Surface modification and adhesion of wood-plastic composite (WPC) treated with UV/ozone

Abstract

Because of the surfaces of wood-plastic composite (WPC) materials are enriched in polymers of low surface energy, they exhibit low adhesion properties. UV/ozone is proposed as surface treatment for increasing the surface energy and adhesion of WPC materials made with different polymers (polyethylene, polypropylene and polyvinyl chloride). UV lamp-WPC surface distance and time of UV exposure were varied for optimizing UV/ozone treatment of WPC, and UV dose used ranged between 2.02 × 10−14 and 5.05 × 10−12 J·s/m2. UV/ozone treatment created new carbon-oxygen polar groups in WPC surfaces and increased their surface energy, mainly their polar component. Furthermore, ablation of the outermost WPC surface was produced, more noticeably by reducing the distance between WPC surface and UV lamp and by increasing the duration of the treatment. Noticeable increase in 180° peel adhesion was obtained in the joints made with UV/ozone treated WPC at 10–30 mm distance during 1–5 min (i.e., UV dose between 5.61 × 10−14 and 2.53 × 10−12 J·s/m2). Although 180° peel strength of joints made with acrylic adhesive tape and UV/ozone treated WPC for 10 min and 10 mm distance (UV dose: 5.05 × 10−12 J·s/m2) was not increased because of dominant effect of ablation over creation of polar groups, the cross-hatch adhesion to different coatings was highly improved, irrespective of the polymer used and the wood content of WPC; however, the surface modifications and adhesion of UV/ozone treated WPC were more marked when its wood content was higher and by using UV dose between 0.10 × 10−12 and 2.53 × 10−12 J·s/m2.