The raw material tape is also called PTFE tape. PTFE is the polymer of tetrafluoroethylene, which is abbreviated as PTFE in English. The basic structure of PTFE is - [CF2] - n. The relative molecular mass of PTFE is relatively large, the low is hundreds of thousands, the high is more than 10 million, generally millions (the degree of polymerization is in the order of 104, while the polyethylene is only 103). Generally, the crystallinity is 90-95%, and the melting temperature is 327-342 °C. The CF2 units in the polytetrafluoroethylene molecule are arranged in a zigzag shape. Since the radius of the fluorine atom is slightly larger than that of the hydrogen, the adjacent CF2 units cannot be completely oriented in trans, but form a helical twisted chain, which is almost covered by the fluorine atoms. the surface of the entire polymer chain. This molecular structure explains the various properties of PTFE. When the temperature is lower than 19°C, a 13/6 helix is formed; at 19°C, a phase transition occurs, and the molecules are slightly unwound, forming a 15/7 helix. Although the cleavage of carbon-carbon bonds and carbon-fluorine bonds in perfluorocarbons requires energy absorption of 346.94 and 484.88 kJ/mol, respectively, the depolymerization of PTFE to 1 mol of tetrafluoroethylene requires only 171.38 kJ of energy. Therefore, during high temperature cracking, PTFE is mainly depolymerized into tetrafluoroethylene. The weight loss rate (%) of polytetrafluoroethylene at 260, 370 and 420 °C was 1 × 10-4, 4 × 10-3 and 9 × 10-2 per hour, respectively. It can be seen that PTFE can be used for a long time at 260 °C. Since highly toxic by-products such as fluorophosgene and perfluoroisobutylene are also produced during high-temperature pyrolysis, special attention should be paid to safety protection and to prevent PTFE from contacting open flames.
