Analysis of the thermogenesis mechanism of natural rubber under high speed strain
This work highlights the relationship of crosslink density, entanglement points and various sulfide crosslinks with the thermogenesis properties of natural rubber (NR). The impact of cross-link and entanglement on thermogenesis properties was evaluated by heat build-up test, swelling behavior, statistical thermodynamic calculation, and classic viscoelastic theory. It was found that cross-link and entanglement points have “pinning” effect to the rubber chain, thus remarkably restricting the motion of the rubber chain and reducing thermogenesis. Besides, the effects of various sulfide crosslinks and cross-link length on thermogenesis were compared and discussed varying the sulfur vulcanization system. It was found that the semi-effective vulcanization system using N-cyclohexyl-2-benzothiazolesulfenamide (CZ) and 2-Mercaptobenzothiazole (M) has the lowest thermogenesis (bottom temperature rise is 7.5°C, middle is 18.7°C), which on account of combined short crosslink length with high rigid rubber chain (crosslink network dominated by mono- and disulfides). As a result, the deformation degree of the rubber chain during curl up-extension and the thermogenesis are further reduced. Finally, a combination of natural film coagulation and semi-effective vulcanization system was used to prepare a low thermogenesis NR, in which bottom and middle temperature rise were only 5.0°C and 14.1°C, respectively.
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