The morphology, properties, and shape memory behavior of polylactic acid/thermoplastic polyurethane blends

Biodegradable polylactic acid (PLA) was compounded with thermoplastic polyurethane (TPU) by twin-screw extrusion at weight ratios of 90/10, 80/20, 70/30, and 60/40. The blends were investigated based on their phase morphology, thermal and mechanical properties, and shape memory properties. The tensile results showed that PLA was successfully toughened by TPU. When the TPU content was 40%, the elongation-at-break increased to 400%. The SEM morphology showed that TPU was dispersed uniformly in the PLA matrix; DMA and DSC results indicated that the two polymers were immiscible. Most interestingly, it was found that the blends exhibited a shape memory behavior and, unlike most of the existing shape memory polymers (SMPs), the PLA/TPU blends could be deformed at room temperature without an extra heating and cooling step. During the deformation process, TPU acted as a toughening agent that prevented the PLA/TPU blends from breaking; thus, the temporary shape could be kept and internal stress was stored in the blends. Upon heating to above the glass transition temperature of PLA (about 60°C), the deformed parts regained their original shapes quickly along with the release of the stress.