Thermally reliable, recyclable and malleable solid–solid phase-change materials through the classical Diels–Alder reaction for sustainable thermal energy storage

Abstract

Conventional solid–solid phase-change materials (SSPCMs) exhibit good thermal energy storage (TES) ability and shape stability, but they cannot be recycled and re-shaped once fabricated due to the chemical cross-links. Hence, endowing SSPCMs with recyclability and malleable properties is advantageous for numerous applications, and contributes to environmental protection. Herein, a novel class of dynamic cross-linked SSPCMs (DC-PCMs) was facilely fabricated by bonding polyethylene glycol (PEG) to a polymeric skeleton through the thermally reversible Diels–Alder (DA) reaction for sustainable TES. PEG segments function as energy-storage units, while the polymeric skeleton affords shape stability and robust mechanical properties. The crystalline structure of DC-PCMs was investigated by X-ray diffraction (XRD), polarized optical microscopy (POM) and differential scanning calorimetry (DSC). DSC characterization also confirms the reversible energy-capture and release ability of DC-PCMs. The results suggest that SSPCMs show typical solid–solid phase transitions within the temperature range from 40 °C to 70 °C and can achieve a high latent heat storage capacity of about 107.2 J g⁻¹. Meanwhile, the thermally reversible DA reaction endows the DC-PCMs with good thermal recyclability and solid-state plasticity. After multiple thermal cycles, DC-PCMs can retain the original mechanical properties and TES ability. Moreover, the DC-PCMs are highly scalable for practical applications because of their uncomplicated and cost-effective fabrication.