CHANGES IN PHYSICO-CHEMICAL CHARACTERISTICS AND STRUCTURES OF WHEAT STRAW SODA LIGNIN AFTER MODIFICATION

麦草碱木素在碱催化下经脱甲基改性可提高其反应活性．本文采用元素分析、扫描电镜、凝胶色谱、１ＨＮＭＲ和１３ＣＮＭＲ波谱较系统地研究脱甲基改性麦草碱木素化学组成、微观表面形态和化学结构的变化．研究结果表明，脱甲基活化改性后，麦草碱木素的甲氧基含量由１０．３％降至６．０９％，而酚羟基和羧基含量分别由２．９８％和４．５８％增至５．５１％和７．１０％．脱甲基改性后氧元素含量下降，改性麦草碱木素的微观形态呈致密的球形，在尺寸上比未改性的麦草碱木素小．改性后麦草碱木素的平均相对分子质量（Ｍｗ）由６２１７降至５１４８，相对分子质量分布情况发生变化．脱甲基改性使苯环上的烷基芳基醚键断开，形成酚羟基，同时，在一定程度上也伴随木素结构单元间化学联接的断裂，体现在其核磁共振波谱和平均相对分子质量的变化．

CHANGES IN PHYSICO_CHEMICAL CHARACTERISTICS AND STRUCTURES OF WHEAT STRAW SODA LIGNIN AFTER MODIFICATION *

The reactivity of wheat straw soda lignin(WSSL) can be improved by demethylation modification. The changes of demethylated WSSL in chemical composition, micromorphology and chemical structure were studied by elemental analyses, scanning electronic microscope, GPC, 1H NMR and 13 C NMR spectra. The results showed that the content of methoxyl group decreased from 10.39% to 6.09%, and the contents of phenolic hydroxyl group and carboxyl group increased from 2.98% and 4.58% to 5.51% and 7.10% respectively after the demethylation. The oxygen content of demethylated WSSL decreased. The particles of demethylated WSSL are spherical, and are smaller in size than unmodified WSSL. The average molecular weight( M w ) of demethylated WSSL decreased from 6 217 to 5 148, and the distribution of molecular weight obviously changed. The demethylation modification led to the break of aryl alkyl ether linkages and the generation of phenolic hydroxyl group, meanwhile, accompanied by the break of other linkages in lignin structure. The changes in 1 H NMR, 13 C NMR and average molecular weight support this conclusion.