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Dynamic Vulcanization of HDPE/EVA Blend Using Silane

Dynamic vulcanization of high-density polyethylene and ethylene vinyl acetate (HDPE/EVA) blends (50/50 wt%) in the mixing chamber of a torque rheometer was investigated. EVA was selectively cross-linked within the HDPE phase by transesterification reaction between ester groups of the EVA and alkoxysilane groups of tetrapropoxysilane, catalyzed by dibutyl tin oxide. Torque level and temperature in the torque rheometer chamber were monitored to follow the evolution of the EVA cross-linking during dynamic vulcanization. The degree of cross-linking of EVA in the HDPE/EVA materials was estimated by the gel content (insoluble EVA fraction). The changes in the HDPE/EVA phase morphology caused by different degrees of EVA cross-linking were investigated by scanning electron microscopy. Melt-state linear viscoelastic properties of the materials were investigated by small amplitude oscillatory shear rheometry. For the composition and processing conditions adopted in this study, the HDPE/EVA showed a coarse co-continuous phase morphology, with large EVA domains interconnected with HDPE domains. Following the dynamic vulcanization, this changed to a more refined co-continuous morphology. The linear viscoelastic relaxation behavior of dynamically vulcanized HDPE/EVA materials suggests the existence of a percolated network structure of high viscous and elastic EVA domains interconnected with thermoplastic HDPE domains.