Clean gases fuel the semiconductor production

The raw material for these plastics is ethylene (which is produced, among others, by our customer Llyondell Basel on the Maasvlakte in Rotterdam). And what they also have in common is that fluorine is added to them, hence the "F" in each name. It is this fluorine that gives them special properties that every fluoropolymer has:

• Lowest coefficient of friction of all solids
• Chemical resistance
• Excellent electrical insulation
• Resistant to very low temperatures
• Out of all plastics best resistant to high temperatures
• Resistance to ageing
• Excellent anti-sticking properties

This last property is why PTFE is used so much for non-stick pans. But in liquid systems or systems with slurries this anti-stick property is also very advantageous because the systems are easier to clean.

This is why these are the plastics we see in medical sterile applications. They are also the plastics we see a lot in food production - they are FDA and IE-1935 approved. Let's take a closer look at each of these plastics in the world of gases and liquids.

Perfluoroalkoxyalkanes (PFA) is a copolymer of hexafluoropropylene and perfluoroethers. It was developed in 1972, also by DuPont. PFA has very similar properties to PTFE, but there are a few key differences in properties between these two fluoropolymers that you should consider when choosing the right one for your process.

Unlike PTFE, PFA polymers have a smaller chain length and greater chain entanglement at the molecular level than other fluoropolymers. That makes PFA tubing more flexible, but it has a shorter flex-life, so it's not as resistant to repeated folding. It also makes PFA have better flow and creep resistance, with thermal stability that approaches or exceeds PTFE. In other words: PFA maintains its close dimensional tolerances and shape over a wide temperature range. PTFE deforms more.

They also contain an oxygen atom at the branches. This results in materials that are more transparent, which is a valued property in laboratories. Especially when working with hazardous chemicals.

PTFE has a slightly higher heat resistance, the melting points of PFA and PTFE are 260°C and 327°C respectively.

Water absorption (permeability) and weathering affect PFA more than PTFE, although PFA is superior in resistance to salts.

Like PTFE, PFA has excellent resistance to cracking and stress and a low coefficient of friction.

The electrical insulating capacity (dielectric strength) of PTFE is excellent, but PFA is still 3-4 times higher. For gas and liquid systems this will not be decisive very often.

PFTE versus PFA summary

PFA is often preferred when high reliability is required in environments with high chemical, thermal and mechanical stresses. But for gas and fluid systems manufacturing, the key difference between PFA and PTFE has not yet been addressed....

PVDF

PVDF is a commonly used plastic in systems. It has much better chemical resistance than many other plastics and is 30% cheaper than PFA.

This makes it a formidable competitor to PFA. In short, PFA is preferred over PVDF in applications where PVDF is not chemically resistant enough and when transparency is important.

Advantages of PVDF

• Cheaper than PFA (about 30%)

Disadvantages of PVDF

• Not transparent.
• Can discolor under the influence of certain chemicals.
• Not as chemically inert as PFA and PTFE.
• Smaller temperature range, especially less suitable for cold applications.

FEP

Improved processing properties over PTFE are also found in fluorinated ethylene propylene (FEP).

FEP can be a cheaper alternative to PFA, with nearly the same properties, especially in hoses. However, FEP is ten times less resistant to repeated bending without fracture than PFA. As a result, in high-end applications, PFA is still preferred to FEP for safety reasons.

For applications other than gas and liquid applications, the differences between PFA and FEP are somewhat greater. Such as the refractive index that makes FEP more suitable for displays.

Advantages of FEP

• Highly transparent Weldable Cheaper than PFA

Disadvantages of FEP

• Vulnerable to repeated bending

And the winner is....

The illustration below shows that there is no big winner among plastics. For every application there is a plastic that is most suitable. This is a PFA diaphragm control valve from Parker that we supply. In this valve PFA, PTFE, PVDF and FKM and stainless steel are used. The shape of the body is too complex to make as milling work and is therefore made of PFA injection moulding. The diaphragm is (modified) PTFE. This way all wetted parts are very chemical resistant. The parts that do not come into contact with the medium are made of PVDF, stainless steel and Viton (a rubbery fluoropolymer).

Ultra Pure Water applications

In ultrapure water (UPW) applications, fluoropolymers provide superior performance. Stainless steels often cannot be used in such applications because ionized water draws ions from the steel, creating iron oxide, hydroxide or carbonate. Fluoropolymers are immune to this degradation.

Cooling systems

Fluoropolymers pose no problems with galvanic corrosion compared to metals in cooling systems. Aluminium has excellent heat transfer and is therefore often used in cooling systems. For example, in the cooling of electronics. To prevent galvanic corrosion problems, the connection of aluminum heat transfer fluid to the system is often made of tubing and fittings made of fluoropolymers.

Curious which products we supply in these plastics? View them in our online catalogue: