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An article to understand the methods, processes and commonly used modifiers of calcium carbonate surface modification
Calcium carbonate is currently the largest amount of inorganic filler in organic polymer-based materials. However, calcium carbonate without surface treatment has poor compatibility with polymers, which is likely to cause uneven dispersion in the polymer-based materials. Cause the interface defects of the composite material and reduce the mechanical strength of the material. As the dosage increases, these shortcomings become more obvious. Therefore, in order to improve the application performance of calcium carbonate filler, it must be surface modified to improve its compatibility or affinity with the polymer base. 1. Calcium carbonate surface modification brief introduction 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 The surface modification should be carried out with the help of equipment. Commonly used surface modification equipment is SLG type continuous powder surface modification machine, high-speed heating mixer, eddy current mill and fluidization modifier, etc. The main factors affecting the surface modification effect of calcium carbonate are: the variety, dosage and usage of the surface modifier (the so-called surface modifier formula); the surface modification temperature and residence time (the surface modification process); the surface modification The degree of dispersion of agents and materials, etc. Among them, the degree of dispersion of surface modifiers and materials 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 adopt a dry method or a wet method. Generally, the wet process uses stearates, such as sodium stearate. (1) Dry-method stearic acid modified calcium carbonate coated acid mill modified calcium carbonate When using continuous powder surface equipment such as SLG powder surface modifier and vortex mill, the material and surface modifier are continuous For simultaneous feeding, stearic acid can be added directly as a solid powder, and the amount depends on the particle size or specific surface area of u200bu200bthe powder, generally 0.8%-1.2% of the mass of calcium carbonate; in high-speed mixers, horizontal paddles Surface coating modification in mixers and other temperature-controllable mixers is generally batch operation. First, add the metered and formulated materials and stearic acid to the modifier together, and mix for 15-60 minutes. In the discharge packaging, the amount 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 better disperse stearic acid and evenly interact with calcium carbonate particles, it is also possible to dilute stearic acid with a solvent (such as absolute ethanol) in advance. Other additives can also be added in an appropriate amount during modification. (2) Stearic acid wet modification of calcium carbonate Wet modification of calcium carbonate is to modify the surface of calcium carbonate in an aqueous solution. The general process is to first saponify stearic acid, then add it to the calcium carbonate slurry, after a certain period of reaction, filter and dry. The dispersion of calcium carbonate in the liquid phase is easier than the dispersion in the gas phase. In addition, by adding a dispersant, the dispersion effect is better, so that the effect of the calcium carbonate particles and the surface modifier molecules in the liquid phase is more uniform. When calcium carbonate particles adsorb stearate, the surface energy is reduced. Even if secondary particles are formed after pressure filtration and drying, their agglomeration binding force is weakened and hard agglomerations are not formed. Its redistribution. Wet surface modification equipment is generally relatively simple, mostly containers with stirrers and static mixers. Strong stirring can improve the efficiency of modification activation and shorten the reaction time, but the performance requirements of the equipment are higher. Although wet surface modification can also be carried out at room temperature, the reaction time is long. Therefore, it is generally necessary to heat the surface for surface modification, and the modification temperature is generally about 50-100°C. Wet surface modification is often used for surface modification of light calcium carbonate and wet ground 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 to fill PVC plastics, cable materials, adhesives, inks, coatings, etc. 3. Coupling agent modified calcium carbonate The coupling agents used for surface modification of calcium carbonate are mainly titanate and aluminate coupling agents, or composite coupling agents. (1) The process flow of dry surface coating modification of titanate coupling agent with titanate coupling agent is shown as the process flow of dry surface coating modification with titanate coupling agent. The performance equipment is a high-speed heating mixer. In order to improve the uniformity of the interaction between the titanate coupling agent and calcium carbonate, inert solvents such as liquid paraffin (white oil), petroleum ether, transformer oil, absolute ethanol, etc. are generally used for dissolution and dilution. The amount of titanate coupling agent depends on the particle size and specific surface area of u200bu200bcalcium carbonate, generally 0.5%-3.0%. The drying temperature of calcium carbonate should be as low as possible below the flash point of the coupling agent, generally 100-120°C.
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