Novel urea‐based compounds as solid‐solid phase change materials: 1,3‐bisstearoylurea and 1,1,3,3‐tetrastearoylurea for thermal energy storage applications

Abstract

1,3-Bisstearoylurea and 1,1,3,3-tetrastearoylurea were produced as solid-solid phase change materials (SS-PCMs) for potential solar thermal energy storage (TES) applications via condensation of urea with the respective amount of carboxyl chloride (stearoyl chloride). Both 1,3-bisstearoylurea and 1,1,3,3-tetrastearoylurea were characterized by Fourier-transform infrared (FT-IR), 1H nuclear magnetic resonance, differential scanning calorimetry (DSC), and thermogravimetric (TG) analysis techniques. 1,3-Bisstearoylurea and 1,1,3,3-tetrastearoylurea had considerable melting/crystallization enthalpy. The reason for crystallization was structural symmetry and flexibility of long alkyl groups there. Di and tetra alkyl groups made it possible to discuss the structure-property relationship for organic PCMs. Besides, the compounds were characterized through DSC and FT-IR spectroscopy before and after thermal cycling to determine their thermal reliability. Solid-solid phase change enthalpies of them for melting and crystallization were found 95.86 and −87.6 Jg−1 for 1,3-bisstearoylurea, respectively and 27.7 and −25.8 Jg−1 for 1,1,3.3-tetrastearoylurea, respectively. Thermal conductivity was studied to increase by simply expanded graphite addition. The thermal endurance limits of 1,3-bisstearoylurea and 1,1,3,3-tetrastearoylurea compounds were studied using TG analysis.