Material behaviourCrystallization controlled shape memory behaviors of dynamically vulcanized poly(l-lactide)/poly(ethylene vinyl acetate) blends

In this work, dynamically vulcanized poly(l-lactide) (PLLA)/poly(ethylene vinyl acetate) (EVA) blends with different compositions were prepared. The morphologies, rheological properties and the crystalline structures of the samples were systematically investigated. The results demonstrated that with the increase of the PLLA component in the dynamically vulcanized samples, the blend morphologies varied from sea-island structure to cocontinuous structure, and then changed to sea-island structure again. A chemically cross-linked structure was introduced into the EVA component. Annealing treatment did not influence the crystallization of the EVA component, but it greatly promoted the cold crystallization of the PLLA component and consequently, a large amount of PLLA crystallites were emerged in the PLLA component. The shape memory behaviors of the dynamically vulcanized samples were detected, and the results showed that the samples exhibited good shape memory behaviors, which were greatly dependent upon the blend compositions and the annealing treatment. Samples with high content of EVA exhibited relatively higher shape fixity ratio (Rf) and shape recovery ratio (Rr). Although annealing treatment induced the decrease of Rf, largely enhanced Rr was obtained for the annealed samples, especially at relatively longer annealing time. The mechanisms for the enhanced shape memory effects of the annealed samples were then analyzed.