Thermoplastics (PTFE and others)

Both unfilled and filled – PTFE is an unbranched, linear, semi-crystalline polymer consisting exclusively of fluorine and carbon.
It belongs to the class of polyhalogen olefins, which also includes PCTFE (polychlorotrifluoroethylene).
Although PTFE is classified as a thermoplastic, it also exhibits properties that require processing methods typically associated with thermosetting plastics.

Special characteristics of PTFE

PTFE is extremely chemically inert. Even aggressive acids such as aqua regia cannot attack PTFE. This is due to the exceptionally strong bond between carbon and fluorine atoms, which prevents many substances from breaking the bond and reacting chemically with PTFE. PTFE is highly resistant to bases, alcohols, ketones, fuels, oils, etc. It is only unstable when exposed to very strong reducing agents (e.g. alkali metals in liquid ammonia) or very strong oxidising agents such as elemental fluorine at elevated temperatures. Operating temperature up to 260 °C Cold resistance down to –200 °C Slightly wax-like surface (less pronounced than PE) Physiologically harmless PTFE has a very low coefficient of friction. PTFE slides on PTFE almost as smoothly as wet ice on wet ice. Static friction equals dynamic friction, enabling a smooth transition from standstill to motion without jerking. In sealing elements made of PTFE (and PTFE compounds), stick-slip effects are virtually eliminated. Due to its extremely low surface tension, almost no materials adhere to PTFE. PTFE is difficult to wet and hardly bondable. Density, hardness and tear resistance can be found in the respective material data sheets. PTFE exhibits high thermal expansion and a phase transformation from a triclinic crystal lattice to a hexagonal lattice at 19 °C, accompanied by a change in volume.

Selected parameters of pure PTFE

Refractive index: approx. 1.38 Specific heat capacity: 0.96 J/(g·K) Thermal conductivity: 0.25 W/(K·m) Permittivity: 2.1 (D150 at 10³ Hz) Dielectric loss factor: 0.3 × 10⁻⁴ at 10³ Hz Specific resistance: 10¹⁸ Ω·cm

POM (also known as polyacetal or acetal) is a high-molecular-weight thermoplastic.
Due to its high stiffness, low coefficient of friction and excellent dimensional and thermal stability, it is particularly suitable for precision components.

Polyamides (abbreviation PA) are linear polymers with regularly repeating amide bonds along the main chain. They offer excellent strength and toughness and good chemical resistance to organic solvents. However, they can be attacked by acids and oxidising chemicals. Polyamides respond to ambient humidity through reversible absorption and release of moisture. PA6 absorbs approximately 2.5–3.5 % water when exposed to ambient air.