Alumina Trihydrate (ATH)

Alumina Trihydrate (ATH), also known as aluminium hydroxide (Al(OH)₃), is the most widely used flame retardant and smoke suppressant globally, with annual consumption exceeding two million tonnes. It is produced primarily as a co-product of the Bayer process for alumina refining, in which bauxite ore is dissolved in caustic soda and the resulting sodium aluminate solution is seeded to precipitate aluminium hydroxide crystals. The precipitated product is filtered, washed, and dried to produce the commercial ATH used in industrial applications.

The fire retardant mechanism operates through two complementary pathways. First, the endothermic dehydration of ATH at approximately 200°C absorbs around 1050 kJ/kg of heat energy, cooling the burning substrate and slowing thermal degradation. Second, the water vapour released during dehydration, approximately 34.6% by weight of the ATH, dilutes combustible gases and oxygen in the flame zone. The alumina residue remaining after dehydration forms a protective ceramic char layer on the substrate surface, providing additional insulation against heat transfer.

ATH is non-toxic, non-halogenated, and produces minimal smoke during combustion. It is compatible with a wide range of polymer systems including polyethylene, polypropylene, EVA, PVC, epoxy, and unsaturated polyester resins.

ATH is available in particle sizes from standard grades (d50 approximately 50 µm) to fine precipitated grades (d50 approximately 1 to 5 µm). Surface-treated grades with silane or stearic acid coatings are available for improved polymer compatibility. ROCC Global supplies ATH in bagged and bulk formats from certified producers in Europe, Asia Pacific, and the Middle East.

ATH is used at high loading levels, typically 40 to 65% by weight of compound, as the primary flame retardant and smoke suppressant in a broad range of polymer applications. In wire and cable compounds, it is the dominant flame retardant in low-smoke zero-halogen formulations based on polyolefin and EVA matrices, providing the combination of fire performance, low smoke density, and low toxicity required by international cable standards including IEC 60332 and EN 50399. In solid surface materials such as Corian and Hi-Macs, fine precipitated ATH is the primary filler and flame retardant in acrylic resin matrices, contributing to fire performance, surface hardness, and the translucent aesthetic of the finished material. In glass fibre reinforced plastics and unsaturated polyester composites, ATH provides flame retardancy in building panels, electrical enclosures, and transport components. In flexible PVC and rubber compounds, it is used in combination with other additives to achieve flame retardancy in flooring, roofing membranes, and conveyor belts.