What are the advantages and disadvantages of polytetrafluoroethylene (PTFE) as a material with the reputation of "King of Plastics"?
Advantages of PTFE
High temperature resistance - the working temperature can reach 250°C.
Low temperature resistance - has good mechanical toughness; even if the temperature drops to -196°C, it can maintain an elongation of 5%.
Corrosion resistance of PTFE tubes - inert to most chemicals and solvents, resistant to strong acids and alkalis, water and various organic solvents.
Weather resistant - has the best aging life among plastics.
High lubrication - the lowest coefficient of friction among solid materials.
Non-adhesive - is the smallest surface tension in solid materials, does not adhere to any substance.
Non-toxic - it is physiologically inert and has no adverse reactions when implanted in the body as an artificial blood vessel and organ for a long time.
Electrical insulation - can withstand 150 volts of high voltage.
The relative molecular mass of polytetrafluoroethylene is relatively large, ranging from hundreds of thousands to over 10 million, and generally to millions (the degree of polymerization is on the order of 10^4, while polyethylene is only on the order of 10^3). Generally, the degree of 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 atoms is slightly larger than that of carbon, the adjacent CF2 units cannot completely follow the trans-cross orientation, but form a helical twisted chain, and the fluorine atoms almost cover 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 untie slightly to form a 15/7 helix.
Disadvantages of PTFE
1. PTFE has "cold flow". That is, the plastic deformation (creep) of material products under long-term continuous load, which brings certain restrictions to its application. For example, when PTFE is used as a gasket, the bolts are tightened tightly for tight sealing, so that when a certain compressive stress is exceeded, the gasket will produce "cold flow" (creep) and be flattened. These shortcomings can be overcome by adding appropriate fillers and improving the structure of parts.
2. PTFE has outstanding non-stick properties, which limits its industrial application. It is an excellent anti-adhesive material, which makes it extremely difficult to adhere to the surface of other objects.
3. The linear expansion coefficient of PTFE is 10 to 20 times that of steel, which is larger than most plastics, and its linear expansion coefficient changes irregularly with the change of temperature. When applying PTFE, if you do not pay enough attention to this aspect of performance, it is easy to cause losses.
