| Enhancing mechanical strengths and water absorption for modeling gypsum is an essential issue in ceramics manufacture. Within the materials of gypsum, β-hemihydrate is harder to be improved on its properties comparing to α-hemihydrate. So β-hemihydrate was selected as the main mould gypsum in this experiment. In this research, polymers are designed and synthesized to improve the mechanical strengths and water absorption for β-hemihydrate, such as eight polyether sulfonates(PCS, PAS-1, PAS-2, PAS-3, PS, PMS, POHS and POHAS) and six polyvinyl alcohol sodium sulfate(PVSNa). The effect of these polymers on the performances and hydration of β-hemihydrate was investigated. Moreover, because PVSNa had a strong improvement on properties of β-hemihydrate, the effect of PVSNa on the performance and hydration of α-hemihydrate was also studied. The main content and conclusions were summarized as follows:1. According to the polymerization rate of the monomers, the appropriate monomer with sulfonic acid group and the feeding modes were determined. Based on higher bending strength, compressive strength and water absorption of gypsum plasters made from β-hemihydrate, the synthetic conditions of polyether polyamide poly sodium sulfonate polymer(PAS) was optimized by single factor experiments and orthogonal test, such as the proportion of monomers, the reaction temperature and the dosage of initiator. The effect of PAS on the performance and crystal morphology of β-hemihydrate was also studied. It was found that PAS increased the aggregation degree of crystals of β-hemihydrate during the hydration. Comparing to the control, the bending strength of mould gypsum was improved up to 7%, the compressive strength of mold gypsum was not changed, and water absorption was decreased by 1% at the optimumal dosage(0.3%). So structure of the polymer should be redesigned and studied the structure-performance relationship of polymers in properties of gypsum plaster further.2. According to the results of single factor, orthogonal experiment and early achievements of the laboratory, eight polyether sodium sulfonates were synthesized. The structureperformance relationship of polymers in hydration of hemihydrate and properties of gypsum plaster were also studied. It was found that PCS with carboxylic group delayed the hydration and make the crystal morphology of hardened gypsum pieces made from β-hemihydrate easier peeling flake and more irregular, so the mechanical strengths were decreased and the water absorption was improved. While the other polyether sodium sulfonates without carboxylic group hardly influenced the hydration of β-hemihydrate, which could improve the mechanical strength and water absorption of gypsum plaster due to making the crystal morphology long columnar, more regular and smooth. In addition, it was found that reserving SMS as one of the raw material was a good choice for polymer applied in gypsum modeling material, PMS was the best choice in the synthetic polyether sodium sulfonates that was applied in modeling gypsum, and the bending strength, the compressive strength and the water absorption were increased 5%, 17% and 5% respectively at the optimum dosage(0.05%).3. Based on the fact that PVA and SO32- can improve the performance of mould gypsum, six PVSNa were synthesized by using chlorosulfonic acid as the sulfonating agent and PVA as the starting material. The effect of PVSNa on the properties of α-hemihydrate and β-hemihydrate were studied. It was found that the mechanical strengths of β-gypsum is related to the sulfonation degree; and the bending strength of α-gypsum decreased with the increasing sulfonation, but the compressive strength changed few. With a dosage of 0.1 w/w %, the bending strength, compressive strength and water absorption of hardened gypsum pieces made from β-hemihydrate was elevated by 29%, 14% and 3% using PVSNa22.76(PVSNa with sulfonated degree of 22.76%), respectively; While those of α-hemihydrate was increased by 9%, 4% and 5% using PVSNa11.6, respectively. |
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