FT-IR Studies of Weathering Effects in Western Redcedar and Southern Pine

Diffuse reflectance infrared spectroscopy has been used to monitor the changes in functional groups on the surface of two woods (western redcedar and southern pine) when they are subjected to a range of artificial weathering conditions. The effects of light only, water only, and light plus water have been studied for a variety of exposure times. The changes in the chemical composition of the wood caused by light plus water is considerably greater than that caused by light only, whereas water alone causes no permanent chemical changes. The effects of some of these weathering conditions have been investigated for wood protected by varnish, for earlywood and latewood and for tangentially, radially, and cross-sectionally cut wood samples. The application of two coats of varnish was found to considerably reduce the weathering effects caused by UV radiation; earlywood undergoes light-only degradation faster than late wood; and the effect of weathering was found to be greatest for cross-sectional cut samples and least for radially cut samples. The weathering profile with depth of penetration has been studied in some detail for western redcedar, and our results show that, after 300 h of continual artificial weathering, the chemical changes are confined to the first 200 μm.