Influence of polysulfonates on the properties of β-calcium sulfate hemihydrate and its hydration

Surfactants have been used to modulate mechanical properties and hydration of calcium sulfate hemihydrates or other cement-like material, especially to improve the properties of cheap materials. In gypsum industry, beta-Hemihydrate (beta-H) costs less than the alpha-hemihydrate but presents lower mechanical strength after hydration. In this study, a group of polysulfonates was designed and synthesized to investigate their structure-performance relationship in hydration of beta-H and properties of the gypsum plaster. It was found that the hydration of beta-H can be modulated by changing the hydrophilic side chain of the polysulfonates, which endowed the gypsum with differential mechanical strength and water absorption. The sodium alkenyl methyl polyoxyethylene ether amide vinyl/ally sulfonate offered the beta-H gypsum highest water absorption, retarded hydration and enhanced mechanical strengths by forming compacter rod crystals. The mechanical strength and water absorption of the gypsum were not in direct proportion to hydrophilicity of the polysulfonates and the molar fraction of sulfonic groups, but related to their McGowan's HLB values. When the HLB values were below 15, the water absorption of beta-H gypsum induced by the polymers increases with the increasing HLB values of the polymers.