Influence of Sulphur Crosslink Distribution on Strain-induced Crystallization and Strength of NR Vulcanizates

Watcharin Sainumsai, Krisda Suchiva, Shigeyuki Toki


The present work is concerned with the study of the effect of the crosslink distribution of accelerated sulphur-vulcanized natural rubber (NR) on tensile properties and strain-induced crystallization (SIC) of NR vulcanizate. The study was made by making assumption that rapid vulcanization reaction would result in a more random network or crosslink distribution and vice versa. Four accelerator types, Guanidine (DPG), Benzothiazole (MBT), Sulphenamide (CBS) and Thiuram (TMTD) were studied at the same level of the crosslink density. It was found that the strains at which SIC began to occur do not change with the cure rate index (CRI) but the rate of SIC and % crystallinity show increasing trends with increasing CRI. Thus, if the assumption made is correct, it may be concluded increasing the heterogeneity of the network facilitated the formation of strain-induced crystallization, resulting in increased rate of SIC and also the crystalline fraction formed. Tensile strength values showed increasing trend with increasing cure rate, therefore, the randomness of the distribution of the sulphur crosslinks.

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