The Use of Lignosulfonates as Water Reducing Agents in the Manufacture of Gypsum Wallboard

Abstract

The chemical treatment of woody materials to produce fibers (pulps) also produces a nearly equal amount of soluble chemicals consisting mainly of modified lignin and carbohydrate degradation products. In most chemical pulp mills, this material is burned to create energy for the recycling of pulping chemicals. A small number of pulp mills, mostly acid sulfite mills, purify the lignin streams and market this material commercially. In 1998, close to one million tons of lignosulfonates were used worldwide in a variety of industrial applications.1 The largest use of this material is as a dispersant of particle slurries such as concrete, clays, gypsum, and dyes.2 In these applications, lignosulfonates must compete with synthetic dispersants such as condensation polymers of formaldehyde with sulfonated naphthalene. Much effort, therefore, has been directed towards increasing the dispersing ability of lignosulfonates in these systems through chemical modifications and physical separations. These processes, however, can also affect other properties of the particle slurries such as setting time, air entrainment, and color. It is very important, therefore, to look at the entire system when considering a lignin modification. In this chapter, the effect that lignosulfonate components and chemical modification reactions have on the function of lignosulfonate dispersants in the manufacture of gypsum wallboard will be discussed.