Low-Cost Cenosphere Microencapsulation Technology for Phase Change Materials: a Sustainable Approach to Improving the Thermal and Mechanical Performance of Construction Materials for Operational Carbon Reduction

Operational carbon emissions from heating, ventilating, cooling, and air conditioning in buildings account for 28% of global greenhouse gas emissions. These emissions can be reduced by improving the energy efficiency of buildings. One way to do this involves incorporating phase change materials (PCM) into cementitious composites to optimize thermal energy storage and regulation. The challenge lies in preventing PCM leakage and maintaining heat transfer efficiency, as existing PCM microcapsules (MPCMs) are costly and compromise the strength of cementitious composites due to their inherent low mechanical properties.To address these limitations, a novel microencapsulation technique was proposed. This involved utilizing cenosphere, a low-cost, high-strength, hollow microsphere derived from coal-burning power plants, as the protective shell for the new MPCM. The PCM in liquid phase can be loaded into the cenosphere after removing a thin silica film through chemical etching, resulting in a cenosphere-PCM microcapsule (CPCM). To seal perforations induced during production, three novel and cost-effective coatings (silica, ethyl cellulose, and bio-inspired silica) were applied to the CPCM.An extensive experimental plan was executed to optimize the etching process, characterize the coated CPCMs, evaluate their energy density, and assess the impact of each coating on the strengths of resulting cementitious composites. Additionally, the thermal performance of the cementitious composites with incorporated microcapsules was thoroughly examined. The results showed that the concentration of the etching agent significantly affects the etching duration, morphology, and size of the perforations on the cenosphere. Furthermore, the results showed that all the microcapsules exhibited superior thermal and mechanical properties compared to existing microcapsules due to their high crushing strength. Generally, the coatings improved the thermal stability of the CPCM accompanied by some reduction in latent heat. This reduction is largely attributed to the thickness of the coating layer. Bio-inspired silica-coated CPCM exhibited the best thermal performance, delayed the thermal decomposition of the PCM by about 50°C, and showed the best thermal performance profile. Cenosphere provides huge potential for the integration of PCM into building materials for thermal energy storage while still maintaining the structural integrity of the cementitious composites.