Although the performance of PTFE is stable, its disadvantages are obvious.
(1) PTFE has "cold flow property". That is, the plastic deformation (creep) of material products under the action of long-term continuous load, which brings certain limitations to its application. For example, when PTFE is used as a gasket, the bolt is screwed tightly for tight sealing, so that when the specific compressive stress is exceeded, the gasket will produce "cold flow" (creep) and be flattened. These shortcomings can be overcome by adding appropriate fillers and improving the structure of parts.
(2) The melt viscosity of polytetrafluoroethylene is very high and does not flow at high temperature. It is above the melting point (327 ℃), and the melt viscosity reaches 1010 PA · S. even when heated to the decomposition temperature, it will not flow. Therefore, it can not be molded by the general thermoplastic molding method, but by the sintering method similar to powder metallurgy.
(3) PTFE has outstanding non viscosity, which limits its industrial application. It is an excellent anti sticking material, which makes it extremely difficult to adhere to the surface of other objects.
(4) PTFE has low thermal conductivity and poor thermal conductivity, which not only prevents it from being used as bearing material, but also makes it impossible to quench thick wall products.
(5) The linear expansion coefficient of PTFE is 10 ~ 20 times of that of steel, which is larger than that of most plastics. The linear expansion coefficient of PTFE varies irregularly with the change of temperature. In the application of PTFE, if not pay enough attention to this aspect of performance, it is easy to cause losses.
(6) When heated above 400 ℃, the pyrolysis rate of polytetrafluoroethylene (PTFE) increases gradually, and the main products are tetrafluoroethylene, PERFLUOROPROPYLENE and octafluorocyclobutane. Above 475 ℃, a small amount of highly toxic perfluoroisobutylene was found in the decomposition product. It should be noted that the heating temperature should not exceed 400 ℃, and the laboratory should have a good ventilation system to facilitate the removal of toxic gases.