Flame Retardancy

Understanding Flame Retardancy

Flame retardancy refers to the ability of a material to resist or delay the spread of fire. When exposed to heat and flame, most materials undergo combustion, releasing volatile gases and generating more heat. However, flame retardant additives can be introduced to modify the material's behavior and minimize the risk of ignition and flame spread. In addition, there are some materials that have good flame retardancy without adding flame retardants. For example, a key property of fluoropolymers is flame retardancy, which makes them valuable and potential in a wide range of fields.

Burning cycle of a polymer

Why Are Fluoropolymers Flame Retardant?

Fluoropolymers are flame retardant due to the presence of fluorine atoms in their chemical structure. The carbon-fluorine (C-F) bond is highly stable and resistant to combustion. When exposed to heat or flame, the strong bond between carbon and fluorine prevents the material from easily vaporizing or decomposing. This inhibits the release of flammable gases and the formation of a volatile fire environment. Additionally, the high thermal stability of fluoropolymers helps them withstand high temperatures without degrading or catching fire. Overall, these properties make fluoropolymers highly resistant to flame propagation, making them effective as flame retardant materials.

Flame Retardant Mechanisms of Fluoropolymers

Fluoropolymers exhibit excellent flame retardant properties due to the unique characteristics of fluorine atoms. Overall, the flame retardancy mechanism of fluoropolymers involves a combination of high thermal stability, low heat release, slow combustion rate, formation of protective char layer, suppression of smoke and toxic gas emission, and inhibition of fuel supply.

The flame retardancy of fluoropolymers is achieved through various mechanisms, including the following:

• Gas Phase Mechanism
  Upon exposure to heat, the flame retardants in fluoropolymers undergo thermal degradation, releasing gases that dilute the oxygen concentration surrounding the material. This reduced oxygen level hinders the combustion process, effectively suppressing the flame spread. Commonly used gases in this mechanism include carbon dioxide (CO₂), water vapor (H₂O), and nitrogen (N₂). These gases act as physical barriers, separating the polymer and the flame.
• Condensed Phase Mechanism
  Fluoropolymers can also undergo condensed phase flame retardancy mechanisms. In this mechanism, the fluoropolymers release flame retardant additives that react with the flame and form a protective layer on the material's surface. This layer acts as a barrier, preventing the flame from reaching the underlying polymer and slowing down the combustion process.

Flame Retardancy Comparison of Fluoropolymers

The flammability and limiting oxygen index reference values for several fluoropolymers are as follows:

Fluoropolymers	Forms	Flammability	Limiting Oxygen Index (LOI, vol%)
PTFE	Fluoropolymer Fluoropolymer films Fluoro coatings Polymer additives	UL-94 V-0	>95
FEP		UL-94 V-0	>95
PFA		UL-94 V-0	>95
PCTFE		UL-94 V-0	>95
PVDF		UL-94 V-0	44
ETFE		UL-94 V-0	30-36
Fluoroelastomer		UL-94 V-0	>75

Reference

1. Lin S C, et al. "Flammability of Fluoropolymers." 2009. 288-297.