Oxidation And Sulfomethylation Of Alkali Extracted Lignin From Corn Stalk

A new type of technical lignins, named as alkali-extracted lignin （AEL）, has beenobtained by the extraction of corn stalk with dilute alkali solution under mild conditions. AELexhibits narrower molecular mass distribution and higher reactivity than soda lignin due to themild separation conditions. AEL is thus expected to be an important raw material of ligninbased products. Soluble lignin was prepared by oxidation and sulfomethylation from AEL.In order to improve the reactivity of lignin, AEL was oxidized by Fenton oxidation andUV oxidation catalyzed by TiO₂respectively. After UV oxidation, the relative molecular massof AEL decreased to5300from8900, demonstrating the degradation of AEL. The content ofphenolic hydroxyl in AEL increased to2.90mmol/g from2.85mmol/g after UV oxidation,demonstrating that UV oxidation resulted in both the cleavage of aryl ether linkages and theoxidation of phenolic hydroxyls. Different results, however, were obtained by Fentonoxidation. After Fenton oxidation, the relative molecular mass of AEL decreased to4900from8900, indicating that AEL was degraded by Fenton oxidation under mild conditions. Thecontent of phenolic hydroxyl in AEL increased to3.35mmol/g from2.85mmol/g. The resultindicated that some aryl ether linkages in AEL were cleaved by Fenton oxidation. Thereactivity of AEL was thus expected to be enhanced.Fenton oxidized AEL （F-OAEL） was aminated and sulfonated. The impacts of aminationand sulfonation on solubility and surface tension were investigated. The surface tension of10g/L aqueous sulfonated lignin solution was reduced to a minimum of41.2mN/m,demonstrating that the surface activity of AEL was improved. However, the solubility of AELwas not good enough though it had been improved by amination and sulfonation.In order to improve the solubility, F-OAEL was sulfomethylated. The impacts ofsulfomethylation on sulfonic group content, solubility, and surface tension of AEL wereinvestigated. The content of sulfonic group significantly increased with the increase of sodiumsulphite to AEL ratio, and the content then remained constant when sodium sulphite to AELratio was1:1. The content of sulfonic group increased with time, and then kept constant at5h.The sulfonic group content of the sulfomethylated AEL achieved a maximum of1.29mmol/gwhen AEL was sulfomethylated at sodium sulfite to AEL ratio of1:1and sulfonate time of5h.The solubility and the surface activity of AEL were obviously improved by sulfomethylation.The sulfomethylation products exhibited good dispersibility and had a potential use as a dyedispersant.