Different modified PTFE gaskets (rPTFE)

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In the previous issue, we discussed that due to its excellent sealing properties, rPTFE is widely used in industries such as chemicals, petroleum, pharmaceuticals, and food processing. However, due to the easy availability of the raw materials used in its production and the fact that the color of rPTFE-modified materials can be easily replicated, many competitors claim that their products are made of rPTFE. So what are the differences among rPTFE products available on the market? I. Raw materials for preparation: Although PTFE is used as the base material, due to different polymerization methods, PTFE exists in the form of suspended material (polymerized by suspension method) and dispersed material (polymerized by dispersion method), that is, suspended polytetrafluoroethylene and dispersed polytetrafluoroethylene. The main method for shaping suspended material (suspended polytetrafluoroethylene) is compression molding: the white powder is mixed with certain additives and molded, after which it is sintered at a temperature higher than the melting point of polytetrafluoroethylene. Through appropriate mechanical processing, various products such as sheets, rods, tubes, and films can be obtained. Dispersed material (dispersed polytetrafluoroethylene) is PTFE in the form of fine powder, produced by dispersion polymerization. Due to the strong fibrous properties of this fine powder (especially at temperatures above 20°C), it is recommended to store, transport, and mix it under conditions of 5–10°C. The molding method for this material involves mixing the additives with the powder, allowing it to sit in an environment at a temperature above 24°C for about 24 hours (to complete the phase transformation), followed by shaping using a piston, drying, and sintering. After being shaped, the dispersed material is prepared through paste extrusion or pushing, followed by processes such as drying and sintering. This processing method is generally known as paste extrusion, or also as pushing extrusion. Although they are both called PTFE, their prices differ by several times; the difference is mainly determined by particle size, with the dispersed material having fine particles and the suspended material having coarser particles. II. Manufacturing Process: As we learned in the previous section, PTFE is a polymer with a relative molecular weight of approximately 100,000 to 500,000 grams per mole. Converting these large molecules into modified PTFE gasket products is not a simple process. Conventional filler-modified PTFE gaskets are generally made by mixing fillers (such as hollow glass microspheres, silica, barium sulfate, etc.) with PTFE resin evenly, molding them into a green body, and then preparing them through high-temperature sintering (turning). Although the colors are similar, its performance is vastly inferior to that of genuine filled modified rPTFE gaskets. To achieve isotropic properties in the sheet material, PTFE resin is thoroughly mixed with fillers and then repeatedly compressed through a lamination process to form a highly fibrous structure. The addition of fillers results in rPTFE gaskets that possess a highly dense structure and uniform, excellent performance, addressing the issue of creep and cold flow that is common in conventional PTFE sealing materials. III. Performance differences: The typical performance difference between PTFE modified with fillers through modification methods and traditionally molded and sintered PTFE modified with fillers lies mainly in its creep resistance. True high-quality rPTFE sealing materials possess a highly fibrous structure within them, thanks to a special manufacturing process, which results in significantly improved creep resistance compared to traditional compression-sintered PTFE. Generally speaking, it is possible to determine whether a material is a good sealing material by examining the leakage amount and creep relaxation rate after sealing with gaskets under the same conditions. That’s all for today’s sharing. What type of rPTFE are you using? How about the sealing performance? Feel free to send a private message or call the number below to talk.