Self-healing of polyamide 6/cyclic olefin copolymer/carbon fiber composites under quasi-static, impact, and fatigue conditions

This study investigates the self-healing capabilities of polyamide 6 (PA6) composites containing a cyclic olefin copolymer (COC) as a healing agent and a discontinuous carbon fiber (CF) reinforcement under quasi-static, impact, and fatigue loading conditions. To this aim, PA6/COC (30 wt%)/CF (20 wt%) composites were prepared via melt-compounding and injection molding. The microstructure, mechanical properties, and self-healing behavior of the composites with COC were compared with those of the reference PA6/CF (20 wt%). Although the addition of COC slightly reduces the quasi-static mechanical properties, it significantly improves the impact resistance. The presence of COC domains allow healing efficiencies (HE) of up to 80 % in impact tests, whereas lower HE values are found in quasi-static fracture tests owing to matrix plasticization hindering the COC flow in the fracture zone. Notably, fatigue testing reveals the ability of PA6/COC/CF composites to repair microdamage during thermal mending, extending their own fatigue life by 77 %, while virgin samples are not able to heal. These results highlight the potential of intrinsic self-healing thermoplastic composites to extend the service life of structural composites, particularly under cyclic loading conditions.