chapter ii experimental -...

Chapter II

Experimental

Chapter II : Experimental

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Introduction

This chapter describes about the laboratory at which the research work carried out,

the specifications and sources of different raw materials used for the research work.

Detailed description about sample preparation techniques, their designation,

morphological characterization and measurement of physico-mechanical properties are

also provided in this chapter.

2.1. Brief about Research Laboratory and its facilities like ISO, NABL

The Research work was carried out at “Indian Rubber manufacturers Research

Association” [IRMRA], Thane, Maharashtra. IRMRA is a Govt. of India affiliated

Research Institute established in 1959, to provide scientific and technological support to

rubber and allied industries. At present, IRMRA is under Administrative control of

Department of Industrial Policy and Promotion (DIPP), Ministry of Commerce and

Industry, Government of India. In the last 5 decades, IRMRA has rendered remarkable

service to rubber and allied Industries and has become internationally well known Centre

of excellence for tyre and Non tyre rubber products. IRMRA is well known for its

expertise in the field of Testing and Investigation, Research Products/Compound

development training & manpower development, consultancy services, and has

diversified its activities in the new sophisticated areas such as Nano technology and

Latex technology as well as Rubber Engineering.

2.2. Materials

Brief description of various raw polymers, Fillers and chemicals used for the

Research work are given below:

2.2.1. Polymers / Rubbers

Selection of Polymer / Rubber / Elastomer is the first step in compounding for any

specific application. Each polymer / elastomer has its own unique properties. All

elastomers are elastic, flexible, tough, and relatively impermeable to both water and air.

Elastomer is macromolecular material which can rapidly return to the approximate shape

from which they have been substantially distorted by a weak stress. Usually, there are


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double bonds in the backbone that can be vulcanized using sulphur in combination with

organic accelerators to give required elastic properties [1]

Table 2.1. Polymers / Rubbers, grade, their source of supply and specification:

S.No Name of Polymer

used

Supplier /

Manufacturer Grade & Specification

1.

Acrylonitrile

Butadiene Rubber

(NBR)

JSR

Corporations

Grade : JSR 230 S

ACN Content : 35 %

Mooney Viscosity : ML1+4(100°C): 56

Sp. Gr. : 0.98

2

Hydrogenated

Acrylonitrile

Butadiene Rubber

(HNBR)

Lanxess

Therban : Grade used : 3907

ACN content :39 %

Mooney Viscosity [ML1+4 @100°C): 70

Residual double bond : 0.9

Density : 0.96

3

Ethylene Propylene

Diene Monomer

Rubber (EPDM)

DSM

Elastomers

Keltan 512: DSM

Ethylene Content: 43.5 %

Mooney Viscosity [ML 1+4 (1000C ): 50

Density: 1.00

Table 2.1 gives the details about various rubbers which have been used in this

research study. These were obtained from the reputed source of manufacturer and also

verified for the purity of the grade and the chemical parameters were specified so that the

consistency of rubber qualities is maintained throughout the research.


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2.2.2 Nanofillers:

Table 2.2 shows the list of various fillers with specification and name of the

suppliers used in this research work

Table 2.2 Nano-fillers, their source of supply and specification:

S.

No.

Name of

Material Manufacturer Grade, if any and specification

1. Nano graphite

powders

Kaiyu industrial

(HK) limited

Chemical Formula: C

Atomic Weight of Carbon: 12.01

Boiling Point: Sublime

Melting Point: 3650oC (6602

oF)

Evaporation Rate: none

Appearance: Grey-black solid

Vapor Pressure: Negligible at room

temperature

Vapor Density: Negligible at room

temperature

Odor: Odorless

2. Nano Clay

Crystal Nanoclay,

Pune.

Crysnano 1010

Crysnano1010 is a natural

montmorillonite modified with

quaternary ammonium salt.

Color : White

Purity : 98 %

Moisture content : < 2 %

Particle size : 90 % passing at 28

3. Nano Silica

Naoshell, USA Nano Shell: 99.8 % pure

Surface Area: 175-225 m2/gm

B.P: 2230 0C

M.P: 1600 0C


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2.2.3 Dispersion aids:

The Table 2.3 shows the dispersion aids, their source of supply and specification:

Table 2.3 Dispersion aids

S.No Name of

dispersion aid

Supplier /

Manufacturer Specification

1. Liq. NBR Nipol

% ACN Content : 28 %

Viscosity : 38-52 cps

Sp. Gr : 0.96

2. DOP Sigma-Aldrich

Physical Form : Liquid

Color : Color less

Boiling Point : 384 °C

Sp. Gr. : 0.980- 0.985 (20 °C)

3. Paraffinic Oil Apar Oil

As per IS 15078

Sp. Gr : 0.88 -0.92

Kinematic viscosity : 18-23 @ 40 °C

Aniline point : 70-90 °C

2.2.4 Activators

Table 2.4 shows the dispersion aids, their source of supply and specification

Table 2.4 Activators

S.No Name of Activators Specification

1. Zinc Oxide

As per IS 3399

Relative Density : 5.58 – 5.68

Moisture content = 1 % max

Loss on ignition @ 850 °C = 1 % max

2. Stearic Acid

As per IS 1676

Moisture content :0.25 %

Ash content @ 550 °C = 0.1 %


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2.2.5 Vulcanizing Agents

Table 2.5 Vulcanizing Agents, source of supply and their specification

S.No Name of curatives / Accelerators Specification

1. Sulphur

Appearance : Yellow fine powder

Ash content : 0.05 %

Heat Loss : 0.5 %

Sp. Gr. : 2.05-2.15

Melting Pt. : 113- 119 °C

2. DCP – 40

Sp. Gr : 1.60 +/- 0.1

40 % peroxide content

3. MBTS

As per IS 8483

Assay : :97 %

M.Pt : 165 °C

2.2.6 Antidegradants

The following antidegradants, listed in Table 2.6 with its specification and these

have been used for mixing as per formulation in the current research work. These

improve heat and oxidation resistance of rubber composite

Table 2.6 Antidegradants

S.No Name of Antidegradants Specification

1. TDQ

(2, 2, 4-trimethyl-1, 2-

dihydroquinoline)

Make: NOCIL

Density -1.110

Ash Content -0.3% max

Softening Point -88-95 0C

2. 6 PPD

N(1.3-dimethyl-butyl)-N'-

phenyl-P-phenylenediamine

Make: NOCIL

Ash Content – 0.08%

Solidifying point ≥ °C – 45.5


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2.3. Vulcanization of Rubbers:

Vulcanization, the process of crosslinking of elastomers, occurs by a chemical

process initiated through some form of energy input. It occurs between two statistically

favorable reactive sites. Such sites are available through double bonds in diene-

containing elastomers, double bonds pendant to the polymer backbone from cure-site

monomers (EPDM, etc.) chemically induced reactive sites left by the abstraction of

backbone hydrogen or halogen atoms. The sites are coupled to each other by covalent

bonding via one or more of the following mechanisms [2]

Carbon-carbon bonds through the backbone.

Insertion of difunctional curatives such as sulfur between reactive sites.

Insertion of di- and multifunctional monomers such as acrylates, phenolics, or

triazines between reactive sites.

In practical vulcanization, the most widely used group of elastomers consists of

those containing a diene site for crosslinking, i.e.; Natural rubber (NR) and Polyisoprene

(IR), Butadiene rubber (BR), Styrene-butadiene rubber (SBR), Isobutylene-isoprene

rubber (Butyl, IIR), and Nitrile-butadiene rubber (NBR) which are crosslinked by using

sulfur as a vulcanizing agent. The basic ingredients for a sulfur cure are:

Sulfur or sulfur donor (cross linker)

Organic accelerator(s)

Zinc oxide and fatty acid (activator)

Fatty Acids

Sulfur. The original and still the most widely used curative because of its versatility and

cost, sulfur exists in the elemental state as an eight-membered ring (S8) [1],. The sulfur

ring opening mechanism, as discussed by Coran[2], , involves either a free radical or an

ionic mechanism. The ionic mechanism is probably more logical, and can be rationalized

in terms of the generalized Lewis acid-base interactions discussed by Jensen which is

given in Table 2.5


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Organic Accelerator(s). These all contain nitrogen and can perform as electron donors or

acceptors as noted by Jensen (1). The mechanisms are discussed in detail by Coran (8)

and appear to proceed in the following steps:

a) The accelerator (Ac) reacts with sulfur (Sx) to give monomeric polysulfides of the

type Ac - (Sx) - Ac, where Ac, is the organic radical derived from the accelerator.

b) The polysulfides can interact with the rubber to give polymeric polysulfides of the

type rubber - (Sx ) - Ac.

c) The rubber polysulfides then react, either directly or through a reactive intermediate,

to give crosslinks or rubber polysulfides of the type rubber- (Sx )-rubber.

Zinc Oxide. This has been an important ingredient since the early days of rubber

compounding. Originally used as an extender to reduce cost, it was subsequently found to

have a reinforcing effect, and was later found to reduce vulcanization time. Organic

accelerators, which further reduce cure times, depend on zinc oxide to activate them. Zinc,

as a metal, is classified as a d-transition element. As such, it is capable of developing

relatively rare 5-coordinate complexes with fatty acid and organic accelerators. In the

crosslinking of chlorine-containing compounds, it readily abstracts chlorine. The zinc

oxide becomes zinc chloride, a very strong Lewis acid, and the reaction proceeds at an

auto catalytic rate. Zinc oxide also is a very effective heat stabilizer in peroxide-cured

elastomers. However, it serves no function in this crosslinking mechanism. The only

adverse reaction of Zinc oxide is in Epichlorohydrin elastomers (e.g., Herclor, Hydrin).

The formation of Zinc Chloride (strong Lewis acid) causes an acid-catalyzed backbone

cleavage. The subsequent effect is a polymer rearrangement that occurs by a Ketoenol

tautomerization mechanism.

Fatty acids. Chemically, these are aliphatic carboxylic acids. The highly polar carboxyl

group is very reactive through its ability to develop covalent and coordinate bonds and its

H-bonding activity. The aliphatic hydrocarbon chain component is equally nonpolar and

as such is highly soluble in nonpolar components. Zinc oxide and fatty acid constitute the

activator system, in which the zinc ion is made soluble by salt formation between the acid

and oxide (1). Fatty acids have long hydrocarbon chains with carbonyl oxygen that probably

coordinates with the zinc through ligand formation. The zinc complex thus formed is


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hydrophilic in the metal center and hydrophobic on the outside, the hydrophobic component

being very soluble in the hydrocarbon (diene) component of the elastomer.

2.4 Formulation for preparing nanocomposites:

2.4.1. NBR Nanocomposites

In this study, four types of nano fillers namely Nanographite, Nanosilica,

Nanoclay and Nano Titanium Dioxide were used. The dosage of nanofillers is kept such

that a significant level of interaction is absorbed.

Acrylonitrile–Butadiene rubber (NBR) / Expanded Graphite (EG) / Carbon black

(CB) micro- and nanocomposites were prepared by two different methods, and the

resulting mechanical and tribological properties were compared with those of NBR / CB

composites. Meanwhile, the effects of graphite dispersion and loading content, as well as

the applied load and sliding velocity on the tribological behavior of the above composites

under dry friction condition were also evaluated. The worn surfaces were analyzed by

scanning electron microscopy (SEM) to understand the wear mechanism. As expected,

the better the dispersion of graphite, the more is remarkable enhancement in tensile and

dynamic mechanical properties, and greater is the reduction in the coefficient of friction

(COF) and specific wear rate (Ws). It was found that a small amount of EG could

effectively decrease COF and Ws of NBR / CB composites because of the formation of

graphite lubricant films. The COF and Ws of NBR / CB / EG composites show a

decreasing trend with a rise in applied load and sliding velocity. NBR / CB / EG

nanocomposite always shows a stable wearing process with relatively low COF and Ws.

It is thought that well-dispersed graphite nano-sheets were beneficial to the formation of

a fine and durable lubricant film.[3]

Above all efforts made by various scientists have lead

us to investigate into the rubber nanocomposite and its synergetic effect on the final out

put that is end product application and evaluation of the same.


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2.4.1.1 NBR-Graphite Nanocomposites

NBR-Graphite Nanocomposites were prepared using the formulation given in

Table 2.7. The dosage of nano graphites were kept varied from 0, 3, 6 & 9 phr as shown

in the Table 2.7 and all other rubber chemical ingredients were kept constant.

Mixing of nanofillers in polymer were carried out in two stages. In the first stage,

the nanographite at different loading 3, 6 and 9 phr were mixed at ambient temperature

in highly viscous liquid Nitrile Rubber [20 phr] and made into a paste like material which

is known as BR-Nanographite master batch.

Table – 2.7 Formulation for preparation of NBR – Graphite-nanocomposites [ phr*]

Ingredients NBG-0 NBG-3 NBG-6 NBG-9

NBR 80 80 80 80

Liq. NBR 20 20 20 20

Sulphur 2 2 2 2

Zinc Oxide 4 4 4 4

Stearic Acid 1 1 1 1

Nanographite 0 3 6 9

MBTS accelerator 0.5 0.5 0.5 0.5

Antidegradants 2 2 2 2

Total Batch weight 109.5 112.5 115.5 118.5

*phr = Parts per hundred gram of rubber

In the second stage, the NBR-Nanographite master batch was blended with NBR

base polymer and then mixed with other rubber compounding chemicals, as per the

formulation given in Table 2.7 such as activators, curatives etc in a laboratory two roll mill.

During mixing sulphur was added in the polymer at initial stage as per conventional

mixing cycle followed by NBR. The rubber compound mixes were then passed several

times in two roll mill to get uniform NBR nanographite based rubber compound. The


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compounded rubber sheet was kept for maturation for 16 hrs and then taken for moulding

of various test specimens as per ASTM standard using hydraulic press at a temperature

150 C. The curing time was obtained from rheological studies carried out at 150 C

using Monsanto Rheometer.

2.4.1.2 NBR-TiO2 Nanocomposites

Mixing of nanofillers in NBR polymer was carried out in two stapes.

1st step:- In the first step, the nano-TiO2 at different loading 1, 3 and 5 phr were mixed

at ambient temperature in highly viscous liquid Nitrile Rubber [20 phr] and made into a

paste like material which is known as “NBR-Nano- TiO2 master batch”.

Table-2.8 Formulation for preparation of NBR – TiO2 nanocomposites [ in phr*]

Compounding Ingredients NBT-0 NBT-1 NBT-3 NBT-5

a. Master Batch

Liq. NBR 20 20 20 20

Nano- TiO2 0 1 3 5

b. Main Formulation

NBR Rubber [JSR 230] 80 80 80 80

Sulphur 2 2 2 2

Zinc Oxide 4 4 4 4


MBTS Accelerator 0.5 0.5 0.5 0.5

Anti-degradants 2 2 2 2



2nd

step:- In the second step, the raw NBR rubber is milled in two roll mill and then

NBR-Nano- TiO2 master batch was added to it to get uniform blending of liquid NBR

and NBR rubber. Then other rubber compounding chemicals, as per the formulation

given in Table 2.8 such as activators, curatives etc were added. During mixing sulphur

was added in the polymer at initial stage to ensure proper dispersion of sulphur in


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polymer matrix. Mixing was carried out in a controlled manner and same procedure was

followed for all the mixes. The mixing cycle time was kept constant for 25 min for all the

mixes. The polymer nanocomposite mixes were then passed several times in two roll mill

to get uniform NBR Nano - TiO2 based polymer nanocomposite.

2.4.1.3 NBR-Silica Nanocomposites

NBR- Silica Nanocomposites were prepared using the formulation given in Table 2.9.

The dosage of nanosilica were kept varied from 0, 1, 3 & 5 phr as shown in the Table 2.9

and all other rubber chemical ingredients were kept constant.

The formulation used for mixing NBR rubber and compounding ingredients is

tabulated in Table 2.9

Table-2.9 Formulation for preparation of NBR –Silica-nanocomposites [in phr*]

Compounding Ingredients NBS-0 NBS-1 NBS-3 NBS-5

a. Master Batch

Liq. NBR 20 20 20 20

Nano-silica 0 1 3 5

b. Main Formulation

NBR Rubber [JSR 230] 80 80 80 80

Sulphur 2 2 2 2

Zinc Oxide 4 4 4 4


MBTS Accelerator 0.5 0.5 0.5 0.5

Anti-degradants 2 2 2 2




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Mixing of nanofillers in NBR polymer was carried out in two steps.

1st step:- In the first step, the nano-silica at different loading 1, 3 and 5 phr were mixed

at ambient temperature in highly viscous liquid Nitrile Rubber [20 phr] and made into a

paste like material which is known as “NBR-Nano-silica master batch”.

2nd

step: - In the second step, the raw NBR rubber is milled in two roll mill and then

NBR-Nano-Silica master batch” was added to it to get uniform blending of liquid NBR

and NBR rubber. Then other rubber compounding chemicals, as per the formulation

given in Table 2.9 such as activators, curatives etc were added. During mixing sulphur

was added in the polymer at initial stage to ensure proper dispersion of sulphur in

polymer matrix. Mixing was carried out in a controlled manner and same procedure was

followed for all the mixes. The mixing cycle time was kept constant at 25 min for all the

mixes. The polymer nanocomposite mixes were then passed several times in two roll mill

to get uniform NBR Nano-silica based polymer nanocomposite.

2.4.1.4 NBR-Clay Nanocomposites

NBR-Clay Nanocomposites were prepared using the formulation given in Table

2.10 The dosage of nanoclay were kept varied from 0, 1, 3, 5 & 7 phr as shown in Table

2.10 and all other rubber chemical ingredients were kept constant.

Table-2.10 Formulation for preparation of NBR – Clay-nanocomposites [in phr*]

Compounding Ingredients* NC 0 NC1 NC 3 NC 5 NC 7

NBR-JSR 230 100 100 100 100 100

Sulphur 2 2 2 2 2

Zinc oxide 4 4 4 4 4

Stearic acid 1 1 1 1 1

Nano Clay 0 1 3 5 7

DOP 10 10 10 10 10

TDQ 1 1 1 1 1

6PPD 1 1 1 1 1

MBTS 0.5 0.5 0.5 0.5 0.5

Total Weight 119.5 120.5 122.5 124.5 126.5



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The compounds were mixed in a laboratory size (225 x 100 mm) mixing mill at a

friction ratio of 1 : 1.25 according to ASTM D 3182 standards while carefully controlling the

temperature, nip gap, mixing time, and uniform cutting operation. The temperature range for

mixing was maintained at 80 °C by carefully circulating water. After mixing, the elastomer

compositions were molded in an electrically heated hydraulic press to optimum cure (90% of

the maximum cure) using molding conditions determined by a Monsanto Rheometer.

2.4.2 HNBR Nanocomposites

In this study, two types of nano fillers namely Nanosilica and Nanoclay were used.

2.4.2.1 HNBR-Clay Nanocomposites

HNBR-Clay Nanocomposite was prepared using the formulation given in Table 2.11.

The dosage of nanoclay were kept varied from 0, 3, 5 & 7 phr as shown in the Table 2.11

and all other rubber chemical ingredients were kept constant.

Conventional Mixing:

Table 2.11 Formulations for preparation of HNBR clay nanocomposite

Compounding Ingredients HNC 0 HNC 3 HNC 5 HNC 7

HNBR- Therban®3907 100 100 100 100

Dioctyl phthalate oil 20 20 20 20

MMT - Nano clay 0 3 5 7

Dicumyl Peroxide – 40 6 6 6 6

Total Batch Weight 126 129 131 133

The compound was prepared as per the compounding formulation given in

Table-2.11. Polymer nano compounds were prepared by mixing HNBR and other

compounding chemicals using a open two roll mixing mill operated at room temperature

and the speed ratio of the two rolls were maintained at 1:1.2. Mixing was completed

within 20 minutes and maintained similar mixing conditions for all compounds.


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Mixing with dispersed nanoclay

Table 2.12: Formulation for preparation of HNBR-clay nanocomposite using DOP as

dispersion oil

Compounding Ingredients Control DNC 3 DNC 5 DNC 7

Dispersion of MMT Nano Clay in DOP oil

Dioctyl phthalate oil 20 20 20 20

MMT - Nano clay 0 3 5 7

Mixing of Dispersion in Main polymer matrix

HNBR- Therban®3907, 100 100 100 100

Dicumyl peroxide – 40 6 6 6 6

2.4.2.2 HNBR-Silica Nanocomposites :

NBR- Silica Nanocomposites were prepared using the formulation given in Table

2.13 The dosage of nanosilica were kept varied from 0, 1, 3 & 5 phr as shown in the Table

2.13 and all other rubber chemical ingredients were kept constant.

Table 2.13 Formulation for preparation of HNBR – Nano Silica Nanocomposites [phr*]

Compounding Ingredients H 0 HNS 1 HNS 3 HNS 5

HNBR Rubber 100 100 100 100

Zinc Oxide 3 3 3 3

Stearic acid 1 1 1 1

TAC 1 1 1 1

Nano silica 0 1 3 5

DCP 40 3.5 3.5 3.5 3.5

Total Batch Weight 178.5 179.5 181.5 183.5

2.4.3 EPDM Nanocomposites

Ethylene-propylene rubbers are valuable for their excellent resistance to heat,

oxidation, ozone and weather ageing due to their stable, saturated polymer backbone

structure. As non-polar elastomers, they have good electrical resistivity, as well as resistance


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to polar solvents, such as water, acids, alkalies, phosphate esters and many ketones and

alcohols. Amorphous or low crystalline grades have excellent low temperature flexibility

with glass transition points of about minus 60°C. Heat ageing resistance up to 130°C can

be obtained with properly selected sulfur acceleration system and heat resistance up to

160°C can be obtained with peroxide cured compounds. Compression set resistance is

good, particularly at high temperatures, if sulfur donor or peroxide cure systems are used.

These polymers respond well to high filler and plasticizer loading, providing economical

compounds. They can develop high tensile and tear properties, excellent abrasion

resistance, as well as improved oil swell resistance and flame retardance. An attempt was

made to use nanofillers in EPDM matrix to improve the heat resistance, electrical

resistance properties.

In this study, two types of nano fillers namely Nanosilica and Nanoclay were used

and the nanocomposites were prepared and characterized [3-4]

2.4.3.1 EPDM-Silica Nanocomposites

EPDM – Silica Nanocomposites were prepared using the formulation given in

Table 2.14 The dosage of nanoclay were varied from 0, 1, 3, 5 & 7 phr as shown in the

Table 2.14 and all other rubber chemical ingredients were kept constant.

Table 2.14 Formulation for preparation of EPDM – Silica Nanocomposites

Compounding Ingredients E 0 ENS 1 ENS 3 ENS 5

EPDM-Keltan 512 100 100 100 100

Zinc Oxide 5 5 5 5

Paraffinic oil 5 5 5 5

Nano silica 0 1 3 5

DCP 40 4 4 4 4



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2.4.2 EPDM-Clay Nanocomposites

EPDM –Clay Nanocomposites were prepared using the formulation given in

Table 2.15 The dosage of nanoclay were kept varied from 0, 1, 3, 5 & 7 phr as shown in

the Table 2.15 and all other rubber chemical ingredients were kept constant.

Table 2.15 Formulation for preparation of EPDM – clay Nanocomposites

Compounding Ingredients EN 0 ENC 3 ENC 5 ENC 7

EPDM- Keltan 512 100 100 100 100

Zinc Oxide 5 5 5 5

Paraffinic oil 5 5 5 5

Nano clay 0 3 5 7

Di- cumyl peroxide - 40 4 4 4 4


2.5. Mixing and homogenization on a mixing mill

Mixing is the process of making a thorough and uniform dispersion of various

ingredients in polymer matrix by shearing it in between two parallel rollers rotating

inwards. Mixing was carried out on a laboratory two roll mixing mill (size 6” x 12”) as

per ASTM D 3182–89. The mixing was carried out at a friction ratio of 1:1.25. The mill

opening was set at 0.2 mm and the elastomer was passed through the rolls twice without

banding. This was then banded on the slow roll with mill opening at 1.4 mm and was

increased to 1.9 mm as the band became smooth. The temperature of the rolls was

maintained at 70±5 °C. The compounding ingredients were added as per procedure given

in ASTM D 3182–89 in the following order: activator, filler, accelerator and curing

agents. Before the addition of accelerator and sulphur, the batch was thoroughly cooled

to avoid any scorching of rubber compound. After mixing all the ingredients,

homogenization of the compound was carried out by passing the rolled stock end wise six

times at a mill opening of 0.8 mm. The mill was opened to give a minimum stock

thickness of 6 mm and the stock was passed through the rolls four times folding it back

on itself each time.


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2.6. Cure characteristics

Cure characteristics of the mixes were determined as per ASTM D 2084–1995

using Rubber Process Analyzer (RPA 2000–Alpha technologies, Fig 2.1, It uses two

directly heated, opposed biconical dies that are designed to achieve a constant shear

gradient over the entire sample chamber. The sample of approximately 5 g was placed in

the lower die that is oscillated through a small deformation angle (0-2º) at a frequency of

50 cpm. The torque transducer on the upper die senses the forces being transmitted

through the rubber. The torque is plotted as a function of time and the curve is called a

cure graph. The important data that could be taken from the torque-time curve are

minimum torque ML(T90) ,maximum torque. (MH), scorch time (T10), and optimum

cure time.

Fig 2.1. Monsanto R-100 ODR

Rubber Process Analyzer

The rubber compound mixes were then passed several times in two roll mill to get

uniform NBR nanosilica based rubber compound. The curing time was obtained from

rheological studies carried out using RPA-2000.

Fig 2.2 RPA-2000


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2.7. Moulding

Moulding is a process of curing the compound by means of heat and pressure.

It includes many different methods like compression moulding, injection and transfer

moulding. Here we are mainly dealing with compression moulding technique because the

flow properties of rubber are very poor and it does not fill the mould cavities by using

other moulding techniques.8” X 8” X 2mm and 6” X 6” X 2mm sheets are compression

moulded using a 14” X 14” twin double daylight hydraulic Compression set buttons are

also compression moulded in the same press. Curing is done at 150 °C for NBR rubber

and 160 °C for EPDM and HNBR rubbers for a particular time which is obtained from

Rheological study.

2.6. Vulcanized samples

The compounded rubber sheet was kept for maturation for 16 hrs and then taken

for moulding of various test specimens as per ASTM standard using hydraulic press at a

temperature 150 C or 160 C as per the rheological data.

Time between vulcanization and testing:

For all test purposes, the minimum time between vulcanization and testing was

kept 16 hrs.

2.8. Mechanical properties

The thickness of the dumbbell was measured at the centre and at each end of the

test length with the help of thickness gauge. The median value of the three measurements

was taken to calculate the area of the cross-section. The width of the test piece was 4 mm

which was taken as the distance between the cutting edges of the die in the narrow part.

Tensile tests were carried out according to ASTM D412-98 on dumb-bell shaped

specimens using a universal tensile machine, Zwick 1445. Dumb-bell test pieces shall

have the outline shown in Fig.2.3. Measure the thickness at the centre and at each end of

the test length with the thickness gauge. The median value of the three measurements

shall be used in calculating the area of the cross-section. The nominal rate of traverse of

the moving grip was kept 500 mm/min.


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Fig 2.3 dumb-bell shaped specimens as per ASTM D 412

These tests were carried out using dumbbell specimens. The measurements were

carried out at a cross head speed of 500 mm/min on a Zwick tensile test in accordance

with ASTM D 412.

Fig 2.4 Tensile testing machine

2.9. Hardness:

The testing was done as per ASTM D 2240–1997 using Shore A type Durometer.


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Fig 2.5 Shore A type Durometer

Hardness of the samples were measured by a Durometer (Shore A type, ASTM D

2240) using the test button of 12 mm thickness. To get repeatable results, the hardness

tester was held in position with the centre of the indentor at least 12 mm from the edges

of the test piece and the pressure foot is applied to the test piece as rapidly as possible,

without shock, keeping the foot parallel to the surface of the test piece and ensuring that

the indenter is normal to the rubber surface. The reading was taken within 1 s after the

pressure foot is in firm contact with the test piece.

2.10 Ageing studies

All rubbers are subjected to deterioration at high temperature. Volume change and

Compression set are both influenced by heat. Hardness is influenced in a complex way.

The first effect of high temperature is to soften the compound. This is a physical change,

and will reverse when the temperature drops. In high pressure application the product

may begin to flow through the clearance gap as the temperature rises due to this softening

effect. With increasing time at high temperature, chemical changes occur. These

generally cause an increase in hardness, along with volume and compression set changes.

Changes in tensile strength and elongation are also involved. Being chemical in nature,

these changes are not reversible. The changes induced by low temperature are primarily

physical and reversible. An elastomer will almost completely regain its original

properties when warmed.

Effect of nanofillers on the properties of accelerated ageing and heat resistance of

polymer nanocomposites were performed to estimate the relative resistance of polymer

nanocomposites [having no and different doses of nanofillers] to deterioration with the

passage of time. For this purpose, the polymer nanocomposites were subjected to


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controlled deteriorating influences for definite periods, after which appropriate properties

are measured and compared with the corresponding properties of the unaged polymer

nanocomposites. In accelerated ageing, the polymer nanocomposites is subjected to a test

environment intended to produce the effect of natural ageing in a shorter time. In case of

heat resistance tests, the polymer nanocomposites is subjected to prolonged period at the

same temperature as that in service.

2.11 Tear Strength

The tear specimen was clamped on the testing machine, taking care that the bite

of the jaws shall be at the centre of the tab ends and in line with the direction of load

application. Apply the load with a lower jaw speed of 500 mm per minute. After rupture

of the specimen, the breaking load was printed and recorded together with the average

thickness of the specimen.

Calculation - Tear strength is calculated by dividing the load in kg by thickness in

centimeter of the test specimen and is expressed as kg/cm thickness.

F

Tear Strength = ---------

D

Fig 2.6 Tear strength specimen

Where, F is the maximum force, in newtons, and the median force, in Newton

recorded in tensile machine. D is the median thickness, in millimeters, of the test piece.

Determine the median and the range of the values for each direction of testing.


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2.12. Thermal Degradation Studies

Thermo gravimetric analysis was done using Perkin Elmer Instrument, Diamond

TG-DTA, (Waltham, MA, USA) (Fig.2.7). The samples (3-5 mg) were heated from

ambient temperature to 800 °C in the furnace of the instrument under oxygen atmosphere

at 100 ml/min and at a heating rate of 20 °C/min and the data of weight loss Vs

temperature were recorded. Although the experiments were recorded in nitrogen as well

as in air, there was major difference amongst the samples when oxygen was used as the

medium. The analysis of the thermo gravimetric (TG) and derivative thermo gravimetric

curves (DTG) was done in oxygen and the onset temperature, weight loss at major

degradation steps and temperature corresponding to the maximum value in the derivative

thermogram were recorded. The temperature at which maximum degradation took place

is denoted as Tmax and onset temperature of degradation is denoted as Ti. The error in the

measurement was ± 1 °C.

Fig. 2.7 TGA, Perkin Elmer Instrument

Thermal decomposition is a chemical process in which solid material generates

volatile fragments which can burn above the solid material. Polymer can break down

thermally by oxidative process or by the action of heat. In the presence of oxidants, the

decomposition process is accelerated. There are several ways in which polymers decompose:

random-chain scission, end-chain scission, chain stripping and cross-linking. The most

common types of degradation occur through chemical reactions at the molecular level.

The thermal degradation kinetics in polymers are more complicated than in inorganic


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materials due to the nature of polydispersity of polymer chains. Upon thermal excitation,

the covalent bonds in polymer chains undergo complex vibration and rotation motions

within their local space. With further excitation these bonds can break to form a variety

of fragment radicals or small molecules, which may further mutually recombine or break.

Ultimately, the resulting fragments may be vaporized, diffused out, or carbonized. The

thermal behavior of materials can be improved if the information about the thermal

degradation kinetics and degradation mechanisms can be employed to decrease the

thermal degradation rate or increase the heat resistance. Thermogravimetric analysis

(TGA) is an excellent tool for studying the kinetics of thermal degradation.

It provides information on frequency factor, activation energy, and overall reaction order.

However, it does not provide clear information on thermal degradation mechanisms.

Polymer chains undergo degradation (depolymerization) through a variety of mechanisms

including shear action, chemical attack, and nuclear, ultraviolet, and ultrasonic irradiation.

2.13 Energy-dispersive X-ray spectroscopy

EDS makes use of the X-ray spectrum emitted by a solid sample bombarded with

a focused beam of electrons to obtain a localized chemical analysis. All elements from

atomic number 4 (Be) to 92 (U) can be detected in principle, though not all instruments

are equipped for 'light'

Fig 2.8 Energy-dispersive X-ray spectroscopy

elements (Z < 10). Qualitative analysis involves the identification of the lines in the

spectrum and is fairly straightforward owing to the simplicity of X-ray spectra.

Quantitative analysis (determination of the concentrations of the elements present) entails


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measuring line intensities for each element in the sample and for the same elements in

calibration Standards of known composition

2.14 Fourier Transforms Infra-Red spectroscopy

FT-IR spectra of thin films were recorded using a Fourier Transform Infrared

Spectrophotometer (Nicolet, Model 410, USA) using ATR technique (Fig.2.9).

All the clays show a sharp band around 3627 cm-1

, resulting from the O-H

stretching, vibration of the silicate and a broad band between 3550-3100 cm-1

,

characteristic of the stretching and deformation vibrations of the interlayer water. Infrared

signal of adsorbed H2O is visible also around 1635 cm-1

(bending vibrations).

Fig 2.9 Fourier transforms infra-red spectroscopy/ATR

Additionally, the absorption pick at about 1040 cm-1

is ascribed to Si-O-Si

stretching vibrations of clays. The other two absorption bands are around 520 cm-1

and

465 cm-1

derived from Al-O stretching and Si-O bending vibrations of silicate. The

organo-montmorillonites display some bands which are not exhibited by the pristine clay.

These bands appear at 2920, 2850 and 1468 cm-1

and are attributed to the C–H vibrations

of the methylene groups (asymmetric stretching, symmetric stretching and bending,

respectively) from chemical structure of the organo-modifiers.


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2.15 X-ray diffraction studies

Small angle X-ray diffraction (XRD) study of the Nanocomposites were

performed at room temperature using a Philips PW 1710 diffractometer in the angular

range of 0˚ to 10˚ 2θ (SAXD). The target was copper and the (Cu Kα) radiation

(λ= 1.540598˚A) was obtained on applying 50 KV voltage to the generator and the

current was 40 mA. The basal spacing of nano graphite layers was estimated from the

position of the plane peak in the SAXD intensity profile. Specimens for X-ray diffraction

were taken from compression-molded sheets of 2 mm thickness.

Fig 2.10 X-ray diffraction

2.16 Electrical properties

The electrical behavior of rubber products used in particular applications is

important for a variety of reasons such as safety, static changes, current transmission, etc.

This test method is useful in predicting the behavior of such rubber products.

2.17 Barrier Properties

Several studies demonstrated that nanofillers highly improve barrier properties of

nanocomposite films. This behaviour is due to creating a „tortuous path‟. Air as

illustrated in the fig. that retards the progress of the gas molecules through the matrix. Air

permeability studies were conducted with circular specimens (diameter 9 cm, IS: 3400

part 21-1980) (Fig 2.12).


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Fig 2.11 Air Permeability Tester

The cavity of a test cell, maintained at a constant temperature, is divided by a disc

test piece into a high pressure and a low (atmospheric) pressure side. The high pressure

side is connected to a constant pressure gas reservoir or is of such volume that once filled,

it stays at practically constant pressure. The gas permeates into the low pressure side,

which is of a very low volume and connected to a capillary tube; this is provided for

measuring the permeated volume, while keeping or restoring the same low pressure within

this side. Absolute pressure for the high pressure side is maintained in the range of 0.3 to 1.5

MPa* and for low pressure side it is maintained at the prevailing atmospheric pressure.

For normal comparison of permeability of different rubber vulcanizates, the test

temperature is a standard laboratory temperature ( 27 + 1 oC) , but higher preferred

temperature may be used where conditions are required to approximate to the service

temperature of rubber products. When higher preferred temperatures are used, the

capillary tube shall be brought to the test temperature and maintained at that temperature

throughout the test.


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2.18 Transmission Electron Microscopy (TEM)

The samples for TEM analysis were prepared by ultracryomicrotomy with a Leica

Ultracut UCT (Leica Microsystems GmbH, Vienna, Austria). Freshly sharpened glass

knives with cutting edges of 45° were used to obtain cryosections of about 100 nm

thicknesse at -90 °C. The cryosections were collected individually in sucrose solution and

directly supported on a copper grid of 300 mesh size. Microscopy was performed with

JEOL 2100, Japan (Fig. 2.13). Transmission electron microscope was operated at an

accelerating voltage of 200 KV.

Fig 2.12 Transmission Electron Microscopy


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2.19 References:

1. Richard Karpeles and Anthony V. Grossi, “EPDM Rubber Technology”, Handbook of

Elastomers, 2nd

Ed., Anil K. Bhowmick and Howard L. Stephens [Editors], pp. 845-876,

Marcel Decker, Inc., New York (2001).

2. Lei Wang, Li Qun Zhang, Ming Tian, Materials and Design 39 450–457 (2012).

3. Gary Ver Strate, “Ethylene Propylene Elastomers”, Encyclopedia of Polymer Science &

Engineering, vol. 6, pp. 522-564 (1986).

4. John A. Riedel and Robert Vander Laan, “Ethylene Propylene Rubbers”, The Vanderbilt

Rubber Handbook, 13th

Ed., pp. 123-148, R.T. Vanderbilt Co., Inc., Norwalk, CT (1990).

chapter ii experimental -...

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