Photografting of argon plasma-treated graphite/PEEK laminate to enhance its adhesion

Abstract

Graphite/PEEK laminates were treated by argon plasma followed by air aging and then photografting of α- glycidyl ω- acrylate bisphenol A(GABA) to improve their adhesion characteristics. The effects of plasma time and power and photografting time on the epoxy bonded single lap shear joints between graphite/PEEK laminates were investigated. An optimum photografting time was found at which the single lap shear strength was optimized to 37 MPa compared to 28 MPa and 7 MPa obtained with air-aged argon plasma activated and pristine samples, respectively. Argon plasma treatment followed by air aging of graphite/PEEK laminate introduces surface peroxides and hydroperoxides and these when cleaved with ultraviolet (UV) light in the presence of the GABA monomer results in covalent grafting of the latter to PEEK/graphite laminate surface. The epoxy functionality of the GABA monomer then reacts with the epoxy adhesive. X-ray photoelectron spectroscopy (XPS) confirms the appearance of surface peroxides and hydroperoxides on air-aged argon plasma treated samples and disappearance of the same with UV irradiation. With UV irradiation of the air-aged argon plasma treated samples, XPS indicates the appearance of ester groups. Without the grafting monomer, UV irradiation in air cleaves the peroxide and causes oxidation resulting in the formation of surface esters. In the presence of the grafting monomer, UV irradiation results in covalent bonding of the monomer to the peroxide/hydroperoxide through the acrylate functionality resulting in increased concentration of ether linkages as confirmed by our XPS data; the ester functionality present in the grafted monomer caused the appearance of the ester peak in the XPS spectrum.

Keywords:

• Argon plasma
• PEEK
• grafting
• UV
• photografting
• adhesive.