桉木光诱导氧化降解研究

Photoinduced oxidative degradation of Eucalyptus wood and SCMP

本文研究了尾叶桉（Eucalyptusurophylla）木粉在光照射下其木素和多聚糖的变化行为．研究表明，在光照射下木素及木素结构单元中的甲氧基含量降低，多聚糖含量降低，铜价升高．UV分析可知，木素光降解产物中羰基或与苯环共轭的乙烯双键结构较多．经GC－MS分析鉴定出尾叶桉SCMP浆40种低分子量木素光氧化降解产物，其中丁香基型占58．10％，愈疮木基型占18．75％，其它占21．93％，主要降解产物包括丁香醛、2－羟基－3－丁香基丙酸、3，4－二羟基苯甲酸,2－丁香基乙醇、丁香酸、丁香酸和香兰素等.另外也研究了光降解过程中木素自由基变化行为。ESR分析测定表明，光照射产生的自由基在纯的氮气或二氧化碳中相对稳定，在空气或氧气中游离基迅速衰减，从而证实光诱导氧化作用是木材或富含木素化学机械浆光降解的重要作用。

This article dealt with the chemical changes in both the lignin and the polysaccaridic part of irradiated Eucalyptus urophylla wood meal.This is characterized by a decrease in lignin content, a reduction in methoxyl content, a reduction in polysaccaride content and an increase in copper number. By GC-MS technique about 40 compounds of low molecular weight lignin, when exposed to light, were identified from E. urophylla SCMP as their trimethylsilyl derivatives. The main degradation products include syringaldehyde, 2-hydroxy-3-guaiacylpropanoic acid, protocatechic acid t 2-syringylethanol, syringic acid, syringol and vanillin etc. In all 40 compounds, the syringyl compound is 58. 10%, the guaiacyl compound is 18. 75%, and others is 21. 93%. This paper also investigated the characteristics of free radicals produced by light in different atmospheres. By using ESR analytical technique it is demonstrated that the formation of free radicals is a direct effect of photoenergy and probably is independent of the presence of oxygen.They appear to be relatively stable in highly purified nitrogen or carbon dioxide, but in air or oxygent a measurable decay of free radical concentration was observed. This suggests that photoinduced oxidation is an important mechanism in the degradation of wood or lignin-rich high-yield pulps.