Preparation of composite phase change materials for thermal energy storage systems and determination of their properties

Phase Change Materials (PCMs) are new generation smart materials used for the storage of latent thermal energy during phase change at constant temperature by taking the heat in the environment or releasing it to the environment, allowing the continuity of thermal comfort. In this thesis study, paraffin-based shape-stabilized composite phase change materials containing modified cellulose nanocrystal (CNC) and cellulose nanofibril (CNF) fillers for thermal energy storage applications were produced and characterized. Firstly, cellulose-based nanomaterials were modified by ice-templating method in the presence of cetyl trimethyl ammonium bromide (CTAB). In the first part of the study, n-hexadecane (n-HD) -based composite PCMs with modified CNF skeleton were produced. As a result of the analyzes performed, the PCM composite with 50% CTAB-CNF - 50% n-HD composition has the highest PCM content (26.05%), while the latent heat value and peak melting temperature of this composite are found to be 54.7 J/g and 20.54 °C, respectively. In addition, the composite material produced did not show any leakage at high temperatures and remained stable in shape. In the second part of the study, hierarchical porous carbon-based templates containing different amounts of modified cellulose nanocrystals were synthesized. It was observed that the increase in amount of filler improved the pore morphology and the composite with the best morphology was the PHPC1.0 support material. The PHPC1.0 composite with 1.0% filler was found to have the highest thermal stability compared to the porous template without filler. The highest compression modulus values belong to PHPC0.75 and PHPC1.0 support materials, respectively. PHPC1.0 selected among the porous templates obtained was used as a composite matrix in the production of composite PCMs containing n-hexadecane. The phase transition temperature and thermal energy storage capacity of PHPC1.0 composite PCM were determined as Tpeak-melting = 22.7 ºC and ΔHmelting = 117 J / g, respectively and n-hexadecane content was calculated as 55.71%. Keywords: Phase change material, composite material, thermal energy storage, cellulose nanofibril (CNF), cellulose nanocrystal (CNC)