CHAPTER IV PROCESSING BEHAVIOUR, CURE CHARACTERISTICS, STRESS …shodhganga.inflibnet.ac.in/bitstream/10603/36105/8/08... · 2018-07-02 · The delta Mooney viscosities were determined

99

CHAPTER IV

PROCESSING BEHAVIOUR, CURE CHARACTERISTICS, STRESS

STRAIN PROPERTIES AND AGING BEHAVIOUR OF THE S1552

RUBBER SAMPLES

A. Processing Behaviour

The subject of processability of rubbers has, in the recent years, attracted the

attention of many workers. The term processability of rubber describes the

behaviours of raw rubbers during their conversion to useful products such as tyres,

hoses, mechanical goods, footwears etc. Because of poor scientific understanding

in rubber processing, the rubber industry still uses some of the same processing

equipment such as the two roll steam heated mill invented long ago. However,

processability of rubber is not a single property. The basic three steps(1) in

elastomer processing are:

1. Blending of elastomers by mastication and mixing of compounding

ingredients,

2. Forming the compound upto a semifinal form, and

3. Final shaping and setting

Step 1 is carried out on a two roll mill or in a banbury mixture. In factories,

where internal mixers (banbury) are not available, two roll mill mixing is the only

technique available for the dispersion and mixing of the compounding ingredients.

The two roll mill which has two rolls moving at different speeds to produce shear,

is used to blend the compounding ingredients such as fillers, activators, processing

aids and vulcanizing agents etc. Even in cases, where initial mastication and

mixing of compounding ingredients other than the vulcanizing agents is done in a

100

banbury mixer, the two roll mill is still used to blend in vulcanizing agents to

avoid scorching or premature vulcanization of the compounded stock.

In the 2nd and the 3rd steps also the two roll mill is commonly used for

continuous feeding to a calendar or an extruder etc. Thus mill behaviour of the raw

rubber as well as its compounds is very important and critical.

Tokita and White(2) have classified the observed mill behaviour of several

different rubbers into the following four regions:

1. Rubber stays mainly in the bank of the mill. This is the region of poor

processing.

2. Tight elastic band clinging to the front mill roll. This is desirable and means

the elastomer has good processability.

3. Material hanging as a bag off the roll, torn and granulated in the mill nip.

This is undesirable as it would lead to poor dispersion of compounding

ingredients.

4. Transparent fluid film occurring at high temperature.

Rubber generally do not exhibit all the four regions of mill behaviour. A

good processable rubber should exhibit only the first two regions and the second

region should be achieved at the earliest.

ChiKai Shih(3) studied the mill behaviour of ethylenepropylene hexadiene

terpolymer. They found that in general agreement with Tokita and White(2), the

milling characteristics of the polymer changes from elastic band region 2 to

crumbling bag region 3 and then to a viscoelastic fluid region 4 as the temperature

is increased from 5C to 175C. He has regarded the 23 transition as a failure

process which is time and temperature dependent.

101

Mooney viscometer has retained an important role in the production of SBR

for monitoring the polymerization reaction and for providing a final viscosity

value for the end product. In the rubber industry, the Mooney viscosity (ML1+4 at

100C) has been used for specification of flow property of rubbers.(4)

Delta Mooney viscosity that is change in Mooney viscosity with time has a

reasonable correlation with black incorporation time and is, therefore, an

indication of processability of rubbers.(5)

Change in Mooney viscosity generally occurs as a result of either chain

scission reaction due to mechanical degradation of the polymer molecules or as a

result of branching or crosslinking reaction in which the degraded chains reattach

to the polymer molecules(6), Fig. 1. The chain scission reaction would normally

lead to lowering of Mooney viscosity whereas the crosslinking reaction would

result in increase in Mooney viscosity of a given rubber sample. The net result

thus depends on predominance of one of these reactions.

CH3 CH2 CH CH CH2 CH3

CH3 CH2 CH CH CH2 CH3CH3+* *

Chain Scission Reaction

CH3 CH2 CH CH CH2 CH3 CH2 CH3CH3+ *

CH3 CH CH CH CH2 CH3

CH2

CH3

and so on

Cross-linking Reaction

Fig. 1

102

(i) Mixing & Mill Behaviour

In order to determine processability, curing characteristics and stressstrain

characteristics of the fourteen S1552 rubber samples prepared as per the details

given in Chapter II of this work, all the samples were compounded as per ASTM

Standard Recipe(7), given in Table1, on a laboratory two roll mill (manufactured

by Stewart Bolling & Co., U.S.A.) having 6|| outside diameter rolls maintained at

50C. Batch factor used was 4.0 (i.e. the batch size is obtained by multiplying the

recipe by 4). Mixing of all the fourteen rubber samples was carried out in

accordance with ASTM D15(7) and their mill behaviour was observed.(814) In

some samples, which were found to be relatively poorly processable, time cycles

for mixing various ingredients could not be adhered to and this further confirmed

their poor procesability. The results obtained have been summarized in Table 2.

Table 1

STANDARD RECIPE USED FOR MIXING OF THE FOURTEEN (14)

SAMPLES OF S1552 NUMBERS

Materials used: Parts of Weight

Rubber 100

Higher Abrasion Furnace Black (NBS378) 50

Zinc Oxide (NBS370) 3

Stearic Acid (NBS372) 1.0

Sulphur (NBS371) 1.75

TBBS (ntert, butyl 12 benzothiazole

sulfonamide) (NBA384)

1.0

Batch Factor 4.0

103

TABLE 2

MILL BEHAVIOUR OF THE FOURTEEN SAMPLES OF S1552 RUBBER

Mixing Data Sample No. Standard Mixing Time as

per ASTM D156

1 1A 2 2A 3 3A 4 4A 5 5A 6 7 8 9

1. Time for smooth band formation minutes

1.5 1.5 1.5 1.5 2.0 2.0 3.0 3.0 * * 2.0 4.0 2.0 3.0

2. Total Mastication Time Minutes

7 7 7 7 7 7 7 7 7 7 7 7 7 7 7

3. Time for Mixing Sulphur, Minutes

2 2 2 2 2 2 2.5 2.5 2.5 2.5 2 2.5 2 2.5 2

4. Time for Mixing Stearic Acid, Minutes

2 2 2 2 2 2 2 2 2.5 2.5 2 2 2 2 2

5. Time required for half carbon black absorption, Minutes

2 2 2 2 2 2 2.5 2.5 5 5 2 4 2 3

6. Time for Mixing carbon black, Minutes

10 10 10 10 10 10 10 10 12 12 10 10 10 10 10

104

TABLE 2 Contd…

MILL BEHAVIOUR OF THE FOURTEEN SAMPLES OF S1552 RUBBER

Mixing Data Sample No. Standard Mixing Time as

per ASTM D156

1 1A 2 2A 3 3A 4 4A 5 5A 6 7 8 9

7. Whether Bagging was observed.

No No No No No No No No Yes Yes No Yes No No

8. Time for mixing other ingredients, Minutes

3 3 3 3 3 3 3 3 4 4 3 3.5 3 3 3

9. OverallProcess ability

Good Good Good Good Good Good Fair Fair Poor Poor Good Poor Good Fair to

Poor

*Formation of smooth band free from holes was not observed even in 7 minutes of mastication

105

It can be seen from the results summarized in Table 2 that samples 1, 1A, 2,

2A, 3, 3A, 6 and 8 exhibited good processability. This was indicated by the fact

that these samples required only 1.52 minutes for smooth band formation.

However, total mastication time was maintained same at 7 minutes for all the

samples. These samples exhibited excellent carbon black absorption characteristics

also as they required only 2 minutes to absorb half amount of the carbon black.

Further, no bagging was observed in case of these samples.

Samples 4, 4A and 9 exhibited relatively poor processability as they

required longer time (3 minutes) for smooth band formation than the samples

referred to in the preceeding paragraph which exhibited good processability.

Further these samples 4, 4A and 9 also required longer time for dispersion of

sulphur and absorption of carbon black. However, no bagging throughout the

mixing operation was observed and as such their processability was taken as fair.

Sample NO. 9 was, however, inferior to others in this group of samples as it

required marginally higher time for half carbon black absorption and the sample

was, therefore, classed as fair to poor with respect to its processability.(1517)

Samples 5, 5A and 7 exhibited poor processability. These samples did not

exhibit smooth elastic band formation free from holes within the seven minutes of

mastication. Further these samples also exhibited bagging during mixing of the

carbon black and much higher time for absorption of carbon black and all the other

ingredients than the remaining other samples. Sample 7 was the next to samples 5

& 5A in order of poor processability as indicated by longer time required for

formation of smooth band and absorption of carbon black and other ingredients.

Sample 7, however, showed only little bagging as compared to samples 5 & 5A.

106

(ii) Mooney viscosity and Delta Mooney Viscosities

The Mooney visocosities and the delta Mooney viscosities of all the

fourteen rubber samples were determined on a Mooney viscometer, manufactured

by Scott Testers Inc., U.S.A. ASTM Method D1646(8) was used for determination

of the Mooney viscosity of the rubber samples.

The delta Mooney viscosities were determined by extending the running

period of the Viscometer to 15 minutes and noting down the Mooney viscometer

reading every minute. Change in Mooney viscosity between the readings at 1 and

7 minutes and between the readings at 1 and 15 minutes were recorded as delta

Mooney viscosities. The results obtained have(1821) been summarized in the

attached Table 3.

The results of the Mooney viscosity of the rubber samples were found to be

23 units higher than those obtained while determining the Mooney viscosities of

the contained polymers of the corresponding lattices. This was due to difference in

the method used for preparation of rubber samples for determination of the

Mooney viscosity and was as would normally be expected. The values of the

Mooney viscosities obtained on final dried rubber were, however, more

representative of the true Mooney viscosity of the rubber.

B. Curing Characteristics

Raw rubber is soft and plastic and can be shaped into desired and products.

By process of vulcanization the raw rubber is converted into a hard elastic and

rigid material which does not change its shape. During the process of

vulcanization three dimensional chemical crosslinks are produced in the polymer

molecules to give rigidity to the polymer net work.(9)

107

TABLE 3

MOONEY VISCOSITY AND DELTA MOONEY VISCOSITY OF THE FOURTEEN SAMPLES OF S1552 RUBBER

Temperature of the Platens .. 100C Type of Rotor used .. Large Time of Preheating .. 1 minute

Mooney Data Sample No.

1 1A 2 2A 3 3A 4 4A 5 5A 6 7 8 9

Mooney Readings:

after 1 minutes 47 51 52 57 60 66 68 73 86 92 61 59 60 62

after 2 minutes 42 46 47 54 57 62 66 71 85 91 57 54 59 59

after 3 minutes 37 41 43.5 50 54 59 63 69 85 91 53.5 51 54 55

after 4 minutes 33 38 41 46 50 56 60 67 85 91 49.5 49 50 51

after 5 minutes 31 35 39 44 48 52 57 65 83 90 46.5 48 47 50

after 6 minutes 30 34 37 41 46.5 50 55 64 81 88 46 47.5 45 49.5

after 7 minutes 28.5 33 35.5 40 45 49 54 61 79 86 45 47 43 48.5

after 8 minutes 27.5 32 34.5 39 44 47 53 59.5 77 85.5 44 46 42 47

after 9 minutes 27 31.5 33.5 38.5 43.5 46.5 52 58.5 75 83 44 44.5 41 45.5

after 10 minutes 26 31 33 38 43 46 51.5 58.5 73 81 43.5 43 40 45

after 11 minutes 25.5 31 32.5 38 43 46 51 56.5 71 79 43 42.5 40 45

108

TABLE 3 Contd…

MOONEY VISCOSITY AND DELTA MOONEY VISCOSITY OF THE FOURTEEN SAMPLES OF S1552 RUBBER

Temperature of the Platens .. 100C Type of Rotor used .. Large Time of Preheating .. 1 minute

Mooney Data Sample No.

1 1A 2 2A 3 3A 4 4A 5 5A 6 7 8 9

after 12 minutes 25.5 30.5 32 37.5 42 45.5 51 56 70 78.5 42.5 42 39 44.5

after 13 minutes 25 30.5 32 37.5 41 45.5 50.5 56.5 70 77 42 42 39 44.5

after 14 minutes 25 30 31.5 37 40.5 45 50 56 70 76 41 42 39 44

after 15 minutes 24.5 30 31 37 40 45 50 56 70 76 41 42 39 44

Mooney Viscosity, ML1+4 at

100C.

33 38 41 46 50 56 60 67 85 91 49.5 49 50 51

Delta Mooney, ML17 18.5 18 16.5 17 16 17 14 12 5 4 16 12 17 13.5

Delta Mooney, ML115 22.5 21 21 20 20 21 18 17 16 16 20 17 21 18

109

For shaping a rubber compound into final desired shape of the end product it is

necessary for the rubber compound to flow in the mould so as to completely fill it.

It is, therefore, also necessary that no crosslinks should be produced in the rubber

molecules before the rubber compound has been finally shaped in the mould

otherwise the flow properties of the rubber compound would be seriously affected.

Premature vulcanization of rubber compound before final shaping of the

compound is called scorching and is undesirable.(10)

The time to scorch of a rubber compound can be determined on a Mooney

viscometer and is defined as the total time required for rise of Mooney viscosity 5

units above the minimum value. The rate at which the vulcanization of a rubber

compound occurs is also an important characteristic of the rubber compound. The

Mooney time to cure is defined as the total time required for obtaining minimum

viscosity and then a rise of 35 units of Mooney viscosity above the minimum

value. Cure index is defined as the time required for rise of Mooney viscosity from

5 units to 35 units and is thus equal to cure time minus scorch time.(11, 2225)

Scorch time, cure time and cure index of all the fourteen saples of S1552

rubber were determined in accordance with ASTM D1646(8) using large rotor at

platen temperature of 126C and the results obtained were summarized in

Tables417. Scorch time, cure time and cure index values for the rubber samples

were determined from Figs. 215 and the results were entered in the

corresponding Table 4 to 17. Compound viscosity was taken as the 1+4 minutes

reading of the Mooney viscometer during determination of time to scorch, time to

cure and cure index of the rubber samples.

110

Table 4

Cure Characteristics of Sample No. 1 of S1552 Rubber

Type of Instrument used : Mooney Viscometer

Rotor used : Large

Temperature of platens : 126C

Time (Minutes) Mooney Reading Time (Minutes) Mooney Reading

1 Preheating 18 55

2 71 19 55

3 64 20 55.5

4 60.5 21 56

5 56 22 57

6 55 23 57.5

7 54.5 24 58

8 54 25 59

9 54 26 61

10 54.5 27 63.5

11 54 28 66

12 54.5 30 72

13 54.5 30 72

14 54.5 31 75.5

15 54.5 32 81.5

16 55 33 87

17 55 34 95

Compound Mooney Viscosity, ML1+4 at 126C : 56

Minimum Mooney Viscosity, MV at 126C : 54

Time to Scorch = ta at MV + 5, minutes : 24.8

Time to Cure = t35 at MV + 35, minutes : 33.2

Cure Index = t35 ts : 8.4

111

Table 5

Cure Characteristics of Sample No. 1A of S1552 Rubber


Rotor used : Large



1 Preheating 18 55

2 73 19 55

3 68 20 55.5

4 63 21 56

5 59 22 56.5

6 57 23 57

7 56 24 59

8 55.5 25 60

9 55.5 26 62

10 55.5 27 64.5

11 55 28 67

12 55.5 29 70

13 55.5 30 73

14 55 31 76

15 55 32 62

16 55 33 90

17 55 34 100



Time to Scorch, minutes : 25

Time to Cure, minutes : 33

Cure Index : 8

112

Table 6



Rotor used : Large



1 Preheating 17 61

2 74 18 61

3 69 19 62

4 65 20 62

5 63 21 62

6 62 22 63

7 61 23 64

8 61 24 65

9 60 25 67

10 60 26 70

11 60 27 73

12 60 28 77

13 60 29 82

14 60 30 89

15 60 31 98

16 60



Time to Scorch, minutes : 23.8

Time to Cure, minutes : 30.8

Cure Index : 7.0

113

Table 7



Rotor used : Large



1 Preheating 17 62.5

2 74 18 62.5

3 68 19 63

4 65 20 63

5 64 21 63.5

6 63.5 22 64

7 62.5 23 65

8 62.5 24 66

9 62 25 67.5

10 62 26 69.5

11 62 27 72.5

12 62 28 75.5

13 62 29 80

14 62.5 30 85.5

15 62 31 92

16 62 32 103.5





Cure Index : 6.6

114

Table 8



Rotor used : Large



1 Preheating 16 67

2 75 17 67.5

3 71 18 68

4 69 19 68

5 67 20 68.5

6 66 21 70

7 66 22 71

8 66 23 73

9 66 24 75

10 66 25 79

11 66 26 83

12 66 27 88

13 66 28 95

14 66 29 104

15 65





Cure Index : 6.7

115

Table 9



Rotor used : Large




2 76 18 68

3 72 19 68

4 70 20 68.5

5 69 21 69

6 68 22 69.5

7 67 23 70

8 67.5 24 70.5

9 67 25 72

10 67 26 74

11 67 27 76.5

12 67 28 79.5

13 67 29 83

14 67 30 88

15 67 31 96

16 67.5 32 105





Cure Index : 6.7

116

Table 10



Rotor used : Large



1 Preheating 15 65

2 77 16 65

3 74 17 65.5

4 72 18 66

5 70 19 67

6 68 20 68

7 66 21 70

8 65 22 73

9 65 23 76

10 65 24 80

11 65 25 85

12 65 26 91

13 65 27 98.5

14 65 28 107





Cure Index : 6.2

117

Table 11



Rotor used : Large



1 Preheating 16 76

2 84 17 76

3 78 18 76

4 75 19 77

5 74 20 77.5

6 74 21 78

7 74 22 79

8 74 23 80

9 74 24 82

10 74 25 85

11 74 26 90

12 74 27 98

13 74 28 108

14 74 29 124

15 75





Cure Index : 6

118

Table 12



Rotor used : Large



1 Preheating 13 67

2 85 14 68

3 80 15 69.5

4 75 16 71.5

5 72 17 73.5

6 69 18 76.5

7 68 19 79.5

8 67.5 20 84.5

9 67 21 84.5

10 67 22 91

11 67 22 101

12 67 23 115





Cure Index : 5.8

119

Table 13



Rotor used : Large



1 Preheating 13 83

2 93 14 83.5

3 87 15 84

4 83 16 85

5 81 17 86

6 81 18 88

7 81 19 90

8 81 20 93

9 81 21 97

10 81.5 22 102

11 82 23 110

12 92.5 24 120





Cure Index : 6.6

120

Table 14



Rotor used : Large



1 Preheating 17 63

2 70 18 63.5

3 65 19 63.5

4 63 20 64

5 63 21 65

6 63 22 66

7 63 23 67.5

8 63 24 70

9 63 25 73

10 63 26 76

11 63 27 79

12 63 28 83

13 63 29 87

14 63 30 91

15 63 31 96

16 63 32 103





Cure Index : 8.0

121

Table 15



Rotor used : Large




2 68 14 63

3 64 15 64

4 62 16 65

5 62 17 67.5

6 62 18 70

7 62 19 73

8 62 20 77

9 62 21 83

10 62 22 90

11 62 23 99

12 62





Cure Index : 6

122

Table 16



Rotor used : Large



1 Preheating 16 61

2 74 17 61

3 69 18 62

4 65 19 62

5 63 20 62

6 62 21 63

7 61 22 64

8 61 23 65

9 60 24 67

10 60 25 70

11 60 26 73

12 60 27 77

13 60 28 82

14 60 29 89

15 60 30 98





Cure Index : 6.9

123

Table 17



Rotor used : Large



1 Preheating 13 62

2 69 14 63

3 64 15 64

4 63 16 65

5 62 17 67

6 61 18 70

7 61 19 74

8 61 20 79

9 61 21 83

10 61 22 89

11 61 23 97

12 61 24 108





Cure Index : 6.3

124

C. StressStrain Properties of Unaged and Aged Samples of the S1552

Rubber

(i) StressStrain Properties of the Unaged Samples:

The rubber compounds of the fourteen samples of S1552 rubber prepared

using standard recipe given in Table 1 under Section ‘A’ of this Chapter were

cured in a four cavity standard mould conforming to ASTM D15(12) using a

hydraulic curing press manufactured by M/s Steward Bolling & Co., U.S.A. All

the rubber compounds were cured for a period of 35 minutes at a temperature of

292F.

The vulcanized rubber test slabs thus obtained were conditioned in a room

maintained at 25 1C and about 35% relative humidity for a period of atleast 16

hours. Standard dumbbell test pieces were cut by means of pneumatically

operated dumbbell cutting machine fitted with standard die conforming to

standard ‘DumbBell Die C’ as per ASTM D412.(13)

Stressstrain properties such as tensile strength, 300% modulus and

elongation at break of all the fourteen samples of S1552 rubber were then

determined on a Tensile Testing Machine, manufactured by Scott Testers, Inc.

U.S.A. Three dumbbell pieces for each rubber sample were tested in accordance

with ASTM D412(14) and the machine of the three respective values were taken

as the characteristics of the rubber tested. The results obtained were summarized in

Tables 18 to 31.

125

Table 18

StressStrain Properties of vulcanized sample No. 1 of S1552 Rubber before

and after Air Aging

Compounding Recipe : As given in Table 1, Chapter 4,

Temperature of cure : 292F

Time of cure : 35 minutes

Properties Before Aging DumbBell Medium

1 2 3

Tensile Strength, kg/cm2 209 210 210 210

300% Modulus, kg/cm2 146 146 147 146

Elongation at break, % 470 470 470 470

Properties After Aging for 120

hours at 100 1C

DumbBell

1| 2| 3|



% Deterioration based on original

value

Tensile Strength 20.0

Elongation at break 66.0

126

Table 19

StressStrain Properties of vulcanized sample No. 1A of S1552 Rubber

before and after Air Aging





1 2 3


300% Modulus, kg/cm2 153 154 154 154



hours at 100 1C

DumbBell

1| 2| 3|



% Deterioration based on

original value



127

Table 20


and after Air Aging





1 2 3


300% Modulus, kg/cm2 149 152 152 152



hours at 100 1C

DumbBell

1| 2| 3|




original value



128

Table 21







1 2 3


300% Modulus, kg/cm2 162 162 162 162



hours at 100 1C

DumbBell

1| 2| 3|




original value



129

Table 22


and after Air Aging





1 2 3


300% Modulus, kg/cm2 161 162 162 162



hours at 100 1C

DumbBell

1| 2| 3|




original value



130

Table 23







1 2 3


300% Modulus, kg/cm2 171 172 172 172



hours at 100 1C

DumbBell

1| 2| 3|




original value



131

Table 24


and after Air Aging





1 2 3


300% Modulus, kg/cm2 185 185 185 185



hours at 100 1C

DumbBell

1| 2| 3|




original value



132

Table 25







1 2 3


300% Modulus, kg/cm2 190 190 190 190



hours at 100 1C

DumbBell

1| 2| 3|




original value



133

Table 26


and after Air Aging





1 2 3


300% Modulus, kg/cm2 200 201 200 200



hours at 100 1C

DumbBell

1| 2| 3|




original value



134

Table 27







1 2 3


300% Modulus, kg/cm2 200 198 198 198



hours at 100 1C

DumbBell

1| 2| 3|




original value



135

Table 28


and after Air Aging





1 2 3


300% Modulus, kg/cm2 170 171 170 170



hours at 100 1C

DumbBell

1| 2| 3|




original value



136

Table 29


and after Air Aging





1 2 3


300% Modulus, kg/cm2 163 165 167 165



hours at 100 1C

DumbBell

1| 2| 3|




original value



137

Table 30


and after Air Aging





1 2 3


300% Modulus, kg/cm2 172 172 172 172



hours at 100 1C

DumbBell

1| 2| 3|




original value



138

Table 31


and after Air Aging





1 2 3


300% Modulus, kg/cm2 174 174 174 174



hours at 100 1C

DumbBell

1| 2| 3|




original value



139

(ii) StressStrain Properties of the Aged Samples:(2628)

In order to estimate the effect of aging on the stressstrin properties of the

vulcanized rubber samples, tensile strength and elongation at break of the

vulcanisates prepared from all the fourteen rubber samples were also determined

after air aging of 3 dumbbell pieces from each rubber sample in a forced draught

oven maintained at 100 1C for a period of 120 hours. Only one set of 3

dumbbell pieces from one rubber sample was aged at a time to avoid any adverse

effect of one set of samples on the other. The dumbbell test pieces were hanged

by means of clips and a rod in the centre of the oven to avoid direct contact with

any metal part of the oven. At the end of 120 hours of aging, the dumbbell test

pieces were taken out of the oven and allowed to cool and condition in a room

maintained at 25 1C and about 35% relative humidity for atleast 16 hours.

Tensile strength and elongation at break of the aged samples were then determined

using the same tensile testing machine as used for the unaged samples and the

results obtained were compared with the original values to determine deterioration

in properties as a percentage of the original value of the unaged samples. These

results were also summarized in Table 18 to 31 alongwith the results of tensile

strength, 300% modulus and elongation atbreak of the unaged samples.

140

CHAPTERIV

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CHAPTER IV PROCESSING BEHAVIOUR, CURE CHARACTERISTICS, STRESS …shodhganga.inflibnet.ac.in/bitstream/10603/36105/8/08... · 2018-07-02 · The delta Mooney viscosities were determined