feed (slow) roller and mid roller were adjusted according
to the requirement. The speed of the rolls was fixed in this model and no temperature
control had been installed. The speed of the feed (slow) roller was 31 rpm, the center
roller 84 rpm and the apron (fast) roller was 174 rpm with each roller diameter of 6.35
cm. The distances between the rollers were chosen in accordance to the manufacturer’s
40
recommendation for efficient and safe operation. The eccentricity of the roller was
roughly 10µm, which was a major constraint for adjusting the distance between the
rollers (the minimum distance used was 40µm as suggested by the laboratory technician).
Material was transferred from the center roll to the apron roll by adhesion and removed
from the apron roll by a wooden stick that runs against the roll. The dispersion is
achieved by the shear forces generated between adjacent rolls. The parameters that were
adjusted between different samples were the number of passes and the distances between
the rollers. Table 1 summarizes the parameters used for mixing.
Figure 3-1: The three roll milling machine with all its major features and components [93].
41
Table 3-2: Summary of mixing techniques and parameters tested on resin mix with 4 wt% of Cloisite 20A.
Sample Name Mixing Technique Temperature (°C) Parameter Tested Ultra_60 Ultrasonication 50 Mixing time
(60 minutes) Ultra_30 Ultrasonication 50 Mixing time
(30 minutes) TRM_F40_B100 TRM 25 Roller distance
(F= 40 µm; B = 100 µm) TRM_F60_B150 TRM 25 Roller distance
(F= 60 µm; B = 150 µm) TRM_F80_B200 TRM 25 Roller distance
(F = 80 µm; B = 200 µm)3Pass_F40_B100 TRM 25 Number of passes
(3 passes) 1Pass_F40_B100 TRM 25 Number of passes
(1 pass)
Ultrasonication method used in this study, generates alternating low-pressure and high
pressure waves in liquids, leading to the formation and violent collapse of small vacuum
bubbles. This phenomenon is termed cavitation and causes high speed impinging liquid
jets and strong hydrodynamic shear-forces. These effects are used for the
deagglomeration and milling nano-size clays as required for better dispersion of these
clays in to the resin system. Ultrasonication was applied for 30 minutes and 60 minutes,
and the organo-clay content was 4 wt% of the final composite composition. The
ultrasonication used in this study was a D-78224 Singen/Htw by ELMA. A sinusoidal
frequency was applied during this process at a temperature of about 50°C to avoid any
localized heating effects. The mixing process involves the mixture in a closed container,
thereby minimizing any possibility of styrene evaporation. The mass of the samples were
measured before and after ultrasonication process confirmed that less than 0.1% of mass
loss was caused by this mixing process.
42
Figure 3-2: The mould used to cure samples used for X-ray analysis and DMA testing.
The samples described in Table 3-2 were cured by adding 1.5% of the MIBKP catalyst
and pouring the sample into a mould (see Figure 3-2). The mould consisted of a Teflon
insert which had 12 openings, each of which was 50mm x 4mm x 2mm (L x W x D). A
Thermal Product Solutions (TPS) oven (model PRO 750) was used to cure the samples
using the following cure cycle. The mould has an opening for pressure inlet. This opening
was connected to the air pressure supply through a pressure regulator. The regulator was
set to provide a pressure of 551.58 kPa (80 psi). The samples were cured with a ramp
from 25°C to 80°C in one hour followed by a hold at 80°C for one hour and then cooled
down to 25°C in one hour. During this entire curing process, the pressure was kept
constant at 80psi. After cool down the samples were removed from the Teflon inserts and
stored away in zip lock bags to be used later for x-ray analysis and DMA tests.
3.2.2. X-ray diffraction
As seen in literature commonly, X-ray diffraction has been used to study the dispersion
on nanoclays with in the system. The X-ray diffraction (XRD) was performed at McGill
University on a Max 3100 X-ray generator with Cu radiation (40KV, 20mA) in the small
angle X-ray scattering mode (SAXS). Diffraction was performed from 2° to 10° at a scan
rate of 1°/min with a step size of 0.05°. The diffraction beam was monochromated before
43
detection. The clay powder and clay-UP samples were placed on a sample holder using
clay. The sample (17mm x 12mm x 2mm) was made by using a mould that consisted of a
Teflon insert. The Teflon insert had 12 openings, each of which was 50mm x 4mm x
2mm. Three samples were then cut to length (17mm) using a blade and placed together
on the sample holder to achieve an equivalent width of about 12mm.
3.2.3. Sample preparation for to characterize the effects of nanoclays
Once the optimum mixing method (OMM) has been established, the next step was to
characterize the resin and study the effects of adding Cloisite 20A nanoclays to the R580
pre-formulated resin using the OMM. For the following sections, the resin sample was
prepared by adding the 0wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt% and 5 wt% of Cloisite 20A
nanoclays into the resin and mixing it manually until a homogenous mixture was
obtained. Once this homogenous mixture was obtained, the optimum mixing method
(OMM) that was developed in section 4.1 was applied to each sample in order to
uniformly disperse the clays into the mixture and characterized the system using cure
kinetics, viscosity measurements, dynamic mechanical analysis (DMA), glass transition
Tg measurements and volumetric shrinkage measurements. These techniques are
discussed in the following sections.
3.2.4. Cure kinetics
A TA Instruments Q100 differential scanning calorimeter was used to determine the heat
of reaction and cure kinetics of UP/LPA/St/clay resin samples. This task was assisted by
the Universal Analysis software provided by TA Instruments. A two-step calibration was
performed before the series of tests. The cell resistance and capacitance calibration was
carried out using two equal weight sapphire discs. Cell constant and temperature
calibration was then conducted using pure indium. The resin scans were performed on
samples having a mass between 5 mg and 15 mg, with an average of 12.96 ± 1.98 mg,
sealed in hermetic aluminum pans withstand 2 atm internal pressure before being sealed
and placed in the DSC. Dynamic scans from room temperature to 220°C at a rate of
44
3°C/min were used in nitrogen atmosphere to determine the resin total heat of reaction.
The total reaction exotherms were calculated from the area under the scanning DSC heat
flow curves (Eq. 3-1). The exotherms data can be converted to reaction rate and degree of
cure as a function of time by assuming that the total reaction exotherm corresponds to a
fully cured resin or a degree of cure of one. The dynamic scans were performed on resin
with 0 wt%, 2 wt%, 3wt%, 4 wt% and 5 wt% of nanoclays. Two samples were prepared
according to the procedure described in Section 3.2.3 and polymerization was initiated by
adding 1.5% of MIBKP , for a total of ten DSC samples.
r
t
HtH
dttH
dttH)(
)(
)(
0
0 =
∫
∫∞ (Eq. 3-1)
3.2.5. Rheology and volumetric shrinkage measurements
The AR 2000 Series rheometer from TA Instruments was used in association with the
Rheology Advantage Data Analysis software to measure the viscosity and volumetric
cure shrinkage of the resin through a modified procedure. The viscosity tests were
performed first to study the effects of the two mixing methods discussed in Section 3.2.1
on the resin system by using a flow test and then later study the effects of adding
nanoclays on the viscosity (sample prepared as discussed in Section 3.2.3).
The viscosity (η) of a liquid is then defined as the stress divided by the rate of change of
strain (dγ/dt). Newton’s original postulate can then be phrased as that the viscosity of a
material is constant: the stress is proportional to the flow rate. The more easily a liquid
flows, the lower the viscosity.
Parallel plate arrangement (25mm in diameter) was used at 25°C to study the effect of
viscosity with shear rate. Figure 3-3 shows the 25 mm diameter parallel plate setup.
Calibration procedure including rotational mapping, inertia of the plates (1.17 ± 0.04
μN.m.s2) and “zero gap” was performed before each test. The shear rate was varied from
45
0.1 s-1 to 10 s-1 in flow test and the variations of viscosity were studied. Steady state flow
mode was used, which applies successive shear values and data is sampled at equilibrium
conditions of 25°C. The rheological tests were conducted on uncured resin samples. The
main features of such curves are most easily seen if the data are plotted on logarithmic
axes (i.e. with 0.1, 1, 10 etc. equally spaced). For parallel plate geometry, the shear rate
and the shear stress experienced by the sample vary with radial position, and the viscosity
calculated is “Newtonian equivalent” i.e. the assumption is made that viscosity is
independent of the shear rate. The exact viscosity is then obtained by using the stress
correction transformation in the rheology advantage data.
Fixed plate
Rotating plate
Normal force Fz
Gap
Fixed plate
Rotating plate
Normal force Fz
Gap
Figure 3-3: Parallel plate setup on the rheometer
The volumetric shrinkage tests were carried out at 40°C for the pre-formulated R580-
ZPE-14 resin system in accordance to the resin manufacturer’s guidance. However, some
tests were also required for the base resin. These tests were conducted at 80°C as guided
by the technicians. When the temperature reached a steady state, the resin was injected
between the plates in order to obtain in initial gap of approximately 1000 μm. Due to the
viscous resin, the volume of each sample was hard to control precisely. Before gelation,
the rheometer was set to oscillation mode at the desired isothermal temperature of 40°C
with a maximum angular strain of 15% at 0.2 Hz. When the viscosity | η*| reached 1000
Pa.s (this where G’ and G’’ cross over), the second step was initiated, which set the
46
normal force applied on the sample to 0.1 N. This procedure was designed to measure the
shrinkage based on the gap change between the parallel plates. A constant force was
applied on the resin sample throughout its shrinkage after gelation. The volumetric
shrinkage was calculated using Eq. 3-2, based on the assumption that the resin was
incompressible with a constant Poisson’s ratio of 0.5 [44]:
1311
3
0
0 −⎥⎦
⎤⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛ −+=Δ
hhh
v (Eq. 3-2)
where ∆v is the volumetric strain or shrinkage, h (μm) is the gap between the plates at any
time and h0 (μm) is the initial gap.
3.2.6. Dynamic mechanical analyzer (DMA)
The storage modulus and the loss modulus of the UP/LPA/St/Clay mixture were
measured as a function of temperature using the DMA in flexion mode. The DMA used
was a Q800 from TA Instruments. Dynamic mechanical analysis of the sample beam in
single cantilever bending mode was performed and the elastic modulus values were
obtained as a function of the test temperature. Material was heated at a constant rate.
While heating, the material is deformed (oscillated) at a constant displacement
(amplitude) over a range of frequencies and the mechanical properties measured. The
temperature range over which these results were analyzed were between 30°C and 140°C.
The compliance of the apparatus was less than 0.6 μm N−1 which was determined by a
prior calibration of DMA in single cantilever mode. The moment applied to the sample
was set at 0.9µNm with average sample size of 17.6mm x 3.85mm x 2mm.The samples
were cured with a ramp from 25°C to 80°C in one hour followed by a hold at 80°C for
one hour and then cooled down to 25°C in one hour. The amplitude for these studies was
determined by studying the linear viscoelastic region using with a frequency of 1 Hz. The
linear region can be measured for a material using a strain sweep test. In a strain sweep
test, the frequency of the test is fixed and the amplitude is incrementally increased. Once
the storage modulus and the loss modulus were obtained for samples with clay content
47
0%, 2%, 3%, 4% and 5%, the glass transition temperatures for these samples were
defined as the onset temperature for decrease in the storage modulus.
48
4. Results and discussions This section will look at the results obtained as per the experimental plan in appendix A.
Section 4.2 discusses the results obtained from the two mixing techniques, ultrasonication
and shear mixing using the three roll mill. Section 4.2 discusses the rheological properties
as a result of applying these mixing techniques and identifying the optimum mixing
method (OMM). Section 4.3 discusses the rheological properties of nanocomposites as a
function of nanoclay content, section 4.4 discuses the volumetric shrinkage, section 4.5
displays the mechanical properties and section 4.6 shows the cure kinetics.
4.1. X-ray diffraction
In this section, X-ray diffraction was used to study the crystallographic spacing of the
silicate layers as they are dispersed into the R580-ZPE-14 resin system using the
ultrasonication and three-roll milling machine. The first part of this section consists of
identifying the best dispersion results from each of the mixing techniques (ultrasonication
and three-roll mill) and then comparing them to each other. Two set of samples were
prepared as discussed in section 3.2.2. Both results obtained were identical; therefore, one
was selected to be displayed here.
The incorporation of nanoscale-layered silicates within thermosetting resins presented
unique challenges. Curing of thermosetting involves the interaction of chemical kinetics
(as explained in section 2.2.2) and the changing physical and mechanical properties. Near
vitrification, the kinetics is affected by the local viscosity. The viscosity, in turn, is a
function of the temperature and the extent of reaction. In thermal cures of
nanocomposites, the level of exfoliation or intercalation of the silicate layers maybe
impacted by the competition between the growing network formation, which tend to
impede the ability of silicate layers to separate, and the lower viscosity, which will tend
to ease physical separation of silicate sheets. Once cross-linking proceeds, the molecular
weight of the resin and the viscosity increase, both of which will impede silicate mobility,
and hence exfoliation.
49
The position of the initial peak provides information on the size of the developing
structure through the relationship between basal plane separation, d and the wavelength λ
(Bragg’s law, Eq. 2-1). The relative intensity provides information on the number of
scattering structures, regardless of whether they are oriented aggregates or individual
sheets and the peak breadth provides information on the scattering domains. Broader
peaks correspond to smaller scattering domains, sharper peaks to larger domains.
4.1.1. Effect of TRM roller distance
The first sets of mixing procedures were carried out by adjusting the roller distances on
the three-roll milling machine. Cloisite 20A nanoclay was mixed at room temperature
with clay content of 4 wt% of R580-ZPE-14 as described in section 3.2.1. The ratio of
distance between back roll and center roll to the distance between front roll and center
roll was always kept constant at 2.5:1. This was to make sure to eliminate any
inconsistencies that may result if this ratio is altered. During the application of the TRM,
we have experienced some difficulties. The major concern was the styrene evaporation
from the polyester resin during the processes, which caused a dramatic increase of the
viscosity. Styrene evaporation was accelerated due to heat occurred on the rolling mills
due to higher shear effect. The polyester resin with high viscosity stacked on the rolls and
it caused some difficulties for the collection of the resin, due to the uncontrolled styrene
evaporation, and thus the final styrene compositions with in the resin blends were
unknown. Similar problems may have occurred while applying the sonication technique,
but less than 0.1% change in mass was observed for this technique, indicating negligible
styrene evaporation. Figure 4-1 shows the X-ray diffraction spectra for Cloisite 20A
composite with clay loading of 4 wt%. A prominent peak corresponding to the basal
spacing of pure Cloisite 20A occurs at a d spacing (interlayer spacing) of 2.4 nm (3.32°
2θ) is clearly seen (calculated using Eq. 2-1). As seen from Figure 4-1 the distances
between the rollers have a significant effect on the level of exfoliation. The shift in the
peak and the broadened peak with less intensity are characteristic of increasingly
disordered intercalated structures (i.e. a decrease in the degree of coherent layer
stacking). As the distance between the rollers decreases, the peak intensity decreases and
50
shifts slightly to lower angles, indicating increased d-spacing which has been linked to
intercalated/ exfoliated structures. However, as mentioned earlier, the increased shearing
effect due to smaller roller distances have caused styrene evaporation leading to rapid
increase in viscosity. This rapid increase in viscosity will hinder exfoliation (as discussed
in the next section).
2 3 4 5 6 7 8 9 102θ (Degrees)
Inte
nsity
(a.u
.)
TRM F=80 B=200
TRM F=60 B=150
TRM F=40 B=100
Cloisite 20A
Figure 4-1: Effect of the roller spacing on dispersion of the resin with 4 wt% Cloisite 20A
4.1.2. Effect of mixing time
The following set of experiments was performed to evaluate the effect of time (or number
of passes for the TRM) on the dispersion of the nanoclays. As seen in section 2.2.4 the
mixing time has a significant influence on the dispersion of nanoclays in the resin system.
Figure 4-2 shows the effect of number of passes when using the TRM and the different
mixing times when using the ultrasonication. As expected, the peak intensity decreases
with the increase in number of passes while the roller distance is kept constant leading to
a better intercalated system. With each additional pass the nanoclay resin system is
subjected to additional shearing resulting in increased penetration of the resin into the
silicate layers. A more detailed insight suggests that stress induces the break up of large
51
clay particles into dispersed stacks of silicate tactoid, followed by additional shearing of
tactoid into smaller stacks of silicate platelets. Similar results are seen for the TRM and
shear mixing techniques [14, 33, 40, 85]. Figure 4-2 also shows the XRD pattern for
different sonication times. There is a reduction in the intensity for increased sonication
time. This again reflects that increasing the sonication time leads to increased intercalated
mixtures which can be seen from the broadening of the peak (which reflects smaller
scattering domain), shift of the intensity peak to lower angles (increased interlayer
spacing) and slight increase in viscosity. Finally, the two mixing techniques are compared
in Figure 4-3. The results clearly favour the sample from ultrasonication as it shows
better dispersion. One of the factors for this result could also be the increased viscosity of
the mixture during the TRM process due to styrene evaporation. It is believed that an
increase in viscosity will impede the ability of silicate layers to separate and form
exfoliated structures. However, it would be interesting to see the effect of using
sequential mixing (styrene and LPA added post mixing) on the dispersion of clays in
polyester resin. Table 4-1 displays the d-spacing of the various samples under
consideration. Although the d-spacing remains the same for ultrasonication sample
(Ultra_60) and TRM sample (TRM F=40 B=100), the reduced intensity and broadened
peak for the Ultra_60 sample confirms better dispersion.
52
2 3 4 5 6 7 8 9 102θ (Degrees)
Inte
nsity
(a.u
.)Ultra_30min Ultra_60min TRM 3 passes TRM 1 pass Cloisite 20A
Figure 4-2: XRD patterns showing the effect of time (ultrasonication) and number of passes (TRM)
for 4 wt% Cloisite 20 A. Table 4-1: XRD analysis showing the d-spacing for different samples
Sample name Mixing technique Parameter tested d –spacing (nm)Cloisite 20A - - 2.4
Ultra_60 Ultrasonication Mixing time (60 minutes)
3.89
Ultra_30 Ultrasonication Mixing time (30 minutes)
3.63
TRM F=40 B=100 TRM Roller distance (F= 40 µm; B = 100 µm)
3.89
TRM F=60 B=150 TRM Roller distance (F= 60 µm; B = 150 µm)
3.63
TRM F=80 B=200 TRM Roller distance (F = 80 µm; B = 200 µm)
3.47
TRM F=40 B=100 3 Pass
TRM Number of passes (3 passes)
3.47
TRM F=40 B=100 1 Pass
TRM Number of passes (1 pass)
3.39
53
2 3 4 5 6 7 8 9 10
2θ (Degrees)
Inte
nsity
(a.u
.)TRM F=40 B=100 - 3 Pass
Ultra_60min
Cloisite 20A
Figure 4-3: XRD Pattern comparing ultrasonication and TRM methods – 4 wt% Cloisite 20A
4.2. Rheological behaviour during mixing process
This section discusses the results showing the viscosity variation due to the application of
the different mixing techniques and compliments the discussions in previous section. It is
well known that the level of exfoliation affects the viscosity. Hence this section will be
used as another tool in identifying the technique which results in greater level of
exfoliation.
54
0.01
0.1
1
10
100
0.1 1 10Shear Rate (1/s)
Vis
cosi
ty (P
a.s) TRM - 1 Pass
Ultrasonication 60 minTRM - 3 PassNeat Resin
Figure 4-4: Viscosity as a function of shear rate for different mixing techniques at 25°C
``
Figure 4-5: Schematic of the variation in viscosity as a result of the mixing process. This schematic summarizes the different effects that change the viscosities. Solid line is neat resin; round dots is
ultrasonication for 60 minutes; long dash dots is TRM 1 pass; square dots is TRM 3 pass.
Exfo
liatio
n Vis
cosi
ty (P
a.s)
Exfo
liatio
n +
styr
ene
evap
oura
tion
Shear Rate (1/s)
55
As seen in Figure 4-4, mixing techniques clearly have an effect on the viscosity. While
samples from all different mixing techniques showed a significant increase in the
viscosity, the change for each sample was different. The samples from the TRM process
showed the most increase in viscosity when compared to the ultrasonication samples. As
discussed previously (section 4.1), the increase in viscosity can be linked to a
combination of increased exfoliation of the clay particles into the resin system and
styrene evaporation. When we consider the results discussed in section 4.1 (where the X-
ray diffraction results showed better dispersion for the sonication samples (Figure 4-3)) it
can be concluded that styrene evaporation was the dominant factor for the increase in
viscosity in TRM samples. Since, the change in mass for the sonication samples was less
0.1%, the viscosity increase of these samples when compared to the neat as received resin
system can be related to increased levels of exfoliation (also confirmed by X-ray
diffraction results in section 4.1). Similarly, when we compare the TRM viscosities only,
it can be seen that increasing the number of passes increases the viscosity. At the same
time, Figure 4-2 confirms better dispersion with the increase in number of passes. So it
can be said about the TRM that styrene evaporation along with exfoliation affects the
viscosity. Figure 4-5 shows a schematic of the effects that causes the increase in
viscosity. As discussed earlier, for ultrasonication technique, there is no styrene
evaporation. However, there needs to be more work done that will establish the quantity
of styrene evaporation. Sequential mixing method that involves addition of styrene and
LPA after the mixing process is one such method. A base resin can be mixed with the
clays and the change in viscosity can be measured. This change in viscosity can then be
directly associated with exfoliation only. Therefore, with the simultaneous mixing
method TRM does not provide conclusive and satisfactory dispersion. These results are
significant, indicating the potential of the sequential synthesizing technique for UP based
nanocomposites, where process such as TRM can be tested and utilized. In such cases,
the increase in viscosity can be used as an alternative tool (or as a verification process) to
measure the dispersion of clays in UP-clay systems.
56
4.3. Rheological behaviour on addition of nanoclays
In order to quantify the performance of the liquid resin mix tested for this work, the
viscosity increase due to the presence of nanoclays has been characterized using a
parallel plate rheometer.
In liquid composite moulding, the viscosity of the resin is very important in order to
ensure proper impregnation of the fibrous reinforcements. A large increase in viscosity
induces slower impregnation of the reinforcements that results in longer cycle time or
improper impregnation which could cause a decrease in mechanical properties.
4.3.1. Rheological characterization of pre-promoted unsaturated polyester
This section determines the behaviour of the resin as received from manufacturer. It is
important to see if Newtonian behaviour is observed for this resin. The test was carried
out by studying the viscosity as a function of the shear rate. The shear rate was varied
between 0 – 10 s-1. The result of the change in viscosity as a function of shear rate is
shown in Figure 4-6. As seen in Figure 4-6 the viscosity tends stay constant with
increase in the shear rate. This is typical of a Newtonian fluid, which states that the stress
is proportional to flow rate.
57
0.01
0.1
1
0.1 1 10
Shear Rate (1/s)
Vis
cosi
ty (P
a.s)
R580-ZPE-14
Figure 4-6: Characteristic Newtonian behaviour of the as received R580-ZPE-14 resin system. Tests
were carried out at 25°C
4.3.2. Effect of adding nanoclays on viscosity
Figure 4-7 displays the viscosity of the resin system with clay content 1 – 4 wt% as a
function of the shear rate. The scattered data and initial high values are due to instability
of the flow at these frequencies. It is important to mention here that the rheometer used in
this experiment makes an assumption of Newtonian behaviour in regards to the liquid.
Therefore the results should only be interpreted in relative terms and not in absolute
terms.
58
0.01
0.1
1
10
100
0.1 1 10Shear Rate (1/s)
Vis
cosi
ty (P
a.s)
1 wt%2 wt%3 wt%4 wt%Neat resin
Figure 4-7: Viscosity as a function of shear rate for different clay content at 25°C
using ultrasonication for 60 minutes at 50°C.
As expected, there is an increase in resin viscosity with the increase in nanoclay content.
This viscosity increase is related to the increase of the contact surface between the clay
and the polymer molecules, which induces higher resistance during the shear stress. As
the clay particles increase so does the clay-resin interactions, which cause an increase in
resistance to flow, therefore increasing the viscosity. Further more, the change from
Newtonian to pseudo plastic behaviour may also be attributed to the strong interaction
between layered silicates and the polymer. The decrease in viscosity (shear thinning) with
increased shear rate may be attributed to the orientation of the layered silicate particles
parallel to the direction of flow. This reorientation of the clay particles causes the
resistance to flow to decrease and hence cause a reduction in the viscosity. The increase
of viscosity when compared to the original resin system also signifies the intercalation of
the clay particles into the resin mix. However, other factors like styrene evaporation due
to localized heating (which maybe hard to control with sealed mold or other practical
methods) may also influence the viscosity.
59
4.3.3. Effect of nanoclays on the gel point
It was seen in section 2.3.5 that addition of nanoclays changed the cure kinetics of the
resin system. One way to establish the effect on the rate of cure reaction is to study the
variation in viscosity with curing time. It is known that as the polymerization reaction
occurs, the viscosity of the system increases as the polymer chains cross link and
increases the density. Rheological tests carried out to study the shrinkage effects were
used to study the change in viscosity. Before gelation, the tests were carried out in
oscillation mode at isothermal temperature of 40°C. The gel time was defined as the time
when the viscosity, η*, reaches a value of 1000 Pa.s.
As seen from Figure 4-8, there is a significant difference in the rheological behaviour of
the neat resin system and nano-modified resin system. One important observation made
was that the viscosity had increased for both systems (when compared to its value at
25°C, before the addition of the initiator) before the tests were initiated. This indicates
that the system is unstable at room temperature and starts the polymerization reaction as
soon as the initiator is added. This sort of behaviour prevents the observation of very
initial stages of reaction. Hence, it should be taken into consideration for any future work
that maybe carried out using this system. From Figure 4-8, it can also be observed that
the increase is viscosity is much quicker for the nano-modified resin system as opposed
to the neat resin system. The neat resin system reaches the gel point at about 230 seconds
where as the nano-modified resin system with 4 wt% Cloisite 20A reaches the gel point
in 106 seconds. Clearly, there is an increase in the reaction rate. This is agreement with
the results obtained in the literature, where it is seen that the addition of clays in epoxy
and polyester based systems has a catalytic effect. This means that the polymerization
reaction proceeds much quickly. DSC results shown in section 4.6 will be used to verify
these observations. However, it is important to mention that a decrease in the gelation
time for an already fast acting system poses significant problems in terms of
characterization and manufacturing.
60
1
10
100
1000
0 50 100 150 200 250Time (s)
Vis
cosit
y (P
a.s)
0 wt% Cloisite 20A4 wt% Cloisite 20A
Figure 4-8: Viscosity as a function of curing time until the gel point. Tests were carried out under
oscillation mode at 40°C.
4.4. Storage modulus
4.4.1. Determining the LVR (linear viscoelastic region)
The DMA tests were conducted under constant displacement mode. In order to use DMA
to accurately determine mechanical properties and develop morphological relationships,
the material must be deformed at an amplitude that is within the linear viscoelastic region
of the material. Within the linear viscoelastic region, the materials response is
independent of the magnitude of the deformation and the materials structure is
maintained in tact (unbroken). Characterization of the material within the linear region
yields a more accurate picture of the structure of the polymer. Therefore, any differences
in the structure of polymers can easily be measured as differences in the dynamic
mechanical properties. Special care should be given when selecting an amplitude for a
DMA test. As a general rule of thumb, solids are linear at strains less then 0.1% (0.001
strain units). However, this is a general rule and may not apply to all samples so the
61
linear region may require verification. The linear region can be measured for a material
using a strain sweep test. In a strain sweep test, the frequency of the test is fixed and the
amplitude is incrementally increased. To determine the linear viscoelastic region, the
storage modulus is plotted against the amplitude (in log scale) as the amplitude is the
control variable, as show in Figure 4-9. The test was carried out 25°C with the sample
containing 3 wt% Cloisite 20A, in order to determine the linear viscoelastic region.
As seen in Figure 4-9 the R580-ZPE-14 resin system has a linear region between the
amplitude of 8 µm and 25µm, between which the storage modulus remains unchanged.
Therefore, the displacement control tests were carried out at amplitude of 15µm
(approximate mid point of the LVR).
2.25
2.3
2.35
2.4
2.45
2.5
2.55
1 10 100 1000
Amplitude (µm)
Stor
age
Mod
ulus
(GPa
)
LVR Range
15 µm
Figure 4-9: Storage modulus as function of amplitude at 25C. The sample contains 3 w% of Cloisite
20A prepared using ultrasonication for 60 minutes at 50°C.
4.4.2. Effect of post cure
This section will briefly identify the effects of post cure on the storage modulus and loss
modulus values. The sample was prepared first using 3 wt% Cloisite 20A as described in
62
section 3.2.3. This was used for testing to determine the effect of no post cure. Another
sample prepared with same procedure as described earlier but then was post cure with a
temperature ramp to 150°C at 3°C/min. The results are shown below in Figure 4-10.
As seen below, there is a slight effect on the values from storage modulus and the loss
modulus due to post curing. From the results below, we observe about a 10% decrease in
both storage modulus and loss modulus at 30°C. This is slightly surprisingly, as one
would expect higher storage modulus as result of post curing (due to increased stiffness).
However, the trend and behaviour is the same for both samples, indicating no obvious
preference of one method over the other. Therefore, for future results, no post cure shall
be applied.
0
0.5
1
1.5
2
2.5
3
3.5
30 50 70 90 110 130 150 170 190 210Temperature (°C)
Stor
age
Mod
ulus
(GPa
)
0
20
40
60
80
100
120
140
160
180
Los
s Mod
ulus
(MPa
)
Storage modulus - post cureStorage modulus - no post cureLoss modulus - post cureLoss modulus - no post cure
Figure 4-10: Effect of post curing on storage modulus and loss modulus for samples made with 3
wt% Cloisite 20A. The tests were carried out at 25°C.
63
4.4.3. Effect of nanoclays on storage and loss modulus
The storage modulus of the UP/LPA/clay polyester was measured using the DMA in
single cantilever beam mode. The results are shown in Figure 4-11. Increasing the clay
content has a stiffening effect on the storage modulus, although this effect decreases with
increases in temperature. There is a significant improvement in the storage modulus as
the clay content is increase from 0 wt % to 5 wt% (from 2.73 GPa to 3.15 GPa). This
improvement of the flexural modulus was already observed and explained by several
factors [40, 76]. It is known that these clays have high elastic modulus and high aspect
ratio which contribute to the improvement of the material. It was also found that due to
the mismatch of the CTE of the resin and the clay, a compression zone of a few nano-
meters was created around the nano-particles [76]. These compression zones improve the
stress transfer between the polymer and the nanoclays thereby improving the modulus.
Figure 4-13 along with Table 4-2 clearly shows about 16% increase in the storage
modulus with only 5 wt% addition of nanoclays. The error bars shown in Figure 4-13
(and elsewhere) were calculated from the standard deviation calculated from the data set.
Therefore, as seen in the literature, only a small amount of nanoclays can cause
significant improvement in the storage modulus.
64
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
30 40 50 60 70 80 90 100 110 120 130 140Temperature (°C)
Stor
age
Mod
ulus
(GPa
)5 wt% Cloisite 20A4 wt% Cloisite 20A 3 wt% Cloisite 20A2 wt%Cloisite 20A0 wt% Cloisite 20A
Figure 4-11: Storage modulus as a function of temperature with the addition of Cloisite 20A. Samples
were prepared by using ultrasonication for 60 minutes at 50°C.
0
20
40
60
80
100
120
140
160
180
30 40 50 60 70 80 90 100 110 120 130 140Temperatue (°C)
Los
s mod
ulus
(MPa
)
5 wt% Cloisite 20A4 wt% Cloisite 20A3 wt% Cloisite 20A2 wt% Cloisite 20A0 wt% Cloisite 20A
Figure 4-12: Loss modulus as a function of temperature with the addition of Cloisite 20A. Samples
were prepared by using ultrasonication for 60 minutes at 50°C.
65
2.50
2.75
3.00
3.25
3.50
0 1 2 3 4 5
Clay Content (%)
Stor
age
Mod
olus
(GPa
)
Figure 4-13: Increasing trend of the storage modulus with increase in clay content measured at 30°C
Table 4-2: Percentage increase in the storage modulus at 30°C with addition of Cloisite 20A1
Cloisite 20A Content Storage modulus (GPa) Percentage change (%)
0 2.71 ± 0.065 0.00
2 2.98 ± 0.036 9.65
3 3.00 ± 0.031 10.50
4 3.13 ± 0.035 15.29
5 3.15 ± 0.051 16.00
1 Errors are calculated from the standard variation for the data set
66
4.5. Glass transition temperature
4.5.1. Establishing evaluation criteria for the glass transition temperature (Tg)
The glass transition temperature is defined in many different ways. Some of these ways
are; the onset point of the loss in storage modulus curve, half length of the storage
modulus curve, peak of the tan delta curve or the peak of loss modulus. All these
measurements can be made from the data obtained during the displacement control tests
using the DMA. Although, some papers are found where the Tg is measured using the
DSC, majority of the researchers prefer using the onset of drop in modulus or the half
length of storage modulus curve, as the glass transition temperature.
Figure 4-14 shows the method of evaluating glass transition temperature using the storage
modulus and loss modulus curves. The onset point and the half length of the storage
modulus curve, which is measured using the universal analysis software is defined as the
glass transition temperature. Similarly, the peak of the loss modulus curve is identified
using the software and is defined as another means to measure the glass transition
temperature. It can be clearly seen these techniques provide different values for the glass
transition temperature with the most conservative value obtained using the onset of drop
in storage modulus. The values obtained using the half length method and the peak of
loss modulus method are very close to each other. The following section will discuss the
effects of adding nanoclays on the glass transition temperature using each of these
methods, while comparing the general trend obtained. One of the other method common
used to identify the Tg is the peak of tan delta curve. However, results obtained for the tan
delta curves from the DMA show some unusual behaviour. As seen from Figure 4-15,
there seems to be an initial increase (marked as unusual behaviour when compared to the
literature) followed by a peak. Secondly, when we compare the values obtained by the
methods outlined above, the value obtained by tan delta method is significantly higher.
Therefore, in the following section only the first three methods (onset of drop in storage
modulus, half length of storage modulus and peak of loss modulus) shall be used to
identify the Tg.
67
0
0.5
1
1.5
2
2.5
3
30 40 50 60 70 80 90 100 110 120 130 140Temperature (°C)
Stor
age
Mod
ulus
(GPa
)
0
20
40
60
80
100
120
140
160
Los
s Mod
ulus
(MPa
)
Storage ModulusLoss Modulus
Onset Point: 72.03°C
Half length:103.03°C
Peak point:104.53°C
Figure 4-14: Evaluation of glass transition temperature using storage modulus and loss modulus. The
sample contains 0 wt% Cloisite 20A prepared using ultrasonication for 60 minutes at 50°C.
68
0
0.05
0.1
0.15
0.2
0.25
0.3
30 50 70 90 110 130 150 170 190 210
Temperature (°C)
Tan
Del
ta
Unusual behaviour
Peak Point: 151.46°C
Figure 4-15: Tan delta curve for 0 wt% Cloisite 20A prepared using Ultrasonication for 60 minutes
at 50°C. The peak of tan delta curve is known to correspond to the glass transition temperature.
69
4.5.2. Effect of nanoclays
Table 4-3 shows the glass transition temperatures obtained using three different criteria,
that is: onset of drop in storage modulus, half length of storage modulus and peak of loss
modulus. It seen clearly that the trend is similar for all three criteria. All these criteria
show a general trend of decrease in the Tg with increase in the clay content. As expected,
the onset of the storage modulus provides the most conservative value for the glass
transition temperature. For applications, this value is most critical and therefore, the onset
point of drop in storage modulus will be used as the evaluation criteria (as is also
preferred by many researchers). Figure 4-16 shows the results from using the onset of
drop in storage modulus criteria and Table 4-4 shows the change in value for the glass
transition temperature for the nanocomposite. As discussed in section 2.3.3 some
researchers show improved glass transition temperature while some show a reduction
both of which can be linked to the molecular interaction of the clay and the resin.
The glass transition process is related to molecular motion at a structural level, which
involves several molecular segments, Tg’s are considered to be affected by both
molecular packing and chain conformation (chain rigidity and linearity). Figure 4-16
shows that the Tg decreases as the clay content is increased. The lowest Tg was observed
for 4 wt% of Cloisite 20A (-11.58°C) as seen from Table 4-4. In general, an increase in
Tg has been linked to the strong adhesion between polymer and the clays. This strong
adhesion restricts the motion near the organic-inorganic interface, which may shorten the
polymer chain (increase in thermal stability). On the same note, a decrease in Tg has been
linked to the weak adhesion between the clay particles, which generally results in lower
cross-link density and longer polymer chains which causes a decrease in the Tg. Lower
reactivity of resin (shown by results in the following section) generally results in lower
cross linking density of the cured resin (and longer polymer chains) which are less
thermally stable than shorter chains. Since loss modulus is defined as the energy
dissipated into heat when a material is deformed, an increase in the loss modulus with
increase in clay content as shown in Figure 4-12 signifies less thermally stable longer
70
polymer chains and lower cross linked density that was caused due to the reduced
reactivity.
Table 4-3: Glass transition temperature as measured from three different criteria
Cloisite 20A
Content
Half Length of
Storage Modulus
(°C)
Onset point of drop
in storage modulus
(°C)
Peak of loss modulus
(°C)
0 103.03 ± 0.4325 72.30 ± 0.1850 104.10 ± 0.2150
2 101.97 ± 0.4525 72.02 ± 0.3300 103.29 ± 0.3800
3 99.89 ± 0.1750 69.61 ± 0.2800 102.59 ± 0.2050
4 98.47 ± 0.2725 60.72 ± 0.3100 98.20 ± 0.4000
5 100.70 ± 0.3550 63.47 ± 0.3150 99.50 ± 0.2050
For the R580 resin system used in this research, it is clear that the addition of Cloisite
20A has a decreasing trend for the Tg of the nanocomposites. This is because Tg can be
significantly decreased by addition of nanoclays into the polymer matrix. Smaller
molecules of the clays embed themselves between the polymer chains, increasing the
spacing and free volume, and allowing them to move past one another even at lower
temperatures.
71
60
62
64
66
68
70
72
74
0 1 2 3 4 5Clay Content (%)
Tem
pera
ture
(°C
)
Figure 4-16: Glass transition temperature as a function of clay content at 30°C. The onset of loss in
storage modulus is used as the evaluation criteria
Table 4-4: Glass transition values measured using the half length criteria of the storage modulus
Cloisite 20A Content Glass transition temperature (°C) Change (°C)
0 72.30 ± 0.1850 0.00
2 72.02 ± 0.3300 -0.28
3 69.61 ± 0.2800 -2.69
4 60.72 ± 0.3100 -11.58
5 63.47 ± 0.3150 -8.60
4.6. Cure Kinetics
There are two factors which have opposite influences on the thermal stability of
polyester-clay nanocomposites. Firstly, as most papers have proven that the addition of
nanoclays to resin system have decreased their cure reactivity [56, 86], which can be also
72
demonstrated by the decreased glass transition temperatures, as shown in Figure 4-16.
Secondly, some researchers have shown [72] silicate layers have a property to show good
barrier to gases such as oxygen and nitrogen, they can insulate the underlying materials
and slow the mass loss rate of decomposition products.
Figure 4-17 clearly shows a reduction in the total heat of reaction (calculated from the
area under the heat flow curve and normalized with the mass of resin for different clay
loadings). This reduction in heat of reaction can be traced to the intercalation of clay
particles within the resin which prevents cross-linking leading to lower reactivity. Lower
reactivity of resin generally results in longer polymer chain (and lower cross linking
density of the cured resin) which are less thermally stable than shorter chains. Since loss
modulus is defined as the energy dissipated into heat when a material is deformed, an
increase in the loss modulus with increase in clay content as shown in Figure 4-11
signifies less thermally stable longer polymer chains and lower cross linked density that
was caused due to the reduced reactivity. Hence, the reduction of total heat of reaction,
increase in modulus and reduced glass transition temperature are all results of structural
effects caused due to the intercalation/ exfoliation of clays. These effects cause an
increase in the length of the polymer chain and reduce the reactivity. Figure 4-19 shows
the heat flow curves for the nanocomposite resin system with different nanoclay content.
As seen from the curves, the onset temperature of the cure reaction and the peak, both
shift to a lower temperature. This has been seen in the literature and it confirms the
explanation that the addition of nanoclays to the resin has a catalytic effect, initiating the
cure reaction at an earlier stage because of the longer polymer chains that are thermally
less stable.
Figure 4-18 shows the cure rate as a function of the degree of cure. The cure rate was
calculated using the heat curves from the DSC and applying the following equation:
73
( )( )01 α
α−
−=
R
sampleinbaseline
Hmqq
dtd &&
Eq. 4-1
Where α is the degree of cure,
baselineq& is the heat flow rate at the base line in J/s
inq& is the heat flow rate from the resin sample from the DSC in J/s
msample is the mass of the resin only in g
HR is the total heat of reaction in J/g
The degree of cure, α is calculated by integrating the cure rate and the time. The graph
shows the broadening and reduction of the cure rate as the clay content increases.
Therefore, as seen in many of the previous work, the addition of nano-particles in the
resin has a catalytic effect while decreasing the cure activity of the resin system.
200
240
280
320
360
400
0 1 2 3 4 5
Clay content (%)
Tot
al h
eat o
f rea
ctio
n (J
/g)
Figure 4-17: Total heat of reaction as a function of clay content when using ultrasonication for 60
minutes at 50°C.
74
0
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
0.0014
0 0.2 0.4 0.6 0.8 1
Degree of Cure
Cur
e ra
te (1
/s)
5 %wt Cloisite 20A3 wt% Cloisite 20A2 wt% Cloisite 20A0 wt% Cloisite 20A
Figure 4-18: Cure rate as a function of degree of cure for various clay content mixed using
ultrasonication for 60 minutes at 50°C.
-0.4
0.1
0.6
1.1
1.6
2.1
2.6
3.1
3.6
0 20 40 60 80 100 120 140Temperature
Hea
t flo
w (J
/g)
5 wt% Cloisite 20A3 wt% Cloisite 20A2 wt% Cloisite 20A0 wt % Cloisite20A
Figure 4-19: Heat flow curves for nanocomposites synthesized using ultrasonication for 60 minutes at
50°C.
75
4.7. Volumetric Shrinkage
Volumetric shrinkage has been known to play an important role in the surface finish of
the composite parts. Section 4.7.1 discusses the results of the effect of nanoclays on
shrinkage, where as section 4.7.2 discusses styrene and LPA effects
4.7.1. Effect of nanoclays on pre-formulated and pre-promoted resin
As explained in Section 3.2.5, the volumetric cure shrinkage of the resin was measured
with a modified rheometer procedure. In step 1, no normal force was applied because the
resin was still in its liquid state. It was assumed that there was no cure shrinkage, as is
confirmed by the constant gap value. In step 2, the target force value of 0.1 N was
reached after approximately 240 seconds (~4 minutes). The cure shrinkage or LPA
expansion should cause a change in this normal force, which would be adjusted through
the gap between the plates. However, as seen from Figure 4-20 the resin system under
investigation does not show any shrinkage control (no typical phase separation and micro
cracking behaviour is observed). This is believed to be so because the pre-formulated and
the pre-promoted system do not under go the phase separation stage which is believed to
be the driving mechanism for shrinkage control. However, further investigation into this
is recommended as future work.
Figure 4-20 also shows the result when R580 was mixed with 4 wt% of nanoclays using
the optimum mixing method (OMM). As seen there is no significant improvement (only
about 3% reduction) in the shrinkage control mechanism. This is because the nanoclays
are believed to be useful in increasing the phase separation effect rather than initiating it.
This means, that for nanoclays to have a significant impact on volumetric shrinkage, it is
necessary to first have a phase separation mechanism. The nanoclays are then believed to
be attracted to the LPA rich region, where they increase the reaction rate, causing an
earlier on set of microvoid formation that causes an earlier onset of the shrinkage control
mechanism. Six identical tests were conducted to check the volumetric shrinkage and
similar results were obtained. Further investigation was halted due to insufficient
76
shrinkage control behaviour. Therefore it is important to first establish a working
UP/LPA/St processing parameter for this resin system before adding the clays. However,
it would be interesting to mix these clays with a UP/St/LPA system that has already
shown some shrinkage control. Even though significant shrinkage control mechanism is
not observed for these systems, there is a significant decrease in the volumetric
shrinkage. The pre-formulated resin has volumetric shrinkage of about 11% where as the
pre-formulated resin has a volumetric shrinkage of about 7-8%. This suggests that even
though the clays in themselves do not have a great impact, they certainly provide some
benefits in terms of the volumetric shrinkage. The pre-formulated resin R580-ZPE-14
does not show any shrinkage control and hence it will be useful to investigate the effect
of styrene and LPA on the shrinkage control mechanism for this pure resin without the
LPA, styrene and cobalt. Previous studies [44, 45] have studied the effects of styrene and
LPA on the shrinkage control mechanism. Therefore, in due to time constraints and the
scope of this research, only a few preliminary tests have been conducted to re-emphasize
these effects and show how they affect the shrinkage control mechanism.
4.7.2. Effect of LPA and styrene on shrinkage control of the base resin
As mentioned earlier, this section will discuss some preliminary results of the effect of
styrene and LPA on the base resin used for the pre-formulated R580-ZPE-14. The base
resin used was T580-63 also manufactured by AOC. The LPA used to for these tests was
LP40-A containing 60% styrene and manufactured by Ashland. The choice of LPA and
its initial value was used after studying Landry’s work [94]. As mentioned in section
3.2.5, these tests were carried out at an isothermal temperature of 80°C.
Figure 4-21 shows the effects of adding LPA to the base resin. As it can be seen, with
15% LPA, the shrinkage reduces to about 6%. When the LPA quantity was increased
from 15% to 25% the final volumetric shrinkage remains about the same. However, there
is a slight hint of the shrinkage control mechanism (due to phase separation and micro
cracks). The shrinkage control effect is seen as you see a sudden drop in shrinkage during
the isothermal cure. Although, the final shrinkage remains the same, it can be concluded
77
that LPA/St interaction has changed (no microscopy tests were conducted but several
literature papers [17, 60] could be found to confirm this) causing some phase separation
and micro cracks.
0
2
4
6
8
10
12
14
0 1000 2000 3000 4000 5000Time (s)
Vol
umet
ric
shri
nkag
e (%
)
0 wt% Cloisite 20A4 wt% Cloisite 20A
Figure 4-20: Volumetric shrinkage (shown as positive) for the R580 resin system and modified R580
system with 4 wt% Cloisite 20A at 40°C Similarly, Figure 4-22 shows how changing the styrene content affects the shrinkage of
the base resin. As seen below in the figure, changing the styrene content by 5% displays a
difference in the shrinkage behaviour. As discussed in section 2.3.4, the shrinkage
behaviour during the curing of UP resin is dependent on the unique and optimum mix of
UP/St/LPA. These properties have been extensively studied before and are highlighted in
section 2.3.4. The results presented in Figure 4-21 and Figure 4-22 clearly shows how
these parameters affect the shrinkage. Therefore, these results compliment the
suggestions made in the previous sections in regards to the need to establish a good
UP/St/LPA resin system. It is important to note here that these results are only
preliminary findings and further investigation would be required to establish the optimum
mixture of UP/St/LPA resin system using this base resin.
78
0
2
4
6
8
10
12
14
0 500 1000 1500 2000 2500 3000 3500Time(s)
Volu
met
ric S
hrin
akge
(%)
15%LPA+35%St25% LPA + 35%StT580-63
Figure 4-21: Effect of LPA on shrinkage control of T580-63 (base resin for R580-ZPE-14) at 80°C
0
2
4
6
8
10
12
14
0 500 1000 1500 2000 2500 3000 3500Time(s)
Volu
met
ric S
hrin
kage
(%)
15%LPA+35%St15%LPA+30% StT580-63
Figure 4-22: Effect of styrene on shrinkage of T580-63 (base resin for R580-ZPE-14) at 80°C
79
5. Conclusion There are three main research objectives related to: a) Studying various synthesizing
techniques and learning how to identify a suitable synthesizing technique, b) studying
two mixing techniques under various conditions and alterations of parameters in order to
develop an optimum mixing method (OMM), (c) using the OMM, study the effects of
nanoclay content on the resin physical and mechanical properties.
a) Synthesizing nanocomposites:
As mentioned earlier, three synthesizing techniques were available for use with
the pre-formulated resin. However, only simultaneous mixing was appropriate as
solvent mixing involved heating and causing the evaporation of the solvent. This
might have caused styrene evaporation hence was not considered. Similarly,
sequential mixing could not have been employed as the resin was already pre-
formulated.
b) Developing the optimum mixing method (OMM):
It was seen that increasing time (for ultrasonication) and the number of passes (for
TRM) increased the dispersion of the clays into the resin.
Increasing the shearing effect by means of reducing the roller distance also
increases dispersion
Two primary factors, styrene evaporation and increase in exfoliation, influenced
the viscosity during the mixing procedure. It was found that the TRM samples
showed more increase in viscosity when compared to the ultrasonication samples.
But from the X-ray analysis ultrasonication showed better dispersion. Therefore it
can be concluded that the dominant factor in the increase of viscosity of TRM
samples was the styrene evaporation. There was less than 0.1% change in mass
observed for ultrasonication samples, indicating minimum styrene evaporation.
It was seen that the dominant factor in viscosity increase for TRM mixing
changes from styrene evaporation to increased exfoliation. Therefore it TRM
provides a potential in sequential mixing.
80
The optimum mixing method (OMM) was developed. Ultrasonication at 50°C for
60 minutes gave improved dispersion and was selected to apply for further
investigation on the effect of nanoclays on physical and mechanical properties.
It can be concluded that TRM is not suitable for polyester systems containing
styrene, as the dramatic increase in viscosity causes a decrease in exfoliation.
c) Nanoclay effects:
It has been clearly seen that adding nanoclays had increased the viscosity of the
resin mix. It has been suggested that the increased clay-resin interactions leads to
this
Upto16% increase in storage modulus has been observed for 5 wt% clay content.
This has been linked to the high elastic modulus and aspect ratio of the clay
particles
Glass transition temperature, which has been the area of debate amongst many
researchers, has been decreased. This and the decrease in cure activity as seen
from the DSC results has been due reduction in cross-link density and longer,
thermally less stable polymer chains.
5.1. Future Work
Synthesizes of nanocomposites have been under investigation for several years especially
with epoxy resins. This research have opened up a new window towards synthesizes of
nanocomposites using unsaturated polyester resin. The future work involved could look
into two basic areas:
a) Sequential mixing of polyester resin:
As pointed out in this research, TRM could be a useful tool in the dispersing nanoclays
within the nanocomposite system. It is seen that synthesizes and mixing technique has a
significant effect on the final morphology and hence the behaviour of the
nanocomposites. Styrene-free polyester resin could be initially used to disperse the clays
and then studied for the required mechanical and physical properties.
81
b) Resin characterization models
TEM samples to verify and confirm the XRD results
Develop cure kinetics model and viscosity models from DSC and rheometer data.
Develop cure shrinkage model from rheometer data (or an alternate method) after
establishing a valid UP/LPA/St combination
Use well characterized resin to manufacture panels and measure surface
roughness for the final finished part
Apply the methodology of design of experiments to identify the nanoclays and
additives for best surface finish.
c) Preform characterization:
Resin characterization was extensively performed, but it is also needed to characterize the
preform as it has an effect on the surface quality of the parts:
Identify the preform characteristics (surface veil and structural mat) to investigate.
Measure preform fibre diameter, fibre volume fraction and orientation
distribution.
Investigate fibre preform variability.
Relate the preform characteristics to the surface finish of RTM panels.
82
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93
APPENDIX A Test plan for optimum mixing method (OMM) and resin
characterization
94
Experimental plans for the mixing nanoclay with UP
Phase I
Verification of optimal conditions
Objective: To verify which of the two mixing methods give better result for dispersion
using the X-ray diffraction method
Ultrasound parameters to be considered:
• Frequency kind
• Mixing Methodology
• Amount of clays
• Power (amplitude)
• Temperature
• Time
Suggested line of Action:
• Frequency to be used is degassing (sinusoidal). Ultrasound (constant
frequency) is not used because previous literature results show better
dispersion with sinusoidal frequency setting
• Two mixing methods are to be used. Nanoclays in LPA and nanoclays in UP
resin.
• 4 wt% clay will be used to make sure the effects of clays are clearly visible
when comparing it with three roll mill (TRM)
• Temperature will be fixed at 50°C – To ensure temperature rise due to
ultrasonication does not interact with the results.
• Amplitude is fixed at the machine
• The time used shall be 60 minutes to ensure appropriate dispersion (in
accordance to previous literature data)
• The effects of the two mixing methodology will be studied by using the
shrinkage tests.
95
Three Roll Mill (TRM) parameters to be considered
• Speed of rotation
• Amount of nanoclays
• Distance between rollers
• Temperature
• Number of cycle
Suggested line of Action:
• Speed of rotation is fixed
• 5% nanoclay will be used to compare with ultrasonication results
• Distance between rollers shall be adjusted. Best of the results will then be
compared to the best results from ultrasonication
• Temperature will be constant at 25°C as for ultrasonication
• Number of cycle will be varied to study dispersion
Table A 1: Parameter comparison of ultrasonication and TRM mixing methods
Ultrasonication TRM
Frequency type: Sinusoidal or
constant frequency
Speed between the rollers:
Constant
Power (amplitude): Constant Distance between the rollers:
Varied for three different
distances
Temperature: 50°C Temperature: 25°C
Mixing time: Varied for two
different times
Number of passes: Varied for two
different number of passes
Clay content: constant at 4 wt% Clay content: constant at 4 wt%
96
Table A 2: Test plan to determine optimum mixing method (OMM)
Tests for optimum mixing method (OMM)
4% Cloisite20A clay will be used as the clay content Amplitude on the Ultrasound is fixed X-ray diffraction tests will be used to analyze results for dispersion The variables X,Y,Z define spacing between the middle and back rollers in µm The numbers 1,2,3 define the distance between middle and front rollers in µm Sample
#
Name Variable
Parameter
Frequency/
Spacing
Temp Time/ No.
Of Cycle
1 LPA-clay Mixture
(ultrasonication)
Mixing
Methodology
Degassing
(pulsation)
50 60 min
2 Resin-Clay Mixture
(ultrasonication)
Mixing
Methodology
Degassing
(pulsation)
50 30 min
3 Spacing X1
(TRM)
Roller Spacing Back – X
Front – 1
25 3 Cyc
4 Spacing Y1
(TRM)
Roller Spacing Back – Y
Front - 2
25 3 Cyc
5 Spacing Z1
(TRM)
Roller Spacing Back – Z
Front – 3
25 3 Cyc
6 Spacing X2
(TRM)
Roller Spacing Back – X
Front – 2
25 3 Cyc
7 Spacing Y2
(TRM)
Roller Spacing Back – Y
Front - 2
25 3 Cyc
8 Spacing Z2
(TRM)
Roller Spacing Back – Z
Front – 2
25 3 Cyc
9 Spacing X3
(TRM)
Roller Spacing Back – X
Front – 3
25 3 Cyc
10 Spacing Y3
(TRM)
Roller Spacing Back – Y
Front – 3
25 3 Cyc
11 Spacing Z3
(TRM)
Roller Spacing Back – Z
Front – 3
25 3 Cyc
97
Measure the dispersion for the two methods
Choose the best results from the two mixing tools
Compare the two mixing tools and identify the optimum conditions.
Conclusion: A mixing methodology and optimum condition has been established. This is
now OMM (Optimum mixing method).
Phase II
Effect of nanoclay content on rheological properties, cure kinetics, storage modulus,
glass transition temperature and volumetric shrinkage
Objective: To study the effect of the nanoclay content on volumetric shrinkage using the
OMM established in Phase I
Parameters are used as established in Phase I
Table A 3: Resin Characterization tests summary
Tests for Effect of Nanoclays
OMM established earlier will be used to study effects of nanoclays
Sample
#
Sample Name Variable
Parameter
Validation Tests
0 0 wt% Cloisite
20A
Clay weight DSC, Shrinkage, DMA (Storage
modulus, Tg)
2 2 wt% Cloisite
20A
Clay weight DSC, Shrinkage, DMA (Storage
modulus, Tg)
3 3 wt% Cloisite
20A
Clay weight DSC, Shrinkage, DMA (Storage
modulus, Tg)
4 4 wt% Cloisite
20A
Clay weight DSC, Shrinkage, DMA (Storage
modulus, Tg)
5 5 wt% Cloisite
20A
Clay weight DSC, Shrinkage, DMA (Storage
modulus, Tg)
98
APPENDIX B Preliminary DSC and shrinkage results on T580-63 pure
resin
99
Dynamic Scan at 10C/min
0.0E+00
5.0E-04
1.0E-03
1.5E-03
2.0E-03
2.5E-03
3.0E-03
3.5E-03
4.0E-03
0 200 400 600 800 1000 1200 1400 1600 1800 2000
Cure Time (sec)
Cur
e R
ate
(/s)
0
0.2
0.4
0.6
0.8
1
Deg
ree
of C
ure
(-)
Cure Rate Degree of Cure
Figure B 1: Dynamic DSC scan at 10°C/min for T580-63 with 3% cobalt 1% and MEKP catalyst
Peak: 74°C
Total heat of reaction: 377 J/g
Max DOC – 0.99
100
0.0E+002.0E-044.0E-046.0E-048.0E-041.0E-031.2E-031.4E-031.6E-031.8E-032.0E-03
0 300 600 900 1200 1500 1800 2100 2400 2700 3000
Cure Time (sec)
Cur
e R
ate
(/s)
0
0.2
0.4
0.6
0.8
1
Deg
ree
of C
ure
(%)
Cure Rate Degree of Cure
Figure B 2: Dynamic DSC scan at 3°C/min for T580-63 with 3% cobalt 1% and MEKP catalyst
101
Dynamic scan at 3C/min
0.0E+00
4.0E-04
8.0E-04
1.2E-03
1.6E-03
2.0E-03
0 300 600 900 1200 1500 1800 2100 2400 2700 3000
Cure Time (sec)
Cur
e R
ate
(/s)
0
0.2
0.4
0.6
0.8
1
Deg
ree
of C
ure
(-)
Cure Rate Degree of Cure
Figure B 3: Dynamic DSC scan at 3°C/min for T580-63 with 1.5% cobalt 1% and MEKP catalyst
102
Dynamic Scan at 3C/min
0.0E+00
4.0E-04
8.0E-04
1.2E-03
1.6E-03
2.0E-03
0 300 600 900 1200 1500 1800 2100 2400 2700 3000
Cure Time (sec)
Cur
e R
ate
(/s)
0
0.2
0.4
0.6
0.8
1
Deg
ree
of C
ure
(%)
Cure Rate Degree of Cure
Figure B 4: Dynamic DSC scan at 3°C/min for T580-63 with 1.5% cobalt 1% and MIBKP catalyst
Initial peak
Peak: 94°C
Total heat of reaction: 355 J/g
Max DOC – 0.99
103
Isothermal Scan at 75C
0.0E+00
5.0E-04
1.0E-03
1.5E-03
2.0E-03
2.5E-03
3.0E-03
3.5E-03
0 300 600 900 1200 1500 1800 2100 2400 2700 3000
Cure Time (sec)
Cur
e R
ate
(/s)
0
0.2
0.4
0.6
0.8
1
Deg
ree
of C
ure
(%)
Cure Rate Degree of Cure
Figure B 5: Isothermal scan at 75C for T580-63 resin + 1.5% cobalt 3% + 1.5% MIBKP
Initial reaction observed as well
Fast reaction with peak at 150 sec
104
0
1
2
3
4
5
6
7
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8DOC
Vol
umet
ric
Shri
nkag
e %
Figure B 6: Volumetric Shrinkage results as a function of DOC for T580-63 resin with 1.5% Cobalt
3% and MIBKP at 75°C,