Adhesion enhancement of Poly(etheretherketone) via surface-initiated photopolymerization of glycidyl methacrylate

Poly(etheretherketone) (PEEK) is a high-performance engineering thermoplastic with high heat deflection temperature. Owing to its low surface free energy, the untreated PEEK adherend may exhibit low bond shear strength with epoxy adhesives. This work presents a method to improve the adhesion performance of PEEK with epoxy adhesives through poly(glycidyl methacrylate) (PGMA) grafting. The PGMA-grafted PEEK (PEEK-g-PGMA) was prepared via surface-initiated photopolymerization under 2 and 8 mW/cm(2), respectively. The influence of the irradiation duration and the removal of the polymerization inhibitor from the monomer on PGMA grafting are discussed herein. The results showed that (1) the PEEK-g-PGMA is obtained from the photopolymerization under 2 and 8 mW/cm(2) of UV irradiation; (2) the long durations of the UV exposure promoted the formation of brushes; and (3) the polymerization inhibitor only slightly inhibited the polymerization, but effectively prevented the auto-polymerization of monomer solution during the UV irradiation. The enhanced performance of the epoxy adhesives was demonstrated by the single-lap shear tests using PEEK-g-PGMA joints. Under optimized concoctions, the lap shear strength of PEEK-g-PGMA was significantly enhanced to 15.1 MPa which is seven times higher than that of unmodified PEEK (2.5 MPa).