Dual-level packaged phase change materials - thermal conductivity and mechanical properties

Phase change materials (PCMs) which possess high thermal conductivity and excellent mechanical property have been prepared in this work according to a dual-level packaging technology. Porous graphite foam with bulk density of 0.25 g/cm3 which is derived from worm-like expanded graphite is infiltrated by liquid paraffin. The as-infiltrated graphite foam is ball milled into small spheres with diameter of 1-3 mm. Then the spheres are sprayed with a pre-polymer composed of epoxy resin and its curing agent. These spheres are finally hot-pressing at 30 °C for 6 h under 1 MPa to obtain the PCMs. Correspondingly, porous graphite works as the first-level packaging (core) while epoxy resin film acts as the second-level packaging (shell) of paraffin. The thermal conductivity of PCM composites reach to 4.98 W/m K. Meanwhile, the compressive strength of PCM composites keeps a very stable value of 19.50 MPa when temperature increases from 25 to 90 °C. The excellent shape-stability of PCM is attributed to its dual-level packaging structure in which porous graphite prevents the leaking of liquid paraffin from the core and epoxy resin provides a strong polymer network at high temperature.