Photoyellowing behavior of non-phenolic lignin models representative of end groups and beta-ether structures
Artikel i vetenskaplig tidskrift, 2004

Lignin model compounds representative of etherified end groups [(E)-3-(3,4-dimethoxyphenyl)-2-propenl-ol (1), (E)-3-(3,4-dimethoxyphenyl) propenal (2)] and βethers, [1-(3,4-dimethoxyphenyl)-3-hydroxy-2-(2-methoxy- phenoxy)-1-propanone (3), erythiro-1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)- 1,3-propanediol (4)] have been applied to filter paper and subjected to accelerated photoaging with UV/VIS-light. The changes in optical properties were monitored. In case of all the models, the brightness decreased and the b*-value increased as a result of irradiation, which shows that they are sensitive to light simulating sunlight behind window-glass. In the case of the end group models, the photo-products identified were veratraldehyde and veratric acid together with the Z-isomers of the starting materials. In the case of the cinnamyl alcohol 1, photo-oxidation to the cinnamaldehyde 2 was observed. The irradiation of the αt-carbonylic βether 3 resulted in the homolytic cleavage of the CβO bond and a recombination that led to a β-5 dimer [1-(3,4-dimethoxyphenyl)-3-hydroxy-2-(2-hydroxy-3-methoxyphenyl)- 1-propanone] and a β-1 dimer [1-(3,4-dimethoxyphenyl)-3-hydroxy-2-(4- hydroxy-3-methoxyphenyl)-l-propanone]. The monomeric products veratraldehyde, vanillin, acetoveratrone, and 1-(3,4-dimethoxyphenyl)-3-hydroxy-l-propanone were also formed. The only photoproduct conclusively identified in experiments with the arylglycerol-β-aryl ether 4 was veratraldehyde and most of the starting material was unaffected by the irradiation. The addition of a photosensitizer (acetoveratrone) to this type of model prior to irradiation resulted in some increase in discoloration.



lignin models





Jim Parkås

Chalmers University of Technology

Magnus Paulsson

Stora Enso Research

Chalmers University of Technology

Shiming Li

Chalmers, Institutionen för kemiteknik och miljövetenskap, Skogsindustriell kemiteknik

Knut Lundquist

Chalmers, Institutionen för kemiteknik och miljövetenskap, Skogsindustriell kemiteknik

U. Westermark

Lulea tekniska Universitet

Nordic Pulp and Paper Research Journal

0283-2631 (ISSN)

Vol. 19 146-154


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