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The volume of natural rubber vulcanizates varied slightly during stretching. Hydrostatic weighing method was adopted in this study to study the volume change. By measuring the volume change of natural rubber compounds filled with different grades and different loadings of carbon black during extension, the corresponding volume variation-elongation (ΔV/V-ε) curves were created, and the differences of ΔV/V-ε curves among different carbon black compounds were discussed. The stress differences between different samples were normalized and the ΔV/(Vσ)-ε curves were plotted. Scanning electron microscope was utilized to observe the emergence and variation process of cavities in various stretched states. X-ray diffraction was used to explore the change of crystallinity of the rubber after stretching to a certain elongation. Based on the experimental results, the damage at the filler-rubber matrix interface and within the fillers agglomerates would be discussed.

The effect of main chain modification during reversion on strain-induced crystallization (SIC) of unfilled natural rubber (NR) and synthetic polyisoprene rubber (IR) cured with a conventional vulcanization system has been investigated. To eliminate the interference of crosslink density, vulcanizates were prepared using different amounts of curatives, chosen to give mainly monosulfidic or carbon-carbon crosslinks, having similar crosslink densities to the conventional compound at different states of reversion. Crystallinity was characterized by the degree of stress softening, and the contents of trans-methine were qualitatively and quantitatively analyzed by Fourier transform infrared spectroscopy. It was found that crosslink density exerts much greater influence on crystallinity than crosslink structure. At the same crosslink density, SIC of NR vulcanizates after reversion is lower than that of samples cured with tetramethylthiuram disulfide or dicumyl peroxid to the optimum cure state, which might be attributed to molecular main chain modification during reversion. NR was found to have better reversion resistance than IR.

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