One reader of the blog asked Lectromec to compare products for wire circuit protection. A couple of the common wire insulations on the market are based on the PTFE and ETFE polymers. PTFE (DuPont trade name Teflon®) is a fluorocarbon and is constructed with carbon and fluorine atoms, whereas ETFE is a carbon, fluorine, and hydrogen based material. The following discusses the advantages and disadvantages of each.
Considering the physical properties of both of the polymers, there are some differences between the two. The tensile strength of ETFE can be as much as 34% greater than PTFE. PTFE is more flexible and has a much higher (66%) elongation to break. Additionally, PTFE does have a significant advantage is the coefficient of friction. PTFE has a coefficient of friction one-third of ETFE making it a more ideal wire insulator for areas where wire bundles may chafe against one another.
There are also notable differences in the thermal properties of each material. The melting temperature of PTFE is 327oC and ETFE 267oC, but both of these materials begin to soften below at lower temperatures. As such, the operating temperature of the materials is lower. Further, PTFE has a Limiting Oxygen Index (the minimum percentage concentration of oxygen at which the polymer will burn) greater than 95% whereas ETFE is somewhere between 30-36%, meaning that PTFE should be considered in higher oxygen environments.
If you are interested in aerospace wire separation you may want to read Lectromec’s Seven Considerations for Aerospace Wire Separation article.
An area of concern with both of these materials is the outgassing of fluorine over extended durations (outgassing is when the constituent parts of an insulation, in the case of PTFE and ETFE – fluorine, escape from the insulation). The free fluorine atoms from these materials can create corrosive hydrofluoric acid which is of greatest concern in enclosed areas.
Lastly, it should be noted that there is also cross-linked ETFE wire on the market. The cross-linked ETFE (XL-ETFE) process creates bonds between the ETFE polymers, making the material stronger and having a higher temperature rating. There are other differences in performance, but overall, XL-ETFE can be considered a more hardened material.
In general, there is no perfect wire for all conditions, just one better meets the physical, electrical, and chemical conditions of a given environment. If you are looking for a material with high mechanical toughness and low friction properties, a PTFE wire should be considered over an ETFE wire. ETFE should be considered in high-energy radiation environments.
Michael Traskos
President, Lectromec
michael.traskos@lectromec.comMichael has been involved in wire degradation and failure assessments for more than a decade. He has worked on dozens of projects assessing the reliability and qualification of EWIS components.