Chemical characteristics of surfaces of hardwood and softwood deterioratedby weathering

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.