Evaluation of Surface Treatments and Adhesion Performance on Thermoplastic Composites

This project was conducted at Linköping University in collaboration with Saab Dynamics to investigate the post-processing of thermoplastic aramid fiber composites, with the goal of improving adhesion for both adhesives and paint. The primary objective was to assess whether surface treatment methods currently used for thermoset composites could be effectively applied to thermoplastics, or if alternative approaches would give better results. Surface treatments including abrasion, plasma treatment, and priming were evaluated for their impact on adhesion. Two adhesives, one ethyl cyanoacrylate-based and one epoxy-based adhesive, were tested. Adhesion performance was assessed using lap-shear strength testing for bonded joints, and pull-off and cross-cut testing for painted surfaces. The results indicate that while some surface treatment and bonding methods used for thermosets can be adapted to thermoplastics, their effectiveness varies. Plasma treatment combined with the ethyl cyanoacrylate-based adhesive showed the highest bond strength in the lap-shear strength test. In the paint adhesion tests, untreated samples achieved the highest average breaking strength among the thermoplastic composites in the pull-off test, while abraded surfaces showed the highest adhesion in the cross-cut test. However, factors such as delamination and surface irregularities highlight the need for further research to validate the consistency and applicability of these methods for thermoplastic composites.