Flame retardancy of polyisocyanurate-polyurethane foams: use of different charring agents

The influence of different charring agents on physical-mechanical properties and fire behaviour of polyisocyanurate-polyurethane (PIR-PUR) foams has been investigated. In particular the use of varying amounts of ammonium polyphosphate, melamine cyanurate and expandable graphite has been analysed; all, when involved in fire, lead to the formation of a char layer on the polymer surface, but their ways of flame retardancy are different. The results obtained show that the higher the filler content the lower the compression strength; in particular the worst results have been obtained in the presence of melamine cyanurate. Moreover, the presence of ammonium polyphosphate or melamine cyanurate causes any significant worsening on thermal conductivity, while expandable graphite leads to a quite marked increase of the thermal conductivity. The fire behaviour has been studied by means of cone calorimeter apparatus and oxygen index test; it has been observed that the best results, i.e. the lowest rate of heat release and the highest oxygen index, are achieved with expandable graphite. Also the ammonium polyphosphate brings slight improvement in fire behaviour, whereas the effect of melamine cyanurate is negligible. © 2002 Elsevier Science Ltd. All rights reserved.