Effect of water content on the phase transition temperature, latent heat and water uptake of PEG polymers acting as endothermal-hydroscopic materials

Both hydroscopic materials and phase change materials represent popular research topics. This paper proposes PEG polymers as endothermal-hydroscopic materials adjusting the temperature and humidity of an environment. A homogeneous PEG mixture with different water contents is prepared via a mutual diffusion methodology in a high-temperature environment. The as-prepared mixture is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and isothermal adsorption. The XRD and SEM results indicate that the crystallinity decreases as the moisture content increases, and the primary particles disappear. According to the DSC results, both the phase transition temperature and latent heat exhibit a negative linear relationship with the water content. Isothermal adsorption curves indicate that water molecules uniformly dispersed in the polymer can optimize its microstructure, providing a mass transfer channel for water vapour. Additionally, PEG2000 exhibits the best endothermal-hydroscopic performance. The PEG2000 phase transition temperature and latent heat decrease by 6.7 °C and 28.9 J g −1 , respectively, when a 10 % liquid is added to the polymer. The D-value (change value) is clearly lower than those of PEG4000 (10.9 °C and 36.9 J g −1 ) and PEG8000 (10.1 °C and 55.2 J g −1 ). In addition, the PEG2000 water uptake is 198 g kg −1 for 6 h.