Novel method for microencapsulation of oxalic acid with ethyl cellulose shell for sustained-release performance

In this study, a novel method was employed for the coacervation of ethyl cellulose (EC) that was induced by polydimethylsiloxane to achieve the encapsulation of oxalic acid (OA). The prepared OA microcapsules were used to delay an in-situ exothermic reaction between ammonium chloride (NH4Cl) and sodium nitrite (NaNO2) during hydraulic gel fracturing for oil extraction. The chemical compositions and crystalline structures of the microcapsules were investigated by Fourier-transform infrared spectroscopy and X-ray powder diffraction analysis, respectively. Scanning electron microscopy and optical microscopy measurements showed that the microcapsules exhibited perfect core-shell structures. The layer-by-layer mode of coating coacervated EC on the OA was also indicated by optical microscopy. The sustained-release performance of the microcapsules could be regulated by adjusting the core/shell ratio. The sustained-release time required to attain the concentration peak of OA microcapsules prepared at a core/shell ratio of 1:2 was 185 min, as analyzed by UV–vis spectroscopy at room temperature. Further, the catalytic performances of OA microcapsules for a model system of in-situ exothermic hydraulic gel fracturing were investigated. Thus, a novel method to microencapsulate water-soluble core materials within EC shells was explored. It was shown that the prepared [email protected] microcapsules possessed suitable sustained-release properties.