SHAPE MEMORY BEHAVIOR OF CARBON NANOTUBE FILLED SEGMENTED POLYURETHANE COMPOSITES UNDER VARIABLE STRESSES

Abstract

ABSTRACT Composites of the segmented polyurethane (SPU) elastomer with different loadings of multiwall carbon nanotubes (MWCNTs) were prepared. Atomic force microscopy and X-ray diffraction were used to study the surface topography and structural aspects of the samples. Thermogravimetric analysis was performed in order to estimate the thermal stability of the composite samples. Two sets of cyclic thermomechanical experiments, both at sub-ambient conditions, were conducted for the evaluation of shape memory performance of the samples using modulated thermomechanical analysis. The first set of experiments was designed to estimate the shape memory performance under stress free or unconstraint conditions, while the second set was planned for the constraint conditions by application of variable stresses. The experimental parameters were so chosen that differences in shape memory response of matrix and composites were clearly distinguished and demonstrated. It was found that MWCNTs strongly affect the shape memory performance of the SPU and reduce the recovery speed under unconstraint conditions. While under constraint conditions, the extent of recovery and recovery speed of composites was found to depend on the applied load and nanotube concentration in the composites.