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PEEK vs PTFE

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:

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


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


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


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


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.

Electrodes

working electrode

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Contributors


Edited by

Dr. Amelia Wood

Application Scientist

References


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