Flexible polyurethane foams: Flammability

Polyurethane flexible foam is a very versatile, high quality cushioning material. By its chemical nature, polyurethane foam is a combustible material. Test methods have been progressively introduced to classify the fire behaviour of foam and legislation based on these tests has been introduced in various countries to ensure that the foam complies with these fire standards. A notable example of this is British Standard 5852 on which the United Kingdom bedding and furniture legislation is based. The influence of formulation variables such as the type and particle size of the filler, the foam density, the air flow (openness) are some of the well documented parameters. Another important variable is the liquid flame retardant (halogenated phosphate type) which is the objective of the present study. This paper provides a basic understanding of foam combustibility based on the British Standard 5852 test method. Dynamic weight loss made with two types of liquid flame retardants with and without melamine is used to provide this understanding. Thermogravimetric analysis and cone calorimeter have been used to support the discussion. In melamine free foams, our study has shown that the decomposition temperature of the liquid flame retardant is a key parameter, which governs the foam combustion. In melamine containing foams, the overall combustion behavior is dependant on the type of liquid flame retardant used. However, intrinsic differences do exist and synergy is seen between melamine and liquid flame retardant under specific conditions. Applying this basic understanding and the actual combustion standards, foam producers can attain flexibility in designing cost effective foam formulations.