Phosphonium-modified layered silicate epoxy resins nanocomposites and their combinations with ATH and organo-phosphorus fire retardants

Phosphonium-modified layered silicate epoxy resin nanocomposites were evaluated by testing the thermal/thermo-mechanical properties [differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), torsional pendulum, Sharpy toughness], flammability (limiting oxygen index LOI) and fire behavior (cone calorimeter with different irradiations). The morphology of the composites was determined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The drying conditions of phosphonium-modified layered silicate were varied in order to improve the nanocomposite formation and properties. The results were compared with using a commercial ammonium-modified montmorillonite. Enhanced nanocomposite formation was found for the commercial systems due to the amount of excess surfactant, but this effect was overcompensated through the advanced morphology of the phosphonium-modified systems. Several fire retardancy mechanisms and their specific influence on the different fire properties, such as ignitability, flammability, flame spread, total heat release (fire load), and the production of CO and smoke were discussed comprehensively. The main mechanism of layered silicate is a barrier formation influencing the flame spread in developing fires. Several minor mechanisms are significant, but important fire properties such as flammability or fire load are hardly influenced. Hence combinations with aluminum hydroxide and organo-phosphorus flame retardants were evaluated. The combination with aluminum hydroxide was a promising approach since it shows superposition in properties such as the fire load and only in some properties very little antagonism. The combination with an organo-phosphorus flame retardant disillusions, since it was characterized mainly by antagonism. Copyright (C) 2006 John Wiley & Sons, Ltd.