Firebrake ZB

Firebrake ZB

Protection for polymers

This unique zinc borate combines the best of zinc and boron oxides with water release. Use it to develop fire-retardant formulations processable up to 290°C.
Firebrake fire protection

Help Prevent Fire in Plastic and Rubber Compounds

Firebrake® ZB is a unique zinc borate that combines the optimum effects of zinc and boron oxides with water release for flame-retardant formulations processable up to 554°F (290°C).

The product has multi functional fire-retardant applications in plastic and rubber compounds. Because Firebrake ZB releases its water of hydration at temperatures exceeding 554°F (290°C), it can be used in systems that require high processing temperatures. Firebrake ZB has a refractive index similar to that of most polymer systems, so it retains considerable translucency and enables the use of low pigment loading. It can be fed to extruders, calenders, or injection molding equipment, much like other solid polymer additives.


Firebrake ZB is used as a flame retardant, char promoter, afterglow and smoke suppressant, and anti-arc agent in polymer systems, including:
  • Polyvinyl chloride
  • Nylon
  • Epoxy
  • Polyethylene
  • Polypropylene
  • Polyesters
  • Thermoplastic elastomers
  • Rubbers

Depending on the base polymer that you use and the fire protection standards that need to be met, you can use Firebrake ZB to partially or completely replace other fire-retardant additives such as antimony oxide. (In some systems, Firebrake ZB displays synergism with antimony oxide.) In halogen-containing systems, use three to 25 parts of Firebrake ZB per 100 parts of resin (phr). In halogen-free systems, the recommended level is in the range of 10 to 250 phr, normally used in conjunction with alumina trihydrate, magnesium hydroxide, or a silicone polymer. (Examples of starting point formulations are available upon request.)

For situations that demand maximum fire-test performance as well as film forming and adhesion, Firebrake ZB is available in fine and extra-fine formulations: Firebrake ZB-Fine and Firebrake ZB-XF, respectively. The XF grade has no particles greater than 12 microns (as determined by laser diffraction) and is suitable for more critical flame retardant applications.

Firebrake ZB combines the best of zinc and boron oxides with water release. Use it to develop fire-retardant formulations processable up to 290°C.



Depending on the base polymer and fire standards,
Firebrake ZB can partially or fully replace other fire-retardant additives, such as antimony oxide.


Available Grades
  • ZB
  • ZB-Fine
  • ZB-XF (Extra Fine)
Chemical and Physical Properties

Refractive Index: 1.58

Median Particle Size (laser diffraction):

Firebrake ZB-Fine: ≤ 2.5 microns Firebrake ZB-XF: ≤ 2.2 microns

Molecular weight: 434.67

Specific gravity: 2.77

Appearance: White, crystal like powder

Solubility: Less than 0.28% in water at room temperature

Stability: Thermally stable up to 554°F(290°C); can be hydrolyzed by strong acids and bases

Chemical Composition (Theoretical)

Boric oxide, B2O3: 48.05%

Zinc oxide, ZnO: 37.44%

Water of crystallization, H2O: 14.51%

Anhydrous equivalent: 85.49%

Containers: Products may be available in bulk, IBCs, or small bags.

U.S. Borax, part of Rio Tinto, is a global leader in the supply and science of borates—naturally-occurring minerals containing boron and other elements. We are 1,000 people serving 500 customers with more than 1,700 delivery locations globally. We supply 30% of the world’s need for refined borates from our world-class mine in Boron, California, about 100 miles east of Los Angeles.  Learn more about Rio Tinto

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