What is expanded polytetrafluoroethylene?

Update:22 Dec 2018
Summary:

Polytetrafluoroethylene (abbreviated as teflon, commonl […]

Polytetrafluoroethylene (abbreviated as teflon, commonly referred to as "non-stick coating" or "easy to clean materials." This material is resistant to acids and alkalis, resistant to various organic solvents, and is almost insoluble in all solvents. At the same time, PTFE has the characteristics of high temperature resistance, and its friction coefficient is extremely low, so it can be used as a lubricant to clean the inner layer of the water pipe.
The relative molecular mass of PTFE is relatively large, hundreds of thousands of low, and more than 10 million

It is generally in the millions (the degree of polymerization is on the order of 10^4, while the polyethylene is only at 10^3). The crystallinity is generally 90 to 95%, and the melting temperature is 327 to 342 °C. The CF2 units in the PTFE molecule are arranged in a zigzag shape. Since the radius of the fluorine atom is slightly larger than that of the carbon, the adjacent CF2 units cannot be completely cross-oriented, but form a helical twisted chain, and the fluorine atoms are almost covered. The surface of the entire polymer chain. This molecular structure explains the various properties of polytetrafluoroethylene. When the temperature is lower than 19 ° C, a 13/6 helix is formed; at 19 ° C, a phase change occurs, and the molecules are slightly untwisted to form a 15/7 helix.