Cone Calorimeter Study of Inorganic Salts as Flame Retardants in Polyurethane Adhesive with Limestone Filler

A cone calorimeter was used to test inorganic water-releasing and low-melting compounds as flame retardants in polyurethane adhesive samples. Sodium metasilicate pentahydrate, potassium carbonate mixed with silica gel, sodium hydrogen carbonate, calcium oxalate monohydrate, zinc and magnesium chloride mixed with potassium chloride, aluminium and magnesium hydroxides, ammonium polyphosphate (APP), sodium and potassium phosphates were tested. These additives were used to partially (10-20%) replace the limestone used as a filler in the adhesive. Thermo-gravimetric analysis was used to study decomposition and melting of the inorganic compounds. The results showed that sodium metasilicate monohydrate formed a protective layer of sodium silicate on the sample surface, significantly delaying the time to ignition. Addition of APP resulted in the lowest overall heat release rate curve.