Solvent-free preparation of bio-based polyethylene glycol/wood flour composites as novel shape-stabilized phase change materials for solar thermal energy storage

Vacuum adsorption was conducted to fabricate bio-based polyethylene glycol (PEG)/wood flour (WF) composites as novel shape-stable phase change materials (SSPCMs). The structure–property relationships and comprehensive performance of PEG/WF phase change materials (PCMs) prepared with different average molecular weights of PEG and different length-to-diameter ratios of WF were investigated through various characterization techniques. The relationship between the average molecular weight and mass content of PEG with the properties and structure of the prepared PEG/WF PCMs was evaluated. Leakage test results showed that WF with a high length-to-diameter ratio (HWF) exhibited much higher adsorption capacity for PEG than that of WF with a low length-to-diameter ratio (LWF). The maximum adsorption content of PEG was found to be 70 wt% in those PEG/HWF PCMs and both proceeded with excellent shape stability without leakage when the average molecular weight of PEG was more than 4000. The maximum content of PEG1000 in novel PEG/HWF PCMs without any leakage above the melting point of PEG was 75 wt%. Fourier transform infrared (FT-IR) spectroscopy results indicated that physical interactions occurred between WF and PEG, but chemical reactions did not take place. X-ray diffraction (XRD) analysis demonstrated that the crystallization of PEG in SSPCMs decreased. Differential scanning calorimetry (DSC) analysis demonstrated that the phase transition temperature did not depend on the content and length-to-diameter ratio of the WF. Simultaneously, the highest melting latent heat of the prepared PEG/HWF SSPCM was 108.6 J/g, and its enthalpy efficiency reached more than 75.05%. Thermal cycling test and TGA analysis results demonstrated that PEG/WF SSPCMs had good thermal reliability and chemical stability and showed potential for applications in solar thermal energy storage and biomass energy.