COMPARATIVE-STUDY OF STONE-GROUND WOOD PULP AND NATIVE WOOD .3. APPLICATION OF FLUORESCENCE SPECTROSCOPY TO A STUDY OF THE WEATHERING OF STONE-GROUND PULP AND NATIVE WOOD

The fluorescence spectra of chemically treated and weathered paper made from stone-ground wood pulp (SGWP) and thin sections of wood treated in a similar manner have been recorded. Very little difference was found between the paper and wood samples. Chemical treatment included reduction with sodium borohydride and photochemical bleaching with thiourea dioxide. The samples were subjected to photobleaching of the fluorescent chromophores, and the wood samples and paper exhibited a photochromic effect. Of particular significance was the observation that borohydride-reduced and thiourea-dioxide-photobleached wood perform differently in the photobleaching experiments from their paper counterparts. These differences are attributed to the mechanochemistry which occurs during pulping, producing species such as stilbenes which are present in the paper but not in the wood. When borohydride-reduced SGWP and wood are weathered, much of the short-wavelength fluorescence is lost and an increase in longer wavelength emission is observed. Reduction by borohydride of the weathered samples leads to partial recovery of the shorter wavelength fluorescence. These observations are interpreted as being due to photoreactions of 4-hydroxy-3-methoxycinnamyl alcohol residues.