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Although the properties of PTFE are stable, its disadvantages are also obvious.
(1) Polytetrafluoroethylene has "cold flow." That is, the plastic deformation (creep) of a material product under a continuous load for a long period of time imposes certain limitations on its application. When PTFE is used as a gasket, the bolts are tightened tightly so that when a specific compressive stress is exceeded, the gasket will “cold” (creep) and be flattened. These disadvantages can be overcome by adding suitable fillers and improving the structure of the parts.
(2) PTFE has a high melt viscosity and does not flow at high temperatures. It has a melting point (327 °C) or higher, and has a melt viscosity of 1 010 Pa.s. Even if heated to the decomposition temperature, it does not flow. This makes it impossible to use ordinary thermoplastic molding methods, but to use powder metallurgy-like sintering. Method molding.
(3) PTFE has outstanding non-stickiness, limiting its industrial applications. It is an excellent anti-sticking material, which in turn makes it extremely difficult to adhere to the surfaces of Other objects.
(4) PTFE has low thermal conductivity and poor thermal conductivity, which not only prevents it from being used as a bearing material, but also makes it impossible to quench hard-walled products.
(5) The coefficient of linear expansion of PTFE is 10 to 20 times that of steel, which is larger than that of most plastics. The coefficient of linear expansion of the PTFE varies very irregularly with temperature. When PTFE is used, it is easy to cause losses if there is not enough attention to performance in this area.
(6) When heated above 400°C, the cracking rate of PTFE gradually increases, and the decomposition products are mainly tetrafluoroethylene, perfluoropropylene and octafluorocyclobutane. Above 475°C, the decomposition products have extremely small amounts of highly toxic perfluoroisobutene. Note that the heating temperature should not exceed 400 °C, and the laboratory should have a good ventilation system to help eliminate toxic gases.
