Abstract:

In order to improve the water solubility and increase the relative molecular mass of wheat straw alkali lignin (W AL) , the modification of W AL by oxidation and sulfomethylation was carried out with F enton 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 Mw 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.

Key words: alkali lignin, modification, Fenton agent, oxidation, sulfomethylation