Effect of addition of nanosized UV absorbers on the physico-mechanical and thermal properties of an exterior waterborne stain for wood

This study describes the effects of the addition of inorganic nanosized UV absorbers on physico-mechanical and thermal properties of an exterior commercial acrylic-based waterborne stain for wood. Electronic microscopy and water vapor (WV) permeability measurements were performed to characterize the free films of the acrylic stain and resulting nanocomposite coatings. An accelerated weathering method was used to evaluate aging behavior of the coatings on wood through appearance, T_g, abrasion resistance, adhesion strength, hardness and Young's modulus changes. In addition to improving the protection against UV, the doped TiO₂ and silica-coated ZnO nanoparticles in powder form have improved the abrasion resistance and barrier effect against water vapor diffusion of the acrylic stain. For most of nanocomposite coatings, the addition of ZnO hydrophilic nanoparticles in predispersed form has resulted in a decrease in WV permeability, while the adhesion strength and abrasion resistance of those coatings were negatively affected. The addition of ZnO nanoparticles has decreased the T_g of the acrylic stain. Finally, the accelerated weathering has induced an increase in T_g, hardness, Young's modulus (stiffness) and an increase in apparent adhesion strength and abrasion resistance of the coatings. The T_g values of the aged nanocomposite coatings were lower than that of unmodified acrylic stain.