Development of liquid-crystalline shape-memory polyurethane composites based on polyurethane with semi-crystalline reversible phase and hexadecyloxybenzoic acid for self-healing applications

Shape memory materials and self-healing materials have attracted considerable attention in recent years. This paper reports the development of a liquid-crystalline shape-memory-polyurethane (LC-SMPU) composite based on SMPU and hexadecyloxybenzoic acid (HOBA) for self-healing applications. The results demonstrate that HOBA is physically mixed with SMPU resulting in a semi-crystalline reversible phase and forming LC-SMPU composites. The two-phase separated structure comprises an SMPU matrix and a HOBA phase. The HOBA phase exhibits a reversible nematic phase within a temperature range of 101-130 degrees C, while the SMPU matrix acts as a stable polymeric film for various applications. Both the semi-crystalline soft phase of the SMPU matrix and the HOBA crystalline phase can be used to trigger shape memory effects. The LC-SMPU composites display not only triple-shape memory behaviours but also self-healing behaviours due to the heating-induced bleeding behaviour of HOBA in the liquid crystalline state and their subsequent recrystallisation upon cooling.