Effect of cross-links which occur during continuous chemical stress-relaxation

Abstract Temperature dependence of the chemical stress relaxation in oxygen of a series of natural rubber vulcanizates, extracted and unextracted, with the same pretreatment was investigated. Decrease of tension to about 50 per cent of the original was followed, using the half lives as a measure of velocity. The following observations were made: 1) Relaxation velocity of unextracted thiuram vulcanizates increases with increasing sulfur content; the activation energy decreases. 2) The relaxation velocities of extracted thiuram vulcanizates are independent of sulfur content of the mixtures and significantly greater than those of unextracted samples. This is caused by the loss of dithiocarbamate on extraction. 3) Other natural rubber vulcanizates (dithiocarbamate, MBT and peroxide vulcanizates) give the same relaxation half lives after extraction. 4) The relative importance of random scission and crosslink scission was discussed.

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Chemical Stress Relaxation of NR Networks Prepared in the Swollen State

Rubber Chemistry and Technology ◽

10.5254/1.3538216 ◽

1986 ◽

Vol 59 (4) ◽

pp. 541-550 ◽

Cited By ~ 1

Author(s):

Kyung-Do Suh ◽

Hidetoshi Oikawa ◽

Kenkichi Murakami

Keyword(s):

Stress Relaxation ◽

Network Structure ◽

Three Dimensional ◽

Polymer Chains ◽

Chemical Stress ◽

Network Chain ◽

Crosslinking Process ◽

Dimensional Network ◽

Chemical Relaxation ◽

The Difference

Abstract From the experimental results of the present investigation, it is apparent that two kinds of networks which have a different three-dimensional network structure give quite different behavior of chemical stress relaxation, even if both networks have the same network chain density. The difference in three-dimensional network structure for the two kinds of rubber arises from the degree of entanglement, which changes with the concentration of the polymer chains prior to the crosslinking process. The direct cause of chemical relaxation is due to the scission of network chains by degradation, whereas the total relaxation is caused by the change of geometrical conformation of network chains. This then casts doubt on the basic concept of chemorheology which is represented by Equation 2.

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Longitudinal Cracking in a Carbon Black Filled Natural Rubber Vulcanizate during Chemical Stress Relaxation

Rubber Chemistry and Technology ◽

10.5254/1.3538477 ◽

1998 ◽

Vol 71 (2) ◽

pp. 157-167 ◽

Cited By ~ 5

Author(s):

G. R. Hamed ◽

J. Zhao

Keyword(s):

Stress Relaxation ◽

Carbon Black ◽

Natural Rubber ◽

Longitudinal Crack ◽

Chemical Stress ◽

Loading Direction ◽

Rubber Vulcanizate ◽

Edge Cracks ◽

Forced Air ◽

Oxidative Attack

Abstract Thin specimens of a black-filled, natural rubber vulcanizate have been held in uniaxial tension at 72°C and 200% elongation in a forced air oven. After substantial oxidative attack (inferred from stress relaxation), small edge cracks formed. Initially, these cracks grew perpendicular to the loading direction, but, upon reaching about 0.1 mm in depth, longitudinal crack growth commenced and fracture progressed by a kind of 0°-peel process with “splitting-off” of successive strands of rubber. This phenomenon is attributed to anisotropy in strength caused both by straining and by oxidative attack.

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