The degradation of wood surfaces exposed to UV light which leads to poor performance of clear coatings is understood to be due to delignification via a mechanism involving free radicals. Certain wood preservatives most notably CCA are able to photostabilise wood and therefore they may reduce the concentration of free radicals formed when treated wood is exposed to ultraviolet light. As a first step to prove this hypothesis we have treated a number of thin Scots pine veneers with two different commonly used wood preservatives (CCA, ACQ) and two effective photostabilising treatments (HEBP, DHBP). Treated veneers were then placed in an ESR spectrometer which allowed the samples to be exposed to UV radiation while the spectra were recorded. The spectra were compared with that obtained using untreated wood. The results are very encouraging showing a smaller concentration of free radicals in preservative treated veneers than in untreated controls and there is also marked differences between the various treatments. More work is needed to establish a direct relationship between free radical concentration as measured by ESR spectroscopy and prolonged longevity of a wood surface exposed outdoors. Ultimately ESR spectroscopy has the potential to substitute time consuming and costly weathering trials, at least for screening of large numbers of unknown compounds for their ability to prevent the photodegradation of wood.

Download document (219 kb)
free for the members of IRG. Available if purchased.

Purchase this document