Antimony trioxide has been, for decades, a widely used flame retardant in rubbers, plastics, and textiles due to its high effectiveness, allowing for the reduction of fire propagation in industrial and consumer applications. However, growing concerns about the toxicity and environmental impact of antimony trioxide have driven the search for more sustainable, efficient, and safer alternatives.

In this article, we will explore what antimony trioxide is, its uses as a flame retardant in rubbers, its limitations, and the viable alternatives that can replace or reduce its use.

Antimony trioxide (Sb₂O₃) is an inorganic compound that acts synergistically with halogenated flame retardants. Its main function in rubber compounds is to stop the chain decomposition reaction generated in the gas phase, acting as a sealing mechanism against oxygen.

Its effectiveness and ease of incorporation into formulations have made it an industry standard in rubbers used mainly for cables, conveyor belts, automotive gaskets, and flame-retardant coatings. However, its high toxicity and release into the environment, as well as exposure during rubber mixing and extrusion processes, represent a risk.

Among the main limitations of continuing to use antimony trioxide in rubbers as a flame retardant are its toxicity—since some studies indicate it may be carcinogenic after prolonged exposure—as well as its environmental impact, as its production or disposal can contaminate water and soil.

In addition, there is growing regulatory pressure in the European Union to reduce hazardous compounds in consumer materials, which forces companies to seek antimony-free alternatives.

Furthermore, the current geopolitical situation and its use in other industries, such as electronics, have caused its price to rise significantly in recent months, reducing its availability and making it a much less economical option.

There are different strategies to replace or reduce the use of antimony trioxide in rubber applications without sacrificing flame-retardant performance. Among the most notable are:

1. Phosphorus-based flame retardants

Flame retardants containing organic and inorganic phosphorus have proven to be effective alternatives to antimony trioxide, functioning in both the gas and condensed phases by acting as an intumescent system.
These compounds can be combined with halogen-free systems to achieve environmentally friendly formulations.

2. Metal hydroxides (Aluminum and magnesium hydroxide)

Aluminum and magnesium hydroxides act as flame retardants by absorbing heat and releasing water, which lowers the material’s temperature and dilutes combustible gases.

3. Synergistic systems with zinc and boron compounds

The use of zinc borates and boron compounds as flame retardants can improve fire performance by acting primarily as smoke suppressants. AKISAN ZB is a powder-format additive produced by NASIKA, designed for flame retardancy and smoke suppression.

4. Nanocomposites as flame retardants

The incorporation of clays, carbon nanotubes, and expanded graphite in small proportions within rubber matrices can significantly enhance fire resistance by reducing flame propagation speed, improving the mechanical properties of rubber, and decreasing smoke generation, while creating a char layer that hinders flame spread.

avanFIRE GR-8 is a product by AVANZARE consisting of a combination of graphene-derived materials that exhibit exceptional synergy with other flame retardant additives containing polyphosphates and hydroxides. This additive enhances the fire resistance performance of the compound by promoting the formation of a char layer, which is highly effective at preventing further supply of fuel and oxidizers to the flame, reducing dripping, and distributing the energy produced by the flame (heat).

Although antimony trioxide has been an effective flame retardant option in rubbers for many years, its toxicity and associated environmental impact have driven the industry toward more sustainable alternatives. Phosphorus-based flame retardants, metal hydroxides, synergistic systems with boron and zinc compounds, and nanocomposite technologies are emerging as the main options to replace antimony trioxide, enabling companies to comply with safety and sustainability regulations without sacrificing the quality or performance of their products.

If your company is considering transitioning to antimony trioxide-free formulations, now is the time to evaluate these cleaner and safer alternatives that we at AVANZARE and NASIKA can offer you, positioning your brand at the forefront of the rubber industry.