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 mad e from stone-ground wood pulp (SGWP) and thin sections of wood treated in a similar manner have been recorded. Very little difference was fo und between the paper and wood samples. Chemical treatment included re duction with sodium borohydride and photochemical bleaching with thiou rea dioxide. The samples were subjected to photobleaching of the fluor escent chromophores, and the wood samples and paper exhibited a photoc hromic effect. Of particular significance was the observation that bor ohydride-reduced and thiourea-dioxide-photobleached wood perform diffe rently in the photobleaching experiments from their paper counterparts . These differences are attributed to the mechanochemistry which occur s during pulping, producing species such as stilbenes which are presen t 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 b y borohydride of the weathered samples leads to partial recovery of th e shorter wavelength fluorescence. These observations are interpreted as being due to photoreactions of 4-hydroxy-3-methoxycinnamyl alcohol residues.