Carboxylated alkali lignin sulphonate dye dispersant and preparation method thereof

The invention discloses a carboxylated alkali lignin sulphonate dye dispersant and a preparation method. The reaction raw materials comprises the following formula by mass fraction: 100 parts of alkali lignin, 20-60 parts of sulfonating agent, 2-20 parts of aldehydes compound and 20-45 parts of carboxylic acid compound. The alkali lignin is prepared by acidification of bamboo, Chinese oak, poplar, Eucalyptus, birch, a papermaking black liquor by a masson pine alkali method, the mass percentage is 95%. The preparation method comprises the following steps: preparing alkali lignin to a solution with mass fraction of 20-40%, then adding the sulfonating agent and the aldehydes compound for sulfomethylation reaction to prepare alkali lignin sulphonate, and the alkali lignin sulphonate is subjected to a carboxylation reaction with the carboxylic acid compound to prepare the carboxylated alkali lignin sulphonate. The prepared carboxylated alkali lignin sulphonate contains sulfonic group and carboxyl group, can be used as the dye dispersant, and has good dispersibility to the disperse dyes. Phenolic hydroxyl group with reductibility is subjected to the reaction in a modification reaction, so that reduction to an azo dye and contamination to the dispersant can be greatly reduced.