What is Polytetrafluoroethylene? (PTFE)

February 2016


Polytetrafluoroethylene  – Chemical Compound (PTFE)

Generally, PTFE is a tough, flexible, non-resilient material of average tensile strength but with great thermal properties and excellent resistance to chemicals and passage of electric current. The coefficient of friction is unusually low and believed to be lower than any other solids. PTFE is an outstanding insulator over a wide range of temperatures and frequency. The volume resistivity is above 1018 (Ω.m) with power factor very negligible over a huge range of temperatures. The chemical resistance of PTFE is outstanding, there are no solvents which could dissolve PTFE at room temperature and the surface of PTFE at room temperature is affected only by molten alkali and fluorine in some cases.

Properties such as chemical inertness, outstanding weathering & heat resistance, excellent electrical insulation and low co-efficient of friction enables PTFE to be exploited in diverse range of applications such as seals, gaskets, valves, pump parts, wire insulation, insulated transformers, PCB, surface coatings, etc.

PTFE is also used in missiles and aircraft where high temperature resistance is required.

PTFE is a thermoplastic. However due to its high viscosity, PTFE cannot be processed using conventional polymer processing techniques. Hence, PTFE is processed by cold shaping operation followed by heat treatment (sintering) during which polymer particles fuse to form a solid moulding.

Fluorine is a highly reactive element with highest electronegativity's of all elements. The electronegativity of Carbon is significantly lower than Fluorine. As a consequence, the unshared electron pair is pulled towards F from C and resulting in high electron density / Polarity around F. The fluorine atom, being larger, does not allow planar zigzag packing in crystallisation resulting in twisted zigzag morphology with F atoms packing tightly in spiral C-C skeleton. The compact interlocking of Fluorine atoms alongside stronger and stable C-F bonds are the reasons for high heat stability (melting point of 327°C) of PTFE.

The electron affinity causes F atoms to be negatively charged and expected to have higher intra-molecular and intermolecular forces. However, the dipole moments of neighbouring symmetrical structures cancel the dipole moments and leaving PTFE in a neutral electronic state. And consequently, this physical phenomenon leads to a low coefficient of friction, low surface energy, high elongation, low strength and low abrasion resistance. Also, electronic balance and molecular neutrality lead to very high chemical resistance, low dielectric constant and high volume or surface resistance.

In the molecular level, PTFE is a linear polymer with great molecular weight (Length of Polymer Chains) and Crystallinity level of 50-70% depending on the processing conditions.

 

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