SURFACE-STRUCTURES AND ADHESION ENHANCEMENT OF POLY(TETRAFLUOROETHYLENE) FILMS AFTER MODIFICATION BY GRAFT-COPOLYMERIZATION WITH GLYCIDYL METHACRYLATE

Surface modifications of Ar plasma-pretreated poly(tetrafluoroethylene ) (PTFE) film were carried out via near-UV light-induced graft copolym erization with glycidyl methacrylate (GMA). The structure and chemical composition of the copolymer surface and interface were studied by an gle-resolved X-ray photoelectron spectroscopy (XPS). For PTFE substrat e with a substantial amount of grafting, the grafted GMA polymer penet rates or becomes partially submerged beneath a thin surface layer of d ense substrate chains to form a stratified surface microstructure. The concentration of the surface-grafted GMA polymer increases with the p lasma pretreatment time, the near-UV light illumination time, and the monomer concentration. The GMA graft copolymerized PTFE surfaces adher e strongly to one another when brought into direct contact and cured ( i) in the presence of a diamine alone or (ii) in the presence of an ep oxy adhesive (epoxy resin plus diamine curing agent). In the presence of diamine alone, failure occurs in the interfacial region. For epoxy adhesive-promoted adhesion, the failure mode is cohesive, i.e. it take s place in the bulk of one of the delaminated PTFE films. The lap shea r strengths in both cases increase with the amount of surface-grafted epoxide polymer. The development of the adhesion strength depends on t he concentration of the surface graft, the microstructure of the graft copolymerized PTFE surface, the interfacial reactions, and the nature of the bonding agent.