Enhanced adhesion effect of epoxy resin on carbon fiber-reinforced Poly(etheretherketone) via surface initiated photopolymerization of glycidyl methacrylate

Adhesives for carbon fiber-reinforced poly (etheretherketone) (CFR-PEEK) have attracted the interest of researchers as an effective means for bonding this newly developed lightweight and high-performance composite structures. In this study, we developed a method to overcome the lack of interaction between adherends and adhesives through the modification of glycidyl methacrylate (GMA) brushes via surface-initiated photopolymerization. To achieve a better formation of PGMA brushes, some parameters of the surface-initiated photopolymerization, for example, light intensities (e.g., 2, 4, and 8 mW/cm²) and exposure durations (e.g., 15, 30, 45, 60, 90, 120 min) of ultraviolet (UV) treatment, were optimized. The joints using the adherends with an optimized PGMA layer exhibited more than a two-fold increase in the ultimate lap shear strength compared to that using the bare CFR-PEEK adherends, when a commercially available epoxy film adhesive, FM 309-1, is utilized. The influence of the UV intensities was further revealed via a double cantilever beam test, and the adherends with the modification under 4 mW/cm² of UV irradiation for 2 h exhibited the best performance, owing to the higher grafting density of the PGMA brushes.