Thermal volatilisation analysis of TDI-based flexible polyurethane foam

Abstract

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 degrees C under vacuum but does not become significant until temperatures greater than 300 degrees C

Thermal degradation of new and aged urethane foam and epon 826 epoxy.

“…It is believed that the samples in the presence of a vacuum do not change degradation pathways, but rather cause volatilization of degradation products [2], however this study can neither confirm or deny such results. In light of this assumption the use of the TDS system was employed for several reasons.…”

The role of isocyanates in fire toxicity

“…The observed weight loss in this initial stage was approximately 3 %, suggesting that the chemical bonds in the polymer were unbroken and that no isocyanates were released (Jiao et al 2013). In the first step of the thermal degradation process, starting from around 200°C, the urethane bonds in the polymer are broken (Allan et al 2014). In this stage, a high amount of isocyanates and polyols are released as a yellow smoke (Levchik & Weil 2004;Jiao et al 2013;Woolley 1972).…”

“…The most studied materials for the generation of isocyanates during thermal degradation are PUR and PIR foams. The thermal degradation of isocyanate-based PUR foams has been described as a two-or three-stage process (Jiao et al 2013;Allan et al 2014;Sui et al 2014;Lefebvre et al 2004;Woolley 1972), see Fig. 1.…”

“…As the temperature increases the polyol segments start to decompose into aliphatic ether alcohols (Allan et al 2014). Above 300-500°C the remaining residues decompose into volatiles such as CO, CO 2 , benzene alkyls and aliphatic alcohols with branched chains (Allan et al 2014;Jiao et al 2013).…”

“…Above 300-500°C the remaining residues decompose into volatiles such as CO, CO 2 , benzene alkyls and aliphatic alcohols with branched chains (Allan et al 2014;Jiao et al 2013). The rate of the thermal degradation of isocyanate-based materials is increased in the presence of oxygen (Jiao et al 2013;Levchik & Weil 2004).…”