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What Is FR Fabric
- Apr 18, 2018 -

Flame resistant (FR)  are used to manufacture FR clothing, which is worn by workers in many industries as the “last line of defense” against serious injury from arc flash, flash fire, molten metal, and combustible dust. These fabrics are self-extinguishing; they do not ignite and continue to burn once the heat source is removed, and they do not melt.


What are inherent FR fibers?

Inherently FR fabrics are knit or woven from fibers that have flame resistance built into their chemical structures. Interestingly, while the word inherent denotes a core property, or something that is innately and naturally a part of the whole, all inherent fibers in use today are engineered by humans. Because the FR engineering is done during creation of the fiber itself and is an inseparable part of the fiber.


What is treated FR fabric?

Treated fabric begins as a product that is flammable (typically a cotton or a cotton rich blend) and then flame retardants are engineered into the fabric to create flame resistance. There are a number of different treated technologies being used in the world today, and the best of these technologies create a flame resistant polymer inside the hollow core of the cotton fibers—producing fabrics that are guaranteed FR for the life of the garment.

THPC has industrial importance in the production of crease-resistant and flame-retardant finishes on cotton textiles and other cellulosic fabrics.[3] A flame-retardant finish can be prepared from THPC by the Proban Process,[4] in which THPC is treated with urea. The urea condenses with the hydroxymethyl groups on THPC. The phosphonium structure is converted to phosphine oxide as the result of this reaction.[5]


[P(CH2OH)4]Cl + NH2CONH2 → (HOCH2)2POCH2NHCONH2 + HCl + HCHO + H2 + H2O

This reaction proceeds rapidly, forming insoluble high molecular weight polymers. The resulting product is applied to the fabrics in a "pad-dry process." This treated material is then treated with ammonia and ammonia hydroxide to produce fibers that are flame-retardant.


THPC can condense with many other types of monomers in addition to urea. These monomers include amines, phenols, and polybasic acids and anhydrides.

Tetrakis(hydroxymethyl)phosphonium chloride (THPC) is an organophosphorus compound with the chemical formula [P(CH2OH)4]Cl. The cation P(CH2OH)4+ is four-coordinate, as is typical for phosphonium salts. THPC has applications as a precursor to fire-retardant materials,[1] as well as a microbicide in commercial and industrial water systems.


How does the chemistry of FR fabric work?

To understand FR fabric engineering, it is first important to understand fire. Fire is the product of a chemical reaction requiring heat, fuel, and oxygen. All FR fabrics (inherent and treated) are engineered to remove or reduce the presence of one or more of those components by interrupting the combustion process. Combustion is the chain reaction of heat breaking down material into fuel, which reacts with oxygen to create more heat, breaking down the material into more fuel, and so on. Depending on the type of FR fabric, this process can be interrupted by removing the fuel source, removing heat from impacting the fabric, or displacing oxygen. Most common FR fabrics char instead of burning, which acts to both remove fuel and block heat, and modacrylic fabrics also contain an active process that displaces oxygen. While the science of combustion and FR fabric is highly technical, understanding the properties of fire can provide the building blocks for greater insight into FR fabric technologies.