PEEK vs PTFE

The choice of whether to use PEEK (polyether ether ketone) or PTFE (polytetrafluoroethylene, Teflon) comes down to the conditions of your planned experiments. The key polymer properties to consider are:

• Chemical Resistance
• Mechanical Stability
• Thermal Stability
• Electrical Insulation

If your experiment requires a specific chemical environment that isn’t compatible with one of the polymers then this is your priority. The same applies to mechanical toughness, thermal stability and electrical insulation. The conditions of your experiment dictate which polymer you should pick.

PEEK vs PTFE Chemical Resistance

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PEEK exhibits good solvent compatibility with a lot of electrolytes typically used in electrochemistry. However, there are a few that will readily dissolve PEEK and some that can cause some deformation (see the table below ).

PTFE on the other hand is mostly inert. It will react with alkali metals and can be dissolved in perfluorokerosenes and perfluorinated oils. So, if you want to use any of the solvents listed below as your electrolyte, you may want to purchase a working electrode with a PTFE body.

Incompatible with PEEK

May discolour or deform PEEK

Aqua regia - HNO3 + HCl Benzenesulfonic acid - C6H5SO3H (aq) Bromine - Br2 Carbolic Acid (Phenol) - C6H5OH Carbon Disulfide - CS2 Chlorine (aqueous and anhydrous liquid) - Cl2 Chlorosulfonic acid - pure ClSO3H Chromic Acid - aqueous H2CrO4 >50% Dibromoethane - C2H5Br2 Ethylene bromide (anhydrous) - pure CH2CHBr Fuming sulphuric acid (Oleum) - pure H2SO Hydrobromic acid - aqueous HBr Hydrofluoric acid - concentrated aqueous HF Nitric acid - aqueous HNO3 >50% Sulphuric acid - concentrated >75% H2SO4 Sulphurous acid - aqueous H2SO3

Boric acid - aqueous H3BO3 Sulphuric acid - 20-30% H2SO4 Chloroethanol (ethylene chlorohydrine) - pure ClCH2CH2OH Chromic acid - 30-50% aqueous H2CrO4 Dichloromethane (methylene chloride) - pure CH2Cl2 Dimethyl sulfoxide (DMSO) - pure (CH3)2SO Ethylene chlorohydrin (chloroethanol) - pure ClCH2CH2OH Formaldehyde solution (formalin) - aqueous CH2O Formic acid - pure HCOOH Hydrochloric acid - aqueous 36% HCl Hydroxybenzene (carbolic acid, phenol) - aqueous C6H5OH Iodine with potassium iodine - aqueous I2 + KI Methylene chloride (dichloromethane) - pure CH2Cl Methyl ethyl ketone (2-butanon) - pure CH3COCH2CH3 Nitric acid - aqueous (40%) HNO3 Nitrobenzene - pure C6H5NO2 Nitrotoluenes (o-, m-, p) - pure C6H4(NO3)(CH3) Phenol (hydroxybenzene, carbolic acid) – diluted aqueous C6H5OH Sodium chromate - aqueous NaCrO4

PEEK vs PTFE Mechanical Stability

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Property	PEEK	PTFE	Best Performer
Tensile Strength / MPa	90-100	25-35	PEEK
Elongation / %	30-40	350-400	PEEK
Compressive Strength / MPa	140	30-40	PEEK
Shore Hardness / D	85	55	PEEK
Flexural Modulus / MPa	3900	495	PEEK
Coefficient of Friction	0.35-0.45	0.03-0.05	PTFE

According to the mechanical property data there are key differences between PEEK and PTFE. PEEK is extremely strong and resistant to deformation making it suitable for experiments where the electrode might be put under physical stress or repeated mechanical cycling. A downside to this strength is that the standard alumina electrode polishing powders won’t wear down the PEEK. So, it’s possible that, eventually, the electrode material might wear enough that it is no longer flush with the PEEK body. A machine polisher can prevent this.

PTFE has a low coefficient of friction which minimizes wear and tear in experiments where the electrode might be moved or adjusted frequently. This contributes to the longevity of the electrochemical cell set up, especially in systems that involve frequent assembly and disassembly.

PEEK vs PTFE Thermal Stability

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Property	PEEK	PTFE
Coefficient of linear thermal expansion / K	5 x 10-5	14 x 10-5

PEEK has a lower coefficient of thermal expansion, and the coefficient increases more linearly with temperature (at least up to 80-100 °C). This thermal stability is crucial when using PEEK electrodes in high-temperature electrochemical processes.

Whereas PTFE electrodes can be unsuitable for applications that require high temperature thermal cycling. Although PTFE has a relatively high melting point (327 °C) and low linear thermal expansion under 25 °C, above 25 the coefficient of thermal expansion increases nonlinearly. At experiments at high temperatures there is chance that the PTFE body will begin to protrude beyond the electrode material, or that electrolyte can seep between the electrode material and the PTFE body.

PEEK vs PTFE Electrical Insulation

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Property	PEEK	PTFE
Dielectric Strength kV/mm	50	50-150
Volume Resistivity Ohm/m	1013 -1014	1016 -1018

While both polymers are highly insulating, PTFE is more resistant to voltage and acts as a better insulator than PEEK. These properties helps prevent unwanted electrical currents from passing through the body of the electrode, ensuring that all current is focused on the electrode surface where the electrochemical reaction takes place.

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