A Study of the Low Smoke Potential, Flame Resistance and Processibility of High Index Polyisocyanurate Rigid Foam

Recent advances in our isocyanate and catalyst development programmes have stimulated a re-examination of the rigid polyisocyanurate (PIR) foams, and a study has been undertaken to explore the limits of flame resistance, low smoke emission and processibility in these systems. An experimental investigation was therefore carried out to determine the influence of the main PIR formulation parameters on fire and smoke performance of the derived foam. The results demonstrated that low smoke values can be obtained in non fire retarded PIR foams at isocyanate indices of approximately 400. However, to ensure high oxygen index together with low smoke emission, it was found to be necessary to use both high weight fractions of isocyanate (above 0.8) and isocyanate indices above 600. In such systems the addition of low levels of phosphorus containing fire retardants was particularly beneficial in increasing the fire resistance of the foam without increasing smoke emission significantly. Further benefits were obtained by the use of the high functionality MDI variants. These results indicated that this technology can provide PIR foams with an oxygen index up to 29% and an NBS smoke chamber optical density to levels as low as 100. Finally it was demonstrated that the manufacturing difficulties that are traditionally associated with high index PIR formulations can be overcome by the use of a novel catalyst package. Thus a novel class of foam insulation having high isocyanate index and high weight fraction of isocyanate has been identified and given the name ‘SHINDEX’ foam. Because the need for expensive fire retardants is minimised, it is expected that this material will be cost effective for technically demanding applications and should increase the market penetration of isocyanate based foam insulation.