Sulfite pulping of wood chips produces a pulping liquor rich in sulfonated aryl alkyl ether polymers called lignosulfonates. Ultrafiltration of these liquors produces concentrates of these lignosulfonates some of which are present as a salt of the cation used to buffer the cook. Ultrafiltration concentrates of calcium lignosulfonates were found to undergo significant viscosity increases when made alkaline. Gels can be formed from 42% solids from spruce and birch calcium lignosulfonates in a few minutes by making the solution 15% on solids in sodium hydroxide. A molecular weight distribution analysis of spruce calcium lignosulfonates and decationized samples by gel chromatography showed a drop in molecular weight suggesting that the calcium ion holds together portions of the lignosulfonates. Additions of calcium back to an ion exchanged sample showed no gel formation, only the formation of a precipitate.
ASJC Scopus subject areas
- Agricultural and Biological Sciences(all)