UV stabilization of wood by impregnation of zinc oxide nano-dispersions

As a natural raw material, wood is subject to various environmental influences during use. UV radia-tion, moisture, insects, fungi and microorganisms lead to a reduction in durability in exterior and interi-or areas. Living organisms in particular can be easily regulated in various ways via moisture. UV radia-tion, however, leads to a deterioration of the surface quality, especially in visible application areas, as the wood components are damaged and decomposed on a molecular level. Lignin is particularly sus-ceptible to this. UV-stabilizing properties of nanoparticles of some metal oxides, including zinc oxide, can provide a remedy. Studies on coating agents on wooden surfaces of Wrightia tinctoria based on zinc oxide nanoparticles (ZnO) showed a reduction in photo yellowing. This approach was taken up due to the promising results, ZnO nanodispersions based on propylene glycol (PG) were introduced into the microscopic structure of spruce (Picea abies) and beech (Fagus sylvatica) by means of whole-cell impregnation. In this work, among other things, the effect of the nanodispersions on the stability of the optical appearance against UV exposure due to artificial weathering was evaluated. Furthermore, the material uptake of the ZnO nanodispersions was investigated and insights into the penetration of the dispersions into the microstructure of the wood were obtained using SEM imaging. Untreated reference samples show significant photo-yellowing. 1% ZnO increases the UV stability of the treated surfaces significantly. It was shown that the uptake of the nanodispersions is independent of the proportion of ZnO, and that the impregnating agents are better absorbed by spruce wood (ap-prox. 200%) than beech wood (approx. 70%). Already a 2% ZnO nanodispersion leads to a saturation of ZnO in the cell structure of the treated wood, for spruce as well as beech. The SEM investigation gave a revealing insight into the penetration behaviour in the microstructure of the wood.