Applications of Aluminum Hydroxide Flame Retardants

Aluminum hydroxide is currently the most widely used and extensively applied inorganic flame retardant additive. It not only suppresses flame spread but also inhibits smoke generation and absorbs toxic gases such as hydrogen halides, thereby finding broad application.

Aluminum hydroxide is currently the most widely used and extensively applied inorganic flame retardant additive. It not only suppresses flame spread but also inhibits smoke generation and absorbs toxic gases such as hydrogen halides, thereby finding broad application.

Aluminum hydroxide flame retardants decompose at 200-300°C. This decomposition triggers a dehydration reaction that absorbs significant heat from polymer material surfaces, thereby lowering the surface temperature of burning materials. Simultaneously, the dehydration process generates large amounts of water vapor, diluting combustible gases and oxygen concentrations. The decomposition residue, Al₂O₃, forms a dense oxide layer. These residues deposit on material surfaces, limiting combustible gas generation while providing thermal insulation and oxygen isolation, thereby achieving smoke suppression. Additionally, aluminum hydroxide absorbs acidic gases. With its moderate cost, it remains the most widely used filler-type flame retardant.

Industrial aluminum hydroxide flame retardants are primarily produced via the aluminate decomposition method, which is further categorized into the Bayer process and the lime-alkali calcination process based on raw materials and technology. The Bayer process involves leaching alumina from bauxite using heated sodium hydroxide solution to obtain sodium aluminate solution. After separating the solution from residue (red mud), the temperature is lowered, and aluminum hydroxide is added as a seed crystal. Through stirring, sodium aluminate decomposes to precipitate aluminum hydroxide. The lime-alkali sintering process is suitable for processing high-silica bauxite. Bauxite, sodium carbonate, and lime are mixed in specific proportions and sintered in a rotary kiln to form a clinker composed of sodium aluminate, sodium ferrate, calcium metasilicate, and sodium titanate. The clinker is then leached with dilute alkali solution to extract sodium aluminate. Under controlled conditions, the solution is separated from the residue (red mud). The sodium aluminate solution undergoes specialized desilification for purification. CO₂ gas is bubbled through the refined sodium aluminate solution, and seeding is added with stirring to obtain aluminum hydroxide.

Applications of Aluminum Hydroxide as a Flame Retardant:

Aluminum hydroxide boasts exceptionally broad utility. It serves not only as a flame retardant but also as a smoke suppressant and agent for reducing corrosive gas emissions in materials. While effective as a standalone compound, it is frequently blended with other flame retardants. For polymers processed at temperatures below ATH's decomposition range (190–230°C), ATH serves as an excellent flame retardant material for elastomers, thermosetting resins, and thermoplastic plastics. It is also extensively used in styrene-butadiene latex for producing flame-retardant carpets, as well as in manufacturing flame-retardant insulated rubber cables, insulation foams, conveyor belts, roofing membranes, and hoses. It is incorporated into bathroom fixtures, decorative wall panels, various covers, automotive protective shields, seating, truck components, and electronic components including insulators and circuit boards, as well as construction tools. Nano-aluminum hydroxide can also be applied in engineering plastics.