Light-Induced Yellowing of Mechanical and Ultra-High Yield Pulps. I. Effect of Methylation, NaBH4, Reduction and Ascorbic Acid on Chromophore Formation
作者:
JohnA. Schmidt,
Cyril Heitner,
期刊:
Journal of Wood Chemistry and Technology
(Taylor Available online 1991)
卷期:
Volume 11,
issue 4
页码: 397-418
ISSN:0277-3813
年代: 1991
DOI:10.1080/02773819108051083
出版商: Taylor & Francis Group
数据来源: Taylor
摘要:
Absorption difference spectra of bleached TMP irradiated with near-uv light exhibited two apparent absorption maxima at π 410 nm and 330 nm. Experiments with borohydride-reduced pulp suggest that photochemical formation of aromatic carbonyls contributes to the λ = 330 nm peak. Chromophore formation followed an apparently first-order rate law, and the rate was unaffected by methylation of phenolic hydroxyl groups, or by exhaustive reduction of carbonyl groups with NaBH4. Methylation of phenolic hydroxyl, while having no effect on the kinetics of chromophore formation, did decrease the maximum change in absorption coefficient, ΔK∞. Treatment of bleached TMP with ascorbic acid slowed light-induced yellowing substantially; significant yellowing occurred only after 2 hours. Light-induced bleaching of a chromophore with λmaxπ 350 nm, possibly a stilbene, occurred during the first 90 minutes of irradiation.
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