A Comparison of the Effect of Different Flame Retardants on the Compressive Strength and Fire Behaviour of Rigid Polyurethane Foams

The influence of fire retardants on compressive strength and fire behaviour of rigid polyurethane foams was studied. The flame retardants studied included ammonium polyphosphate, melamine cyanurate, aluminum trihydrate, borax, and expanded graphite. The Limited Oxygen Index (LOI) showed that ammonium polyphosphate was consistently the most effective fire retardant at all filler levels tested. The one notable exception was expanded graphite, which produced an LOI of 22.7% at a relatively low 3.2% filler content. In general, the cell size decreased, and compressive strength increased, as filler % was increased. One exception to this trend was borax, which led to a significant loss in compression strength of PU when it was added at the 15% level.