|Chemical name||Aluminium tri-hydroxide|
|H phrases according to GHS Labelling||none|
Suppliers / trade names (pinfa member companies)
|Huber||Hydral, Martinal, MoldX, Hymod, SB, HN|
|Foams||PUR Rigid foam||Applicable|
|PUR flexible foam||Applicable|
|Polyethylene foam (PE)||Applicable|
|Wire and cables||PE/EVA||Applicable|
|Others||Paper/Wood||Could be applied|
Aluminium Tri Hydrate (ATH) is an inorganic white fine crystalline, non-hygroscopic powder. Its solubility in water and organic solvents is very low. By volume, ATH is the largest flame retardant (FR) used in diverse end applications. The working principle is based on the thermal decomposition of aluminium hydroxide into aluminium oxide and water(vapour). This endothermic reaction starts at about 200 °C and consumes energy from the ignition source. The generated water vapour cools the polymer surface and dilutes the concentration of burnable gases in the surroundings. The remaining metal oxide residue has a high internal surface where sooty particles, respectively polycyclic aromatic hydrocarbons, are absorbed, making ATH also a smoke suppressant. The oxide layer acts as a barrier protecting the polymer against further decomposition.
ATH is commercially available in grain sizes ranging from 0.5 – 80 µm in median particle size (D50). In Halogen Free Flame Retardant (HFFR) wire and cables (W&C), one of the largest markets for ATH, fine precipitated ATH is used in sheathing and insulation. HFFR-compounds are based on blends of EVA ((poly(ethylene-co-vinyl acetate)) and LLDPE (Linear Low Density Polyethylene). In plasticised PVC fine precipitated ATH is used as FR and smoke suppressant. Major use is in so called Low Smoke Flame Retardant (LSFR) cables. Another very important end application is thermal insulation foams made of PVC/NBR blends. These elastomers have also to fulfil severe fire resistant requirements, especially when used for e.g. insulating heating and plumbing pipework in multi store buildings. Other applications are floorings based on PVC, EPDM or other polymers, used in public area buildings, and conveyor belts used in mines, power plants and in public buildings like airports (NR/NBR based).
Coarser ATH types produced by grinding are used in large volume in thermoset applications. Cast resins and glass fibre reinforced products like BMC (Bulk Moulding Compounds) and SMC (Sheet Moulding Compounds) are processed in electrical and electronic appliances as well as in construction applications.
In an United States environmental Protection Agency report on „Flame Retardants In Printed Circuit Boards, December 2014“, Aluminium hydroxide has been shown to have a favourable environmental and health profile. Aluminium hydroxide is listed as GRAS (Generally Recognized as Safe) under Code of Federal Regulations and therefore is considered as safe in food and food packaging applications.
The absolute environment friendliness and their favourable price-performance ratio make ATH a sustainable flame retardant.
1. Alexander B. et al. “Non-halogenated Flame Retardant Handbook”, Scrivener Publishing LLC., USA
(2014), ISBN 978-1-118-68624-9.
2. Nabaltec AG, Brochure: “Mineral based flame retardancy with metal hydrates” (03/2019).
3. Nabaltec AG, Brochure: “Metal hydrates for thermosets” (03/2019).
4. Code of Federal Regulations, Food and Drugs (FDA), 21 CFR Ch. I (April 1, 2006 edition).
5. Wikipedia entry: https://en.wikipedia.org/wiki/Flame_retardant (6-26-2019).
6. Wikipedia entry: https://en.wikipedia.org/wiki/Aluminium_hydroxide (6-26-2019).