Papermaking additives from kraft lignin

Kraft lignin separated from industrial black liquor by carbon dioxide precipitation can be modified by different chemical reactions : thermal hydroxymethylation, oxidation, condensation and urea-condensation. The lignin derivatives thus obtained show increased functionality and higher molecular weight. Testing in corrugating medium paper furnish indicates that lignin derivatives can contribute to improving strength characteristics up to 30%, thus assuring economical utilization of the fibrous material.