Synthesis and Encapsulation of a Novel Kind of Long-Chain Hydroxy Ester Phase Change Materials

Abstract

A B S T R A C TThe majority of commonly used organic phase change materials (PCMs) are currently alkanes, fatty acids, paraffins, polyols, esters, and so forth. In this paper, a series of novel long-chain PCMs, containing both ester and hydroxyl bifunctional groups, are designed and synthesized with the objective of achieving high latent heat and high thermal stability. The study employs long-chain fatty acids and 1,6 hexanediol as starting materials and precisely controls the reaction conditions to synthesize novel long-chain hydroxyester PCMs with ferric chloride as catalyst under a vacuum environment. The purity of the hydroxyester is determined by Fourier transform infrared spectroscopy (FT-IR), and their thermal properties are measured by differential scanning calorimeter (DSC) and thermogravimetric analyzer (TGA). The results demonstrate that the reaction process is mild and controllable, and the obtained products are of high purity. The resulting hydroxyester PCMs exhibit a significant melting process between 30 and 60 °C with low supercooling and high latent heat exceeding 210 J/g. Furthermore, the hydroxyester PCMs show good thermostability with a temperature of 5% weight loss higher than 200 °C. In comparison to alkanes, aliphatic alcohols, and fatty acids with the same carbon chain length, the hydroxyesters display higher latent heat and better thermal stability due to the presence of ester and hydroxyl bifunctional groups. Considering the appropriate phase change temperature, hydroxy lauric acid 1,6 hexanediol ester is further encapsulated with melamine formaldehyde resin as a shell, resulting in spherical microcapsules with a particle size of approximately 21.7 μm. The enthalpies of the obtained microcapsules are measured as high as 163.7 J/g at a core-shell ratio of 3:1, which suggests that these PCMs are promising for use in energy storage.

Keywords: hydroxyester phase change materials, latent heat, energy storage microcapsules