PTFE Teflon properties
Polytetrafluoroethylene (PTFE) is a fully fluorinated, semi-crystalline fluoropolymer with a semi-transparent white color, having a density of 2.15 g/cm³ (2150 kg/m³). It stands out for its exceptional chemical resistance, very low coefficient of friction, high thermal stability (up to 180 °C in continuous use), and excellent dielectric properties. It is a thermoplastic that cannot be processed by conventional melt processing, but rather by powder sintering.
Chemical composition
Section titled “Chemical composition”The molecular formula of PTFE is (C₂F₄)n, composed exclusively of carbon and fluorine atoms. The strength of the carbon–fluorine bond gives it practically universal chemical inertness, being chemically inert to almost all aggressive agents, although it can be attacked by molten alkali metals or fluorine gas at high pressure.
Mechanical properties
Section titled “Mechanical properties”Virgin PTFE has a tensile strength of 25 MPa (3.6 ksi) and an elongation at break of 400 %. Mechanical properties may vary according to grade and processing:
| Property | SI Value | Imperial Value |
|---|---|---|
| Density | 2.15 g/cm³ | 134 lb/ft³ |
| Surface hardness | Shore D 63 | Shore D 63 |
| Tensile strength | 25 MPa | 3.6 ksi |
| Flexural modulus | 0.70 GPa | 102 ksi |
| Elongation at break | 400 % | 400 % |
| Yield strain | 70 % | 70 % |
| Impact resistance (Izod notched) | 0.16 kJ/m | 0.03 ft·lb/in |
The values correspond to unfilled and unreinforced PTFE. Grades with mineral or glass fillers significantly modify strength and stiffness.
Physical properties
Section titled “Physical properties”The density of unfilled PTFE is 2.15 g/cm³ (2150 kg/m³), water absorption at 24 h is less than 0.01 %, and its static coefficient of friction is one of the lowest among solids, with typical values between 0.04 and 0.10. The low polarizability of fluorine gives it extreme hydrophobicity and excellent non-stick properties.
| Property | SI Value | Imperial Value |
|---|---|---|
| Density | 2150 kg/m³ | 134 lb/ft³ |
| Water absorption (24 h) | < 0.01 % | < 0.01 % |
| Static coefficient of friction | 0.04 – 0.10 | 0.04 – 0.10 |
| Oxygen index | 95 % | 95 % |
Thermal properties
Section titled “Thermal properties”The melting point of PTFE is around 327 °C (620 °F), while the recommended maximum continuous use temperature is 180 °C (360 °F). Thermal conductivity is low, with a typical value of 0.25 W/(m·K) [1.73 BTU·in/(hr·ft²·°F)], and it has a relatively high coefficient of linear expansion.
| Property | SI Value | Imperial Value |
|---|---|---|
| Melting point | ~327 °C | ~620 °F |
| Maximum continuous use temperature | 180 °C | 360 °F |
| Thermal conductivity | 0.25 W/(m·K) | 1.73 BTU·in/(hr·ft²·°F) |
| Coefficient of linear expansion | 15 × 10⁻⁵ /°C | 8.3 × 10⁻⁵ /°F |
| Deflection temperature under load (HDT @ 0.45 MPa) | 121 °C | 250 °F |
| Deflection temperature under load (HDT @ 1.80 MPa) | 54 °C | 129 °F |
| Flammability rating (UL94) | V‑0 | V‑0 |
Electrical properties
Section titled “Electrical properties”PTFE has a dielectric constant of 2.1 at 1 kHz and a dissipation factor of 0.0001, which makes it ideal for high frequency insulation. Its volume resistivity reaches 10¹⁸ Ω·cm (18 log Ω·cm) and dielectric strength is 45 MV/m (45 kV/mm).
| Property | SI Value | Imperial Value |
|---|---|---|
| Dielectric constant (1 kHz) | 2.1 | 2.1 |
| Dissipation factor (1 kHz) | 0.0001 | 0.0001 |
| Volume resistivity | 10¹⁸ Ω·cm | 10¹⁸ Ω·cm |
| Dielectric strength | 45 MV/m | 1143 V/mil |
Chemical resistance
Section titled “Chemical resistance”PTFE is inert to practically all chemicals, including acids, bases, solvents, and strong oxidizing agents, even at elevated temperatures. It is only attacked by molten alkali metals, elemental fluorine under pressure, and some chlorofluorinated derivatives at high temperature. This resistance makes it the material of choice for gaskets, linings, and seals in extremely aggressive environments.
Processing
Section titled “Processing”PTFE cannot be processed by conventional thermoplastic methods (injection or melt extrusion) due to its extremely high melt viscosity. Parts are obtained by powder sintering (compression molding of preforms and subsequent firing at ~370–380 °C), paste extrusion (for tubes and thin profiles) or ram extrusion. It does not require pre-drying and does not exhibit significant mold shrinkage.
Applications by industry
Section titled “Applications by industry”| Industry | Typical applications |
|---|---|
| Chemical processing | Tank and pipe linings, gaskets, diaphragms, valves, seals (O‑rings), packings |
| Mechanical | Bearings, bushings, piston rings, sliding supports, low-friction guides |
| Electrical/Electronics | High-temperature and high-frequency insulation, cable coatings, connectors |
| Food and kitchen | Non-stick coatings for pans, trays and kitchen utensils |
| Medical | Catheters, vascular grafts, coatings for surgical instruments |
| Aerospace and automotive | Fuel and hydraulic fluid hoses, washers, gaskets |
Comparison with similar materials
Section titled “Comparison with similar materials”PTFE is frequently compared with other technical fluoropolymers. Unlike FEP and PFA, PTFE is not melt-processable by conventional methods but offers a slightly higher continuous use temperature and lower coefficient of friction.
| Property | PTFE | FEP | PFA | ETFE |
|---|---|---|---|---|
| Maximum continuous use temperature | 180 °C (360 °F) | 200 °C (390 °F) | 260 °C (500 °F) | 150 °C (300 °F) |
| Density | 2.15 g/cm³ | 2.15 g/cm³ | 2.15 g/cm³ | 1.70 g/cm³ |
| Tensile strength | 25 MPa | 23 MPa | 28 MPa | 45 MPa |
| Melt processability | No | Yes | Yes | Yes |
| Dielectric constant (1 kHz) | 2.1 | 2.0 | 2.1 | 2.6 |
| Dynamic coefficient of friction | 0.04 – 0.10 | 0.08 – 0.20 | 0.08 – 0.20 | 0.20 – 0.40 |
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the maximum continuous use temperature of PTFE?
Section titled “What is the maximum continuous use temperature of PTFE?”The recommended maximum continuous use temperature is 180 °C (360 °F), being able to withstand brief peaks near melting (~327 °C) without immediate degradation.
What is the density of virgin PTFE?
Section titled “What is the density of virgin PTFE?”The typical density of unfilled PTFE is 2.15 g/cm³ (2150 kg/m³), although it can vary between 2.10 and 2.20 g/cm³ depending on grade and processing.
What tensile strength does PTFE have?
Section titled “What tensile strength does PTFE have?”The tensile strength of virgin PTFE is 25 MPa (3.6 ksi), with an elongation at break of 400 %, although these values are modified with the addition of fillers.
Can PTFE be machined?
Section titled “Can PTFE be machined?”Yes, PTFE is easily machined using a lathe, milling machine or conventional drill; its Shore D hardness of 63 and low shear strength require sharp tools and occasional cooling.
What coefficient of friction does PTFE have?
Section titled “What coefficient of friction does PTFE have?”The static coefficient of friction of PTFE is between 0.04 and 0.10, being one of the lowest among engineering materials, especially dry against steel.
What is the dielectric constant of PTFE at 1 kHz?
Section titled “What is the dielectric constant of PTFE at 1 kHz?”The dielectric constant at 1 kHz is 2.1, combined with an extremely low dissipation factor of 0.0001, ideal for high frequency applications.
References consulted
Section titled “References consulted”- azom.com: https://www.azom.com/article.aspx?ArticleID=804
- engineeringtoolbox.com: https://www.engineeringtoolbox.com/polymer-properties-d_1222.html
- steelnumber.com: https://www.steelnumber.com/en/steel_composition_eu.php?name_id=519
References
Section titled “References”- azom.com: https://www.azom.com/article.aspx?ArticleID=804
- engineeringtoolbox.com: https://www.engineeringtoolbox.com/polymer-properties-d_1222.html
- steelnumber.com: https://www.steelnumber.com/en/steel_composition_eu.php?name_id=519