Triple-shape memory properties of thermoplastic polyurethane/olefin block copolymer/polycaprolactone blends

Thermoplastic polyurethane (TPU)/olefin block copolymer (OBC)/polycaprolactone (PCL) blends (70/20/10 and 50/30/20) were melt-blended to form the first environmental OBC-based triple-shape memory polymer blends. In this work, PCL with low crystalline temperature (switching phase), OBC with medium crystalline temperature (switching phase), and TPU with high crystalline temperature (fixed phase) could form an alternative triple-shape memory polymer (TSMP). Two compatibilizers, OBC-g-glycidyl methacrylate (OBC-g-GMA) and dicumyl peroxide, were confirmed to show a synergistic effect in enhancing the compatibility further through the morphological observation. Crystallinity of both OBC and PCL in the blends with or without modification decreased in comparison with that of pure resin. For dual-shape behaviors, the shape fixing ratio (Rf) and shape recovery ratio (Rr) were up to 96.3% and 91.2% for the GMA and peroxide-modified blends (50/30/20). The higher amount of TPU didn't give higher recovery ratio, but instead slightly lower Rr due to the morphology difference. For triple-shape behaviors, both TPU/OBC/PCL blend compositions with or without GMA or peroxide modifications gave high R-f(C -> B) values in the first fixing stage, but slightly lower values R-f(B -> A) in the second fixing stage, especially for (70/20/10) case. On the other hand, a reverse trend was observed for two recovery stages. To enhance the R-f(B -> A) in the second fixing stage, higher deformation temperatures were considered, and a measurable increment on R-f(B -> A) was attained. Through this subtle adjustment on the temperature difference between high and low deformation temperatures, the theoretical multi-shape memory shape could be readily tailored to meet different applications.