Comparative surface and adhesion properties of mechanical abrasion, flame and radiation-based surface treated wood plastic composites made with different polymers

Wood plastic composites (WPCs) show low surface energy and poor adhesion properties, and they can be improved by applying surface treatment. In this study three WPCs made with polyethylene, polypropylene and poly(vinyl chloride) have been treated by mechanical abrasion, flame and radiation-based (UV/ozone, atmospheric pressure plasma torch, Ar:O2 low pressure plasma) treatments. The influence of the wood content and polymer nature in the WPC on the surface modifications and adhesion properties produced by the surface treatments has been assessed. The surface treatments by mechanical abrasion and flame produced slight changes in the WPC surface, mainly in roughness, irrespective of the wood content and polymer nature in the WPC. The radiation-based surface treatments were the most efficient in increasing the surface energy (particularly the polar component) and produced ablation and surface oxidation of the WPC, the most noticeable modifications were obtained in the WPCs made with polyolefin. The adhesion (180° peel strength and cross-hatch adhesion) of the WPCs made with polyolefin was enhanced by surface treatment with both plasmas, irrespective of the adhesive or coating nature, and a relationship between the surface modifications produced by the plasma treatments and the adhesion was found. The surface modifications by the different treatments were less marked for the WPC made with poly(vinyl chloride) due to its smooth surface, low wood content and the existence of carbonate filler in its composition; furthermore, lower adhesion than for the surface treated WPCs made with polyolefin was obtained, and the highest 180° peel strength and cross-hatch adhesion were obtained with different surface treatments, the adhesion also depended on the coating nature. The effectiveness of the surface treatment in improving the adhesion of the WPCs depended on their wood content, polymer nature and surface roughness.