Solvent-free synthesis and properties of novel solid-solid phase change materials with biodegradable castor oil for thermal energy storage

Polyurethane polymers were directly synthesized via bulk polymerization as novel solid-solid phase change materials (SSPCMs) for thermal energy storage. Polyethylene glycols (PEGs) with 4000 and 6000 g/mol number average molecular weight were used as phase change functional chain, castor oil as the skeleton, diphenylmethane diisocyanate (MDI) and hexamethylene diisocyanate (HDI) were individually served as coupling reagent. The molecular structure, crystalline properties, phase change performances, thermal reliability and stability of the synthesized SSPCMs were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and thermogravimetry analysis (TG), respectively. The XRD patterns and POM images showed that the synthesized SSPCMs have the same crystalline structure and confined crystallization compared with pristine PEG. The DSC results indicated that the synthesized SSPCMs have high latent heats and a suitable phase change temperature range, and the maximum latent heats in melting and freezing process for the SSPCMs are 117.70 J/g and 109.00 J/g, respectively. Thermal cycling test and TG analysis results indicated that synthesized SSPCMs have good thermal reliability and stability. The prepared SSPCMs show large potential application in the area of solar energy storage.