Effects of thermal treatment on the mechanical properties of poly(p-phenylene benzobisoxazole) fiber reinforced phenolic resin composite materials

Abstract

Thermal degradation behaviors of the poly(p-phenylene benzobisoxazole) (PBO) fiber and phenolic resin matrix were investigated. The unidirectional PBO fiber reinforced phenolic resin composite material laminates were fabricated and exposed in a muffle furnace of 300°C, 550°C, 700°C, and 800°C for 5min, respectively, to study the effects of thermal treatment on mechanical properties of the composites. After undergone thermal treatments at 300°C, 550°C and 700°C for 5min, the flexural strength was reduced by 17%, 37% and 80%, respectively, the flexural modulus was decreased by 5%, 14% and 48%, respectively, and the interlaminar shear strength (ILSS) was lowered by 12%, 48% and 80%, respectively. Thermal treatment at 300°C, the phenolic resin began to pyrolyze and shrink resulted in the irreversible damage of the composites. After 550°C thermal treatment, the phenolic resin pyrolyzed mostly but the PBO fiber had no obvious pyrolyze, the interface had sever broken. After 700°C thermal treatment, the phenolic resin formed amorphous carbonaceous and PBO fiber pyrolyzed mostly so the mechanical properties dropped dramatically. At being heated at 800°C for 5min, the fiber was nearly totally pyrolyzed and and kept fibrous carbonaceous although the specimen became too brittle to stand any load thereon.