Polylactide-based thermoplastic shape memory polymer nanocomposites

The effect of nano-SiO2 on the mechanical and shape memory (SM) properties of polylactide-based copolyester (PLAE) with glass transition temperature (Tg) below body temperature was investigated. Modulated differential scanning calorimetry (MDSC) experiment was utilized to study the glass transition, crystallization and melting of PLAE. Conventional DSC was used to investigate the crystallinity of PLAE and its nanocomposites (PLAEs). Field emission scanning electron microscope (FESEM) and wide-angle X-ray diffraction (WAXD) were used to characterize the microstructures and crystal structures of PLAEs. Tensile tests were carried out to investigate the mechanical properties at room temperature and elevated temperature. Dynamic mechanical properties (DMA) and stress relaxation experiments were used to study the dynamic mechanical properties and stress relaxation behaviors of PLAEs. SM properties were characterized by various methods, such as elevated temperature tensile experiments, cyclic thermal mechanical tests and physical shape recovery tests. The results show that PLAE and its nanocomposites with low SiO2 loading content (1 and 3 wt.%) possess good shape fixity and recovery ratio with a trigger temperature around body temperature. The addition of nano-SiO2 causes the crystallinity reduction of PLA chains and chain segments. For nanocomposites with better dispersion of nano-SiO2 particles (1 and 3 wt.%), higher elastic modulus can be attributed to mechanical reinforcement, resulting in better SM properties. PLAEs have potential applications in biomedical areas such as smart punctual plugs because of the low trigger temperature.