Water insensitive and solvent-free synthesis of biodegradable solid–solid phase change materials based on poly (ethylene glycol) for thermal energy storage

Abstract

Usually, polyethylene glycol (PEG)-based biodegradable solid-solid phase change materials (BSSPCMs) are synthesized with isocyanate and PEG, removing water is necessary due to the sensitivity to water of isocyanate groups. In this study, a water insensitive synthetic scheme based on carboxyl and aziridinyl was employed to prepare PEG-based BSSPCMs via solvent-free bulk polymerization: First, a carboxyl modified polyethylene glycol was synthesized through esterification reaction of citric acid and PEG with the molar ratio 2:1. Then, the BSSPCMs were prepared based on an self-curing and organic solvent-free process, using trimethylolpropane tris(1-aziridine propionate) as the cross-linking agent. The chemical structure, crystalline properties, phase change properties, thermal stability, and reliability were investigated by Fourier transform infrared spectroscopy, X-ray diffraction, polarizing optical microscopy, differential scanning calorimetry, thermogravimetric analysis, and accelerated thermal cycling testing, respectively. Solid–solid phase change behavior was testified by the leakage test. The biodegradation experiment was conducted to prove the biodegradability of solid–solid PCMs. The results indicated that BSSPCMs had a similar crystalline structure to PEG, and the crystal size was smaller than PEG. The phase change temperature of BSSPCMs was in the range of 25–65°C, and the latent heat of phase change materials (PCMs) was about 103–108 J/g. Moreover, the extent of supercooling of BSSPCMs was reduced. Thermogravimetric analysis and accelerated thermal cycling test results confirmed the considerable thermal stability and reliability of BSSPCMs. The prepared PCMs also exhibited a good biodegradability in the natural environment.