Are you looking for a group of exceptionally chemical resistant plastics? Check out fluoropolymers. These fluorocarbon-based plastics are composed of multiple strong carbon-fluorine bonds. This carbon-fluorine bond, called ‘C-F’ for short, is one of the strongest single bonds known to science. The multitude of C-F bonds in fluoropolymers gives these plastics extraordinary resistance to solvents, acids and bases.
Fluoropolymers were first serendipitously discovered in 1938 when Roy Plunkett at DuPont was experimenting with some tetrafluoroethylene gas. He accidently made PTFE (polytetrafluoroethylene), known commonly as Teflon®. Since that lucky day, many fluoropolymers have been developed, including PVDF (poly vinylidene difluoride); ETFE (polyethylenetetrafluoroethylene); FEP(fluorinated ethylene propylene); PFA (perfluoroalkoxy); ECTFE (ethylene chlorotrifluoroethylene) and PCTFE (polychlorotrifluoroethylene).
Even non-plastics experts have probably seen Teflon® in action, even if they don’t realize it, as the material is commonly used to coat nonstick cookware. With high heat resistance, excellent chemical resistance and a very low coefficient of friction this plastic is well suited to that purpose. (Although Teflon® is an impressive material, I would advise you not to get too crazy with your cookware. As the author has personally experienced, Teflon® spatulas and cooking spoons will melt if left over open flame. Say, the open flame of a gas range stovetop. But that’s a story for another day…) But there is so much more to the story of fluoropolymers than pots and pans.
Fluoroplastics are resistant to an extensive list of chemicals at temperatures between 20° C/68° F and 212°C/100°F including:
|Alcohols||Fatty acids||Salt-metals etchants||Ethers|
|Acid fumes||Polymer solvents||Aromatic hydrocarbons|
|Aromatic solvents||Halogens bases||Functional aromatics|
Some of the specific chemicals that fluoropolymers can resist include:
|Acetone||Hydrobomic acid (concentrated)||Sodium carbonate|
|Acetyl salicylic acid||Hydrofluoroic acid 75%||Sulfur dioxide 96%|
|Bromine||Hydrogen peroxide 90%||Sulfuric acid 95%|
|Calcium chloride||Nitric acid 90%||Tricholorethylene|
|Carbon tetrachloride||Methylene chloride|
|Chlorine wet||Diesel oil|
|Ferric chloride||Phosphoric acid 95%|
|Formic acid||Phosphorous chlorides|
And there are many more. The outstanding chemical resistance of fluoropolymers make them ideal for use in many different engineering applications including:
|substitute bones for nose, skull, ear, knee and hip parts||bearings||scrubber linings||chemical tanks, pumps, and fuel lines|
|biomedical material for artificial corneas and heart valves||cams||high end paints for metals|
|plastic lab ware and tubing||valve seats||chemical handling|
|semiconductor processing equipment||linings of pipes||spray nozzles|
Fluoropolymers also have a very low coefficient of friction making them naturally very slippery. Indeed PFA is said to be the only material that a gecko cannot stick to. Because of their low coefficient of friction fluoropolymers are known to be hard to glue. There is even a fluoropolymer paint designed to cause insects to slide off surfaces. This slipperiness and non-porousness makes fluoropolymers naturally anti-microbial and a good pick for medical applications.
Additionally, fluoropolymers are hydrophobic in that neither water nor water containing substances can wet them. They also have a flammability rating of UL94 V-0 so they are self-extinguishing. Fluoropolymers also have excellent dielectric properties, making them great insulators.
Fluoropolymers are also known for continuous service in extreme temperatures. PFA performs up to 260°C/500°F while FEP can sustain 200°C/393°F. ETFE has values of 150°C/302°F. Many fluoropolymers can withstand cryrogenic temperature. PTFE can withstand temperature values of -240°C/-400°F to 260°C/500°F. ECTFE also has excellent cryogenic properties and performs well between -76°C/-105°F to 150°C/302°F while PVDF can withstand temperatures of -30°C/-22°F to 150 °C/302°F. PCTFE performs well in a temperature range of -240°C/-400°F to 204°C/400° F°.
The down side of fluoropolymers is that they are not all that strong. With a tensile strength of 7800 psi/53.8MPa PCTFE is the one of the strongest along with ECTFE with also has a UTI of 7800 psi/53.8MPa. ETFE comes in next at 7500 psi/51.7MPa. PVDF has an ultimate tensile strength of 4000-6000 psi/27.6-41.4MPa and PFA has values of 4300psi/24MPa. The ultimate tensile strength of PTFE is 2,500-4,000psi/17.2-27.6 MPa while FEP is 3,000 psi/20.7 MPa. But if extreme chemical resistance, slipperiness or low flammability is required and tensile strength is not an issue, make sure you check out fluoropolymers.
Looking for more information on chemical resistant plastics? Check out our Material Guide!