Optimization On Particle Morphology Of Poly(Tetrafluoroethylene) Dispersion Resins

Polytetrafluoroethylene (PTFE) is successfully used as sealing, coating and insulation materials due to its excellent chemical and high temperature resistance, insulation and non-adhesive properties, et al. PTFE dispersion resin is an important type of PTFE resins, which exhibits high production technology and product quality requirements, and high value. The home made PTFE dispersion resin exhibit poor oil absorption and extension properties, compared with the abroad advanced PTFE dispersion resins. In this thesis, the particle morphology of PTFE dispersion resins were optimized and the application properties of PTFE resins synthesized before and after the technological improvement were compared.TFE dispersion polymerization process is a typical chemical process connecting with gas-liquid mass transfer. The vertical self-suctioning agitated vessels were initially used in Jushen Fluoro Chemical Corporation. The shear on PTFE primary particles was greater since a greater speed should be applied for vertical vessels to guarantee the mass transfer rate. Thus, the PTFE primary particles were easy to deform and the rod-like primary particles with smaller size were dominant in the PTFE dispersion. Although the length-radius ratio decreased as the concentration of dispersant decreased, the near spherical shape primary particles were still difficult to obtain. In order to overcome the above problem, the horizontal agitated vessel with high mass transfer efficiency were designed and applied in TFE dispersion polymerization. It was found that the PTFE primary particles with near spherical shape could be prepared at range of the experimental concentration of dispersant. The particles size increased and the size distribution widened as the concentration of dispersant decreased. The concentration of dispersant was optimized as 1.75g/l water.In considering the greater aggregation degree and lower porosity of the initial PTFE dispersion resins, the coagulation technology was optimized in the original industrial devise. It was found that the coagulation time and agitation speed had great influences on the morphology of PTFE resin. The aggregation degree increased and the porosity decreased as the coagulation time and agitation speed increased. The optimized coagulation conditions were as follows:coagulation equipment: (?) 1000*2000Coagulation time: 15minCoagulation temperature: 15～20℃Agitation speed: 95rpmThe application properties of PTFE dispersion resins produced before and after the technology improvement were compared. It was found that the molecular weight and tensile strength of PTFE produced in the horizontal agitated vessel and with optimized particles morphology, was greater than that of PTFE produced in the vertical self-suctioning agitated vessels. The sealing sheets produced using PTFE dispersion resins with improved particle morphology had uniform thickness, good surface characteristics and suitable hardness.