High density polyethylene (HDPE) - Graphite composite manufactured by extrusion: A novel way to fabricate phase change materials for thermal energy storage

Thermal energy storage (TES) has the potential to facilitate the deployment of renewable energy through addressing the demand-supply mismatch, ultimately leading to the decarbonisation of heat supply. Among the TES technologies, latent heat based TES with composite phase change materials (PCMs) has shown great potential, which has attracted significant attention in recent years. However, large scale and reliable manufacturing methods for composite PCMs are still largely lacking. Here, we present a study aimed to develop, for the first time, an extrusion process capable of fabricating high density polyethylene based graphite PCM composites at a high throughput and with enhanced thermal properties. The PCM composites were fabricated under different extrusion process parameters and characterized for their thermo-physical properties by multiple techniques including differential scanning calorimetry, thermal gravitational analyzer, and Fourier transform infrared spectroscopy. The results show that the extrusion process has the potential to fabricate PCM composite bars in a continuous fashion with a manufacturing throughput higher than traditional method; the fabricated PCM composites show enhanced properties (e.g. up to +70% increase in thermal diffusivity); and there is a clear link between extrusion process parameters and PCMs properties. Microstructural analyses show a more homogeneous structure with a lower extrusion speed; whereas a high extrusion speed gives a more microscopically heterogeneous structure with visible graphite agglomerates distributed relatively homogeneous macroscopically; and a higher graphite content gives a larger agglomerate size. The results of this work suggest that the elucidation of composition-process-property relationships is crucial: for a given formulation (composition), only through fine tuning of high throughput manufacturing process can make it possible to achieve the desired performance of the PCM composites. (C) 2018 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.