Rubber Flame Retardants- How to Choose? Rubber materials, due to their excellent elasticity and sealing properties, are widely used in fields such as automotive, electronics, and wire and cable. However, their limiting oxygen index (LOI) is generally low—natural rubber is only about 18%, making it highly flammable. To correctly select a flame retardant for rubber, multiple factors such as the type of rubber substrate, flame retardancy grade requirements, environmental regulations, and cost must be considered comprehensively.
The halogen-antimony system offers high flame retardancy efficiency with low addition levels (5%-20%), but it causes significant environmental pollution and releases toxic gases during combustion. Inorganic flame retardants (aluminum hydroxide, magnesium hydroxide) are environmentally friendly and produce low smoke, but they require high filling amounts (50%-70%), which markedly affects the mechanical properties of rubber. Phosphorus-nitrogen halogen-free flame retardants combine high efficiency and environmental advantages, making them the current mainstream trend.
Natural Rubber (NR) and Styrene-Butadiene Rubber (SBR): These have high flame retardancy requirements, and intumescent flame retardants (IFR) are recommended. Studies show that adding 50 parts of IFR can achieve UL94 V-0 grade for NR, increase the LOI to 27%, and achieve an optimal balance between flame retardancy and physical properties.
Ethylene Propylene Diene Monomer (EPDM) Rubber: It has excellent thermal stability and is suitable for halogen-free systems based on aluminum hydroxide (ATH). The best synergistic effect is achieved when ATH is combined with organic montmorillonite (OMMT), achieving an LOI of up to 34.5%.
Chloroprene Rubber (CR): It inherently contains chlorine, providing self-extinguishing properties. By combining it with flame retardant synergists such as antimony trioxide and zinc borate, the flame retardancy grade can be further improved.
Silicone Rubber: It has a certain degree of inherent flame retardancy. Adding a small amount of platinum catalyst and aluminum hydroxide can meet the requirements.
When selecting a flame retardant, it is also necessary to clarify the target flame retardancy standard (e.g., UL94 V-0), environmental certification requirements (RoHS, REACH), and the color of the product (red phosphorus is not suitable for colored products). Through scientific synergistic formulation design, an optimal balance among flame retardancy efficiency, physical properties, and cost can be achieved.
