Fouad Laoutid, Materia Nova (Belgium), presented tests on calcium hydroxides (hydrated limes and hydrated dolomite limes) as flame retardants for polyethylene and EVA polymers, in combination with other inorganic PIN FRs (ATH and MDH). All of these inorganic compounds offer positive environment and health profiles.
The calcium hydroxides are readily available, as they are today produced and widely used in both agriculture (soil liming to correct pH) and industry (glass, chemicals, flue gas treatment …). Calcium hydroxides release water at a higher temperature than ATH and MDH, so extending the temperature range of fire protection, and also contribute to increase char cohesion (by generation of calcium carbonate mineral char). Combination with zinc borate further reduced peak heat release and improved char cohesion. However, calcium hydroxide is water soluble, so cannot be used as such as a flame retardant. In contrast, hydrated or partially hydrated dolimes (Ca(OH)2.Mg(OH)2 or Ca(OH)2.Mg(OH)2.MgO ) are not water soluble. Using these calco-magnesian compounds was shown to reduce pHRR during cone calorimeter test and to generate a cohesive mineral residue during the combustion.