In Situ Sustained-Release Microcapsules to Improve the Impermeability of Cement Mortars: Preparation and Characterization

Sustained-release microcapsules provide a promising way to improve the curing efficiency and impermeability of cement-based composites. In this study, with potassium persulfate (KPS) as the core and polypyrrole (Ppy)/glycerol as the shell, KPS/Ppy microcapsules with excellent sustained-release performance were prepared using emulsion polymerization. The chemical structure, elemental composition, thermal stability, microstructure, and release properties of microcapsules were characterized by Fourier Infrared Spectroscopy (FTIR), Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), Thermogravimetric Analysis (TGA), Laser Particle Sizing, and Conductivity Testing. Results indicate that the release characteristics of the microcapsules could be controlled by changing the content of polypyrrole/glycerol as well as the synthesis time, and a complete release time of 25 h could be realized with 1.43 wt% polypyrrole/glycerol synthesized for 6 h, which can meet the requirement that the polymerization is continually initiated to form a plugging structure after the initial hydration reaction of the cement mortar to realize the impermeability. Additionally, the sustained-release microcapsules, monomers, and coupling agents were mixed to prepare the cement mortar, which revealed significantly improved impermeability with no obvious loss of the compressive strength. Therefore, the prepared microcapsules have tunable sustained-release characteristics, which could be applied in cement-based composites for various requirements.