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PTFE: Properties and Applications

General information about fluoropolymers

A fluoropolymer is a polymer obtained by chemical means. Fluoropolymers contain fluorine atoms due to which they have a high chemical resistance. Strong oxidizers have no effect on them even at high temperatures. Fluoropolymers are poorly soluble or insoluble in most organic solvents, are insoluble in water and are water-repellent. They are used to make goods with high dielectric properties, resistance to corrosive mediums, and the ability to operate ate temperatures of up to +260 °C.
Fluoropolymers are characterized by a high electric strength, a low coefficient of friction, and a high durability. Products made of fluoropolymers are resistant to various corrosive mediums at room temperature and elevated temperatures, are durable and radiation-resistant, have a low gas permeability, are non-flammable or self-extinguishing when ignited. Fluoropolymers have a high heat resistance (up to +300 °C).

Polytetrafluoroethylene (PTFE)

The most widely used fluoropolymer is PTFE, and it is for good reason. PTFE has the highest chemical resistance to all organic acids, alkalis, organic solvents, oxidizers and other corrosive mediums. This quality of PTFE finds its use in the production of reactor lining, vertical vessels, valves, pumps, sealing parts operating in contact with corrosive mediums, tanks for storing corrosive substances and pipelines meant for transporting highly corrosive mediums. Due to its unique properties PTFE is used in the electrical, chemical, food and consumer goods industries, as well as in the energy, mechanical engineering, instrument making, medical and many other industries.
PTFE is not resistant to molten alkali metals or their solutions in ammonia, to atomic fluorine, and to chlorine trifluoride at elevated temperatures.

GOST requirements (GOST 10007-80) to the main characteristics of PTFE

Density, kg/m3 2120-2200
Crystalline melting temperature, °С 327
Glass transition temperature, °С -120
Vicat softening temperature, °С 110
Specific heat capacity, kJ/(kg∙K) 1.04
Thermal conductivity, W/mK 0.25
Thermal linear expansion coefficient *10-5, °С-1 8-25
Minimum operating temperature, °С -269
Maximum operating temperature, °С 260
Water absorption in 24 hours, % 0
Brinell hardness, MPa 29.4-39.2
Coefficient of friction on steel 0.04
Volume resistivity, Ω⋅m 1015-1018

PTFE: production and grades

PTFE is mainly produced by radical polymerization (or copolymerization) of monomers in bulk, suspension or emulsion in an organic or aqueous medium with the addition of various initiation agents, or in the gas phase under the influence of ionizing or UV radiation (this process is rarely used).

Compression moulding is used to produce half-finished parts of simple shapes (plates, disks, cylinders, bushings, rings, etc), which in most cases are subjected to further mechanical processing in order to give them more complex shapes and precision. However, there are compression methods for producing products of complex configuration (such as bellows, tubes with flanges, etc) with the use of PTFE powder.

Depending on the properties and purposes PTFE is produced in the following grades:

  • S (Russian code С) – this grade is used to produce special products;

  • P (Russian code П) – this grade is used to produce electrically insulating films and film for capacitors;

  • PN (Russian code ПН) – this grade is used to produce electrical products and other products with increased reliability;

  • O (Russian code О) – this grade is used to produce products and compositions for general purpose;

  • T (Russian code Т) – this grade is used to produce thick-walled products and pipelines.

PTFE processing

PTFE should be processed in accordance with the sanitary norms and regulations for rooms with supply and exhaust ventilation. Heating devices and devices with surfaces of +260 °С can be operated only in a vent hood with ventilation turned on.

PTFE can be hardened if a film thickness does not exceed 6 mm. PTFE that has gone through the process of sintering and cooling, especially one that has undergone hardening, cannot be immediately machined.

PTFE products are held at normal temperature for 2-4 days for their dimensions to stabilize, after which those that are going to be used without further processing are measured, and those needing processing can be processed. PTFE products manufactured in accordance with this technique can be operated at temperatures of up to +260 °С.

If PTFE products are operated at low temperatures and there are no strict requirements regarding the precision and stability of their dimensions, presswork can be applied on PTFE workpieces heated to +380 °С to produce end products.

Purchasing PTFE

PTFE can be purchased in the form of granules or workpieces which are subjected to further processing. We at Plastpolymer-Prom manufacture and supply PTFE products to all regions of Russia, as well as to CIS and other countries. You can purchase PTFE by calling our commercial service using the phone numbers given on the page with our contact details.