An experimental method for evaluating isocyanate conversion and trimer formation in polyisocyanate–polyurethane foams

In this paper, we have developed simple though efficient test method for evaluating both isocyanurate formation and isocyanate degree of conversion using FT-IR analyses and have applied them to polyisocyanurate–polyurethane foams to verify the reliability of the results obtained and evaluate the influence of isocyanate index on both these quantities. We have also characterised the foams from a physical–mechanical point of view and demonstrated that the dimensional stability and compression strength of polymers are closely related to isocyanurate content and therefore to isocyanate index. The results obtained have clearly revealed that an increase in isocyanate index leads to an increase in trimer content and consequently to an improvement of mechanical properties; on the other hand, an increase in the isocyanate index brings about a decrease in isocyanate conversion. Moreover, since isocyanurate content and free isocyanate amount affect the fire behaviour of the foam we will apply the procedure proposed in this article to analyse the influence of both factors on the fire behaviour of such foams; the results of our research will be published in a future work.