Flexible Polyurethane Foam with the Flame-retardant Melamine

Flexible polyurethane (PU) foams are widely used in many industrial applications, such as upholstered furniture and mattresses, automotive applications, etc. The chemical nature of the PU, the high air permeability, and the high inner surface area of the foam structure cause this material to be highly flammable. Consequently, the application of flame retardants to flexible PU foams is an important issue. The use of halogenated flame retardants is not considered optimal, in part due to the high emission level and the possible phase-out by the European Risk Assessment Body. Consequently, melamine as a nonhalogenated flame retardant is applied more and more frequently. However, little data is available regarding the application of melamine as an additive in flexible PU. This paper is concerned with the influence of melamine on the synthesis of the PU foam and the resulting material-specific properties. Especially, the increase of viscosity and the high heat capacity of melamine lead to a decrease in foaming growth and rising height with increasing melamine content. This is caused by the reduced drainage rate between the struts and the plateau borders in the foam-forming process. Here, the increase in viscosity follows the Dougherty-Krieger equation with the intrinsic viscosity of k = 3.3. The mechanical properties such as density and compression strength increase with increasing melamine content. Other properties like tensile strength and elongation decrease because of the embedding of the melamine in the PU matrix, which weakens the structure. The air permeation and number of cells also decreases because of the thickened struts caused by the reduced drainage rate in the foaming process. Furthermore, the reaction between the amino groups of melamine and the isocyanate of the PU formulation was investigated by FTIR.