Effect of nanosilica@ chitosan phosphate ester on properties and water resistance of magnesium oxychloride cement

Nanosilica (NS) is used in various composite materials as a good-performance filler. In this study, hydrogen peroxide was used to repair and activate the hydroxyl group on the surface of NS, and chitosan phosphate ester (CPE) was loaded onto the surface of NS through intermolecular dehydration to prepare nanosilica@ chitosan phosphate ester (NS-CPE). The NS-CPE was added to magnesium oxychloride cement (MOC) for the purpose of modifying its water resistance. It was found that the addition of NS-CPE increased the compressive strength of the MOC at different ages, reaching 116 MPa and 127 MPa at 7 days and 28 days, respectively, which were increases of 11.5% and 5.8% compared with unmodified samples. The compressive strength of the modified MOC reached 102 MPa after 28 days of water immersion, which was 8.3% higher than that of samples modified with phosphoric acid after the same duration of water immersion. The results also showed that the addition of NS-CPE increased the fluidity of the MOC slurry, accelerated the hydration reaction rate and refined the pore structure.