FR Design for Foam materials

Recent trends in flame retardancy of polyurethane foams (PUR) and, in general of polymers, have been deeply influenced by regulation requirements and also by the concept of “sustainable development” which implies that the fire retardants should present a low impact on human health and environment during the whole life cycle of the polymer; this concerns then also the toxicity and the density of smoke developed during burning of the materials. Therefore, the reduction of the amounts of brominated compounds used in flame retardancy formulations is actually one of the main aims of the research in this field, although this reduction is not very easy because of their very high effectiveness. In this chapter, novel halogen-free flame retardant systems for polyurethane foams are reviewed and discussed. The chapter deals in particular with charring compounds which may lead to the development of different char morphologies: compact, intumescent and “glassy-like” char layers. The advantages and disadvantages of each system on fire behaviour and thermal stability of polyurethane foams will be analysed. Particular attention will be put on possible synergistic effects arising from suitable mixing of them. The flame retardants analysed are phosphorus-based compounds (phosphates, elementary phosphorous and novel hypophosphites), intumescent systems (for example expandable graphite) as well as glass precursors like borates, alumino-silicates and glass modifiers. Since the recent interest in nanocomposites, potential application and benefits of layered silicates on fire behaviour and thermal stability of PUR foams will be also reported. In order to assess the effectiveness of the systems considered in enhancing the fire behaviour and thermal stability, PUR and PIR-PUR (polyisocyanurate-polyurethane) foams containing different amounts of them were prepared and tested in several ways. In particular the thermal stability, both in inert and oxidizing atmosphere, and fire behaviour through the limiting oxygen index (LOI) and use of cone calorimeter (CC) were analysed. Some results of SBI (Single Burning Item) test were also reported. Also the char morphology and composition were studied through use of scanning electron microscope (SEM) and elementary analysis (EDX, Energy Dispersive X-ray spectroscopy).