Hygrothermal aging mechanisms of CFRP rods based on a multifunctional small-molecule epoxy matrix: From moisture uptake to interfacial degradation

Carbon fiber reinforced polymer (CFRP) rods, with multifunctional small-molecule epoxy matrix, have gained greater potential in cable applications, owing to their better high-temperature or fire resistance. Yet, the complex multi-scale degradation of their high-crosslink density resins in hygrothermal environments is not yet fully understood, and therefore, this study investigates their hygrothermal behavior. First, CFRP rods were immersed in water at 20, 40, 60, and 80 °C for up to 4000 h to evaluate moisture transport; afterwards, the fiber-resin interfacial shear strength (IFSS) degradation was evaluated by short beam shear tests, and dynamic mechanical analysis (DMA) was also employed to quantify hygrothermal-aging effects; finally, microscopic characterization methods, including SEM, FTIR, XPS, and MIP, were utilized to anazyze the chemical composition and interior poral defects evolution. The results indicated that moisture uptake exhibited a two-stage behavior characterized by a diffusion-relaxation model. The IFSS degradation was highly temperature-dependent, accelerating at temperatures above 60°C, and IFSS decreased by 29.93% at 60°C and up to 80.73% at 80°C after 4000 h aging. Besides, DMA results also indicated a significant decline in the glass transition temperature ( T g ) at temperatures above 60°C. SEM/FTIR/XPS results revealed progressive interfacial debonding and confirmed epoxy hydrolysis and oxidation, evidenced by increased hydroxyl, carbonyl, and carboxyl groups. Besides, MIP results further verified elevated porosity and pore coarsening, evolving into continuous macropores at temperatures ≥60°C.