Photoyellowing of peroxide-bleached lignin-rich pulps:a photochemical study on stilbene-hydroquinone chromophores issued from #beta#-5 units of lignin during refining and (or) bleaching

摘要

The contribution of stilbene—parahydroquinone structures, formed from #beta#-5 units during refining and bleach-ing, in photoreversion of peroxide-bleached high-yield puips. was studied using 4’-benzyloxy-2,5-dihydroxy-3.3’-dimethoxystilbene (I), as a model compound. The various photoproducts formed during irradiation of I in solution or adsorbed on cellulose paper were identified. Isomerization of the stilbene double bond and oxidation of the hydroquinone into quinone were observed in solution, whereas in the solid state only the formation of the quinone was found to operate. Our attempts to detect and quantify stilbene—hydroquinones forming from j3-5 units created on perox-ide bleached mechanical pulp were not met with success.