Synthesis and characterization of sisal fibre polyurethane network cross-linked with triple-shape memory properties

In this paper, a thermo-responsive network shape-memory polymer (SMP) which has high elasticity, triple shape-memory properties and rapid shape recovery effects was reported. This new type of shape-memory polyurethane network (denoted SF-SMPs) was successfully synthesized by chemically cross-linking cellulose sisal fibre (SF) with polycaprolactone (PCL). The structures, morphology, and shape-memory properties of the SF-SMPs have been carefully investigated. The results demonstrate that the SF-SMPs form micro-phase separation structures consisting of a semi-crystalline PCL soft phase and an amorphous hard phase. Different contents of polyester sisal fibre (PSF) influence the crystallinity of the PCL soft phases. The cross-linking structures provided a stable network, high elasticity and good thermal stability to the SF-SMPs. Thus, all of the SF-SMPs exhibited triple shape-memory properties, and recover to the original shape immediately. Especially, the sample with the lowest content of PSF (P1) exhibited high (over 91%) shape fixity and 90% shape recovery. The first step of strain recovery is associated with the melting transition of soft segment crystals of the polyurethane matrix, and the second step of strain recovery results from the glass transition of the hard segment. This work demonstrates new cellulose cross-linking structures of SMPs, which will have many applications in future smart science.