PTFE, FEP, PFA Recycling
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1. Introduction
FEP offers excellent chemical inertness, heat and weather resistance, exceptional electrical properties, toughness and durability

2. Chemistry:

FEP is a copolymer of tetrafluoro-ethylene and hexafluoropropylene with the following structure:

2.1. Commercial trade names:

FEP by Du Pont, Dyneon™ by 3M and Neoflon by Daikin

2.2. Advantages:

Very high impact strength. Excellent high frequency electrical properties. Melt processable. Good weathering resistance.

2.3. Disadvantages:

Very expensive, with the lowest strength and stiffness of all the fluoro plastics. Low HDT at 50°C (120°F) accompanied by poor wear resistance.

3. Properties:

The following characteristics contribute to the unique properties of FEP fluorocarbon resins:

• Nonpolarity: The carbon backbone of the linear polymer is completely sheathed by the electron cloud of fluorine atoms, much like a wire core is protected by insulation coating. This ensheathment, and the angles at which the carbon-fluorine bonds are disposed, causes the centers of electronegativity and electropositivity to be perfectly balanced across the polymer chain cross section. As a result, no net charge difference prevails. This nonpolarity of the polymer is partly responsible for its lack of chemical reactivity.

• Low interchain forces: The bond forces between two adjacent polymer chains are significantly lower than the forces within one chain. The “creep” normally associated with PFA PTFE, due to the interpolymer chain entanglement of the pendant structure, is mostly avoided with PFA FEP..

• High C-F and C-C bond strengths are among the strongest in single bond organic chemistry. The polymer must absorb considerable energy to disrupt these bonds. Chemical reactions represent a kinetic and thermodynamic resolution of bond-making and bond-breaking in favor of the most stable system. These bond strengths are hard to overcome.

• Crystallinity: The high degree of crystallinity in these semicrystalline polymers like FEP results in high melting points, mechanical properties, and an integral barrier to migrating, small, nonpolar molecules. Under certain conditions, these molecules penetrate the plastics.

• High degree of polymerization: The unbranched nature of the polymers and their low interpolymer chain attraction requires very long chain lengths to provide load-bearing mechanical properties. The chain length also has an impact on flow and crystallinity of the polymers. These unique properties lead to the following benefits:

• High melting points (327°C [621°F] for PFA PTFE and 260°C [500°F] for PFA FEP). The melting point of PFA PTFE is one of the highest in organic polymer chemistry. Other materials can attain higher temperatures, but they degrade rather than melt. Compared to PFA PTFE, the lower melting temperature of PFA FEP results from lower crystallinity.

• High thermal stability: Due to the strength of the carbon-fluorine and carbon-carbon single bonds, appreciable thermal energy must be absorbed by the polymers before thermal degradation. The rate of decomposition depends on the particular resin, temperature, and heat exposure time; and to a lesser extent, pressure and nature of the environment. At maximum continuous service temperatures, thermal degradation of the resins is minimal. For example, at 400°C, PFA FEP is measured at 4/100,000 of 1 percent, and PFA PTFE at 1/100,000 of 1 percent. At high processing temperatures, adequate ventilation is recommended.

• High upper service temperature ( 204°C [400°F] for PFA FEP) -The polymers’ high melting points and morphological features allow components made from the resin to be used continuously at the stated temperatures. Above this temperature, the component’s physical properties may begin to decrease. The polymer itself, however, will be unaffected if the temperature is insufficient for thermal degradation.

• Insolubility: There is no known solvent for FEP fluorocarbon resins under ordinary conditions.

• Inertness to chemical attack: The intrapolymer-chain bond strengths preclude reaction with most chemicals. Under relatively unusual circumstances the polymer can be made to react. Examples of unusual reagents include:
– Sodium, in a suitable media, etches the fluorocarbon polymer.
– Finely divided metals often interact with the polymer.
– Interhalogen compounds often induce halogen interchange with the fluorine.
– Ionized oxygen in oxygen plasma is often sufficiently energetic to react with the polymer chain.
– Electron bombardment at the megarad level can sever the polymer chain.

• Low coefficient of friction: The low coefficient of friction of FEP results from low interfacial forces between its surface and another material and the comparatively low force to deform.

• Low dielectric constant and dissipation factor: FEP provides low, if not the lowest, values for these parameters. These low values arise from the polymer’s nonpolarity as well as the tight electron hold in the ultrapolymer bonds.

• Low water absorptivity: For FEP to absorb water, the surface must remain wet for a long enough time for water to become physico-chemically associated with the polymer chains, and then it must become included in the polymer bulk structure. Water is a very high energy material and FEP has a very low surface energy. Therefore, these events are energetically incompatible and only occur under special circumstances and to a small extent.

FEP Typical Properties
Property Value
Density (g/cm3) 2.1
Surface Hardness RR45
Tensile Strength (MPa) 14
Flexural Modulus (GPa) 0.6
Notched Izod (kJ/m) 1.06+
Linear Expansion (/°C x 10-5) 5
Elongation at Break (%) 150
Strain at Yield (%) 6
Max. Operating Temp. (°C) 150
Water Absorption (%) 0.01
Oxygen Index (%) 95
Flammability UL94 V0
Volume Resistivity (log ohm.cm) 18
Dielectric Strength (MV/m) 50
Dissipation Factor 1kHz 0.0002
Dielectric Constant 1kHz 2.1
HDT @ 0.45 MPa (°C) 70
HDT @ 1.80 MPa (°C) 50
Material. Drying hrs @ (°C) NA
Melting Temp. Range (°C) 340 – 360
Mould Shrinkage (%) 2.5
Mould Temp. Range (°C) 50 – 200

Applications

Coatings, protective linings, chemical apparatus, wire coverings, glazing film for solar panels.

4. Recycling

Eco USA has various options for recycling FEP polymer scraps.These options depend upon the nature and amount of the scrap destined for recycle. There are two options for recycling the fluoropolymer: re-use or disposal in authorized incinerators.

Various fluorine-containing polymers, especially fluorinated ethylene propylene (FEP), are increasingly common in data wiring insulation because of their exceptional dielectric properties, superb flame resistance, heat resistance, chemical inertness, durability, and flexibility.

For plenum-rated data cable, FEP-insulated wire is often the only option allowed by code, due to fire-safety concerns. Such wire is often wrapped in a PVC jacket, though newer, more stringent “limited combustible” ratings require FEP jacketing. In addition to these performance benefits of FEP, the polymer can be recycled easily, according to DuPont.

Thermoplastics are easily recyclable, compared to thermosets, because the polymer chain does not degrade when melted down. This is because the weaker interactions between polymer chains break down at much lower temperatures than the chemical bonds between monomers. This allows thermoplastics to be recycled indefinitely until the polymers are broken down to the point that the material loses structural integrity.

Thermoplastics have a limit recyclable lifespan due to degradation of the polymers and contamination during the recycling process. Contaminants can be inert materials, which act as fillers, or they can be other plastics, which alters the physical properties of the resulting material.

Eco USA collects the scrap and then processes it into a form suitable for re-use.

4.1. Recovery

A very substantial market exists for recovered fluoropolymers as low friction additives to other materials. For example PTFE FPA or PFA FEP are typically ground into fine powders and used in such products as inks and paints.

4.2. Disposal

Fluoropolymer waste should be incinerated in authorised incinerators. Preferably, non-recyclable fluoropolymers should be sent to incinerators with energy recovery. Disposal in authorised landfills is also acceptable.

Decomposition products:

According to the fire conditions toxic gasses develop, predominantly carbon dioxide, carbon monoxide, hydrofluoric acid, tetrafluoroethylene, hexafluoropropylene, perfluorisobutylene, carbonyl fluoride and other low-molecular fluorohydrocarbons.

Some significant environmental and health concerns have arisen about the whole class of fluoropolymer materials. FEP does not burn easily, but it can emit toxic gases when it gets very hot, even without actual combustion. The primary gas emitted is hydrogen fluoride, which is more dangerous than the hydrogen chloride given off by PVC. Other toxic chemicals can be given off by FEP during fires; these poorly understood thermal degradation products have been referred to collectively as “the supertoxin”.

Article Sources:

1) Fluoropolymers, Vol.2, 1999
2) Du Pont notes on fluoropolymers

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