Photo-stabilization effect of extractives on the photo-degradation of Red pine (Pinus koraiensis Sieb. et Zucc.)

The impact of extractives on the appearance and wettability changes of wood surface during artificial weathering was discussed from the aspect of chemical and structural changes. Un-extracted (CK) and extracted samples were subjected to UV irradiation or a combination of UV and water. The structural damage inflicted on the extracted sample by the combination of UV and water was more severe compared to the CK sample, corresponding to high roughness and the presence of visible cracks on the irradiated surface of the extracted sample. Analysis of FTIR spectra and overall color change (ΔE*) confirmed that ΔE* values correlated well with lignin decay and the generation of carbonyl groups. Furthermore, the wettability of samples aligned closely with changes in the hydrophilic hydroxyl groups determined by FTIR spectra. The presence of extractives in the CK sample retarded the rate of lignin degradation, and the additional carbonyl groups generated by extractives contributed to color changes. Overall, the extracted samples exhibited more pronounced structural deterioration, color changes, increased wettability, and composition degradation compared to the CK sample, underscoring the photo-stabilizing effect of extractives during UV irradiation. Additionally, the erosion of water exacerbated the degradation of chemical composition and structural deterioration, resulting in significant visible alterations and high wettability.