SURFACE CHANGES ON ACETYLATION AND EXPOSURE TO ULTRAVIOLET-RADIATION OF PINUS-RADIATA USING X-RAY PHOTO-ELECTRON SPECTROSCOPY

Various Pinus radiata wood components, solvent extracted and acetylate d, were irradiated with ultraviolet light (lambda(max) = 350nm). The X PS spectrum of the acetylated wood surface resembled that of cellulose acetate suggesting that acetylation removes lignin fi om the wood sur face. The presence of acetylated lignin in the acetic anhydride soluti on following acetylation, identified by IR and NMR, supports this theo ry. This could be a major contributor to the bleaching of wood on acet ylation. The XPS spectra of irradiated wood and lignin showed that pho to-oxidation had occurred in both extracted wood, untreated lignin and acetylated samples. Demethoxylation and/or beta-aryl ether cleavage i n untreated irradiated lignin is supported by the XPS Spectra while de acetylation of irradiated acetylated samples is indicated by decreased C-1 band intensity. Acetylation proved ineffective in preventing phot o-oxidation of wooden surfaces. The depletion of lignin on the wooden surface, (an artefact of acetylation) results in less light absorption thereby retarding photo-induced yellowing. Peroxide treatment of extr acted radiata pine did not deplete surface lignin.