Thermal and electroactive shape memory behaviors of poly(l-lactide)/thermoplastic polyurethane blend induced by carbon nanotubes

Abstract

Poly(L-lactide) (PLLA) based shape memory materials (SMP) recently attracted much attention due to their great potential application in biomedical materials. In this work, we introduced carbon nanotubes (CNTs) into a blend of PLLA/thermoplastic polyurethane (TPU) through a simple melt compounding processing to develop a new kind of PLLA SMP. The effects of CNTs on morphologies of blend composites, the selective location of CNTs, the dynamic mechanical properties of samples and the microstructure of CNTs in the blend composites were characterized using a scanning electron microscope (SEM), a transmission electron microscope (TEM) and rheological measurements, respectively. The results demonstrated that CNTs selectively located in the TPU component and induced apparent change of the blend composite morphology. High content of CNTs also formed the percolated network structure in the material, which resulted in the dramatic decrease of electrical resistivity. The shape memory behaviors of the samples were comparatively investigated in two different conditions, i.e. thermally activated and electrically activated conditions. It was demonstrated that CNTs prevents the thermally activated shape recovery process of the blend composites, especially when CNTs formed the percolated network structure. However, with the aid of electrical actuation, largely accelerated shape recovery process and enhanced degree of shape recovery were achieved for the blend composites containing 5 wt% CNTs, especially at relatively low recovery temperatures. The main mechanism was attributed to the largely enhanced electrical conductivity, which provides more Joule heating in the sample. This work provides an alternative way to develop PLLA-based shape memory materials through a simple melt compounding processing.