Study on chemical conversion of highly condensed lignin into functional materials

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Sulfuric acid lignin (SAL) was selected as highly condensed lignin and was attempted to chemically convert into lignosulfonate as a functional material. Lignosulfonates have high dispersibility and caking, and are most available lignochemicals.SAL is high molecular weight lignin with little reactive functional group. Therefore, the increase of the solubility by depolymerization and of the reactivity is necessary to convert SAL into functional materials. SAL was at first phenolized to activate, and phenolized SAL (PSAL) was obtained. Next PSAL was treated with formaldehyde to introduce a reactive hydroxymethyl group for sulfonation. Neutral sulfonation of the hydroxymethylated product gave soluble lignosulfonate in quantitative yield. A comparison of molecular wight distribution and sulfonic acid group content of the product with those of commercial lignosulfonates indicated the same extent of functionalyty.In order to elucidate reaction mechanisms and side reactions in the above reactions, a lignin model compound with beta-aryl ether structure was selected, and the following results was obtained ; (1) selective phenolation of condensed structure, (2) secondary formation of diarylmethane structure in hydroxymethylation at higher temperature (120ﾟC), (3) higher reactivity of guaiacyl nucleus than p-hydroxyphenyl nucleus in hydroxymethylation, and (4) hygh yields in sulfonation.