Effect of emulsification step on calcium carbonate encapsulated eicosane and incorporation into geopolymer

Abstract

The effect of the emulsification process of the organic n-eicosane as a phase change material (PCM) in an aqueous solution of sodium dodecyl sulfate (SDBS) as a surfactant has been studied regarding the properties of the CaCO₃ microcapsules. Such microcapsules aim to limit interactions between the PCM and the matrix (i.e., leakage and unwanted reactions). Optical and scanning electron microscopy (SEM) shows that the mean size of the n-eicosane capsule is of the order of 5 μm. However, large non-spherical objects which could be clusters of flocculated capsules or the results of encapsulation of coalescing n-eicosane droplets, are observed, particularly when mechanical stirring (MS) is used rather than when an ultra-turrax (UT) or sonotrode (S) is used in the initial emulsification step. These large, partially encapsulated objects could be the cause of the poor results in leakage tests. It is possible to encapsulate n-eicosane inside a calcium carbonate shell, with a greater than 50% encapsulation ratio. The yield of encapsulated n-eicosane measured by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) is similar and shows that 55% n-eicosane core in CaCO₃ shell can be produced. Up to 33 wt.% CaCO₃ microcapsules (with 55% n-eicosane content) have been successfully incorporated into fresh geopolymer paste. This incorporation of 18% (55% × 33%) of PCM does not modify the hardening conditions of the geopolymer since demolding was possible after 2 days at room temperature. DSC curves confirm that the melting reaction with n-eicosane is conserved inside the hardened geopolymer.