Evaluation of Nylon and Polyester Peel Plies Using the Rapid Adhesion Test

Adequate surface preparation of composite parts for adhesive bonding by use of peel plies is highly desirable, yet it remains necessary to test each combination of composite resin system, peel ply, and adhesive for successful adhesion. Furthermore, failure in adhesion, as opposed to interlaminar or cohesive failure, is usually unacceptable for any application. The Rapid Adhesion Test (“RAT”) was developed as a simple, fast Mode I screening process for rejecting component combinations that fail in adhesion, taking advantage of the qualitative nature of this determination. Here, various combinations of 127 °C (260 °F) cure glass fiber reinforced polymer prepreg, nylon and polyester peel plies, and film adhesives were tested using the RAT. It was found that all of the samples prepared with nylon peel plies failed cohesively, whereas all of the samples prepared with polyester peel plies failed in adhesion at least to some degree. The topography of the surfaces to be bonded was characterized using optical and scanning electron microscopy. The surface energy of each surface to be bonded was measured using sessile drop contact angle measurements with at least 3 different fluids. The relationships between surface energy and bond quality are explored.