(279a) Effects of Synthetic Polymers on Mechanical Strength and Water Absorption of Hardened Gypsum Pieces Made from Calcium Sulfate Hemihydrates

    α- or β-Calcium sulfate hemihydrate (α-H or β-H) is commonly used as gypsum-modeling material for ceramics, which require high mechanical strength and water absorption. Polymers may affect the gypsum performance and ratio of water to hemihydrate (W/H). In this experiment, the effect of W/H, the addition and structure of some synthetic polymers on the properties of hardened gypsum piece were investigated. It was found that α-H and β-H are hardly workable in common W/H region; their performances are strictly relevant to W/H. At a W/H as high as 0.7, the more hydrophilic polymers provided an increase in the mechanical strength and water absorption; four sulphur polycarboxylates synthesized were found to maintain or enhance water absorption of β-H, but only the one without carboxyl group led to an increase of the mechanical strength. The results suggest that keeping sulphur and PVA residues in the molecular design will be necessary for polymer structure applied in gypsum modeling material.