Thermally cross-linked and sulphur-cured soft TPVs based on S-EB-S and S-SBR blends

Abstract

Thermoplastic vulcanizate (TPV) is a specific group of elastomer alloy (EA), in which the rubber phase is selectively cross-linked by dynamic vulcanization and dispersed in the presence of a molten thermoplastic phase under intensive mixing. The development of binary blends, utilizing melt-blending technology of poly[styrene-b-(ethylene-co-butylene)-b-styrene] triblock copolymer (S-EB-S) and solution-polymerized styrene butadiene rubber (S-SBR) were investigated, as were the characteristic differences of these blends compared to other soft TPVs. Design of experiments (DOE) has been adopted to execute the optimum processing conditions in terms of mixing temperature, rotor speed and time of mixing by utilizing the Taguchi's L₉ methodology, and the measure of confidence has been accomplished using standard statistical technique of the analysis of variance (ANOVA). A novel, thermally cross-linked (TCL) TPV has emerged as a by-product of DOE. Thereafter, meticulous analysis and characterization have been conducted to understand the newly developed TPV system. Furthermore, both semi-efficient vulcanizate (SEV) and efficient vulcanizate (EV) sulphur-based curing systems have been designed by adopting the optimized processing conditions to cure the rubber phase, and a comparative study has been organized among the TCL, SEV and EV systems. Dynamic mechanical analysis (DMA) has revealed reduced rolling resistance for EV-cured TPVs compared to SEV- and TCL-cured systems, while still maintaining good wet grip by comparing the lost tangent values. Theoretical calculation of viscoelastic properties by adopting the Kerner model predicts primarily co-continuous morphology for the TPV systems, which is in good accordance with the experimental and morphological observations.