Surface modification methods of calcium carbonate
1. Surface treatment of calcium carbonate with inorganic substances
Calcium carbonate has the disadvantages of poor acid resistance and high pH value, which greatly limits its scope of application and usage. The inorganic surface modification of calcium carbonate can produce a double electrostatic layer on the surface of calcium carbonate, thereby reducing the mutual repulsion between particles and reducing the occurrence of accumulation. At the same time, the hydrophilicity of calcium carbonate is increased, so that calcium carbonate can be well wetted in water, thereby increasing the dispersion performance and expanding the scope of application.
The amorphous silicon is precipitated on the surface of calcium carbonate through the hydrolysis of silicofluoride ions, which improves the acid resistance of calcium carbonate.
2. Surface modification of calcium carbonate with organic substances
Organic modification mainly refers to wrapping the organic modifier on the surface of calcium carbonate by chemical or physical methods to change the surface properties of calcium carbonate, thereby increasing the interfacial compatibility and reducing the mutual agglomeration of powders. It is the mainstream surface modification method of calcium carbonate.
Commonly used surface modifiers include fatty acids (salts), phosphates, quaternary ammonium salts, silane coupling agents, titanate coupling agents, aluminate coupling agents, and composite coupling agents.
3. Surface modification of calcium carbonate polymers
Polymer surface modification refers to the formation of a core-shell polymer layer on the surface of calcium carbonate particles. There are two main cases of polymer-modified calcium carbonate: one is that monomers on the surface of calcium carbonate form polymer segments through a polymerization reaction; the other is to dissolve the polymer in an appropriate solvent to form a polymer solution and add calcium carbonate to it. When the polymer gradually adsorbs to the surface of calcium carbonate, the solvent is removed to form a coating. In this way, the polymer can be directional adsorbed to the surface of calcium carbonate to form an effective adsorption layer, reduce the agglomeration of calcium carbonate particles, improve dispersibility, and improve the shortcomings of poor dispersion performance of calcium carbonate during use, so as to achieve the purpose of surface modification
The in-situ polymerization of the surface of nano calcium carbonate is carried out by using olefin monomers under the action of inorganic initiator potassium persulfate, which improves the performance of nano calcium carbonate.
4. Mechanochemical modification of calcium carbonate
Mechanochemical modification mainly uses strong mechanical force to modify the surface of calcium carbonate particles, change the crystal structure of the surface of calcium carbonate, and make the lattice move to a certain extent, thereby enhancing the reactivity with other substances.
By adopting the method of styrene monomer polymerization grafting, the mechanochemical method is used to promote the polymerization of styrene monomer on the surface of calcium carbonate, which reduces the amount of initiator used, improves the mechanical properties of high-impact polystyrene (HIPS), and increases the compatibility between filler and matrix.
This method is mainly effective for calcium carbonate with relatively large particles, but for nano calcium carbonate, due to its small particle size, mechanical force does not have a good effect on it, but it can modify some active sites and groups on the surface, which can enhance the interaction with organic surface modifiers, so nano calcium carbonate can be modified by combining mechanochemistry and other modification methods.
5. High-energy surface modification of calcium carbonate
High-energy surface modification mainly uses high-energy rays, plasma, and other methods to modify the surface of inorganic powders. This method mainly relies on high-energy rays and plasma sources to bombard and touch the surface of calcium carbonate, so that some reactive sites are produced on the surface of calcium carbonate, and then unsaturated monomers (such as vinyl monomers) are added. The unsaturated monomers can react with the active sites on the surface to form a layer of organic film on the surface of inorganic particles.
However, this method is costly and the effect after modification is not very stable, so its application is limited to a certain extent.