Molecular-level modeling and experimental investigation into the high performance nature and low hysteresis of thermoplastic polyurethane/multi-walled carbon nanotube nanocomposites

Multi-walled carbon nanotube (MWCNT) reinforced thermoplastic polyurethane (TPU) nanocomposites were prepared using solution casting techniques and exhibited better thermal stability and improved mechanical performance. Scanning electron microscopy indicated a homogeneous dispersion of the carbon nanotubes (CNT) within the polymeric matrix at low filler loadings and a cluster formation at higher loadings. Stress-strain of the MWCNT-TPU nanocomposites showed optimum performance and lowest hysteresis for the 0.5% MWCNT nanocomposites due to the confinement of the TPU chains between the large number of the nanofiller particles. Molecular modeling showed that low MWCNTs content caused the moduli to increase due to the drastic drop in the number of configurational states accessible to the chains, which resulted in a significant decrease in the entropy of the chains and a corresponding increase in the elastic moduli. Higher MWCNTs loadings caused a restriction in the TPU movement as indicated by its mean-square displacements. The enthalpy of mixing the TPU with MWCNTs was estimated and confirmed the repulsive interactions between the nanoparticles (MWCNT) and the polymeric chains, which created an additional excluded volume that the TPU segments were not allowed to occupy and thus forcing the conformational characteristics of the polymeric chains to deviate away from those of the bulk chains.