Synergistic interfacial effects of sizing agent containing gradient curing agent and pre-heating treated carbon fibers

This investigation focuses on the use of sizing agent containing gradient curing agent from two directions for carbon fibers coupled with pre-heating treatment before fibers combined into composites to improve interfacial adhesion. Growth in interfacial shear strength (IFSS) up to 92.4 % was noticed for fibers functionalized with sizing agent of high-to-low curing agent from fiber-to-resin (CFH -> L), relative to control fibers. This is related to the greatly enhanced interactions at both fiber/sizing and sizing/resin interfaces accompanied by increased interfacial curing degree that generate a stronger interphase. Further optimization of 4.1 % increase in IFSS was achieved for CFH -> L via pre-heating treatment before being composites, while larger IFSS increment of 16.7 % after pre-heating treatment was observed for fibers coated with sizing agent of low-to-high curing agent from fiber-to-resin (CFL -> H). This reveals that pre-heating is more effective for fiber that has weaker interactions with sizing agent. This work is believed to be a preliminary but crucial trial toward obtaining high-performance fiber composites by simply applying it in the already existed fiber production line.