Fire retardant sol–gel coatings for flexible polyurethane foams

Abstract

Flexible polyurethane foam is one of the most versatile materials used in upholstered products; however, untreated polyurethane flexible foams are prone to rapid fire growth. In order to overcome issues encountered by the addition of flame retardant additives during the manufacturing process, the sol–gel process was evaluated to make flexible polyurethane foams flame retardant. Various formulations using different catalysts and monomers were prepared and deposited on flexible polyurethane foams by an impregnation process. Coating morphology was assessed by scanning electron microscopy analyses to optimize the formulation and to obtain a homogenous crack-free coating. Flame retardant properties were measured by mass loss calorimeter and UL 94, and thermal degradation was evaluated by thermogravimetric analysis. Chemical and structural analyses were carried out using attenuated total reflectance Fourier transformed infra-red spectroscopy and electron probe microanalysis. It appears that when a mixture of an appropriate ratio of 3-amino propyl triethoxysilane and diethyl phosphate is prepared in association with tetraethoxysilicate and methyltriethoxysilicate and deposited on flexible polyurethane foam, the coating shows an intumescent behavior when exposed to a flame. The foam also self-extinguishes after 30 seconds of flame application during UL94 test and a 60% reduction of the peak of heat release rate is obtained under mass loss calorimeter conditions.