The effect of curing additive on the mechanical properties of phthalonitrile‐carbon fiber composites

Unidirectional carbon fiber‐reinforced phthalonitrile composite panels were fabricated by prepreg consolidation with bis[4‐(4‐aminophenoxy)phenyl]sulfone ( p ‐BAPS) as the phthalonitrile curing additive. Rheometric measurements and elevated‐temperature, short beam shear tests were used to evaluate the cure of the composite as a function of the cure and postcure conditions. These techniques revealed that a fully cured phthalonitrile composite was obtained when the composite was heated at 375°C for 8 hours. Room‐temperature mechanical properties of the cured composite were then evaluated using short beam shear, tension, and flexural tests. The results are compared with those obtained by curing the phthalonitrile with 1,3‐bis(3‐aminophenoxy)benzene ( m ‐APB). The data indicate that substitution of p ‐BAPS for m ‐APB has little effect on the mechanical properties of the cured composite. Elevated‐temperature, short beam shear studies up to 371°C show that the cured phthalonitrile composite retains approximately 70% of its room‐temperature apparent interlaminar shear strength. The composite also retains 70% of its room‐temperature storage modulus up to 450°C. Polym. Compos. 25:554–561, 2004.