Fabrication of multistage phase change nanocellulose composites with robust mechanical property and high thermal storage capacity

Phase change materials (PCMs) provide indoor thermal comfort without powered equipment, ideal for passive building heating and cooling. This study developed a novel approach to create cellulose nanofiber (CNF) phase change composites with high mechanical properties, superior PCM content, robust thermal stability and decent 3D printing capabilities. By microencapsulating various phase change materials into CNF, adding a small amount of MXene materials, customizing samples with different PCM loads, and using ice template and freeze-drying technology, PCM/CNF composites were formed. Due to the three-dimensional interconnection of the CNF matrix and the coated CNF and MXene on PCM particles, the composites with a high Young's modulus of 2.09 MPa and outstanding thermal stability. Even subsequent to enduring 25 heating and cooling cycles at a temperature of 80 °C, the composites exhibit negligible changes in heat storage capacity, underscoring its durability. Moreover, the composites demonstrate outstanding multi-stage phase transition capabilities and achieves a remarkable PCM load of up to 79 % relative to the composites, coupled with a substantial heat storage capacity of 136.8 J/kg, attributed to the lightweight nature of CNF. This approach surmounts the constraints associated with conventional microencapsulated PCM technology, presenting a promising solution for efficient and sustainable thermal management in buildings.