Switch segment and halloysite nanotube role in the phase separation behavior of shape-memory thermoplastic polyurethane

摘要

Thermoplastic polyurethane consists of hard and soft segments. The difference in glass transition temperature and thermodynamic incompatibility of these segments results in phase separation and shape memory behavior. In this study, the effect of molecular weight of polyol and the amount of nanoparticles on the phase separation and shape memory behavior of polyurethane nanocomposites were studied. Polyurethane was synthesized using poly(tetramethylene glycol) with molecular weights of 1000 and 2000 g/mol, hexamethylene diisocyanate, and 1,4-butanediol by step polymerization. The nanocomposites were synthesized through in situ method containing 1 and 2 wt% of nanoparticle. Phase separation and shape memory behaviors were studied using attenuated total reflectance-Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical thermal analysis, and atomic force microscopy analysis. The results indicated that higher molecular weight polyol with molecular weight of 2000 g mol(-1) shows higher phase separation than the lower molecular weight sample. Also, the addition of nanoparticles results in an increased phase separation due to the halloysite nanotubes tendency to the hard segment. The shape fixity ratio (R-f) and shape recovery ratio (R-r) were in the range of 90% to 100% in all of the synthesized samples. By increasing the nanoparticles content, the shape fixity and shape recovery parameters were increased and decreased, respectively. The study of shape memory behavior also showed that the higher the polyol molecular weight, the better the nanocomposite shape memory behavior.