Thermal stability and fire performance of modified polyisocyanurate foams

The thermal stability and fire behaviour of a series of modified polyisocya nurate foams have been studied by means of TGA analyses and with the help o f a cone calorimeter. These foams were prepared starting from modified isoc yanates, in order to obtain a polyisocyanurate structure including amide an d imide groups. These linkages, obtained by using adipic acid, a mixture of adipic acid and pyromellitic dianhydride and a mixture of adipic acid and terephthalic acid, are thermally more stable than urethane, on which the po lyisocyanurate is modified to reduce the friability caused by the high cros s-linking density. For comparison, two foams, an unmodified polyisocyanurat e (PIR) and a polyurethane (PUR) were also prepared and tested. The results obtained confirm that the amide-modified isocyanurate foam (wit h only adipic acid) exhibited a reduction in friability with respect to the unmodified isocyanurate foam. It is not possible to achieve similar result s if aromatic type of modifiers are added together with adipic acid. The TGA analyses of the foams, evaluated both in inert and oxidising atmosp here, showed that better thermal stability performance was obtained with th e isocyanurate foams modified with only aliphatic amide groups, although no significant differences in behaviour were revealed between the various mod ified isocyanurates. Considerably inferior thermal stability was obtained w ith the PUR foam which shows a different degradation mechanism. For all the polymers the kinetic parameters referring to the degradation reactions wer e also evaluated. However, the greater thermal stability of the modified PIRs did not give ri se to a better fire behaviour, that is the results achieved with the cone c alorimeter showed that the modified isocyanurates have an intermediate beha viour between that of the unmodified PIR and of the PUR. The polyisocyanura te modified with only adipic acid shows a behaviour similar to the unmodifi ed PIR, whilst the introduction of aromatic rings brings about a worsening of many parameters, in particular, smoke emission was very close to that of the polyurethane.