Thermal volatilisation analysis of TDI-based flexible polyurethane foam

The thermal degradation behaviour of a polyurethane foam, synthesised from TDI and a polyether polyol, is reported. The thermal degradation behaviour of this material was evaluated by a combination of thermogravimetric analysis (TGA) and thermal volatilisation analysis (TVA). The results demonstrated that the thermal degradation is a complex process which consists of competing mechanisms which yield an array of degradation products. The TVA results revealed that the degradation occurs in two steps, with the initial step corresponding to degradation of the urethane linkages by two competing mechanisms. The first mechanism, proposed to be the predominant mechanism, involves simple depolymerisation of the urethane bond to yield TDI and polyol. A second, competing mechanism is proposed to occur which involves dissociation of the urethane linkages to yield DAT, CO2 and alkene-terminated polyol chains. The second degradation step has been shown to involve degradation of the polyol which was regenerated in the first degradation step. This is proposed to occur by random radical chain scission of the polyol to yield propene, formaldehyde, acetaldehyde, C3H6O isomers and high molar mass polyol chain fragments of various structures. Isothermal TVA studies have revealed that this occurs as low as 250 °C under vacuum but does not become significant until temperatures greater than 300 °C.