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The critical pressure of pure PTFE material is about 27.5MPa. The compressive strength of PTFE material decreases with the increase of pressing pressure; the compressive modulus increases with the increase of pressing pressure. Finally, it is determined that the molding pressure of PTFE is 27.5MPa. The determined sintering process is: sintering temperature is 380℃, holding time is 4h, heating rate is 80℃/h at 200℃, 60℃/h above 200℃, and cooling rate is furnace cooling. It also has good electrical properties, and its electrical insulation is not affected by temperature. It is known as the "Plastic King".
(1) Preparation of monomer tetrafluoroethylene: Trichloromethane is used as raw material in the industry. Trichloromethane is fluorinated with anhydrous hydrofluoric acid. The reaction temperature is above 65℃. Antimony pentachloride is used as a catalyst. Finally, heat is used. Tetrafluoroethylene is made by cracking method; (Tetrafluoroethylene can also be made by the reaction of zinc with tetrafluorodichloroethane at high temperature.)
(2) Preparation of polytetrafluoroethylene: in an enamel or stainless steel polymerizer, use water as the medium, potassium persulfate as the initiator, perfluorocarboxylic ammonium salt as the dispersant, fluorocarbon as the stabilizer, and tetrafluoroethylene Polytetrafluoroethylene is obtained by redox polymerization. Add various additives into the reaction kettle, the tetrafluoroethylene monomer enters the polymerization kettle in the gaseous phase, adjust the temperature in the kettle to 25°C, then add a certain amount of activator (sodium bisulfite), and initiate the polymerization through the oxidation and reduction system. Continuously add monomers during the polymerization process and keep the polymerization pressure 0.49～0.78MPa. The dispersion obtained after polymerization is diluted with water to a certain concentration, and the temperature is adjusted to 15～20℃. After condensing with mechanical stirring, it is washed and dried with water. That is, this product is a fine-grained resin.