Surface Modification Processes for Modified Calcium Carbonate
Modified calcium carbonate is an efficient inorganic material; among its many applications, it stands out as a nanomaterial. Compared with other similar functional products, it boasts advantages such as readily available raw materials, high quality at low cost, fine particle size, strong tinting strength, non-toxicity to living organisms, and a broad selection of surface modifiers.
With the nanosizing of calcium carbonate particles, two inherent drawbacks also arise: first, the smaller the particle size, the higher the surface adsorption; consequently, the particles tend to agglomerate and cannot be well dispersed within the polymer matrix. Second, as an inorganic filler, nano-sized calcium carbonate has a hydrophilic surface and poor oleophobicity, resulting in weak interfacial adhesion with the polymer matrix. Under external mechanical impact, this can easily lead to interfacial defects, thereby degrading the material’s performance.
At present, in order to fully exploit the nanotechnological benefits of nano-calcium carbonate, enhance its permeability within composite materials, and improve the performance of filled composites, effective modification processes and surface-modification techniques are employed, with particular emphasis on surface modification. Current surface-modification approaches mainly include the following: surfactant modification, silane coupling-agent modification, modification using reactive monomers and bioactive macromolecules, and point-convergence modification. 1. Surfactant Modification: Surface-modifying nano-calcium carbonate with surfactants is one of the most mature and widely used techniques in the industrial modification of calcium carbonate. Currently, a wide variety of surfactants are available for this purpose, characterized by large production volumes, high quality, and cost-effectiveness. In addition, polymer-based modification of nano-calcium carbonate is also an excellent approach. 2. Silane Coupling-Agent Modification: Coupling agents can be classified according to their structure into aluminosilicate types, titanate types, and aluminate types. One end of a silane coupling-agent molecule contains a polar functional group that can chemically react with surface groups on calcium-carbonate particles, forming relatively stable ionic bonds; the other end can either undergo chemical reactions with organic polymer chains or physically adsorb onto them, thereby enhancing the material’s physical and mechanical properties. 3. Polymer Modification: Polymers can selectively adhere to the surface of calcium carbonate, imparting a positive charge to the particles and forming a chemico-physical adsorption layer on the surface. This prevents calcium-carbonate particles from agglomerating and improves their dispersibility. 4. Reactive Monomer and Bioactive Macromolecule Modification: The optical activity of reactive monomers, combined with their interaction with nano-calcium carbonate, can effectively disperse the nanoparticles. Moreover, the reactivity of these monomers—particularly their unsaturated double bonds—enables them to undergo thermal polymerization with isoprene rubber, yielding thermally cross-linked polymers that strengthen the compatibility between nano-calcium carbonate and polymeric matrices and enhance its application in plastics. 5. Point-Convergence Modification: In the point-convergence method, nano-sized particles are first uniformly dispersed in a monomer matrix, after which a cross-linking agent induces aggregation. As a result, the nanoparticles or molecular structures are evenly distributed throughout the polymer matrix, forming a point-convergent polymeric material. This multi-component convergence not only achieves uniform dispersion of the filler particles but also preserves their nanoscale characteristics.
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