PTFE was the first fluoropolymer to be discovered. It is also the most difficult to process. Because its melt temperature is only a few degrees shy of its degradation temperature, it cannot be melt-processed. PTFE is processed using a sintering method, where the material is heated to a temperature below its melting point for an extended period of time. The PTFE crystals unravel and interlock with each other, allowing the plastic to take the shape it is intended to take. PTFE has been used in the medical industry as early as the 1960s. Today, it is typically used for split-sheath introducers and dilators, as well as lubricious catheter liners and heatshrink tubing. Because of the chemical stability and low coefficient of friction, PTFE is an ideal catheter liner.
Fluoropolymers are chemically similar to polyolefins, with the exception of substituting fluorine for hydrogen. This drastically changes the properties. Fluorine’s electronegativity causes the bond between carbon and fluorine to be the strongest bond in organic chemistry. This strong bond lends itself to fluoropolymers, achieving high temperature resistance, lubricity, electrical resistance, dielectric strength, and low reactivity.
All of these properties lend to fluoropolymers being extremely biocompatible, and thus ideal for medical applications. Their drawback is in long-term-use applications under load, as fluoropolymers are notorious for cold-flow, or material creep.
FEP is very similar to PTFE chemically. It adds on a CF3 pendant group every fourth carbon, which dramatically lowers its crystallinity. Because it is less crystalline than PTFE, its melt temperature is lower, which allows it to be melt-processed. All of its other material properties are nearly identical to those of PTFE. It is used for a variety of purposes where sterilization and heat resistance are the biggest factors. It can also be used to make high-temperature heatshrink tubing used for reflow catheter layups.
ECTFE is a copolymer of PE and PCTFE. It is known for impact strength and good low temperature properties. For this reason, it is used as a gasket material for stored gases, particularly oxygen. It can also be used as a filtering material.
EFEP is a copolymer of FEP and polyethylene. This fluoropolymer is special because it can bond with other materials without requiring an etching step, yet it still retains the chemical resistance that is the trademark of fluoropolymers. It is also more optically clear than other fluoropolymers.
ETFE is a copolymer of PTFE and polyethylene. This allows the polymer to take on some of the properties of both individual plastics. It is also very resistant to UV light. It is used for medical applications that involve exposure to UV light on a regular basis. It is often considered a high strength version of FEP or PFA.
PCTFE is known primarily for its low water vapor transmission rate. Because of this, it is often used in packaging of things that are extremely moisture-sensitive. It is also used for chemical-resistant barriers and coatings. The addition of the chlorine atom into its structure dramatically lowers its melting temperature due to chlorine’s bulkiness.
Perfluoroalkoxy (PFA) is the melt-processable fluoropolymer with the highest temperature resistance. It is often compared with FEP, which it surpasses in fatigue life, but falls short in moisture resistance. Its advantage in medical applications is that it is similar to PTFE in fatigue life but can be manufactured in more complex ways as it is melt-processable.
Polyvinylidene fluoride (PVDF) is used when chemical purity is a must. It also demonstrates piezoelectric behavior, which is a contraction or expansion in response to a magnetic field. It is a popular material used to create tools used for protein separation.