Preparation of electroactive shape memory polyurethane/graphene nanocomposites and investigation of relationship between rheology, morphology and electrical properties

Abstract In this study, electroactive shape-memory polyurethane/graphene nanosheets nanocomposites were prepared. Shape-memory polyurethane (SMPU) was synthesized from polycaprolactone-diols (PCL-diols) with a molecular weight of 4000 g/mol, hexamethylene diisocyanate (HDI), and 1,4-butanediol (BDO) with a molar ratio of 5 (HDI)/4 (BDO)/1 (PCL) via solution polymerization. Nanocomposites were prepared from neat SMPU and mono-layered fluffy graphene nanosheets through solution mixing method. Electrical resistivity test was employed to investigate the electrical conductivity threshold of the nanocomposites. The results showed that the nanocomposites with graphene content higher than 1.5 wt% had a reasonable conductivity to respond to the electrical current. Fourier transform infrared (FTIR) spectroscopy confirmed the interaction between graphene nanosheets and SMPU chains by variation of hydrogen bonding content. Differential scanning calorimetry (DSC) thermograms and X-ray diffraction (XRD) patterns showed that the crystalline structures of SMPU have been changed by incorporating of graphene nanosheets. Rheological examination showed that the percolation threshold to create a graphene network structure was 1.5 wt%. Field emission scanning electron microscopy (FE-SEM) images revealed percolation of graphene nanosheets in the electrically conductive nanocomposites. Mechanical and shape-memory tests revealed that the mechanical properties and shape-memory parameters were improved by the addition of graphene nanosheets. The changes in surface temperature under the examination with voltage of 75 V indicated that the temperature of the electrically conductive samples was significantly increased by flowing of electrical current. This increase in temperature led responsivity to the electrical current in SMPU nanocomposites containing 2 and 3 wt% graphene nanosheets.