[Science Stickers] Do you know the advantages and disadvantages of PTFE?

As a material with the reputation of "Plastic King", what are the advantages and disadvantages of polytetrafluoroethylene (PTFE)? Let us understand together.

advantage

High temperature resistance-the working temperature can reach 250℃.

Low temperature resistance-has good mechanical toughness; even if the temperature drops to -196 ℃, it can maintain 5% elongation.

PTFE tube is corrosion-resistant-it is inert to most chemicals and solvents, and can withstand strong acids and alkalis, water and various organic solvents.

Weather resistance-has the best aging life among plastics.

High lubrication-is the lowest coefficient of friction among solid materials.

No adhesion-it is the smallest surface tension among solid materials, and does not adhere to any substance.

Non-toxic and harmful-with physiological inertia, as an artificial blood vessel and organ implanted in the body for a long time without adverse reactions.

Electrical insulation-can withstand 1500 volts high voltage.

The relative molecular mass of polytetrafluoroethylene is relatively large, the low is hundreds of thousands, the high is more than 10 million, and generally millions (the degree of polymerization is on the order of 10^4, while that of polyethylene is only 10^3). Generally, the crystallinity is 90-95%, and the melting temperature is 327-342°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 in trans, but form a helical twisted chain, almost covered by the fluorine atom 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 unwound to form a 15/7 helix.

Disadvantage

1. PTFE has "cold flow". That is, the plastic deformation (creep) of the material product under the action of continuous load for a long time, which brings certain restrictions to its application. For example, when PTFE is used as a gasket, the bolts are tightened very tightly for a tight seal, so that when the specified compressive stress is exceeded, the gasket will produce "cold flow" (creep) and be crushed. These shortcomings can be overcome by adding appropriate fillers and improving the structure of the parts.

2. PTFE has outstanding non-stick properties, which limits its industrial application. It is an excellent anti-adhesive material, and this performance makes it extremely difficult to adhere to the surface of other objects.

3. The linear expansion coefficient of PTFE is 10-20 times that of steel, which is larger than most plastics, and its linear expansion coefficient changes very irregularly with the change of temperature. In the application of PTFE, if insufficient attention is paid to this aspect of performance, it is easy to cause losses.

This article comes from the Internet, only for learning and communication, no commercial purpose.

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