Preparation, Characterization And Preliminary Study For The Application Of Shape Memory Polyurethane-silica Hybrids

Shape memory polyurethane (SMPU) is wildly concerned as its shape memory characteristics, good elastic resilience and shock resistance. However, pure SMPU has some deficiency such as strength and elastic modulus is not high enough, low thermal resistance, and biggish coefficient of thermal expansion around the glass transition temperature (Tg), which affect the effective use of the unique property. In this study, nano-silica was employed in SMPU to prepare SMPU-silica hybrids, and a characterization to the structure and properties of hybrids was executed, which was expected to improve the mechanical property, meanwhile, enhance the thermal resistance property and stabilize the coefficient of linear thermal expansion of SMPU around Tg. Based on the above, a preliminary study for the application of the hybrids was executed.According to the research on the preparing technique of SMPU-silica hybrids, a method of preparing SMPU-silica hybrids in situ, which the catalyst of solid acid of p-toluenesulfonic acid (PTSA) and the water in air as the hydrolysis source was used in the SMPU-TEOS sol-gel system without additive water was put forward, and the structure of the hybrids was characterized. The results show that, SMPU-silica hybrids prepared with above method exhibited good dispersion, 20-50nm of silica particle diameter and good interfacial bonding property between SMPU and silica, which can provide a novel approach for the preparation of SMPU-silica hybrids.According to the characterization to the mechanical property, thermal property and shape memory property of hybrids, the results show that, the addition of silica can enhance the Tg effectively, and the Tg of the hybrid with 7.5 wt% silica is 10 oC higher than that of pure SMPU. The coefficient of thermal expansion of SMPU developed by silica around Tg reduced, improving the stability of coefficient of thermal expansion obviously. Young's modulus and tensile strength of hybrids enhanced significantly compared with pure SMPU, and showed an optimum for the hybrid with 6 wt% silica. The ratio of shape fixity (Rf (N)) of hybrids is higher than that of pure SMPU obviously. The ratio of total shape recovery (Rr.tol) of hybrids decreases with the increase of cycle numbers and silica content, and Rr.tol tends to be a stable value after the second cycle. It can be obtained a good ratio of individual shape recovery (Rr (N)) equal to 100% after several cycles.A preliminary study for the application was executed based on the characterization to the structure and property of SMPU-silica hybrids. Aramid fiber reinforced SMPU-silica composites were prepared with the matrix of SMPU-silica hybrid, which was expected to improve the interfacial property of composites. The results show that, the interfacial shear strength (IFSS) of aramid fiber/SMPU-silica composites increases obviously, as the decrease of the coefficient of thermal expansion around Tg by the addition of silica and so on. It provides an important basis for the application of SMPU in aramid fiber reinforced composites.