Significantly enhanced structural integrity of adhesively bonded PPS and PEEK composite joints by rapidly UV-irradiating the substrates

A high-power UV-irradiation technique was proposed for the surface treatment of PPS and PEEK composites, aiming to achieve good adhesion with epoxy adhesives. The composite substrates were rapidly UV-irradiated for a duration of between 2–30 s, and then bonded using an aerospace film adhesive to produce joints. Tensile lap-shear strength and mode-I and mode-II fracture energies of the adhesive joints were investigated. It was observed that the application of a short-time UV-irradiation to the substrates transformed the failure mode of the specimens from adhesion failure to substrate damage in all cases. This consequently resulted in remarkable improvements in the mechanical and fracture performance of the adhesive joints. For example, the lap-shear strength increased from 11.8 MPa to 31.7 MPa upon UV-irradiating the PPS composites for 3 s, and from 8.3 MPa to 37.3 MPa by applying a 5 s UV-irradiation to the PEEK composites. Moreover, the mode-I and mode-II fracture energies significantly increased from ∼50 J/m2 to ∼1500 J/m2 and from <300 J/m2 to ∼7000 J/m2, respectively for both of the adhesively bonded PEEK and PPS composite joints.