Hexenuronic acid groups in pulping and bleaching chemistry

Hexenuronic acid groups are formed in xylan chains during kraft pulping. Th ese acid groups cause increased consumption of bleaching chemicals, decreas ed brightness, greater brightness reversion, and poorer metal removal. Thes e hexenuronic acid groups can be selectively removed by an acid treatment, and bleaching chemicals can be saved as a result. This review of current kn owledge of hexenuronic acid chemistry includes discussions of the structure , the stability and reactivity, the preparation and quantification, and the formation and degradation of hexenuronic acid during kraft pulping and ble aching.