Shape Memory Properties of Melt-Blended Olefin Block Copolymer (OBC)/Ethylene-Vinyl Acetate Blends

Abstract

The completely crosslinked shape memory polymer blends (SMPs) traditionally suffer from recycling problems due to their network structure. In this paper we describe the thermal, mechanical, and shape memory behavior of physical blends of OBC (Olefin block copolymer) and EVA (Ethylene-vinyl acetate copolymer), with and without modification of one or both of the components, prepared using a melt-blending method. These behaviors of the modified blends, based on maleated OBC (OBC-g-MA) and/or vinyltriethoxysilane (VTEOS) modified EVA, included OBC/EVA-g-VTEOS, OBC-g-MA/EVA, and OBC-g-MA/EVA-g-VTEOS blends; they were investigated to compare with the OBC/EVA blend. The SEM (scanning electron microscopy) observations showed that the compatibility of the silane and maleic anhydride modified OBC/EVA blends were better than that of the unmodified OBC/EVA blend. The crystallization temperatures of OBC and EVA in the modified blends were higher than those in the neat blend. The OBC-g-MA/EVA-g-VTEOS blend had the highest modulus and thermal stability of all investigated blend systems due to the numerous interactions between maleic anhydride and silane. The shape memory performance, as defined by the shape fixity ratio (Rf) and shape recovery ratio (Rr), was higher for the modified blends of one or both of the modified components than that for the OBC/EVA blend. These modified blends were readily reprocessible, like thermoplastic vulcanizates, and still retained shape memory behavior, in contrast with the fully crosslinked shape memory polymer blends; thus they were also improved in terms of the environmental aspects of processing.