Cockle shell microencapsulation of phase change materials for thermal regulation

Organic phase change materials offer high density thermal energy storage capabilities but suffer from poor dimensional stability, resulting in liquid leakage or pump-out during the phase transition process. While conventional microencapsulation provides elevated structural integration, the shell materials typically rely on synthetic polymers that are environmentally hazardous and thermally insulating. Furthermore, traditional synthesis methods for packaging face sustainability limitations. Here we develop eco-friendly microencapsulated phase change materials (MPCMs) by upcycling cockle shells, a major waste product of the marine aquaculture industry, into a high-purity calcium carbonate (CaCO 3 ) shell precursor, utilizing n -tetracosane as the core material. The structural and thermal properties of the synthesized MPCMs were systematically characterized and composites were fabricated by dispersing the capsules within a polymer matrix to evaluate their practical thermal regulation performance. In particular, the cockle shell-derived CaCO 3 formed a robust inorganic shell, achieving an encapsulation ratio of 54.64 %. Therefore, MPCMs exhibited a high latent heat of 135.83 J/g and maintained excellent thermal reliability over 40 thermal cycles. Additionally, the MPCMs-integrated polymer composites demonstrated effective thermal buffering, achieving a reduction of temperature relative to the initial temperature by 6.3 °C compared with the control sample. This upcycling strategy transforms marine waste into an energy storage medium, offering a scalable path for developing eco-friendly thermal regulators to prevent overheating in battery modules and sensitive electronics.