Thermal Stability and Fire Performance of Modified Polyisocyanurate Foams

Abstract

The thermal stability and fire behaviour of a series of modified polyisocyanurate foams have been studied by means of TGA analyses and with the help of a cone calorimeter. These foams were prepared starting from modified isocyanates, in order to obtain a polyisocyanurate structure including amide and 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 polyisocyanurate is modified to reduce the friability caused by the high cross-linking density. For comparison, two foams, an unmodified polyisocyanurate (PIR) and a polyurethane (PUR) were also prepared and tested.

The results obtained confirm that the amide-modified isocyanurate foam (with only adipic acid) exhibited a reduction in friability with respect to the unmodified isocyanurate foam. It is not possible to achieve similar results if aromatic type of modifiers are added together with adipic acid.

The TGA analyses of the foams, evaluated both in inert and oxidising atmosphere, showed that better thermal stability performance was obtained with the isocyanurate foams modified with only aliphatic amide groups, although no significant differences in behaviour were revealed between the various modified isocyanurates. Considerably inferior thermal stability was obtained with the PUR foam which shows a different degradation mechanism. For all the polymers the kinetic parameters referring to the degradation reactions were also evaluated.

However, the greater thermal stability of the modified PIRs did not give rise to a better fire behaviour, that is the results achieved with the cone calorimeter showed that the modified isocyanurates have an intermediate behaviour between that of the unmodified PIR and of the PUR. The polyisocyanurate modified with only adipic acid shows a behaviour similar to the unmodified 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.