Results on IR and SBR samples

To confirm our interpretation of the stress-optical diagrams, additional experiments were conducted on the samples prepared from synthetic cis-1,4-polyisoprene (IR) and copolymer of styrene and butadiene (SBR).

The following results support our interpretation.

1

Recipes of rubber samples

2

aNatural Rubber, RSS #1 from MalaysiabN-cyclohexyl-2-benzothiazole sulfenamide, curing temperature with sulfur 140℃

Sample code

NRa (part)

Stearic acid (part)

Active ZnO (part)

CBSb (part)

Sulfur (part)

Total (part)

Curing time (min)

Network chain density ×104 (mol/cm3)

NR1 100 2 1 3 4.5 110.5 10 2.65

NR3 100 2 1 1.5 2.25 106.75 12 2.28

NR5 100 2 1 0.75 1.125 104.88 17 1.48

Sample code

IRa (part)

Stearic acid (part)

Active ZnO (part)

CBSb (part)

Sulfur (part)

Total (part)

Curing time (min)

Network chain density ×104 (mol/cm3)

IR3 100 2 1 1.5 2.25 106.75 24 1.18

aSynthetic cis-1,4-polyisoprene, IR2200 from JSRbN-cyclohexyl-2-benzothiazole sulfenamide, curing temperature with sulfur 140℃

Sample code

SBRa (part)

Stearic acid (part)

Active ZnO (part)

CBSb (part)

Sulfur (part)

Total (part)

Curing time (min)

Network chain density ×104 (mol/cm3)

SBR0 100 2 1 1 1.75 105.75 60 2.35

aCopolymer of styrene and butadiene, SBR1502bN-cyclohexyl-2-benzothiazole sulfenamide, curing temperature with sulfur 150℃

Fast crystallization

Slow crystallization

Do not crystallize

Stress-optical diagrams of SBR

y = 0.0032x

00.0020.0040.0060.0080.01

0.0120.0140.0160.0180.02

0 2 4 6

Δn

True stress (MPa)

SBR

Slow expansion (10mm/min)C = 3.2×10-9 Pa-1 for SBR1502Strain ratio at fracture: ca. 4.1

C. A. Berglund, J. Polym. Sci., Polym. Phy. Ed., 15, 2037 (1977).

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0 2 4 6

Δn

True stress (MPa)

SBR0

x4

x3.5

x3

Gaussian

fracture

Fast expansion (1000mm/min) and subsequent holding indicated in the legend

The “hooks” sloped down to the left because of the absence of crystallinity.

4

00.0050.01

0.0150.02

0.0250.03

0.0350.04

0.0450.05

0 10 20 30 40

Δn

True stress (MPa)

X5NR1NR3NR5IR3Gaussian

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0 5 10

fracture

Slow crystallization of IR

0

0.2

0.4

0.6

0.8

1

1.2

0.1 1 10 100 1000 10000

No

rma

lize

d s

tre

ss

Elapsed time (sec)

X5

NR1NR3NR5IR3

Because of the slower crystallization rate of IR, the “hook” is smaller than those of NR samples. The rate of stress relaxation of the IR sample is also slower.