Thermal treatment to improve the hydrophobicity of ground CaCO3 particles modified with sodium stearate

Abstract The surface modification of calcium carbonate (CaCO3) particles, which is used as a filler, significantly affects the properties of the composed materials. The effects of thermal treatment on ground calcium carbonate (GCC) particles subjected to hydrophobic modification using sodium stearate (RCOONa) were studied. The contact angle of the modified GCC particles increased from 24.7° to 118.9° when the amount of RCOONa added was increased from 0% to 5% and then decreased to 97.5° when the RCOONa content was further increased to 10%. When a large amount of RCOONa was added, RCOO− reacts with Ca2+ and generates (RCOO)2Ca nuclei, which are adsorbed on the surface of the GCC particles, forming a discontinuous (RCOO)2Ca modified layer. After thermal treatment under sealed conditions, the contact angle of the GCC particles modified using 1.5% RCOONa/GCC increased from 112.8° to 139.6°. The thermal stability of the (RCOO)2Ca modified layer was increased, with the temperature increase of the mass-loss peak from 358.0 to 463.0 °C. It is confirmed that the spreading of melted (RCOO)2Ca nuclei on the surface of the GCC particles during the thermal treatment increased the continuity of the modified layer, converting the physical adsorption of the (RCOO)2Ca nuclei into chemisorption. The grafting density of RCOO− on the GCC particle surface after thermal treatment approximates to 5.00/nm2, which is close to the single-molecular-layer grafting density of RCOO−, indicating that excellent modification was achieved.