Nacre-Inspired Polymeric Materials with Body Heat-Responsive Shape-Memory Effect, High Optical Transparence, and Balanced Mechanical Properties
Bingbing Zeng, Lihua Yang, Jingxian Qin, Yu Zheng, Shaoyun Guo
Abstract
In this work, inspired by the hierarchical architecture of nacre, we have fabricated poly(propylene carbonate) (PPC)/thermoplastic polyurethane (TPU) alternating multilayer films via layer-multiplying coextrusion. Based on the glass transition at around 37 °C of PPC, the multilayer films exhibited an outstanding body heat-responsive shape-memory effect (SME) with high shape fixation and recovery ratios (96.1 and 93.6%), much better than the conventional cocontinuous blend with the same compositions. It was revealed that the high phase continuity and abundantly two-dimensional interfaces both capable of promoting stress transferring and load distribution maximally contributed to the SME. Furthermore, the multilayer films showed a superior recovery stress storage capacity and the force generated by shape recovery allowed automatic expansion of the spiral in 37 °C water and efficient lifting of a load 880 times its weight. Different from the opacity of the blend, a high optical transparence was observed in the multilayers because of the parallel assembly of transparent PPC and TPU enabling light to directly pass through the films. Besides, the nacre-like films had layer debonding and layer stepwise breaking during stretching, resulting in a 90% increase in tensile strength, a 70% increase in elongation at break, and onefold improvement in yield stress, compared with those of the blend. Our approach paves a new way for developing bioinspired structural materials with excellent optical, mechanical, and shape-memory properties, which can be extended to different amorphous polymers and elastomers. Also, the materials presented herein have great potential in applications of biomedical devices and soft robotics.