Chemical and Physical Behavior

• Neither solvents like alcohols, esters and ketones nor aggressive acids (such as fuming sulfuric or nitric acid, hydrofluoric acid, etc.) change the properties of PTFE
• Merely when used in coolants (e.g. Freon (R-12), dichlorodifluoromethanes) a reversible 4 – 10% increase  in weight has been measured
• A chemical reaction (browning) of PTFE only occurs with melted or dissolved alkali metals
• At higher temperatures and pressures PTFE reacts with elementary fluoro- and chlorotrifluoride
  
• Monomers like styrene, butadiene or acrylonitrile can penetrate PTFE or modified PTFE in small  amounts, and in the event of conditions triggering a spontaneous polymerization, this may lead to welling of the material

For these reasons, extensive tables and chemical resistance lists are not required for PTFE.

Light and Weather Resistance
PTFE has outstanding light and weather resistance. Consequently, PTFE is suitable for outdoor use and use  in extreme weather conditions without limitation and without any notable changes to its mechanical or  electrical properties.

High-Energy Radiation
PTFE is not radiation-resistant. Consequently, this plastic material should not be used in areas exposed to  radiation. An extremely high dose of radiation may result in the decomposition of PTFE: Due to ruptures  in the molecular chain the polymeric properties of the material successively deteriorate. This  disintegration can ultimately lead to the release of the monomer and thus the release of gaseous TFE in  addition to other corrosive and toxic combinations.

• With an absorbed radiation dose of 102 J/kg the polymeric properties begin to change
• With a radiation dose of 5 · 104 J/kg: reduction of tensile strength by 50-90%. Reduction of ultimate elongation by > 90%.

Combustibility
Combustion tests have shown that of all plastic materials fluoro-polymers are the most difficult to  inflame. The gaseous disintegration products will only ignite within the range of an external flame. After  removing the igniting flame the combustion process stops immediately. The ignition temperature  measured on semi-finished PTFE products according to ASTM D 1929 are within the range of 500 to 560°C, the LOI index (oxygen index) is 95%. According to Underwriters Laboratories (UL) the various PTFE types are listed in fire class V-0. The relative electrical and mechanical temperature index (RTI) for PTFE is  generally at 180°C. If a higher value is required for a particular application, a spezial measurement must be performed.

Physiological Properties
Unfilled PTFE is physiologically inert. FDA, EU and BgVV approvals have been granted. For glass fiber  compounds as well as for fillers PEEK and PPSO2 FDA compliance statements are available. Cyto-toxicity tests have been performed successfully. Consequently, the use of this material is permissible in both medical and food technology applications. A highly positive characteristic in this respect is the material’s resistance to hot vapor, which means that PTFE components used in the medical, pharmaceutical and food industries are well suited for sterilization.

Adhesive Behavior Adhesivity of pure PTFE is very low (anti-adhesive), which is attributable to the shielding of the carbon chain by the fluorine atoms and their low polarization capabilities. As a result, wetting of PTFE is difficult (contact angle with water 126°). This property basically applies to PTFE compounds as well, though to a lesser extent. The wetting behavior of highly filled compounds may differ significantly from unfilled PTFE. This applies to  both water and other solvents as well as to adhesives.

• No adhesion of media with assembly component linings, sheathing, etc.

• Wetting difficulties preclude adhesive bonding of PTFE in this state

Adhesive Bonding Capability
Low intermolecular forces and the low polarization capabilities of the fluorine atoms are the reasons why  PTFE offers poor adhesive bonding capabilities. Adhesive bonding therefore requires a chemical pre-treatment of the surface, e.g. by sodium dissolved in ammonia or through plasma-etching.

Weldability
Yet PTFE may be welded as well under certain conditions. In this case, a PFA hot melt adhesive is used as the coating connecting the two PTFE surfaces. Modified PTFE may also be welded without any welding aids. For thin films/sheets, rail-type contact welding equipment capable of applying the required temperatures  of app. 350°C is suitable. Thicker profiles require a spezial welding process: in the contact zone the two mating surfaces are fused by a local temperature cycle similar to a standard sintering curve.

• PTFE surface does not have to be etched

• Fusion occurs only at very high temperatures 325 – 335°C (@ crystallite melting temperature of PTFE)