Influence of moisture on microwave-induced shape memory thermoplastic polyurethane/graphene nanoplatelets composite

In our present research, we investigated that the moisture played an important role in microwave-induced (MV-induced) shape memory thermoplastic polyurethane (PU)/Graphene nanoplatelets (GNPs) composite. The tests were carried out for pure thermoplastic polyurethane (PU) and a composite having 1 phr GNPs in the PU matrix (namely 1 GPU). When samples exposed in moisture (immersed in water) for long days the thermo-mechanical and shape memory properties such as Tensile strength, glass transition temperature, storage modulus, stretch and recovery strength were decreased. The reason behind these phenomena was the amino and carbonyl groups of PU matrix interact with the water molecules and improved mobility of polymer chain. Glass transition temperature (Tg) was analysed by using Dynamic Mechanical Analyser (DMA) and DSC (Differential Scanning Calorimetric) curves. Further, we found that the PU specimen had no shape recovery during MV irradiations without moisture exposed sample but when moisture exposed PU sample was tested for shape recovery under MV-irradiation it showed shape recovery. With increasing water immersion time (Days) of the PU and 1 GPU samples the MV-induced shape recovery was increased. Because the absorbed water molecules in samples act as a dielectric note heating source for MV irradiations. Due to the moisture, the glass transition temperature reduced to near about 40°C (10 days water immersion samples). So, its novel approach which may be treated as a self-responsive shape memory polymer components when exposed long days in moisture. Shape memory polymer specimens having such unique behaviour (shape recovery without external stimuli) have vital applications for fast actuating, wireless, remote, sensors and actuators.