Chemical Features of Expanded PTFE

Update:24 May 2017
Summary:

The unique properties of the expanded PTFE (ePTFE) film […]

The unique properties of the expanded PTFE (ePTFE) film make it a good choice for many drug applications. At present, the expanded PTFE structure is used to ferment feed air, process gas and tank emissions aseptically filtered. They are also used in powder collectors and ultra low penetrating air (ULPA) filters. The unique nature of expanded PTFE is also being used in many new innovative products and technologies. Freeze trays, product isolators and drug delivery devices are just a few new areas of interest to the pharmaceutical industry.

Teflon or polytetrafluoroethylene (CF2-CF2), the chemical resistance, thermal stability and hydrophobicity are well known. PTFE has these desirable properties due to its unique chemical structure. Since PTFE consists only of carbon and fluorine, PTFE is a simple polymer. PTFE has a long straight carbon skeleton bonded to a fluorine atom. C-C and C-F bonds are very strong. In addition, the electron cloud of the fluorine atom forms a uniform helical sheath that protects the carbon skeleton. The uniform distribution of fluorine atoms makes it non-polar and non-reactive. The combination of strong bonds, protective sheaths and non-polarities makes PTFE very inert and thermally stable. This explains why PTFE is compatible with almost all of the processing and cleaning liquids commonly used in the pharmaceutical industry, including acids, bases and solvents.

Due to the non-reactivity and non-polarity of PTFE, it is difficult to bond. That's why Teflon is a well-known and easy-to-clean product. Since fluorine is the most negatively charged element in the periodic table, it does not want to share electrons with adjacent fluorine atoms. This results in a low surface free energy of PTFE. The lower the surface free energy of the material, the less likely it is to wet the liquid with higher surface energy, such as water. In contrast, some or all of the fluorine atoms of other polymeric film materials are replaced by hydrogen or other elements. This results in weaker bonds and more polar reactive molecules. Substitution also increases the surface free energy. Therefore, these polymers are less hydrophobic, have poor thermal stability and are more reactive than PTFE.