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    What are Flame Retardants?

    Flame retardants are reactive chemicals used as additives in combustible polymers to prevent, delay, or slow down combustion reaction.

St. Louis Group is one of the world's leading producers and sellers of Bolivian Antimony Trioxide (ATO). They produce a robust portfolio of various flame retardant and smoke suppressant additive solutions. 

Flame retardants are reactive additives that integrate into the polymer backbone to improve combustion and fire resistance. They can be applied to materials to prevent the start or spread of fire. Various chemistries can be combined with different polymer systems for overall effectiveness in suppressing the ignition process. With the rise of market demand and innovation in consumer products and industrial applications, flame retardants have become especially critical in the following end markets:


  • Textiles and Fabrics

  • Automotive and transportation parts

  • Electronics and Electrical Devices

  • Wires and Cables

  • Building and Construction

  • Paints and Coatings

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    Textiles and fabrics
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    Automotive and transportation parts
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    Electronics and electrical devices
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    Wires and cables
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    Building and construction materials
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    Paints and coatings
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How Do Flame Retardants Work?

An ignition source such as fuel or oxygen must be present for a fire to begin. Flame and fire retardants work by interfering or reacting with the ignition source, either physically or chemically. The primary mechanism of action is:

  • Physical Dilution: 

In this type, flame retardants act as a thermal sink by absorbing the ignition heat and release of water molecules. The release of water molecules increases the heat capacity of the product and reduces the fuel content by dilution. Examples of flame retardants that act by the physical dilution mechanism are aluminum trihydrate (ATH) and magnesium hydroxide (Mg(OH)2).

  • Chemical Interaction: 

Halogenated flame retardants chemically interact with the ignition process by dissociating into halogen radicals that compete with the free radicals and interrupt the combustion reaction. Halogenated flame retardants are mainly based on bromine and chlorine compounds.

  • Protective Coatings:

In this mechanism, flame retarding additives form a protective fluid or a carbonaceous char that acts as an insulating layer and reduces heat transfer. This type includes Phosphorous and Nitrogen based flame retardants.

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Types of Flame Retardants:

  • Halogenated flame retardants:

Halogenated flame and fire retardants function by releasing halogen radicals that disrupt free radicals in the vapor phase and shut down the combustion process. Halogenated flame retardants include bromine, chlorine, fluorine, and iodine compounds. The most commonly used flame retardant systems, Brominated and Chlorinated chemistries, inhibit the vapor phase reaction by suppressing the supply of flammable gases. Fluorine and Iodine flame retardants are also available but not as common. Halogenated flame retardants are often combined with synergists such as antimony compounds to decrease the loading rate.


  • Halogen-free or non-halogenated flame retardants: 

The demand for halogen-free flame retardants is on the rise, driven by environmental initiatives to decrease the use of halogenated compounds. Non-halogenated flame retardants include phosphorus and nitrogen compounds. Their mode of action is by forming a protective char in the condensed phase or releasing free radicals to displace oxygen in the gas phase that inhibits the flame.

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Types of Halogen-Free Flame Retardants:

Intumescent Flame Retardants: 

Intumescent flame retardants are char forming additives that form a protective barrier of carbon foam film in the condensed phase. The protective layer is formed on the polymer's surface in response to heat, protecting the product from being burnt. 


This carbon char acts as a barrier or insulating layer that interrupts the combustion process from further occurring. Char forming flame retardants offer robust protection by preventing fuel molecules from reaching the flame front and thereby protecting the polymer from further depolymerization. 


Intumescent coatings also don't need synergists to improve the effectiveness and don't degrade the mechanical properties of the polymer. They are often used for applications requiring high flame protection levels, such as building and construction, aerospace, military, wire & cable, automotive, and transportation applications.


Organophosphorus Flame Retardants:

Organophosphorus flame retardants react chemically with free radicals in the gas or the condensed phase during combustion. They act as radical scavengers that are activated by the release of temperature. Unlike halogen compounds, they typically don't need synergists to be effective but can be combined with other halogens to enhance the protection and loading rate. 


Ammonium polyphosphate is one of the most popular non-halogenated phosphorus-based flame retardants. Phosphate esters are supplied in liquid form and are highly effective in urethane foams and engineered resin systems. Although phosphorus compounds are very effective and can be used in various applications, they generate smoke and carbon monoxide gas.

Endothermic Flame Retardants:  

Endothermic flame retardants are mineral-based additives such as aluminum trihydrate (ATH) and magnesium hydroxide (Mg(OH)2). They act by releasing water and carbon dioxides that dilute the fuel available for combustion. Endothermic decomposition cools down the condensation phase, slows down degradation, and absorbs the fuel combustion heat. 


Although mineral fillers are lower in cost and considered greener chemistries, they require higher loading rates to reach the desired level of protection. The higher level of mineral fillers can also affect the polymers' mechanical properties.

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The Benefits of Using Non-Halogenated Flame Retardants:

  • Non-Halogen flame retardants are non-toxic and do not release harmful gases during combustion.
  • Unlike halogen compounds, non-halogenated compounds are not persistent and do not cause bioaccumulation.
  • Non-halogenated flame retardants can function independently and do not require a synergist to provide the necessary
  • performance.
  • Halogen-free flame retardants are greener additives and have no environmental scrutiny or regulatory concerns.

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Featured Grades:

PhosGard® APP is a fine particle flame retardant based on modified Ammonium Polyphosphate that is excellent for use in water-based coatings, polyurethanes, thermosets, and polyolefins. Its primary chemistry is a Phosphorous and Nitrogen blend. 

PhosGard® NH4 is a halogen-free phosphate-based flame retardant with low scorch and volatility. PhosGard NH4 is excellent for flexible urethane foams, engineered resins, and PVC systems. Its primary chemistry is Phosphate Ester. 

CharFlam 200-M is a micronized melamine-based intumescent flame retardant that provides superior protection to paints, coatings, and textiles. Its primary chemistry is Melamine.

BroShield 68-B is a brominated fire retardant containing aromatic and aliphatic bromine. It provides superior protection to coatings, adhesives, and fabric back-coatings. Its primary chemistry is an oligomer of Tetrabromobisphenol A. 

Contact us to speak with a specialist. You can also click below to access the flame retardants selector guide and find out the right solution for your application and formulation needs.

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