Development of composite phase change materials for cold storage and transportation applications and determination of their thermal properties

In this study, composite phase change materials (FDMs) containing eutectic solutions with and without polymer additives, which enable the storage and transportation of products at low temperatures for a certain period, were developed, and their thermal properties were investigated. Composite FDMs containing eutectic solutions of sodium chloride-water (NaCl-H2O), magnesium chloride-water (MgCl2.6H2O-H2O), and lauryl alcohol-caprylic acid (LA-KA), which differ from the FDMs developed in existing literature studies and have the potential to be applied at low temperatures below 0°C, were developed. In the first part of the study, cross-linked sodium polyacrylate (SPA), used in the preparation of FDMs, was synthesized using free radical polymerization with different ratios of monomers. The synthesized polymers were characterized by swelling test, Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and viscosity measurements. It was determined that the swelling and viscosity values of SPA synthesized using 20% by weight acrylic acid were higher compared to those synthesized using 30% and 40% by weight acrylic acid. In the second part of the study, the phase diagrams of NaCl-H2O, MgCl2.6H2O-H2O, KCl-H2O and LA-KA solutions were investigated using the DSC device and the eutectic solution concentrations were determined for the appropriate systems. The eutectic points of NaCl-H2O and LA-KA solutions were found to be 23.3% and 30% by weight, respectively. In the preparation of composite FDMs, anhydrous calcium chloride (CaCl2) and calcium hydroxide (Ca(OH)2) were used as nucleating agents (NAs) to reduce the supercooling temperature of the FDMs; multi-walled carbon nanotube (MWCNT) and halloysite nanotube (HNT) were used to increase thermal conductivity; and SPA was used to prevent the precipitation and phase separation of the nucleating agents. The thermal properties of all developed FDMs were determined through DSC analysis. For the NaCl-H2O eutectic solution system, the lowest melting temperature (-17.3°C) was identified in the eutectic+1%SPA+3%HNT+NA composite FDM system, while the highest latent heat values were obtained from the eutectic+1%SPA, eutectic+1%SPA+NA, eutectic+1%SPA+1%MWCNT and eutectic+1%SPA+1%MWCNT+NA composite FDM systems with values of 199.3 J/g, 200.1 J/g, 199.1 J/g, and 195.9 J/g, respectively. For the MgCl2.6H2O-H2O eutectic solution system, the highest latent heat value was found at the eutectic+1%SPA+3%HNT+NA composite FDM as a 94.9 J/g. The lowest melting temperature for this system was -13.3°C, observed at the eutectic+1%SPA +1%HNT+NA composite FDM. For the LA-KA eutectic solution system, the lowest melting temperature of -7.8°C was detected in the eutectic+1%HNT+NA composite FDM, while the lowest freezing temperature of -4.9°C was obtained in the eutectic+NA composite FDM. The highest latent heat values at melting and freezing temperatures for the LA-KA eutectic solution system were found to be 185.2 J/g and 170.9 J/g, respectively, in the eutectic+1%HNT+NA composite FDM. The eutectic+3%HNT+NA composite FDM provided the lowest supercooling temperature of 0.3°C. The experimental results indicated that the composite FDMs developed within the scope of this thesis have suitable properties for use in products requiring low storage and transportation temperatures, and thus they have the potential to preserve product quality and reduce product loss rates.