Thermomechanical characterization of blends of poly (vinyl acetate) with semicrystalline polymers for shape memory applications

Shape memory effects of polymeric materials have gathered increased attention recently, prompted by an expanding range of potential end-use applications, especially for development of biomedical engineering tools. On the basis of rubber elasticity combined with vitrification or crystallization, many polymers exhibit shape memory, but with varying characteristics such as strain recovery rate, rate at which the new temporary state is fixed, and work capability during recovery. For high stiffness in the temporary form, a need exists for shape memory polymers with T_g greater than room temperature, but with tailored rubber modulus and elasticity derived from physical rather than chemical crosslinks. We have thus pursued the miscible polymer pair, poly(vinyl acetate) (PVAc) and semicrystalline poly(lactic acid) (PLA). Here, crystallization of PLA from a single liquid phase is controlled by the PVAc content, but resulting in a nearly invariant melting transition T _m ∼ 165 °C. Blending PLA with PVAc was found to reduce the crystallinity degree systematically, thus controlling the rubber modulus relevant to recovery work capability. This report gives preliminary results on the thermomechanical properties of such PLA/PVAc blends and the shape memory effects that result. The properties will be further explained in light of the underlying microstructure characterized by x-ray scattering.