Abstract
Extracts from different lignocellulosic sources were applied in the wood veneer dyeing process with the aim of preventing colour changes caused by ultraviolet (UV) degradation. Chestnut (Castanea sativa) fruit shell and bur, and barks from Pinus pinaster, Eucalyptus globulus and Quercus frainetto extracted using water or aqueous solutions of sodium sulphite and/or sodium hydroxide were used. Wood veneers from ash (Fraxinus excelsior), koto (Pterygota bequaertii) and lime (Tilia cordata) were dyed, treated with extracts and subjected to accelerated exposure to UV light for variable lengths of time. The colour degradation was measured and the results were studied using cluster analysis. Pinus pinaster bark extracts were the best protectors for dyed veneers. Chemical changes due to UV exposure were analyzed by X-ray photoelectron spectroscopy. The degraded untreated wood increased its functional groups rich in oxygen, that is, photo-oxidation occurred. Nevertheless chemical bonding of wood treated with extracts hardly underwent changes.
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