Full definition
Flame retardants are essential chemical additives incorporated into various rubber and plastic compounds to enhance fire safety by reducing flammability, slowing flame spread, and promoting self-extinguishing behavior upon removal of an external ignition source. These additives play a crucial role in applications where fire hazards are prevalent, such as automotive, aerospace, and construction sectors. The effectiveness of flame retardants is often evaluated using standard testing methods such as UL 94, which provides ratings (V-0, V-1, V-2) for self-extinguishing properties, and the oxygen index (LOI) test outlined in ASTM D2863 to determine the minimum percentage of oxygen required to sustain combustion. ISO 340 is also relevant for assessing the flame resistance of conveyor belts, particularly in mining applications where compliance with safety regulations is crucial.
The most prevalent type of flame retardant is Alumina trihydrate (ATH, Al₂O₃·3H₂O), which is favored for its non-halogenated nature and low toxicity. ATH releases water vapor when heated to approximately 200°C, which not only cools the surface of the material but also dilutes flammable gases. Typical loading levels range from 50 to 150 parts per hundred rubber (phr). Another option is Magnesium hydroxide (MDH), which operates effectively at elevated temperatures (>300°C) and serves a similar function as ATH. Additionally, Antimony trioxide (Sb₂O₃) acts as a synergist with halogenated flame retardants, requiring only a small loading of 2 to 5 phr for enhanced effectiveness.
Halogenated compounds, such as chlorinated paraffins and decabromodiphenyl ethane, are also effective at lower loadings; however, they face increasing regulatory scrutiny under directives like RoHS and REACH due to environmental and health concerns. Phosphorus-based flame retardants, such as ammonium polyphosphate and red phosphorus, are characterized by their char-forming abilities and low smoke production, making them suitable for applications where smoke generation is a concern. Inherently flame-retardant rubbers such as neoprene (CR, with approximately 36% chlorine content), chlorinated polyethylene (CSM), and fluoroelastomers are also notable for their fire resistance, providing additional options for manufacturers seeking compliance with stringent safety standards like MSHA, ISO 340, and EN 12882 for mine-duty conveyor belts.