Investigation of the effects of thermal, oxidative and irradiation treatments on the behaviour of poly-ethylene glycol as a phase change material in thermal energy storage systems

PEG (poly-ethylene glyco1) with an average molecular weight of 2000 g/mol has been investigated as a phase change material for thermal energy storage applications. PEG sets were maintained at 80 °C for 861 h in air, nitrogen, and vacuum environment; the samples maintained in vacuum were further treated with air for a period of several weeks. Furthermore, another set of PEG samples was exposed to electron radiation in order to modify some of their polymer properties, such as their melting point Tm, their heat of fusion ΔHm, their crystallisation temperature Tc, the heat of crystallisation ΔHc, and their thermal decomposition temperature Tdecomp. The experiments showed that the presence of oxygen led to the degradation of the polymer and to a slight decrease of its melting temperature, while the treatment with electron radiation reduced polymer's heat of fusion. FTIR (Fourier transform infrared spectroscopy) spectrum analysis showed bands assigned to carbonyl/carboxylate functional groups, indicating the degradation of PEG in the presence of air/oxygen.