Did you know that natural & synthetic Magnesium hydroxide can effectively replace ATH as a flame retardant? We would be glad to introduce our various MAGNESIA options...

Basics of Various Flame Retardants

Alumina Tri-Hydrate (ATH) and Magnesium Hydroxide

Like ATH (Al2O3.3H2O), Magnesium hydroxide (Mg(OH)2), is an acid- and halogen-free flame retardant for various plastics. Both hydroxides decompose endothermically when heated according to the reactions:

  • 2Al(OH)3 →Al2O3 + 3H2O
  • Mg(OH)2 → MgO + H2O

The gaseous water phase is believed to envelop the flame, thereby excluding oxygen and diluting flammable gases. Similar to the function of char formed by phosphorous-containing flame retardants, a heat insulating material may form on the surface of the plastic in contact with the flame, reducing the flow of potentially flammable decomposition products to the gas phase where combustion occurs. In both reactions, the decomposition products are non-toxic and the mineral phases, especially MgO, are alkaline, reducing the likelihood of acidic, corrosive gases exiting the plastic.

The physical and chemical properties of magnesium hydroxide and ATH are shown in the Table below. Magnesium hydroxide has a 100oC higher decomposition temperature than ATH, allowing a higher processing temperature in compounding and extruding the plastic. Also, magnesium hydroxide adsorbs more energy during the decomposition process.

Comparison of Properties of Mg(OH)2 and ATH

  Mg(OH)2 Mg(OH)2
Bound Water, % 31.0 34.6
Specific Gravity 2.36 2.42
Mohs Hardness 2.5 3.0
Refractive Index 1.56-1.58 1.57
Initial Decomposition
330°C 230°C
Enthalpy of Decomposition 328 cal/g 280 cal/g

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