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KeywordsLignin Photodegradation β-Ο-4 Lignin modcl compound Phenolic dimer Photochemical bond cleavage 5,5' -O-4Tetramer Frec-radicals α-Carbonyl-phenyl derivatives synthesis Bisulphite pulp (maritime pine) SummaryThe photoyellowing of bleached high yield wood pulp induced by lignin was studied using the title phenolic a-carbonyl -O-4 lignin model L Its photochemical reactivity was examined in both liquid (benzene and buffered aqueous ethanol) and solid (adsorbed on bleached chemical pulp) media and compared to the 4-O-methylated dimer 2. The influence of oxygen during the Irradiation was considered. Efficient photolysis of l (0 r ~ 0.25 in solution) yields monomers, dimers, a tetramer and a complex mixture of oligomers which include coloured substances.The structure and the titration of the photoproducts indicate that an intramolecular β C-O bond cleavage mechanism leading to phenacyl and guaiacoxy radicals is the major pathway of the photodegradative reaction. The phenolic hydrogen abstraction mechanism, evaluated by the formation of the 5-5' tetramer 14 contributes only for 10%. These results support the previous hypothesis ) concerning the -cleavage of α-carbonyl β-Ο-4 dimer units s the primary step in lignin photodegradation.

INTRODUCTIONIn the past fifteen years a great deal of research effort has been dedicated to the understanding of the interfacial properties of surfactant-oil-water systems. This research was backed up by the enhanced oil recovery drive, and all the studies have dealt vith systems containing hydrocarbon oils. However, the resulting physicochemical framevork is extremely useful to understand the influence of the formulation upon most phenomena involving surfactant-oil-water systems even those out of the petroleum industry world.A in-depth monography on theses topics has been recently available (11, as well as some simplified presentation ( 2 ) ; the latter may be considered as the minimum knowledge necessary to understand the generalized formulation concept beyond the HLB-PIT old classics ( 3 ) .In the tvo first papers of this series, it vas shovn that vhatever the formulation variable, there is a strong relationship betveen the phase behavior at equilibrium and the emulsion properties (4, 5). This relationship seems to apply to all systems which contain light hydrocarbons and roughly equal amounts of oil and rater 16-8).