Generally, the crystallinity of ptfe is 90 ~ 95%, and the melting temperature is 327 ~ 342℃. The CF2 units in ptfe are arranged in zigzag shape. Because the radius of fluorine atom is slightly larger than that of hydrogen atom, the adjacent CF2 units cannot completely follow the trans-cross orientation, but form a spiral twisted chain. Fluorine atom almost covers the whole polymer chain. This molecular structure explains the various properties of ptfe. When the temperature is lower than 19℃, 13/6 spiral is formed. A phase transition occurs at 19℃, and the molecules are slightly uncoiled to form a 15/7 helix. It does not melt at 250℃ and does not brittle at -260℃. Teflon is so smooth that ice can't beat it; It is particularly well insulated, with a film thick enough to withstand 1, 500 volts.
1. Polytetrafluoroethylene is produced by free radical polymerization of tetrafluoroethylene. Ptfe has "cold flow". PTFE can only use molding and extrusion processes to make simple products, which is difficult to form. Complex products must be processed by machine tools in the later stage, which limits the production efficiency of products. In the process of processing, materials are wasted too much.
2. That is, the plastic deformation (creep) of material products under continuous load for a long time, which brings certain limitations to its application. For example, when PTFE is used as a gasket, the bolts are screwed so tightly that they exceed the specified compression stress, causing the gasket to produce a "cold flow" (creep) that flattens it. These shortcomings can be overcome by adding appropriate packing and improving the structure of parts.
3. Ptfe has a high melt viscosity and does not flow at high temperatures. It is above the melting point (327℃), the melt viscosity reaches 1010Pa. S, even if heated to the decomposition temperature will not flow, which makes it can not be used in the general thermoplastic molding method, but the sintering method like powder metallurgy.
4.PTFE has outstanding non-viscosity, which limits its industrial application. It is an excellent anti-adhesion material, which makes it very difficult to adhere to the surface of other objects. PTFE has low thermal conductivity and poor thermal conductivity, which not only prevents PTFE from being used as a bearing material, but also prevents it from quenching when making thick-wall products.
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