Patent ID: 8093326

Claim:
A process for dispersing an aqueous calcium sulfate hemihydrate composition and controlling the initial setting and/or final setting time of said aqueous calcium sulfate hemihydrate, comprising the steps of: providing an aqueous calcium sulfate hemihydrate composition having a weight ratio of water/calcium sulfate hemihydrate of 0.55 to 0.75; and admixing with the aqueous calcium sulfate hemihydrate a selected polycarboxylic dispersant, said dispersant comprising between 0.01% and 2% dry weight with respect to the weight of the calcium sulfate hemihydrate, and wherein the polycarboxylic dispersant comprises at least 75% by number, excluding terminal chain units, of a random linear chain formation of structural units (1) and (2) represented by the following formulae: in which X represents a hydrogen atom, an alkali metal, an alkaline-earth metal or an ammonium; said structural units (1) may be identical or different; n is a whole number varying from 1 to 250, m is 0; the propylene oxide groups may or may not be randomly distributed among the ethylene oxide groups; R represents an alkyl group containing 1 to 12 carbon atoms; said structural units (2) may be identical or different; the ratio of the number of structural units (2) to the total number of structural units (1) and (2) being comprised between 5% and 60%, and wherein in a “Smith's Ring” plaster cake test performed at 23° C.±2° C. said dispersant controls the initial and final setting times for the aqueous calcium sulfate hemihydrate composition.