Optimizing the Properties of the Phthalonitrile Composites by Tetrafunctional Epoxy

ABSTRACT To improve the interfacial adhesion between the phthalonitrile resin and the reinforcing fibers, and also to investigate the influence of the addition of epoxy resin on the crosslinking structures and properties, a small amount of high‐performance epoxy resin with four epoxy groups (AG80) in its chemical structure was introduced into a phthalonitrile resin (BAPh) to prepare composites with the basalt fiber cloths. It was found that proper amount of AG80 could increase the curing reactivity of BAPh with lowered curing temperature and shortened gelation time. And AG80 could also improve the interfacial interaction between the resin matrix and the fibers, thus enhancing the flexural strength. With 0.5 wt% of AG80, the flexural strength of BF/0.5EBAPh reached 513.2 MPa, 205.4 MPa higher than that of the BF/BAPh. Moreover, due to the better interfacial interaction and higher curing degree, the thermal properties and dimensional stability also improved when proper amount of epoxy introduced. Specifically, BF/0.5EBAPh showed T g tan δ of 382°C and CTE of 18.2 ppm/K, which were 11°C higher and 12 ppm/K lower than those of the BF/BAPh.