Improving Flame Resistance with BrightSun™ Antimony Oxide

Improving Flame Resistance with BrightSun™ Antimony Oxide

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BrightSun™ antimony oxide is widely used in applications as a fire retardant. It’s found in many items used daily, from electrical apparatuses and textiles to leather and coatings. By itself, antimony oxide has no flame retardant properties. However, when you combine it with halogenated materials (primarily bromine and chlorine), it can be used as a flame retardant synergist in a range of industries.

Typically, a manufacturer will use three to four parts halogenated flame retardants to one part antimony oxide on a weight basis. Any ratio above 4:1 offers little to no difference in protection. The right formulation for your application will depend on many factors, including:

  • Thermal stability
  • Cost
  • Tinting strength
  • Streaking
  • Blendability
  • Flame retardant specifications

There are two flame retardant mechanisms associated with this synergistic system. Let’s take a closer look at both and how BrightSun antimony oxide is used to curb the destructive path of a fire.

1. Free Radical Capture Process

First is the “free radical capture” process, which occurs during the vapor phase. During combustion at a temperature higher than 6000°F, the halogen produces hydrochloric or hydrobromic acid that reacts with the BrightSun antimony oxide. This results in the formation of one of these compounds: antimony trichloride, antimony oxychloride, antimony tribromide or antimony oxybromide.

Antimony trihalides or antimony oxyhalides serve as “free radical traps,” which capture any free radicals that can increase the spread of flames. They are useful for inhibiting flame growth and pyrolysis at all phases of matter.

2. Char Process

The second process is the “char process,” and it takes place in the solid phase. BrightSun antimony oxide aids in the formation of “char” on the substrate, which prevents the release of volatile gases. The char acts as a barrier between the substrate and the vapor phase, decreasing the oxygen available to the substrate. In plastics, antimony oxide also promotes crosslinking to create a more stable thermoset polymer and minimize decomposition.

Alternatives to Antimony Oxide

Sometimes, manufacturers use other compounds in combination with or in place of antimony oxide. Some examples include phosphorus compounds (TCP), magnesium oxide, alumina trihydrate, molybdic oxide, zinc borate or zinc oxide.

These alternatives can lower costs, increase char formation, and reduce smoke. However, replacing antimony oxide with these other retardants greatly reduces flame retardancy. For example, alumina trihydrate is not synergistic with halogenated flame retardants. It exhibits flame retardant properties when it releases water in an endothermic reaction, and, therefore, cannot be used in high temperature processes.

H.M. Royal offers high-quality BrightSun antimony oxide as well as Twinkling Sun products to meet your flame retardant needs. For more information, contact our material experts today.


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