Introduction of Melt-Processable Fluororesin: FEP, PFA, PVDF and ETFE

Fluororesin, also known as fluoropolymer, is a highly versatile material that has several unique properties making it ideal for a variety of applications. It is a type of plastic that is highly resistant to heat, chemicals, and abrasion, making it a popular choice in many industries.

In this article, we will talk about melt-processable fluoropolymers FEP, PFA, PVDF and ETFE resin.

Fluorinated ethylene propylene (FEP) copolymer

FEP is a copolymer of TFE and HFP. The mass ratio of TFE is usually 80%-84% and the mass ratio of HFP is 16%-20%. The introduction of HFP makes the linear structure of PTFE contain a lot of -CF; the branch chain of the groups greatly reduce the crystallinity of PTFE, thus achieving melt processing while maintaining the basic properties of PTFE.

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FEP is the earliest product in the melt-processable fluororesin series, and its operating temperature range is -190 to 205°C. FEP has good processing performance, excellent high and low temperature resistance and excellent chemical stability. The most outstanding performance of FEP is electrical insulation (the dielectric constant is 2.1, the same as PTFE). Superior electrical insulation performance and easy processing performance, low flame spread and low smoke generation make FEP an ideal choice for wire and cable insulation materials.

FEP copolymers are usually divided into several different grades according to the melt flow rate (MFR) of the product: mainly molding grade, general grade, extrusion grade, wire cable grade, and coating grade (50% emulsion).

Perfluoroalkoxy (PFA) polymers

PFA is a resin obtained by free radical copolymerization of TFE monomer and about 3%~5% perfluoroalkoxy vinyl ether (PPVE). It is the most important new type of fluorine-containing polymer, referred to as PFA. Compared with PTFE, due to the presence of perfluoroalkoxy groups in the side chain, the crystallinity of the product is greatly reduced, making PFA melt-processable like FEP, with a melting point of 300~315℃. The softness and spatial rotation of the ether bond on the side chain make the thermal stability of PFA products higher than that of FEP. The long-term use temperature is the same as that of PTFE, both at 260℃, and the mechanical strength and folding resistance are better than PTFE.?PFA retains the good chemical inertness, heat resistance, non-flammability, anti-viscosity and dielectric properties of PTFE.

According to the melt flow rate (MFR), PFA resin can be divided into different grades, such as molding grade, extrusion grade, cable grade, coating grade (mainly for electrostatic spraying materials).

Polyvinylidene fluoride (PVDF)

PVDF is a homopolymer of 1,1-difluoroethylene (VDF) monomer. It is a partially fluorinated polymer initiated by a free radical initiator. It contains 59.4% fluorine and 3% hydrogen (mass fraction). It is a partially crystalline polymer with a crystallinity of 45%~70%. Crystallinity largely affects the rigidity, mechanical strength and impact resistance of PVDF. The long-term use temperature and chemical resistance of PVDF are slightly inferior to those of FEP. The recommended service temperature range is -60~150℃.

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Due to its good high temperature resistance, weather resistance, chemical corrosion resistance, and dielectric properties, PVDF is widely used in coatings, injection molding, water treatment, lithium batteries, and photovoltaic back sheet. The strong electronegativity of fluorine atoms in the C-F bond of PVDF gives it many unique and excellent properties, such as piezoelectricity, dielectricity, thermoelectricity, etc. Therefore, PVDF is widely used in piezoelectric materials, dielectric materials, filter materials, and other application fields.

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According to different polymerization and post-processing processes and different uses, PVDF can be divided into coating grade (ungranulated powder), molding grade, extrusion grade, cable grade, (casting) film grade. Among them, the cable grade is a copolymer with 10%~20% comonomer added to PVDF.

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Ethylene tetrafluoroethylene (ETFE) copolymers

ETFE is a partially fluorinated copolymer resin with ethylene and TFE alternately connected, with the molar ratio of the two being close to 1:1. The zigzag orientation of the ETFE carbon chain forms an orthogonal lattice, which gives ETFE advantages over fluoropolymers: low creep, high tensile strength and high modulus. The attraction between the carbon chains maintains this lattice until the α transition occurs at 110°C. ETFE exhibits extraordinary rigidity and wear resistance over a wide temperature range. It has a good combination of high tensile strength, high impact strength, flexural resistance and creep resistance, and better unifies the excellent mechanical properties of hydrocarbon polymer engineering plastics with the outstanding heat resistance and chemical inertness of perfluoropolymers.

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Although the long-term use temperature of ETFE does not exceed 150°C, which is lower than most fluororesins, its hardness and wear resistance are better than PTFE. If it is cross-linked with peroxide or radiation, the mechanical strength and temperature resistance level can be improved, and it can withstand high temperatures of 240°C for a short time.

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By adding a small amount of modified comonomers, adjusting the polymerization process and other methods to change the crystallinity and other properties, multiple grades with different properties and application ranges can be formed. The main grades are coating grade, film grade, cable grade and molding grade.