Preparation and Characterization of Ethylene Vinyl-Acetate Copolymer/Silicone Blends with Excellent Two-Way Shape Memory Properties

Abstract

This study investigated the preparation of ethylene-vinyl acetate copolymer (EVA) and silicone rubber blends using a melt-blending method. EVA/Silicone-D blends were prepared by using peroxide (Dicumyl peroxide, DCP) as a crosslinking agent. The microstructure, thermal properties, and shape memory behavior were investigated for the EVA/Silicone-D blends. DCP not only could assist the crosslinking of EVA and silicone, but also increase the compatibility of blends. Silicone tended to endow the prepared EVA/silicone shape memory blends with high thermal stability, hydrophobicity, and recovery magnitude. The crystal orientation and crosslinking effects of EVA/Silicone-D blends played key roles in the shape memory behavior. Two-dimensional X-ray diffraction analysis revealed the increased crystal orientation with increasing loads. The one-way shape memory results demonstrated that both Rf (shape fixing ratio) and Rr (shape recovery ratio) values were above 97% after three consecutive shape memory cycles. From two-way shape memory results, it was observed that Ract, actuation magnitudes, contributed from the cooling-induced elongation increased with increasing loads and EVA contents. In addition, owing to this increased molecular orientation with increasing loads, the entropy-driven contribution relative to the overall actuation magnitudes increased accordingly. However, the shape memory response was hindered, when the load exceeded a critical value. With increasing silicone contents, the entropy-driven contribution decreased due to the reduced orientation degree at the tighter networks or increased crystalline EVA contents in the blends.