Electrothermal Phase Change Composite with Flexibility over a Wide Temperature Range for Wearable Thermotherapy

Flexible electrothermal composite phase change materials (PCMs) are promising candidates for portable thermotherapy. However, a great challenge remains to achieve high PCM loading while maintaining reasonable flexibility. Herein, the polypyrrole-decorated melamine foam (PPy@MF) was fabricated and thereafter applied to confine binary PCM mixtures composed of a high-enthalpy long-chain polyethylene glycol (PEG4000) and its short-chain homologue (PEG200) to make the novel PPy@MF-PEG4000+200 composite PCM. At a high loading of up to 74.1% PEG4000 and a high latent heat energy storage density of 150.1 J/g, the composite PCM remained flexible at temperature (−20 °C) far below its phase transition point thanks to the plasticine effect of PEG200. The composite also demonstrated good Joule heating performance, providing fast heating from 28 to 70 °C at low applied voltages (4.5–6.0 V). The energy could be stored efficiently and released to maintain the composites at the proper temperature. The electrothermal performance of the composite remained undisturbed during curved or repeated bending, showing good potential to be used for personal thermal management and thermotherapy.