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[Popular stickers] The advantages and disadvantages of PTFE, do you understand?

Update:15-11-2019
Summary:

Polytetrafluoroethylene (PTFE) as a material with the " […]

Polytetrafluoroethylene (PTFE) as a material with the "plastic king" reputation, what are the advantages and disadvantages, let us take a look at it.
No.1
advantage

High temperature resistance - use working temperature up to 250 °C.
Low temperature resistance - good mechanical toughness; 5% elongation even at temperatures down to -196 °C.
Teflon tubing is corrosion resistant - inert to most chemicals and solvents, resistant to strong acids and bases, water and various organic solvents.

Weather resistant - the best aging life in plastics.
Highly lubricated – the lowest coefficient of friction in solid materials.
Non-adhesive - is the smallest surface tension in solid materials and does not adhere to any substance.
Non-toxic - physiologically inert, long-term implantation of artificial blood vessels and organs without adverse reactions.
Electrical insulation - can withstand 1500 volts high voltage.

The relative molecular mass of PTFE is relatively large, hundreds of thousands of low, more than 10 million high, and generally several million (degree of polymerization is on the order of 10^4, while polyethylene is only 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.

No.2
Disadvantage

1. Polytetrafluoroethylene has "cold flowability". That is, the plastic deformation (creep) of the material product under the action of long-term continuous load, which imposes certain restrictions on its application. For example, when PTFE is used as a gasket, the bolt is tightened tightly so that the gasket is "cold" (creep) and crushed when a certain compressive stress is exceeded. These shortcomings can be overcome by adding appropriate fillers and improving part structure.

2. PTFE has outstanding non-stick properties, which limits its industrial application. It is an excellent release material that makes it extremely difficult to bond to the surface of other objects.

3, PTFE linear expansion coefficient is 10 to 20 times that of steel, larger than most plastics, and its linear expansion coefficient changes very irregularly with temperature changes. When applying PTFE, if the performance of this aspect is not enough, it is easy to cause losses.