The factors that cause weather-induced deterioration of wood surfaces were
determined by chemical and spectroscopic analyses. Albizzia (Paraserianthes
falcata Becker.) and sugi (Cryptomeria japonica D. Don) were exposed to tw
o temperate conditions of natural weathering with and without rainfall and
to accelerated conditions of artificial weathering coupled with ultraviolet
(UV) light irradiation and water flashing. Infrared spectroscopic analysis
showed that the oxidative reaction of lignin was observed under all condit
ions of weathering for both wood species. However, a marked decrease in lig
nin and hemicellulose content were recognized when albizzia woods were expo
sed to weathering with water. Lignin content in the softwood sugi did not d
ecrease as much as in albizzia even in the presence of water, but the modif
ication of lignin macromolecules was assumed to be accelerated by water, as
seen by electron spin resonance spectroscopy. These results showed that th
e presence of water promotes the weathering deterioration of wood under UV
irradiation.