Epoxy Matrix Design for Viscosity and Pot Life Control in CFRP Manufacturing

With the increasing demand for large-scale carbon fiber-reinforced plastic (CFRP) structures in future mobility, wind energy, and aerospace applications, epoxy resin systems that maintain stable processability during long-duration manufacturing have become increasingly important. In this study, epoxy systems based on anhydride curing agents, including methyltetrahydrophthalic anhydride and methylhexahydrophthalic anhydride, and reactive diluents, including butyl glycidyl ether and phenyl glycidyl ether, were designed and optimized for pot life and glass transition behavior. To replicate the processing requirements of large-scale CFRP manufacturing, a minimum pot life of 5 h was set as the target processing window, based on the time required to reach a viscosity of 3000 mPa·s. CFRP specimens fabricated with epoxy systems stored for 5 h after mixing exhibited impregnation behavior comparable to that of specimens prepared under the initial condition, while micro-CT analysis confirmed that void formation was effectively suppressed. Consequently, the mechanical properties of the CFRP specimens were nearly retained even after 5 h of resin storage. These findings indicate that reactive diluent-assisted control of viscosity and pot life is an effective strategy for maintaining impregnation quality and suppressing internal defects during long-duration CFRP processing. This study provides practical design guidelines for epoxy matrix systems suitable for the reliable fabrication of large-scale CFRP structures.