Posted on 06/03/2018 in News 32 2018
Inorganic flame retardant developments

Maryline Desseix, Polyone (pinfa member), presented development and testing of innovative solutions to combine PIN flame retardant performance in polymers with sustainability. Inorganic PIN FRs, such as ATH (aluminium trihydrate) and MDH (magnesium hydroxide) offer positive health and environment profiles, and are water soluble, which ensures that they are not bioaccumulative.

However, these properties are also problematic for use as flame retardants, because water uptake impacts polymers’ mechanical and electrical properties. Polyone tested surface treatment of ATH and MDH using different vinyl, silane, phenyl and siloxanes, then combinations of ageing, water contact and compounding in polyethylene/EVA polymer. Results showed potential advantages and significant variations between different solutions. The possible role of compatibilisers between the inorganic PIN FR and the surface coating merits investigation.

Klaus Rathberger, George H. Luh, presented applications of expandable graphite as a PIN flame retardant. See also AMI FR conference 2016 in pinfa Newsletter n° 61. Expandable graphite can be an effective flame retardant at 15-20% loading, either blended into polymers or applied as a surface coating, as well as being used in fire-protective coatings for structures, on textiles, on roof covering bitumens, in foams or in fire seals. Different grades offer expansion of 50x – 350x for different applications. Applications today include polyurethane foams in aircraft seats, polyurethane and polystyrene building insulation foams, automobile interior linings, special graphites for conductive applications. An issue is that some low quality expandable graphites on the market contain significant levels of chromium as an oxidising agent.

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.

Sophie Duquesne, ENSCL (Ecole Nationale Supérieure de Chimie de Lille), presented applied research projects into PIN flame retardant applications. Development and testing of a lightweight carpet for aviation showed the complexity of smoke density and smoke toxicity, depending on the different elements of the carpet (pile, weft, warp, backing, backcoating) and on whether these are tested separately or together. In another project, phosphorus, silicon and nitrogen based compounds and sodium hydroxide were used to treat flax-PLA (polylactic acid) composites. In a third project, a silicone surface plasma treatment was tested to improve performance of high temperature resistant textiles.

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