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Photoyellowing behavior of non-phenolic lignin models representative of end groups and beta-ether structures

Jim Parkås ; Magnus Paulsson ; Shiming Li (Institutionen för kemiteknik och miljövetenskap, Skogsindustriell kemiteknik) ; Knut Lundquist (Institutionen för kemiteknik och miljövetenskap, Skogsindustriell kemiteknik) ; Ulla Westermark
Nordic Pulp & Paper Research Journal (0283-2631). Vol. 19 (2004), 2, p. 146-154.
[Artikel, refereegranskad vetenskaplig]

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.

Nyckelord: lignin, NMR, structure, photochemistry, lignin models, yellowing



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Denna post skapades 2011-06-06. Senast ändrad 2016-05-19.
CPL Pubid: 141357

 

Institutioner (Chalmers)

Institutionen för kemiteknik och miljövetenskap, Skogsindustriell kemiteknik (2002-2004)

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Materialvetenskap
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Kemi
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