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An article to understand the methods, processes and commonly used modifiers of calcium carbonate surface modification1
Calcium carbonate is the inorganic filler with the largest amount in the organic polymer base material at present. However, the compatibility of calcium carbonate without surface treatment with the polymer is poor, and it is easy to cause uneven dispersion in the polymer base material. Cause interface defects of composite materials and reduce the mechanical strength of materials. These disadvantages become more pronounced as the dosage increases. Therefore, in order to improve the application properties of calcium carbonate fillers, it is necessary to carry out surface modification treatment to improve its compatibility or affinity with polymer binders. 1. Brief description of surface modification of calcium carbonate The surface modification method of calcium carbonate is mainly chemical coating, supplemented by mechanochemistry; the surface modifiers used include stearic acid (salt), titanate coupling agent, aluminum Ester coupling agent, zirconium aluminate coupling agent, random polypropylene, polyethylene wax, etc. Calcium carbonate continuous surface modification process Surface modification is carried out with the help of equipment. Commonly used surface modification equipment is SLG type continuous powder surface modifier, high-speed heating mixer, eddy current mill and fluidized modifier. The main factors affecting the surface modification effect of calcium carbonate are: the variety, amount and usage of surface modifier (so-called surface modifier formula); surface modification temperature and residence time (ie surface modification process); surface modification The degree of dispersion of the agent and material, etc. Among them, the dispersion degree of surface modifier and material mainly depends on the surface modifier. 2. Fatty acid (salt) modified calcium carbonate Stearic acid (salt) is the most commonly used surface modifier for calcium carbonate. The modification process can be either dry or wet. Typically wet processes use stearates, such as sodium stearate. (1) Stearic acid dry modified calcium carbonate coating acid mill modified calcium carbonate uses continuous powder surface equipment such as SLG type powder surface modifier and vortex mill, the material and surface modifier are continuous For simultaneous feeding, stearic acid can be directly added in solid powder form. When the surface coating modification is carried out in the mixer and other temperature-controlled mixers, it is generally operated intermittently. First, the metered and prepared materials and stearic acid are added to the modifier, and mixed for 15-60min. For discharging and packaging, the dosage of stearic acid is about 0.8%-1.5% of the mass of calcium carbonate, and the reaction temperature is controlled at about 100°C. In order to make the stearic acid better disperse and act on the calcium carbonate particles uniformly, the stearic acid can also be diluted with a solvent (such as absolute ethanol) in advance. Other additives can also be added in an appropriate amount during modification. (2) Wet modification of stearic acid The wet modification of calcium carbonate is to modify the surface of calcium carbonate in an aqueous solution. The general process is to saponify stearic acid first, then add it to the calcium carbonate slurry, filter and dry it after a certain time of reaction. The dispersion of calcium carbonate in the liquid phase is easier than that in the gas phase. In addition, by adding a dispersing agent, the dispersing effect is better, so the effect of calcium carbonate particles and surface modifier molecules in the liquid phase is more uniform. When calcium carbonate particles adsorb stearate, the surface energy decreases. Even if secondary particles are formed after pressure filtration and drying, their agglomeration binding force is weakened, and hard agglomeration will not be formed. its redistributed. Wet surface modification equipment is generally relatively simple, mostly containers with agitators and static mixers. Strong stirring can improve the modification activation efficiency and shorten the reaction time, but it requires higher performance of the equipment. Although wet surface modification can also be carried out at room temperature, the reaction time is long. Therefore, surface modification is generally carried out by heating, and the modification temperature is generally about 50-100 °C. Wet surface modification is commonly used for the surface modification of light calcium carbonate and wet-milled ultrafine heavy calcium carbonate. In addition to stearic acid (salt), other fatty acids (salts), such as phosphates and sulfonates, can also be used for surface modification of calcium carbonate. Activated calcium carbonate modified with fatty acid (salt) is mainly used for filling PVC plastics, cable materials, adhesives, inks, coatings, etc. 3. Coupling agent modified calcium carbonate Coupling agents used for surface modification of calcium carbonate are mainly titanate and aluminate coupling agents, or composite coupling agents.
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