Development and characterization of saturated fatty acids and biopolymer based novel multilayer encapsulated phase change materials system for buildings

Application of encapsulated phase change materials (PCM) is becoming an attractive passive measure to develop energy efficient buildings. In the present work, the eutectic mixture of two saturated fatty acids (lauric acid and palmitic acid in 80:20 ratio, HTPCM) was selected and encapsulated in a novel multilayer architecture to develop PCM beads. The bead architecture includes a PCM core enveloped by thermally conductive calcium alginate (Ca-Alg) biopolymer + multiwall carbon nanotubes intermediate shell to promote heat transfer from the core and the outer rugged coating of flyash + water-based polyurethane (PU) to improve mechanical integrity and interlocking with wet cement mortar matrix during mix preparation. The thermal characteristics of four pure PCM (capric acid, lauric acid, myristic acid, and stearic acid) and one eutectic mixture (HTPCM) were measured using differential scanning calorimetry (DSC) to select the suitable PCM as per prevailing local ambient temperature. As per scanning electron microscopy (SEM) results, the average core size is in the range of 1.5 – 2.0 mm and PCM is stored in the bead core as tiny globules separated by Ca-Alg membrane. Single bead compression test performed on multilayer PCM (m-PCM) bead show that the shell of the bead possesses sufficient mechanical strength. The Fourier transformed infrared spectroscopy (FTIR) analysis and thermogravimetric analysis (TGA) studies confirm that the HTPCM and coating materials are chemically / thermally stable through different steps of fabrication and heating / cooling thermal cycles. Finally, the filter paper leakage test showed that the multilayer bead shell can prevent the PCM leakage from the core during bead heating. The various test results reported herein corroborate that the proposed architecture provides good physical properties and mechanical strength to the encapsulated PCM beads.