Thermal energy storage characteristics of myristic acid-palmitic eutectic mixtures encapsulated in PMMA shell

Abstract

Solid-liquid phase change materials (PCMs) have been widely used in thermal energy storage (TES) systems. Fatty acids as organic solid-liquid PCMs have superiority properties like as high latent heat of storage capacity, suitable phase change temperature and low vapor pressure. However, for the use of solid-liquid PCMs are required a storage container. To meet this need, one of the most effective methods is encapsulation of the PCMs with proper polymeric shell. The encapsulation process provides PCMs several benefits such as preventing the liquid PCM outflow during phase transition, eliminating the interaction with its near environment, as well as providing a large surface area per volume. With this regard, the present study is aimed to encapsulate myristic acid-palmitic acid (MA-PA) eutectic mixture with polymethylmethacrylate(PMMA) as shell material. The prepared capsules were characterized using fourier transform infrared (FTIR) spectroscopy. FT-IR results confirmed successful encapsulation of the PCM within PMMA shell. Morphological investigations were made by using polarized optical microscopy (POM) and scanning electron microscopy (SEM) techniques. It can be deduced from the POM and SEM results that the synthesized PMMA/(MA-PA)(1:2) capsules were entirely spherical profile along due to agglomeration difficulty. The diameter distributions of the capsules were determined by particle size distribution (PSD) analysis and the findings showed that the capsules had diameter distributions between 0.1 and 300 µm. By differential scanning calorimetry (DSC) technique the melting temperature and latent heat storage capacity of PMMA/(MA-PA)(1:2) capsules were measured as about 38.0 °C and 100.5 J/g, respectively. The thermogravimetry (TGA) measurements indicated that the capsules were durable thermally up to 250 °C. Additionally, the produced capsules had excellent thermal and chemical stability after 5000 heating/cooling thermal cycles test. Consequently, especially PMMA/(MA-PA)(1:2) capsules are hopeful for TES applications.