engleski

Depth profile of UV-induced wood surface degradation

The depth profile of weathering effects on wood was studied after laboratory ultraviolet exposure of fir-wood. The "Thin strip" method i.e. the measurement of changes in tensile properties of microtomed wood sections, was modified in terms of exposure of batches of strips packed in bundles and exposed in a QUV apparatus. The bundles of strips were exposed untreated, covered with surface strips impregnated with chromium trioxide or ferric nitrate, or protected with free films of clear stain with and without photostabilisers. It has been shown that UV light penetrated the wood surface deeper than 70  m, resulting in changes in tensile strength of strips to a depth of 70 to 140  m. Strength changes in lower levels (down to 280 m from the surface) could not be clearly attributed to the predominant effect of UV light, and were probably controlled by hydrolytic processes. 100 hours of exposure enabled the effectiveness of several treatments to be established. The clear stain enriched with UV absorber and HALS compound type was shown to offer the best protection. Impregnation with aqueous solutions of chromium (VI) trioxide and ferric nitrate proved ineffective in photostabilising the wood surface.

clear wood stain; photostabilisers; thin strip method; UV-exposure; wood surface degradation

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