Cross-linked polyurethane as solid-solid phase change material for low temperature thermal energy storage

Abstract

In this study polyurethanes (PU) are considered as solid-solid phase change material (s-s PCM) for thermal energy storage. Linear PU (PUL) and cross-linked PU (PUX) are synthesized using hexamethylene diisocyanate (HMDI), poly(ethylene glycol) (PEG) and glycerol as cross-linker. The synthesis has been carried out with no solvent or catalyst, these conditions are especially appreciated for environmental and health reasons. PEG with different molecular weights were investigated: 1000 g·mol−1, 1500 g·mol−1 and 2000 g·mol−1. The crystallization of polymers is observed by polarized optic microscopy (POM). The thermal behaviour of the s-s PCM has been investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The effect of PEG’s molecular weight on thermal properties of s-s PCM has been investigated, as well as the effect of reactive stoichiometry and that of the cross-linker content. By varying the different parameters a range of s-s PCM with different properties are synthesized. The temperature transitions were found between 21 °C and 33 °C, and the latent heat between 76 J/g and 103 J/g, depending on the parameters. The hardness of PUX reaches 30 on shore D scale. This feature allows the reduction of the s-s PCM into powder which can be a very interesting property in order to incorporate PCM into various composite materials for thermal energy storage purposes.