Preparation And Properties Of Polyester-based Shape Memory Materials

Shape memory materials are intelligent materials that can respond to external stimuli.Shape memory polymers(SMPs)exhibit high shape memory response rates,lightweight,low cost,and ease of processing,so they are widely used in biomedicine,sensors,smart textiles,etc.In this study,a series of polycaprolactone(PCL)/thermoplastic polyurethane(TPU)SMPs were prepared by the methods of melt blending and in situ polymerization.(1)PCL/TPU blends were prepared by the melt blending method,and the effect of TPU content on the shape memory properties of PCL/TPU blends was investigated.The results showed that with the increase of TPU content,the shape recovery rate of the blends increased since the main contribution of the shape recovery rate of the blends was the soft segment in TPU,while the shape fixation rate gradually decreased.When the TPU content was 10 wt%,the blend presented the best shape memory performance,with a shape recovery rate of 78%and a shape fixation rate of 75%.As seen from the morphology of the blends,with the increase of TPU content,the phase separation degree of the blends gradually increased,resulting in a decrease in the shape fixation rate and mechanical properties of the blends.(2)PCL/TPU copolymers with different TPU contents were prepared by in situ polymerization.The ~1H-NMR analysis showed that caprolactone copolymerized with TPU during the polymerization,forming a PCL/TPU copolymer.The crystalline portion of PCL and the hard segment of TPU acted as stationary phases in the copolymer,the amorphous portion of PCL and the soft segment of TPU acted as reversible phases,and the melting transition of PCL crystals acted as a deformation switch for PCL/TPU shape memory copolymers.The results of shape memory testing showed that the shape memory properties of the copolymer were significantly improved compared to those of PCL/TPU blends prepared by melt blending.The introduction of TPU increased the elastic potential energy of the copolymer,thereby improving the ability of the material to store elastic deformation energy,and the ability to recover deformation after stress removal was also improved.Therefore,the shape recovery rate of the copolymer was higher than that of pure PCL.When the TPU content was 5 wt%,the shape memory performance of the copolymer was the best,with a shape recovery rate of 83.3%and a shape fixation rate of 100%.As the TPU content increased,the storage modulus decreased.Since the driving force for shape recovery depends on the storage modulus,the shape recovery rate of the copolymer decreased.(3)To improve the heat response speed of shape memory of PCL/TPU copolymers,boron nitride(BN)was added to the PCL/TPU copolymer with a TPU content of 10wt%,and PCL/TPU/BN composites were prepared by in situ polymerization.The effects of BN treated by different modification methods on the shape memory properties of PCL/TPU copolymer were investigated.Compared with the PCL/TPU copolymer,BN fillers improved the thermal conductivity of the composite,resulting in a significant increase in the speed of shape recovery.Besides,the composite prepared by adding hydroxylated BN exhibited the fastest shape recovery rate,doubling compared to the PCL/TPU copolymer,with a shape recovery rate of 76.1%and a shape fixation rate of 100%.