Influence of interface interaction on thermal, mechanical and conducting properties of segmented poly (azo-urethane)/carbon nanotube composites

In this research work, solution dispersion technique was employed for the preparation of segmented poly (azo-urethane)/multi-walled carbon nanotube (SPAU/MWCNT) nanocomposites whereas the polyurethane was obtained using single-step procedure. The carboxylated nanotube-based non-compatiblized SPAU/MWCNT and acid chloride functionalized MWCNT-based compatiblized systems were prepared. Afterwards, the hydroxyl end-terminated polyurethane was grafted to acid chloride functional MWCNT through esterification reaction. The grafting to the carboxylated nanotube was achieved via physical interaction. The FTIR spectra confirmed the covalent bonding between the matrix and side-walls of nanotube. Various nanotube loading levels and surface-modified groups were considered to regulate mechanical, thermal and electrical performance of SPAU/MWCNT. The experimental results showed that a moderate loading-level of 5 wt. % MWCNT produced the maximum tensile strength (63.1 MPa) in compatiblized nanocomposites, while the tensile strength of non-compatiblized SPAU/MWCNT was lower (47.25 MPa). Comparative studies based on scanning and transmission electron microscopy of the chemically bonded samples also revealed the covalent coating character and unique nano-fibriller morphology. The dynamic mechanical analysis of nanocomposites showed segmental rigidity due to covalent linking and sample had T_g of 142–152 °C. Addition of acid chloride functionalized MWCNT also contributed to an improvement in the electrical conductivity (2.01-4.31 S cm⁻¹) relative to SPAU/carboxylated MWCNT 1.27-2.86 S cm⁻¹.