Functionalization of multi-walled carbon nanotube and its effect on shape memory behavior of nanocomposite based on thermoplastic polyurethane/polyvinyl chloride/multi-walled carbon nanotube (TPU/PVC/MWCNT)

Nanocomposites based on thermoplastic polyurethane/polyvinyl chloride/multi-walled carbon nanotubes were prepared by a solution method and their shape memory properties were studied. The blend ratios were 70/30, 60/40, and 50/50 (w/w) of thermoplastic elastomer polyurethane/polyvinyl chloride. To improve the dispersion of multi-walled carbon nanotubes, at 0.5% and 1% (wt), in polymer matrices, three-step chemical modifications were performed, including oxidation, chlorination and grafting of poly (ɛ-caprolactone) diol. The occurrence of surface modifications in MWCNTs was monitored using Fourier transform infrared spectroscopy, elemental analysis, scanning electron microscopy and thermal gravimetric analysis techniques. SEM micrographs revealed a good dispersion of MWCNTs in the polymer matrix due to better matrix-filler interactions compared to filler–filler interactions. The results showed that the main indices of shape memory behavior (shape fixity and shape recovery) of nanocomposite samples were affected by the polymer blend ratio, nanoparticle concentration and surface modification. Increasing the content of polyvinyl chloride led to reduced shape fixity and shape recovery, which was attributed to the lack of rigid structural nature of polyvinyl chloride. The presence of nanoparticles contributed to enhanced shape fixity and weaker shape recovery. This can be explained by lower polymer chain mobility in the presence of multi-walled carbon nanotubes. The reduction in chain mobility in nanocomposites reinforced by surface-modified multi-walled carbon nanotubes was more significant due to higher distribution efficiency of nano-scale fillers in the polymer matrix.