Full definition
Chemical additive incorporated into rubber and plastic compounds to reduce flammability, slow flame spread, and/or promote self-extinguishing behavior when the external ignition source is removed. Major types: (1) Alumina trihydrate (ATH, Al₂O₃·3H₂O) — the most widely used; releases water at 200°C, diluting flammable gases and cooling the surface; non-halogenated, low toxicity; 50-150 phr loading required. (2) Magnesium hydroxide (MDH) — similar to ATH but effective at higher temperatures (>300°C). (3) Antimony trioxide (Sb₂O₃) — synergist with halogenated compounds; 2-5 phr. (4) Halogenated compounds (chlorinated paraffins, decabromodiphenyl ethane) — effective at low loading but face increasing regulatory restrictions (RoHS, REACH). (5) Phosphorus-based (ammonium polyphosphate, red phosphorus) — char-forming, low smoke. Testing: UL 94 (V-0, V-1, V-2 ratings for self-extinguishing), oxygen index (LOI — minimum % O₂ to sustain combustion per ASTM D2863), and ISO 340 (conveyor belt flame test). Inherently flame-retardant rubbers: neoprene (CR, ~36% Cl), chlorinated PE (CSM), and fluoroelastomers. For mine-duty conveyor belts, flame resistance is mandatory per MSHA, ISO 340, and EN 12882.