Enhancing both heat resistance and mechanical properties of phthalonitrile composites: Combined effects of carborane and carbon nanotube films

To improve the mechanical performance of phthalonitrile (PN) composites under high temperature and thermo-oxidative conditions, an integrated strategy utilizing carborane and carbon nanotube films (CNF) is proposed. With carborane acting as a catalyst, the PN resin exhibited excellent curing activity and thermal stability, increasing temperature of 5% mass loss (518.9 °C) and high char yield (13.74%) in air atmosphere. Furthermore, the PN composites reinforced with CNF demonstrated superior mechanical properties at elevated temperatures. Specifically, the composites achieved a flexural strength (FS) of 905 MPa and an interlaminar shear strength (ILSS) of 47.1 MPa at 400 °C. In the aging test at 350 °C, the carborane formed a protective boron oxide layer by absorbing oxygen on the resin matrix. This process effectively delayed the occurrence of microcracks and the decomposition of the PN matrix. During the early stages of thermo-oxidative aging, the CNF continued to provide effective reinforcement and thereby maintained the mechanical performance of the composites. Specifically, after 96 h of aging, the flexural strength remains at 1062 MPa (73.24% retention), and after 144 h of aging, the flexural strength maintains 834 MPa (57.52% retention). These results indicate that the developed composites offer strong potential for advanced aerospace and thermal-structural applications.