Study On Gypsum Surface Modification And Its Application In Resin

Gypsum, as one of the widely distributed nonmetallic minerals, is widely used in plastics, rubber, paint and paper industries. But when natural gypsum was used as filler, the compatibility with polymer is not satisfied, the surface modification technology can be needed to improve the dispersion of gypsum with organic polymer base materials.In this work, we broaden and deepen the research on the surface modification of natural gypsum(GY) by stearic acid and the application of the modified gypsum(MGY) in resin. The optimal system of modification was determined by activation index. FT-IR, SEM, XRD, TG, contact angel and compatibility analysis have been combined to analyze the property of MGY. In addition, MGY-PS, MGY-PMMA composites were prepared when MGY is the filler, Polystyrene(PS) or Polymethylmethacrylate(PMMA) is the substrate. To MGY-PS composites, SEM was used to analyze the dispersion of MGY in PS, and mechanical properties, thermal stability were used to evaluate its physical properties. For MGY-PMMA composites, we mainly analyze the mechanical properties, thermal stability and transparency. The main results are as follows:1. When using stearic acid modified GY, modified system for optimum is dosage of modifier 6%, modified temperature 60 oC, modification time 40 min, modified pH 7. In this case, the activation index of obtained MGY can reach to 100%.2. During the process of modification, the stability of GY surface was damaged when the hydroxyl of GY was replaced by stearate radical, so as to achieve the effect of modification. After modification, the thermal stability of GY improved, the contact angel of GY increased from 35.64° to 87.47° and the compatibility between GY and atoleine got enhanced.3. For the MGY-PS composites, great improvement of retardancy was obtained when MGY was added into this system. The flammable PS turned combustible MGY-PS material as the content of MGY was 20%, and when the content of MGY was 50%, the MGY-PS composites became nonflammable material. Besides, compare to pure PS, the tensile strength of the GY-PS(1 : 5) composites was increased by 4%, and the elongation at break was increased by 8%. But the mechanical properties promotion of MGY-PS(1 : 5) composites could be more obvious, for the tensile strength of the MGY-PS composites was about 106% to that of pure PS, and the elongation at break was about 110% to that of pure PS.4. For the MGY-PMMA composites, certain extent improve of thermal stability will be obtained when MGY was added into the system. But the content of MGY will seriously affect the transmittance of the composites. The transmittance of the composites can maintain above 80% as the content of MAG was under 1%. In addition, the mechanical properties of composites can be obviously promoted by adding MGY. When the content of MGY was 2%, the tensile strength of MGY-PMMA was increased by 28% comparing to pure PMMA and the elongation at break increased to 18% of pure PMMA.