Thermal energy storage characteristics of bentonite-based composite PCMs with enhanced thermal conductivity as novel thermal storage building materials

In this work, for latent heat thermal energy storage (LHTES) applications in buildings, bentonite-based form-stable composite phase change materials (Bb-FSPCMs) were produced by impregnation of capric acid (CA), polyethylene glycol (PEG600), dodecanol (DD) and heptadecane (HD) into bentonite clay. The morphological characterization results obtained by scanning electron microscopy (SEM) showed that the bentonite acted as good structural barrier for the organic PCMs homogenously dispersed onto its surface and interlayers. The chemical investigations made by using fourier transform infrared (FT-IR) technique revealed that the attractions between the components of the composites was physical in nature and thus the PCMs were hold by capillary forces. The results of differential scanning calorimetry (DSC) analysis indicated that the prepared Bb-FSPCMs composites including 40 wt% CA, 43 wt% PEG600, 32 wt% DD and 18 wt% HD, respectively had suitable phase change temperature of 4-30°C and good latent heat capacity between 38 and 74 J/g, respectively for solar space heating and cooling applications of buildings envelopes depending on climatic conditions. The results of thermogravimetric (TG) analysis demonstrated that all of the fabricated Bb-FSPCMs had good thermal resistance. The Bb-FSPCMs maintained their LHTES properties even after 1000 heating-cooling cycling. Furthermore, the total heating times of the prepared Bb-FSPCMs were reduced noticeably due to their enhanced thermal conductivity by addition of expanded graphite (EG) in the mass fraction of 5 wt%.