Enhancing the thermal performance of polyethylene glycol phase change material with carbon-based fillers

Abstract

New implementation of phase change materials (PCMs), such as Polyethylene Glycols (PEGs), can alleviate the overconsumption of natural resources and can also be applied in solar-thermal energy conversion applications due to their distinctive semi-crystalline structure. To further enhance the thermal properties of PCMs, carbon-based nanomaterials such as graphene nanoplatelets (GNPs) and milled carbon fibre (MCF) can be incorporated to fabricate PEG-based composites due to their high thermal conductivity. One of the possible drawbacks of the addition of carbon-based fillers is their aggregation at high loadings, leading to a possible reduction in the latent heat of PCM composites. Hence, this study explored the most appropriate loading level (5 wt.%) of carbon-based fillers with pristine PEGs to achieve optimal thermal performance. Specifically, PEG-based composites were synthesised with three fillers (GNPs, graphite and MCF) via a temperature-assisted ultrasonication method and rapid solidification. Then, Raman Spectroscopy was used to quantify the dispersion of fillers among the PEG matrices. The results showed that despite a 32.6 % reduction in enthalpy of fusion to 155.5 J g–1, the addition of 15 wt.% of MCF increased the thermal conductivity up to 0.67 W m–1 K–1, which was approximately 2.5 times higher than that of pristine PEG. Moreover, explanations were provided on the possible heat transfer mechanisms in different types of carbon-based fillers. PEG/MCF PCMs displayed good properties on latent heat, thermal conductivity, aggregation prohibition, volumetric heat capacity, phase change temperature and thermal stability, while PEG/graphite composites exhibited excellent performance on thermal diffusivity, phase change (melting) temperature, specific heat capacity and cyclability.