竹材预水解过程中木质素对半纤维素溶出的抑制作用

The Resistance Effect of Lignin on Hemicelluloses Removal During Bamboo Hydrothermal Prehydrolysis

关键词:  竹材预水解  半纤维素脱除率  木质素  孔隙结构

Key Words:bamboo prehydrolysis  hemicelluloses removal  lignin  pore structure

摘要:以竹片为研究对象，分析预水解过程中半纤维素脱除率与木质素脱除率的关联性，特别是预水解后期木质素对半纤维素溶出的影响。将竹片用植物粉碎机粉碎后，取40～60 目竹粉模拟预水解实验，分析竹粉在预水解过程中的孔隙变化，结合预水解过程中竹片表面微观结构变化及木质素的迁移行为，探讨木质素对半纤维素溶出的抑制作用。结果表明，预水解过程中，半纤维素的脱除率与木质素存在一定关系；预水解前期，木质素和半纤维素同时降解溶出；预水解至一段时间后，木质素和半纤维素脱除率均达到最大值。继续预水解，木质素脱除率急剧下降，而半纤维素脱除率不再提高。环境扫描电子显微镜（ESEM）分析显示预水解后期的竹片表面基本被疏水木质素涂层覆盖，疏水涂层的存在可能会阻碍半纤维素的降解溶出。竹粉的模拟实验结果也证实了预水解后期竹粉的孔体积和孔径明显下降。因此，预水解固体基质中较高的木质素含量及由木质素迁移导致的纤维表面和纤维孔隙结构变化是阻碍预水解后期半纤维素进一步溶出的主要原因。

Abstract:Prehydrolysis is one of the most important steps for dissolving pulp production with an objective of degradation and dissolution of hemicelluloses, but the hemicelluloses removal can only reach to a limit level. In this work， the influence of lignin on the hemicellulose removal especially in the later stage of prehydrolysis was evaluated by the analysis of the relations between lignin and hemicellulose removal. The changes of pore structure of the bamboo powder which was prepared by grinding the bamboo chips and used to implement prehydrolysis simulation， the surface morphology of the bamboo chips， and together with lignin migration were used for elucidating the lignin resistance effect on hemicellulose removal. The results showed that hemicelluloses removal was closely correlated with lignin， both lignin and hemicellulose were degraded and dissolved at the same time in the initial stage of prehydrolysis， most of the hemicelluloses removed when the lignin removal reached to the maximum. As prehydrolysis continued the hemicelluloses removal no longer increased when lignin removal decreased sharply. It was referred from ESEM analysis that extensive pretreatment made the surface of fiber full of hydrophobic lignin coating which hindered the water attack and the diffusion of degradation products. The results from bamboo powder simulation experiment also confirmed that the pore volume and pore diameter of bamboo powder decreased obviously at the later stage of prehydrolysis. The relative high lignin content and the change of microstructure of the fiber caused by lignin migration were the main reasons for hindering hemicelluloses further removal．