Effect of natural weathering on optical properties of transparent wood composite

Transparent wood composite (TWC) is an innovative wood-based polymeric material prepared by the impregnation of a suitable polymer into the lignin-modified wood substrate. TWC has gained significant attention for several outdoor applications including transparent wood smart windows, substrate for solar cells, light management devices and energy-efficient building materials. However, the interaction of TWC with various environmental factors affects its physical aesthetics, chemical and optical properties, thus impairing its effectiveness as an outdoor material. Therefore, the outdoor durability of TWC is important while considering its growing popularity. In this study, the effects of natural weathering on the properties of TWC prepared from two wood species, viz., Melia dubia (Melia) and Populus deltoides (Poplar) were investigated. The effects of weathering on TWC were evaluated in terms of changes in visual appearance, colour parameters, optical transmittance and chemical changes. Prominent colour changes were observed on the samples soon after the exposure to natural environment mainly due to photo-oxidative degradation by solar UV radiation. FTIR measurements revealed chemical degradation of the exposed polymeric materials. The optical transmittance of TWC exposed to natural weathering for 150 days showed colour darkening and a transmittance loss of ∼33–35 %. The addition of a benzotriazole-derived UV absorber (1.75 % conc.) in TWC was found effective in reducing photo-yellowing in TWC and limiting the transmittance loss to 15 %.