PFA VS PTFE

A: Comparison of molecular structures between PFA and PTFE

PTFE is polymerized from the monomer tetrafluoroethylene. In 1938, DuPont first discovered that the most well-known PTFE brand is Teflon ®。 The following diagram shows the structural formula of PTFE, with blue balls representing fluorine atoms (F).

PFA adds a perfluoroalkoxy group, which is equivalent to one fluorine atom in PTFE being replaced by a perfluoroalkoxy group. Connect carbon directly to oxygen, and then connect oxygen to groups such as perfluoromethyl or perfluoroethyl. Compared with PTFE, PFA has higher melt viscosity and lower melt viscosity, which is beneficial for processing. Other performance is basically on par with PTFE. Like PTFE, the formula for PFA was first invented by DuPont, and the most famous PFA formula is Teflon PFA. From a molecular structure perspective, the carbon chains of PFA are relatively short and the degree of entanglement is higher. The following figure shows the structural formula of PFA (the red coil in the bottom right corner of the molecular formula shows perfluoroalkoxy).

B: Explanation and Comparison of Performance Differences between PFA and PTFE

The physical, electrical, and chemical properties of PFA are similar to those of polytetrafluoroethylene! But there are also the following differences to list for everyone.

Physical appearance performance: PFA raw materials are transparent (also known as semi transparent) in granular form, and PFA products are also transparent or semi transparent, with a smooth surface, dense and uniform cross-section. The PTFE raw material is pure white opaque powder, and non modified pure PTFE is white opaque
The biggest difference between them is that PFA can be processed by melting, while PTFE cannot. This means that PFA can be processed using traditional molding techniques such as injection molding, screw extrusion, and transfer molding. PFA has better processability: it can be flipped and welded;

PFA materials have excellent stress cracking resistance and better penetration resistance than PTFE; But the penetration of PFA is not as good as PTFE. Many of the erroneous knowledge online is due to unclear concepts of “permeability resistance” and “penetration”. PFA products have smooth surfaces, dense and uniform cross-sections (although PTFE molecular gaps are more perfect, PFA raw materials form denser structures after melting), and in most cases, PFA has better permeability resistance than PTFE. Just think about DuPont Comus PFA model 951, which has no PTFE penetration resistance that can match this PFA, right. The cleanliness of PFA materials (metal ion leaching and impurity particle leaching are very, very small) is superior to PTFE, especially the cleanliness of high-purity PFA is far superior to PTFE, so PFA is widely used in the semiconductor industry.

Which is better about the bending life (i.e. the ability to withstand repeated folding) of PFA and PTFE? Unable to determine! Any arbitrary conclusion about which one is better is a mistake. This is the most controversial and there are many arbitrary fallacies online. It depends on your specific product structure, bending radius, temperature environment, material selection, and use. Those who agree that PFA has a better bending life include PTFE Daijin M-111 or M-112 modified with an extremely small amount of perfluoroalkoxy group, which is better than pure PTFE Daijin M-18. PFA has stronger density and toughness than PTFE. Those who agree that PTFE has a better bending life may be more indicative of its application in dispersed PTFE. Please consult our AOKERAY for specific information

PFA can maintain strong mechanical strength and burst pressure at relatively high temperatures. But in practical use, PFA’s temperature resistance is not as good as PTFE. PTFE has lower water absorption and better weather resistance. PFA materials may bubble under the action of high-temperature water environment, PTFE solids are not easily affected by moisture, and PTFE friction coefficient is very low; PFA is more susceptible to the influence of alternating wet and dry environments, but in terms of salt spray corrosion resistance, PFA performs better than PTFE.

The dielectric constant of PFA is the same as PTFE, and the dissipation coefficient is very similar. However, the dielectric strength of PFA is much stronger than that of PTFE [PFA’s dielectric strength is 3-4 times that of PTFE, and PFA is better than PTFE in high-frequency (ultra-high frequency/microwave) insulation].

PFA has better elasticity and toughness than PTFE, especially in pipeline applications. As mentioned earlier, PFA has stronger resistance to repeated folding than PTFE (PFA has a better bending life than PTFE). Generally speaking, PTFE has better corrosion resistance than PFA due to its perfluorocarbon composition. Why emphasize “generally”? Because PFA is better only in terms of material density, molecular binding characteristics, and PTFE penetration; But PFA is not perfluorinated, and the oxygen O atom is not as active as the fluorine F atom. More active fluorine atoms, high electronegativity of fluorine, and stronger van der Waals forces of fluorocarbon binding molecules. So PTFE has slightly better corrosion resistance than PFA. However, PTFE has poor processing and forming ability, as well as poor creep resistance, which may be limited in some specific applications.

PTFE is highly sought after in the industrial field due to its superior physical and chemical properties. However, the limitations of its processing methods also limit its application. PFA is actually an improved version of PTFE, which has properties similar to PTFE materials but has excellent processing performance, allowing engineers to easily solve their problems

C: PFA and PTFE application fields

PTFE can be formed by compression or paste extrusion processing; It can also be made into water dispersions for coating, impregnation, or fiber production. PFA can be processed by melting, using traditional injection molding, screw extrusion, transfer molding, etc. PTFE and PFA fluoroplastics are widely used in industries such as atomic energy, national defense, aerospace, electronics, electrical, chemical, mechanical, instrumentation, construction, textile, metal surface treatment, pharmaceuticals, medical, textile, food, metallurgy, etc. They are widely used as high and low temperature resistant, corrosion-resistant materials, insulation materials, anti stick coatings, etc., making them irreplaceable products.

In general, PTFE and PFA have similar applications. So the “PTFE fluoroplastic applications” listed below are almost also PFA applications. However, due to the significantly higher raw material prices of PFA in the market compared to PTFE, as well as the slight difference in performance between PTFE and PFA, the selection bias is slightly different.

PTFE fluoroplastic usage:

1. Universal materials: various rods, tubes, plates, tapes, ropes, packing, gaskets.

2. Anti corrosion category:

① Pipes and accessories: pure polytetrafluoroethylene pipes; PTFE inner lining pipe; Externally wrapped fiberglass steel pipe; Steel composite flange;
② Chemical container lining: PTFE lined kettle; PTFE lined groove; PTFE lined tower;
③ Heat exchanger;
④ Corrugated expansion pipe;
⑤ The main components of valves and pumps;
⑥ Steel wire reinforced full pressure hose;
⑦ Filter material: Polytetrafluoroethylene membrane is a new material that undergoes longitudinal and transverse stretching with a large number of pores inside. By combining it with other fabrics, it can be made into smoke and dust solid-phase anti-corrosion filter bags or good waterproof, breathable, windproof and warm rain gear sportswear, winter clothing, special protective clothing, and lightweight tents. It can also be used for sterile filtration of compressed air for pharmaceutical use, various solvents, and high-purity gas filtration in the electronic industry. PFA cannot be used as a filter membrane air membrane material due to its molecular structure, smooth and dense surface, and melt viscosity. PFA cannot be used for this purpose)

3. Sealing class:

① Static sealing: sandwich gasket; Seat belt; Elastic sealing tape;
② Dynamic sealing (including packing and annular sealing components): V-shaped sealing body – used for shafts, piston rods, and valves; Sealing components inside the turbo pump; Composite sealing ring of polytetrafluoroethylene and rubber; Mechanical seal with expandable bellows.

4. Load bearing class

① Filling PTFE bearings for food, chemical, papermaking, and textile machinery;
② Porous copper impregnated fluoroplastic metal bearings can be used normally under high temperature, high pressure, dry friction, and vacuum conditions; ③ The bearing lining made of composite fabric mixed with polytetrafluoroethylene fiber and glass fiber or other fibers, used for low speed and high load, is made of polytetrafluoroethylene fiber bearings Fill PTFE piston rings, guide rings, machine guide rails, and bridge sliders; (PFA has a higher friction coefficient and lower hardness and rigidity than PTFE. Therefore, some practical applications do not use PFA.)

5. Insulation class:

① C-grade insulation material for wires and cables;
② The protective sleeves of the stator and rotor water inlet pipes and thermocouples of the double water-cooled steam turbine generator;
③ Microwave insulation materials for high-frequency and ultra-high frequency communication equipment and radar;
④ Printed circuit substrates and insulation materials for motors and transformers (including gas transformers);
⑤ Insulation materials for air conditioning, electronic furnaces, various heaters, and sulfur hexafluoride circuit breakers;

6. Anti stick category:

① The PTFE glass cloth coating on the hot roller of the sizing machine can avoid the sticky roller phenomenon caused by chemical sizing, greatly improving production speed and fabric quality;
② Microwave drying conveyor belts in the food industry – compared to conveyor belts made of other materials, they do not absorb microwave energy and are non stick due to their energy-saving and cleaning advantages;
③ Heat sealing sleeve anti stick material for polyethylene bag sealing;
④ Anti stick coating – used for kitchen pots, bread baking molds, frozen food storage trays, electric iron bottoms, and copier rollers;

7. Temperature resistant:

① The driving and transmission device of the microwave oven, such as the coupling device and roller of the microwave oven;
② Temperature resistant accessories for various refrigerators, air conditioners, oxygen concentrators, and compressors;

8. Other categories:

① Human substitute arteries, venous vessels, cardiac membrane, breast augmentation and nose augmentation; (When it comes to bulky PTFE, PFA cannot be applied for this purpose either)
② Endoscope, forceps catheter, trachea, medical urinary tract catheter, surgical vascular bypass;
③ Other medical equipment such as tubes, bottles, filter cloths, etc.

PFA fluoroplastics have better and more commonly used main applications:

1. Suitable for making corrosion-resistant parts, wear reducing and wear-resistant parts, sealing parts, insulation parts, and medical device parts.

2. Insulation layer for high-temperature wires and cables, especially in the field of high-frequency radio, anti-corrosion equipment, sealing materials, pump valve liners, and chemical containers.

3. Semiconductor manufacturing equipment, heat exchangers, steam piping, corrosive medium delivery pipes, wire and cable sheaths, slot insulation pipes, tubes for fully wrapped fluoroplastic O-ring seals