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Aluminium hydroxide (APYRAL)
General Information
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APYRAL® products have a very high chemical purity of at least 99.5 %. The remaining constituents consist mainly of sodium oxide, which is part of the crystal lattice and partly adhering to the APYRAL® surface in hydrated form, as well as traces of iron and silicon compounds. 

Aluminium hydroxide is non-soluble in water with amphoteric characteristics. Due to the sodium oxide components, a watery APYRAL® suspension has a pH value of 8-9. This must be taken into consideration in watery or other alkali-sensitive solvents or dispersions – particularly where other additives are used, which are restricted in use to a certain pH range.  In case of doubt, tests must be made for possible interactions.

In many applications APYRAL® is not only used as flame retardant, but does also fulfil a function as white pigment. Due to its whiteness, APYRAL®  behaves neutral to the colouring of polymers.

The Mohs hardness of 2.5 - 3 causes no problems even in highly filled molten masses. The relatively high heat capacity cp of 1.65 J/gK at 400°K (127°C) has a beneficial effect on the dimensional stability under heat for  APYRAL® filled polymers. This even has priority in some applications.

With a specific density of 2.4 g/cm3, APYRAL®  is a medium-density mineral filler. As a result of the required filling levels, the density of the flame-retarded plastics is increased compared with the unfilled polymer. In total, however, APYRAL® is one of the most attractive flame retardants, even on the basis of a volume-specific cost balance.