Effects of UV-curing epoxy acrylate and urethane acrylate coatings incorporated with ZnO nanoparticles on weathering resistance of thermally modified timber

In this study, the effects of two transparent UV curing coatings (i.e. epoxy acrylate and urethane acrylate) modified by zero, 0.2, and 0.5 loading percent of zinc oxide nanoparticles (ZN) on the weathering resistance of thermally modified timber were investigated. Both coatings improved the weathering resistance of the modified wood; however, epoxy acrylate showed much better performance compared to urethane acrylate. ATR-FTIR results showed no considerable oxidation or chain scission in the epoxy acrylate-coated specimens after six months of weathering, while significant chemical changes occurred in the urethane acrylate-coated specimens. The addition of the nanoparticles reduced the discoloration of both coatings; however, the contact angle and roughness were not significantly affected. Results also showed that the adhesion strength was reduced for both coatings as a result of weathering with the urethane acrylate coating having a lower adhesion strength than the epoxy acrylate. The addition of the ZN, particularly at the higher content, reduced the adhesion strength of the urethane acrylate coating. Generally, the method of fast and simple UV-cured coating of epoxy acrylate alone or coupled with zinc oxide nanoparticles was found to be effective for the protection of thermally modified timber against weathering in outdoor applications.