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Thermoplastic polymers have a storied history. One trait that makes them special is their ability to be repeatedly heated to a softening point, shaped or worked as necessary, and cooled to retain the new shape. Other materials would degrade after undergoing such a process. Thermoplastic polymers can be heated, reshaped, and cooled many times without affecting the overall polymer structure. Over the years, many different types of thermoplastics have been developed. From the well-known polyvinyl chloride (PVC) and polypropylene (PP), to the lesser known and higher performing fluoropolymers that can be either thermoplastics or thermosets.
Choosing the right thermoplastic material for your application requires a bit of research. Some are better suited to resist temperatures, others are designed to be unaffected by a whole host of concentrated chemical compounds, and the cost of the materials varies significantly. We’ve put together this article to help you identify the best fluoropolymer material for your next project.
Fluoropolymers: Plastics for the future
Fluoropolymers have a carbon backbone and consist of tightly packed carbon-fluorine bonds that are not as susceptible to the Van der Waals forces that exists between most atoms and molecules. This trait contributes to the relative chemical inertness of fluoropolymers. PTFE (polytetrafluoroethylene, known by the tradename Teflon) is the first manufactured fluoropolymer and was discovered by DuPont in 1938 however it is not a thermoplastic. Other materials were developed in the subsequent years in an attempt to improve on the difficult processing characteristics of PTFE. Since then, more than a dozen other fluoropolymers have been discovered. Most are ideal for pharmaceutical, biopharmaceutical, specialty chemical, and semi-conductor processing equipment because they have excellent chemical and thermal resistance.
Today, cleanroom environments such as those producing microchips and pharmaceuticals use specialized equipment made with fluoropolymers due to the extremely low level of extractable materials that leach out of the polymer.
Choosing from the acronym soup
Even though it was the first discovered fluoropolymer, PTFE remains one of the most important and is the largest produced by volume. Due to the difficulty in processing, other more specialized fluoropolymers such as the four listed below have gained popularity for industrial usage.
Poly(vinylidene) fluoride (PVDF) is used in the, micro-electronics, architectural coating, and chemical industry. PVDF is used to create chemical resistant pipes, valves and fittings, bearings, pump parts, and heat-shrinkable tubing. It is also used as a coating to improve the chemical and weather resistance of metals such as aluminum and galvanized steel, as a binder in lithium-ion batteries, and as a backing sheet in photovoltaic cells. PVDF is one of the most cost-effective thermoplastics fluoropolymers. PVDF possesses a density of 1,770 kg/m3.
Ethylene ChloroTriFluoroEthylene (ECTFE) possesses a unique combination of properties that are the result of its chemical structure, which consists of a copolymer with ethylene and ChloroTriFluoroEthylene arranged alternately. ECTFE demonstrates excellent resistance to the corrosive influence of heat, strong radiation, and weathering. The material has high impact resistance and shows almost no property changes in a wide temperature range, making it particularly well-suited for demanding industrial applications. Its excellent welding properties and thermoplastic formability also make simple and cost-saving processing possible, both in the workshop and on-site. Compared to PVDF, ECTFE has a better chemical resistance, especially when exposed to lyes (bases). ECTFE possesses a density of 1,680 kg/m3.
Perfluoroalkoxy (PFA) is a true thermoplastics fluoropolymer, capable of being melted and reshaped multiple times. In many ways, it is interchangeable with PTFE in terms of its chemical resistance, melting point, and effective pressure rating. PFA has the highest permeation performance of the fluoropolymers, exceeding even PTFE. It also provides the smoothest and least wettable finish of all of the fluoropolymers. PFA is used extensively in the semi-conductor industry due to its very high purity, near-universal chemical resistance, and high temperature resistance. PFA possesses a density of 2,150 kg/m3.
Fluorinated ethylene propylene (FEP) is another thermoplastic fluoropolymer that exhibits the near-universal chemical resistance of PTFE and PFA, however it is only capable of maximum operating temperatures of 150 degree Celsius. FEP is useful as a sheet lining product that can be used to line complex equipment or tools without the use of expensive molding tools. FEP linings can be bonded together to provide a degree of vacuum performance. In cases where maximum chemical and temperature performance are not the primary concern, FEP provides a less expensive alternative to PFA. FEP possesses a density of 2,150 kg/m3.
Meet specification requirements with AGRU
There are entire books dedicated toward the selection of the right thermoplastic material for each application, but if your primary requirement is chemical resistance then you don’t need to look further than fluoropolymers. These polymers, formed by strong carbon and fluorine bonds, resist the tenuous forces of attraction that affect most atoms and molecules. The applications for products made from these materials are countless and can serve very specific industry niches.
In 2015, for example, AGRU manufactured PFA sheets to be used as the liner material of an ultra high-purity tank for Composites and Metal Products in North East Maryland. The material was selected due to its near-universal chemical resistance and low leachable content. Fluoropolymers shine in such applications. In addition to PFA, AGRU uses PE, PP, PVDF, PVDF-FLEX, ECTFE, and FEP to manufacture sheets, round bars, hollow bars, HV-liner pipes, and fabric-backed pipes, sheets, and other products.
AGRU is continually improving its manufacturing processes and seeking new specifications. In 2017, AGRU PDVF sheets made with Kynar 740 resin became an FM Approvals Listed Cleanroom Material. To earn this specification, the sheets had to be tested for compliance with FM Approvals and pass an ignition, combustion, fire propagation, and parallel panel test. As an FM 4910 cleanroom material, AGRU PVDF Sheets meet cleanroom requirements and are hard to ignite.
- Polymer Properties Database. CROW. Accessed December 11, 2017. http://polymerdatabase.com/polymer%20classes/Polyfluorolefin%20type.html.
- Polymer Database. NIMS. Accessed December 11, 2017. http://polymer.nims.go.jp/PoLyInfo/cgi-bin/pi-id-search.cgi?PID=P050003.