Injection molding of novel polylactic acid/thermoplastic polyurethane (PLA/TPU) blends with shape-memory behavior

This paper presents the development of shape-memory polymers (SMPs) based on amorphous polylactic acid (PLA) and thermoplastic polyurethane (TPU) blends. PLA was melt blended with TPU at weight ratios of 20, 30, and 40%, and then injection molded and hot compressed into permanent shapes. Unlike most of the existing SMPs, all three PLA/TPU blends could be formed (via bending, folding, compression, stretching, etc.) into temporary shapes at room temperature without an extra heating step. Upon heating to above the glass transition temperature of PLA (at 70 °C), the deformed parts regained their original shapes fairly quickly. Differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) tests showed that PLA and TPU were immiscible. The dynamic mechanical analyzer (DMA) data and the mechanical tests, including tensile, compression, and flexural tests, showed that the PLA/TPU with the 80/20 weight ratio had the best shape-memory properties, even if it was somewhat brittle. The 70/30 PLA/TPU blend had the best combination of shape recovery and mechanical properties. The shape memory mechanisms for these types of SMPs are discussed here in detail.