Elucidation of the degradative behavior of coated-wood surfaces exposed to artificial weathering using Raman microspectroscopy

Abstract

The degradation behavior of the surface of coated Japanese cedar (Cryptomeria japonica D. Don) during artificial weathering was examined using confocal Raman microscopy. Microscale chemical imaging revealed a difference in the degradation behavior of the wood-coating interface regions between the penetrating and film-forming coating-treated wood specimens. In the case of the penetrating coating-treated wood, as the weathering time increased, the degree of surface-distributed coating gradually decreased. Lignin in the top-surface cell walls degraded at the exposed surface and cell-lumen side in a similar manner as that observed for uncoated wood. In contrast, the film-forming coating-treated wood exhibited two types of degradation behaviors. In the first type, lignin in the second cell layer was preferentially degraded, and the coating film detached with tearing of the second cell layer. In the second type, lignin degradation proceeded from the boundary between the coating film and the top-surface cell walls, and the film detached with no significant cell wall tearing.