The role of chemical surface modification for structural adhesive bonding on polymers - Washability of chemical functionalization without reducing adhesion

This study investigates the role of surface functionalization to increase adhesion forces on polymers. The effects of two different physical pre-treatment methods (oxygen low-pressure plasma - LPP, vacuum-UV - VUV) are investigated on four different polymer matrices (polyetheretherketone - PEEK, polyetherimide - PEI, polyethersulfone - PES and the epoxy resin RTM6). Polymer surfaces were additionally washed after surface treatment with different polar solvents. Surface chemistry, wettability, and topography were investigated before pretreatment, after pre-treatment and after washing of the samples using x-ray photoelectron spectroscopy (XPS), contact angle measurements and atomic force microscopy (AFM). The results show, that washing of the samples after pre-treatment lead to a chemical surface condition similar to the initial surface. Interestingly, the tensile bond strength of centrifugal adhesion tensile test (GATT) specimens however remained high. In consequence, the thus far widely accepted understanding of surface functionalization as the dominating factor for adhesion promotion on polymers has to be re-evaluated.