Thermal degradation behaviour and kinetic analysis of unsaturated polyester-based composites and IPNs by conventional and modulated thermogravimetric analysis

The thermal degradation behaviour of epoxy/unsaturated polyester based polymer interpenetrating networks (IPNs), and unsaturated polyester containing various flame-retardants have been investigated by TGA and Py/GC/MS. The kinetic parameters of various polymers were analysed by conventional and modulated thermogravimetric analysis (MTGA) methods. The activation energies of degradation were calculated by the Coats-Redfern and MTGA methods, respectively. The results of both conventional and MTGA analyses reveal that the decomposition of IPNs consists of two non-interfering decomposition processes for epoxy polymer and cured unsaturated polyester, respectively. For the flame-retardant containing unsaturated polyesters, ammonium polyphosphate (APP) played an important role in the second-step of the pyrolysis reaction of APP-containing samples. It is important to note that the possibilities of reaction order for these pyrolysis processes are significantly distinguishable by Coats-Redfern method. Furthermore, the activation energies for various samples calculated by MTGA method are on average larger than those calculated from the Coats-Redfern method. The results also reveal that when either the flame-retardant or the epoxy was added to the unsaturated polyester, the heat resistance of the unsaturated polyester was enhanced.