Vulcanization of cis- and trans-polyisoprene and their blends: crystallization characteristics and properties

Crystallization characteristics and properties of cis-1,4-polyisoprene (natural rubber––NR), trans-1,4-polyisoprene (TPI) and their blends were investigated. It was obvious that sulfur-crosslink inhibited cold crystallization but not stretch-induced crystallization of NR vulcanizate and slightly reduced both cold crystallization and stretch-induced crystallization of TPI. Carbon–carbon crosslink was found to reduce only crystallinity of both cold-crystallized NR and TPI vulcanizates. Thus, the strength of the vulcanized samples was dependent on their crystallization behaviors in which higher degree of crystallinity introduced higher tensile strength. The variation of TPI content in the vulcanized blends could cause lower tensile strength and modulus. Accordingly, it suggests the lack of covulcanization which is indicated by a considerable deterioration of the properties.