Polytetrafluoroethylene (PTFE) and perfluoroalkoxy resin (PFA) are two kinds of fluoroplastics widely used in the world. Their properties are very similar. PFA is even called "meltable PTFE". So, what is the difference between them?

molecular structure contrast

PTFE is polymerized from monomer tetrafluoroethylene. DuPont first discovered it in 1938. The most well-known PTFE brand is Teflon?. The following figure shows the structural formula of PTFE, and the yellow balls represent fluorine atoms.

PFA incorporates perfluoroalkoxy groups, corresponding to the substitution of one fluorine atom in PTFE with perfluoroalkoxy groups. Like PTFE, the formula of PFA was first invented by DuPont, and the most famous PFA formula is Teflon PFA. From the molecular structure, the carbon chain of PFA is relatively short, and the degree of chain entanglement is higher. The structural formula of PFA is shown in the following figure.

Performance comparison

Overall, the properties of PFA and PTFE are very similar, their biggest difference is that PFA can be melt-processed, and PTFE can not. This means that PFA can be processed using conventional injection molding and screw extrusion techniques.

PTFE solid is hydrophobic, so it is not easily affected by moisture, and the coefficient of friction is very low; PFA is more easily affected by the alternating wet and dry environment, but in terms of salt spray corrosion resistance, PFA performance is better than PTFE.

PFA has better elasticity than PTFE, especially in pipe applications, but its resistance to repeated folding is slightly inferior to PTFE.

The dielectric constant of PFA is the same as that of PTFE, and the dissipation factor is very similar, however the dielectric strength of PFA is three to four times that of PTFE.

Application field comparison

According to statistics, more than half of the world's PTFE is used to make cables: including connecting wires, coaxial cables, etc. This is because PTFE has excellent dielectric properties, especially in the high-frequency radio field. Combined with its high melting point, PTFE is a high-performance alternative to polyethylene.

Due to its extremely low coefficient of friction, it is also used to make sliding bearings, gears, skateboards, seals, gaskets, bushings, and even lubricants to reduce mechanical friction and improve energy utilization.

Due to its excellent chemical stability, PTFE is also used to make containers and pipes for the storage and transportation of reactive or corrosive chemicals. Of course, the most daily application of PTFE is the non-stick coating of non-stick pans and kitchenware models. PTFE is also shown in the following figure as a non-stick pan coated with PTFE:

PFA is usually used in laboratory equipment, especially as an important reaction or highly corrosive chemical reaction pipeline, because PFA has strong resistance to chemical corrosion, optical transparency and good flexibility, can be very good to avoid chemical pollution caused by metal ions, so it has important applications in the field of analytical chemistry.

In thermal power plants, PFA is used as a lining for heat exchangers. Because the high-temperature gas is passed through the PFA-lined device, the gas can be cooled without damaging the heat exchanger, thereby improving the energy efficiency of the entire plant.

In addition, the use of PFA as a sheet lining for chemical instruments guarantees corrosion resistance, and expensive alloys and metals can be replaced by carbon steel fiber reinforced plastics (FRPs). The following figure shows the PFA tube:

Summary

For a long time in the past, PTFE has been sought after by the industrial field because of its excellent physical and chemical properties. However, the limitations of its processing methods also limit its application. PFA is actually an improved version of PTFE. Its performance is similar to that of PTFE, but it has excellent processing performance, which solves the problems of engineers.