Use of Variable Pressure Scanning Electron Microscopy for in situ Observation of Degradation of Wood Surfaces during Artificial Weathering
F Hatae, Y Kataoka, M Kiguchi, H Matsunaga, J Matsumura
Variable pressure scanning electron microscopy (VPSEM) is capable of observing electrically non-conductive materials like wood without the need to render the surface conductive by applying a coating of gold, platinum or carbon. Hence, there is the possibility that VPSEM could be used to non-destructively follow the structural changes occurring at wood surfaces during weathering, because specimens can be observed initially (before weathering), and then re-examined after exposure to the weather. This study uses VPSEM to examine the time-dependent micro-structural changes occurring at untreated and treated wood surfaces exposed to artificial weathering. Cryptomeria japonica (sugi) sapwood was treated by grafting a UV absorber (UVA) to the wood. We compared the micro-checking of bordered and half-bordered pits at treated (grafted) and untreated wood surfaces exposed to weathering. We hypothesised that the grafting treatment would restrict micro-checking of pits. VPSEM revealed significant micro-checking of pits at untreated surfaces exposed to artificial weathering for only 30 h. The dimensions of pit micro-checks increased when untreated samples were exposed to weathering for an additional 30 h. Pit micro-checking occurred more slowly in sugi sapwood treated with a UV absorber. We conclude that pit micro-checking at wood surfaces exposed to artificial weathering is restricted by grafting a UVA to the wood. We further conclude that VPSEM is a valuable tool to follow the time-dependent micro-structural changes occurring at wood surfaces exposed to weathering.