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Wood degradation under UV irradiation: A lignin characterization

Paper ID Volume ID Publish Year Pages File Format Full-Text
29895 44445 2016 8 PDF Available
Title
Wood degradation under UV irradiation: A lignin characterization
Abstract

•A colour and FTIR-ATR spectroscopy were used for wood photodegradation.•A new way for monitoring wood photodegradation is proposed.•First used of Raman spectroscopy for wood photodegradation characterization.•A local lignin sensitivity is found and a mechanism of degradation is proposed.

The photodegradation of white spruce by artificial ageing was studied by several techniques: colourimetry, FTIR-ATR and FT-Raman spectroscopy. Samples were exposed at a xenon lamp for 2000 h. Two distinct colour changes were found by colourimetric analysis, yellowing and silvering. These colour modifications indicate the formation of chromophoric structures which supports previous FTIR-ATR experiments. The degradation of lignin to generate the first chromophoric group for yellowing and then the appearance of surface layer cellulose. New carbonyl compounds conjugated with double bond at 1615 cm− 1 are probably the second chromophoric group. The crystallinity index was also calculated and showed an increase of cellulose crystallinity by prior degradation of amorphous cellulose. The FT-Raman analysis confirms the wood sensitivity to photodegradation but the most remarkable results is the increase of fluorescence as a function of time. In softwood lignin, the compound able to produce fluorescence is a free rotating 5–5′ linkage of one biphenyl structure. At native state these linkages are not free rotating, this phenomenon means the release of 5–5′ linkage of lignin structure by cleavage of both α carbon linkages (Norrish type I reaction). These data confirm also the photosensitivity of α and β carbon in lignin and the resistance of 5–5′ linkages.

Keywords
Wood; Photodegradation; Raman; FTIR; Colour measurement; Lignin
First Page Preview
Wood degradation under UV irradiation: A lignin characterization
Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology B: Biology - Volume 158, May 2016, Pages 184–191
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering