Effect of argon and nitrogen plasma surface treatment on wettability and adhesive bond strength of PP, HIPS, PVC, PC and PET

The low surface energy of many engineering thermoplastics limits their adhesive bonding performance, making surface activation an essential pre-treatment. This study compares the effects of atmospheric-pressure nitrogen and argon plasma treatments on the wettability and adhesive bond strength of five engineering thermoplastics [polypropylene (PP), high-impact polystyrene (HIPS), poly(vinyl chloride) (PVC), polycarbonate (PC), and polyethylene terephthalate (PET)] under identical processing conditions. Surface wettability was evaluated by water contact angle measurements, while adhesive performance was assessed by lap shear testing. Both plasma gases significantly improved the wettability and adhesive performance of all investigated polymers compared with untreated surfaces. Nitrogen plasma generally produced lower water contact angles, whereas argon plasma provided a wider processing window without visible surface degradation and achieved comparable or even higher bond strength for several polymer–adhesive systems. Although plasma treatment generally increased lap shear strength, the lowest water contact angle did not always correspond to the highest bond strength, demonstrating that adhesion depends not only on wettability but also on plasma-induced changes in surface characteristics and adhesive compatibility. The results provide practical guidance for selecting plasma treatment conditions and demonstrate that optimizing plasma-assisted adhesive bonding requires consideration of both the polymer substrate and the adhesive system.