Cooling rate-dependent mechanical properties of polyphenylene sulfide (PPS) and carbon fiber reinforced PPS (CF/PPS)

This study investigated the effect of cooling rates on the crystallization, thermomechanical, and fracture properties in both semi-crystalline thermoplastic resin (polyphenylene sulfide, PPS) and carbon fiber reinforced PPS (CF/PPS). Our results showed that high crystallinity caused by a slow cooling rate increases the elastic modulus and yield stress but decreases the strength and fracture toughness. This trend is caused by the competing influences between high stiffness of the crystal layer and high ductility of the amorphous layer. Particularly, in neat resin, a transition from brittle to ductile fractures emerged between 1 and 10 °C/min and highly increased the fracture toughness. However, because of the weak bonding between the fiber and PPS, the fracture toughness of CF/PPS was less affected by the cooling rate and was significantly lower than that of neat PPS. This means that the fiber/matrix interface properties are the key factors affecting the mechanical properties of CF/PPS.