Leakage control and characterization of form stable phase change materials: Polymer(matrix)/polymer (PCM) binary blends and natural fiber/polymer(matrix)/ polymer (PCM) ternary composites

Phase change materials (PCM) have a role in lowering energy use in buildings by storing and releasing thermal energy. However, leakage of PCMs when in the melt phase is an issue that must be controlled for widespread adoption. Two approaches have been explored in this research, polymer(matrix)/polymer(PCM) binary blends and wood/polymer(matrix)/polymer(PCM) ternary composites. The test materials were prepared using a combination of extrusion, torque rheometer blending and hot pressing techniques. Material structure and property investigations were conducted to understand the interaction of components and establish leakage behavior of PCMs and predict leakage using measureable parameters based on diffusion theory and Darcy's law.;To investigate the component interactions, the paraffin miscibility in polyethylene and its influence on leakage was determined in three paraffin/PE binary blends. Among three PE-types, HDPE was found to have the lowest miscibility and the slowest leakage behavior. Given this favorable performance, it was chosen as the matrix polymer for use in the following wood/polymer/PCM ternary composites. Comparing the ethalpic behavior, a greater portion of paraffin was available for energy storage in ternary composites than in binary blends.;The leakage performance of paraffin were characterized using the Korsmeyer-Peppas equation and Fickian-diffusion theory. The paraffin leakage rate from the HDPE is considerably slower than blends produced with LDPE or LLDPE resulting in a lower diffusion coefficient. The ternary composites possessed a slower leakage than the binary blends resulting from encapsulation function of wood. Chloroform extraction studies indicated a co-continuous structure in all of the products. This structure provides continuous leakage pathways but the extent of these pathways are controlled by formulation. In ternary composites, the primary factors influencing the extent of these pathways include wood flour size and content, while the PCM leakage is influenced by the PCM surface energy and viscosity. It was found that the capillary tension of the molten PCM in the wood lumen was more effectively controlled by PCM surface tension than wood surface energy. A leakage model was developed based on Darcy's law to describe the movement of molten PCMs within the porous composites. It describes the initial leakage behavior of PCMs well only.