Constructing Localized Distribution and Orientation of Graphite Flakes to Achieve Enhanced Thermal Conductivity in Phase Change Composites for Thermal Energy Utilization

Constructing a cocontinuous structure between high-content phase change materials (PCMs) and low-content polymer supporting matrices is an effective strategy to enhance the heat storage capacity and mechanical strength of shape-stabilized phase change composites (PCCs). However, the unoptimized trade-off between thermal conductivity and heat storage capacity of PCCs limits their range of applications. In this work, polyethylene (PE)/poly(ethylene oxide) (PEO)/graphite (Gt) flakes composites were prepared via melt blending to not only construct a cocontinuous structure between high-content PEO and low-content PE, but also achieve localized distribution of Gt flakes in the interface region of the cocontinuous structure due to the minimization of interfacial energy. Subsequently, the Gt flakes were further oriented along the flow direction of the PE melt under an enhanced extensional and shearing combined force field during multistage stretching extrusion. By adding 9 vol % Gt, the in-plane thermal conductivity and tensile strength of a PCC with localized distribution and orientation of Gt flakes reached 1.6 W/(m·K) and 7.6 MPa, respectively. Finite element analysis indicated that the PCC exhibited highly efficient and directional heat conduction, which was further confirmed by thermoelectric conversion tests showing effective thermal energy utilization. Furthermore, the PCC demonstrates 91% relative enthalpy efficiency, indicating good heat storage properties. This work provides a novel method for simple and continuous fabrication of PCCs with high thermal conductivity, heat storage capacity, and mechanical strength, promoting practical, reliable, and efficient thermal energy utilization.