Photodegradation and Photoprotection of Wood Surfaces

Abstract

Photodegradation of southern yellow pine and its protection have been studied. Scanning electron micrographs showed that most of the cell walls on exposed transverse surfaces were separated at the middle lamella region after only 500 h of ultraviolet light irradiation. Fibers at the surface were degraded severely after 1,000 h of irradiation. Half-bordered pits and bordered pits on exposed radial surfaces were severely damaged by ultraviolet light. Enlargement of pit apertures as well as loss of pit domes was observed. However, wood irradiated on tangential surfaces was quite resistant to UV irradiation; only microchecks were observed. The photodegradative effect on wood surfaces can be mitigated by treating with aqueous solutions of chromic acid or ferric chloride. Only relatively small amounts of these chemicals are needed for effective protection. Possible chemistry and mechanisms of degradation and protection are discussed.