Borate Flame Retardant Is the Ideal Solution

:: Tuesday, February 12, 2019 :: Posted By Maryam Moravej
Construction, industrial, and transportation companies continue the move away from halogenated fire retardants. But modern safety regulations require effective, proven flame retardants for use with wood, polymers, textiles, and electronics. Borates offer an ideal solution.

Borate flame retardant: Uses across industries

Specialized borate compounds—zinc borate flame retardant, for example—have long been used to help retard flame and reduce smoking, arcing, and sparking in numerous applications:
  • Wood construction and wood composites
  • Polymers, plastics, and rubber
  • Cellulose and foam insulation
  • Roofing membranes
  • Mechanical parts and conveyor belts
  • Electronics
  • Electrical wiring, connectors, bobbins, circuit breakers, and housings
  • Transformer components
  • Appliance components
  • Industrial coatings
  • Fabric, upholstery, cotton mattresses, carpet backing, and wall coverings
Companies are looking for effective, non-halogenated products that are compatible with a variety of substrates. In particular, new residential and commercial construction are increasingly benefiting from borate-based fire retardants, as is the transportation industry.

Long-Lasting flame-retardant protection for wood and cellulosic materials

Borates are often used to promote char formation and inhibit smoldering and flame combustion and combustible gas release in burning cellulosic materials. Optibor® boric acid, Neobor® borax pentahydrate, and borax decahydrate are particularly effective in protecting cellulose insulation, wood composites, and the cotton batting used in mattresses.
Optibor is a frequent choice for cellulose insulation, used alone or with one of the following:
  • Neobor
  • Borax decahydrate
  • An ammonium-based mineral compound
  • An aluminum-based mineral compound
  • Gypsum
A combination of Optibor and Neobor or borax decahydrate might provide optimal protection thanks to their resistance to heat and moisture.
The long-term effectiveness of flame-retardant products is an essential consideration for product makers, which has led them to eliminate some types of non-borate choices. Ammonium sulfate forms acidic by-products when combined with moisture—bad news for electrical wiring, copper pipes, steel trusses, and the like. Some governmental regulations have even required the discontinuance of cellulose insulation products that use ammonium sulfate fire retardants. Aluminum-based products are also prone to corrosion concerns or manufacturing issues related to abrasiveness.
By contrast, boric acid and borax do not cause such corrosion. Many wet-spray cellulose installers now insist on using only material treated with these borate-based products.
Another concern is the products’ potential for leaching or dissolution, which can diminish the permanence of the retardancy. Compounds that dissolve under conditions of high humidity (moisture) and heat lower the effectiveness of the retardant. Thus, borate flame retardants’ ability to withstand high temperatures, especially in the presence of high humidity, is another advantage, especially for construction materials such as rafters and insulation.
Combustion tests have shown that borate-treated cellulosic material loses boric acid through evaporation (sublimation) at only a negligible rate up to a temperature of 70°C (158°F)—even at 100% humidity and air exchange rates of 2.0 attic changes per hour. Under those extreme conditions, it would still take 300 years or more to lose enough boric acid to significantly affect combustion.

Better char formation for polymer protection

Borates’ ability to promote char formation is also useful in the protection of polymers, plastics, and rubber. Char:
  • Reduces the duration of a fire
  • Inhibits its spread
  • Provides electrical insulation to protect wiring even after it is burnt
  • Prevents short-circuiting and sparking
In fact, borates not only retard flame and act as an anti-arcing agent, but also suppress smoke and afterglow.
As multipurpose fire-retardant synergists, Firebrake® 500 and Firebrake ZB completely or partially replace antimony oxide in the final product:
  • Firebrake 500 is used as a flame retardant and smoke suppressant in polyetherketone, polysulfone, fluoropolymer, polyester, and nylon. Stable up to 600°C (1,112°F), the product is especially useful in aircraft applications.
  • Firebrake ZB is used as a flame retardant, smoke and afterglow suppressant, and anti-arcing agent in polyvinyl chloride, nylon, epoxy, polyethylene, polypropylene, polyesters, thermoplastic elastomers, and rubbers. The product’s refractive index is similar to most polymer systems, helping it to retain translucency and enabling low-pigment loading. Suitable for processing temperatures as high as 290°C (554°F), Firebrake ZB is used to help protect wires, cables, mining belts, flooring, roofing membrane, and foamed insulation.

U.S. Borax: Emphasis on research and customer service

Manufacturers naturally want to know that their borate supplier is current on both the regulatory and research fronts. U.S. Borax has long placed an emphasis on research, including the use of zinc borate in halogen free-polyolefins and rigid PVC. Our product development projects have also explored encapsulated, surface-treated, and sub-micron zinc borates.
U.S. Borax, a part of Rio Tinto, goes above and beyond to provide extensive, expert customer service in these areas:
  • Our product stewardship team works closely with customers to navigate regulatory application needs.
  • We maintain partnerships with associations and attend conferences to help ensure that we are aware of and fully understand the changing regulatory landscape and keep up to date on industry and technical trends.
  • We provide high quality samples and expert formulating advice—a unique service that is especially valuable for smaller compounders.
Fire retardancy is a broad and complex area. Every polymer system requires different loadings and potentially different materials. Gaining the necessary expertise to navigate all the potential formulations can increase both time and cost effectiveness of customers’ development efforts.
Aside from these benefits, 20 Mule Team® Borax products offer several advantages over antimony oxide or competing borates:
  • Less caking
  • Compatible granulometry with other glass-batch components
  • Consistent and reliable product quality
  • Certificate of authenticity (COA) data in batch formulation
  • Global sourcing and stable, reliable supply of high-quality inputs

Want more information about borate flame retardants?

Visit Boron in Fire Retardancy

Additional Resources


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 650 customers with more than 1,800 delivery locations globally. We supply around 30% of the world’s need for refined borates from our world-class mine in Boron, California, about 100 miles northeast of Los Angeles.  Learn more about Rio Tinto.

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