麦草碱木质素的氧化和磺甲基化改性

Modificaion of Wheat Straw Alkali Lignin by Oxidation and Sulfomethylation

针对麦草碱木质素水溶性差、相对分子质量低的问题,以Fenton试剂为氧化剂、亚硫酸钠为磺化剂对麦草浆碱木质素进行氧化和磺甲基化改性.采用分子轨道理论对碱木质素和羟甲基化碱木质素分子单元进行了电荷密度计算,发现愈创木基单元中苯环上的C-5位最容易进行磺甲基反应.将麦草碱木质素经氧化后进行磺甲基化反应,得到磺甲基化碱木质素,红外光谱测试表明产物中具有磺酸基的特征吸收峰,电导滴定法测得其磺化度为0.96mmol/g,Zeisel法测得甲氧基含量为5.41%,凝胶渗透色谱测得其重均相对分子质量M-w达6 653.当溶液质量浓度为30 g/L时,溶液表面张力达45.3mN/m.水泥净浆流动度测试表明,产物对水泥净浆的分散性能与木质素磺酸钙相近.

In order to improve the water solubility and increase the relative molecular mass of wheat straw alkali lignin （WAL）, the modification of WAL by oxidation and sulfomethylation was carried out with Fenton agent as the oxidant and sodium sulfite as the sulfonating agent. The charge density distributions of the structural elements of aromatic groups in lignin and hydroxymethylignin were analyzed based on the molecular orbital theory, finding out that the possible position of sulfomethylation is C-5 in guaiacyl suit. Then, sulfomethylignin was obtained by the sulfomethylation of WAL after the oxidation. FTIR results show that the product exhibits a typical absorption of sulfomethylate group. The conductometric titration reveals that the content of sulfomethylate group is 0. 96 mmol/g. Moreover, a methoxyl content of 5.41% and a M^-w value of 6653 are respectively measured by the Ziesel method and GPC, and a surface tension of 45.3 mN/m at a solution mass concentration of 30 g/L is measured. A similar dispersion of the product to that of calcium lignosulfonate in cement slurry is finally revealed by fluidity test.