Plasticizers - For Gypsum Wallboard Production

For Gypsum Wallboard Production

Plasticizers can be added to wallboard stucco mixtures to improve workability. In order to reduce the energy in drying wallboard, less water is added, which makes the gypsum mixture very unworkable and difficult to mix, necessitating the use of plasticizers, water reducers or dispersants. Some studies also show that too much of lignosulfonate dispersant could result in a set-retarding effect. Data showed that amorphous crystal formations occurred that detracted from the mechanical needle-like crystal interaction in the core, preventing a stronger core. The sugars, chelating agents in lignosulfonates such as aldonic acids and extractive compounds are mainly responsible for set retardation. These low range water reducing dispersants are commonly manufactured from lignosulfonates, a by-product from the paper industry.

High range superplasticizers (dispersants) have generally been manufactured from sulfonated naphthalene condensate, although polycarboxylic ethers represent more modern alternatives. These high range water reducers are used at 1/2 to 1/3 of the lignosulfonate types.

Traditional lignosulfonate and naphthalene sulfonate based plasticisers disperse the flocculated gypsum particles through a mechanism of electrostatic repulsion (see colloid). In normal plasticisers, the active substances are adsorbed on to the gypsum particles, giving them a negative charge, which leads to repulsion between particles. Lignin and naphthalene sulfonate plasticizers are organic polymers. The long molecules wrap themselves around the gypsum particles, giving them a highly negative charge so that they repel each other.Kirby, Glen H.; Jennifer A. Lewis (2002). "Rheological property evolution in concentrated cement-polyelectrolyte suspensions". Journal of the American Ceramic Society 85 (12): 2989–2994. doi:10.1111/j.1151-2916.2002.tb00568.x. Retrieved 2008-03-27.