Lignosulfonates are widely used as dispersing agents in a variety of particle systems. They function as surface active agents to prevent the formation of aggregates of finely divided insoluble particles in suspension. This results in the formation of more stable dispersions of reduced viscosity and sedimentation. Examples of systems that take advantage of the dispersing nature of lignosulfonates include concrete, clays, oil well muds, dyes, pigments, and gypsum slurries.In the manufacture of gypsum wallboard, industrial stucco and a variety of additives are combined with water to form a slurry which is deposited between paper liners and allowed to harden. The hardening process occurs through the hydration of calcium sulfate hemihydrate(stucco) to the dihydrate form (gypsum). The viscosity of the stucco slurry must be low enough to flow evenly across the paper in the forming section of the manufacturing process. This requires significantly more water than is needed to hydrate the stucco. The excess water is removed in a costly drying step.Stucco slurry viscosity can be reduced through the addition of lignosulfonates. The dispersing nature of lignosulfonates reduces the amount of water needed to make a flowable slurry. This results in reduced energy costs and faster throughput in the drying stage. Improvements are also obtained in certain physical properties of the board including compressive strength, density, and impact strength. Typical addition levels for lignosulfonates are of the order of 1-3 pounds solids per thousand feet of one-half inch wallboard.Lignosulfonates impart a certain degree of retardation to the set (hydration) of gypsum wallboard. In some cases this is a beneficial property as the retardation can prevent the gypsum slurry from setting during the mixing process. In plants running at high speeds, however, retardation is a problem that can only be overcome through the addition of costly accelerators. Mechanistic studies have shown that chelating agents in lignosulfonates such as aldonic acids and extractive compounds are mainly responsible for retardation.Modified lignosulfonate products have been developed which are significantly better dispersants than standard lignosulfonates. One way improved dispersing ability is achieved is through alkaline oxidation. This process increases the extent to which the sulfonated lignin polymer is adsorbed on particle surfaces- thus improving the dispersing nature of the product. The oxidation process, however, also significantly increases the retarding nature of the material.Another method that improves the dispersing nature of lignosulfonates is molecular weight fractionation. Low molecular weight sulfonated lignin polymers are not as efficient dispersants as higher molecular weight materials in industrial stucco slurries. Removal of the low molecular weight fraction through separation technologies such as ultrafiltration, dramatically improves the dispersing ability of the product. Additionally, set retardation is also eliminated. This occurs because most of the retarding chemicals in lignosulfonates are of low molecular weight and are therefore removed.

In addition to functioning as a dispersing agent in gypsum wallboard, lignosulfonates also perform effectively as binders, sequestrants and emulsifiers. They can be found in a broad spectrum of products ranging from coal briquettes to cleaning compounds. Perhaps the best evidence of their versatility is the federal approvals they hold for a variety of food contact usages.