Modification methods of calcium carbonate and application of modifiers

Calcium carbonate is an important and widely used chemical raw material, which is widely used as a reinforcing agent and filler in industries such as rubber, paper, ink, coatings, plastics, food, cosmetics, etc. According to the different production methods of calcium carbonate, it can be divided into light calcium carbonate, heavy calcium carbonate, and nano calcium carbonate.

Light calcium carbonate, also known as precipitated calcium carbonate, is produced through chemical processing methods; Heavy calcium carbonate, also known as ground calcium carbonate, is prepared by directly crushing natural limestone, calcite, chalk, etc. using mechanical methods.

There are certain differences in particle size and surface characteristics between heavy calcium carbonate and light calcium carbonate, resulting in differences in their usage effects.

Nano calcium carbonate refers to calcium carbonate products with particle sizes ranging from 1 to 100nm, including ultrafine and ultrafine calcium carbonate products.

Why modify

Surface modification is an important means to improve the application performance, applicability, market expansion, and usage of calcium carbonate. In the future, functionalization and specialization will become the main trend in the development of calcium carbonate. Through modification, the oil absorption value of calcium carbonate can be reduced, the dispersibility of calcium carbonate can be improved to prevent aggregation, the organic compatibility of calcium carbonate can be improved, and the added value of products can be increased, which is conducive to expanding the high-end application market. Moreover, the market demand for various surface modified specialized calcium carbonate will continue to increase.

Summary of Modification Methods

Modification method of heavy calcium carbonate

Physical coating modification

Physical coating modification is the process of mixing a modifier with heavy calcium carbonate in a certain proportion. Under the action of dispersing force, the modifier adsorbs onto the surface of heavy calcium carbonate through physical forces such as van der Waals force or electrostatic attraction, forming a single-layer, double-layer, or multi-layer coating layer.

Surface chemical modification

Surface chemical modification refers to the use of functional groups in modifier molecules and active sites on the surface of heavy calcium carbonate powder through chemical reactions or adsorption, to coat the surface of heavy calcium carbonate particles with the modifier, enhance the compatibility and dispersibility of heavy calcium carbonate with the filled organic matrix, and thus improve the processing and physical mechanical properties of composite materials.

Mechanochemical modification

Mechanochemical modification is the use of mechanical means such as crushing and friction to shift the lattice and change the crystal structure of heavy calcium carbonate powder, while increasing the system temperature and internal energy.

In the industrial production of heavy calcium carbonate, grinding and surface modification are generally carried out separately. If a modifier is added to the surface of heavy calcium carbonate during the grinding process, not only can the physical and mechanical force of the grinding be utilized to enhance the surface modification effect, but also the agglomeration phenomenon caused by the fine particles of heavy calcium carbonate can be prevented.

Surface sedimentation modification

Surface deposition modification is one of the most commonly used methods for surface modification of inorganic mineral pigments, which involves using appropriate methods to precipitate modifiers on the surface of heavy calcium carbonate.

Suitable for industrial production, the process flow is simple, and by controlling the reaction conditions, suitable particle size and purity can be obtained.

Modification method of light calcium carbonate

Fatty acid (salt) modification

Stearic acid (salt) is the most commonly used surface modifier for calcium carbonate. The modification process can be carried out using either dry or wet methods. Generally, wet processes require the use of stearic acid salts, such as sodium stearate.

In addition to stearic acid (salt), other fatty acids (esters) such as phosphates and sulfonates can also be used for surface modification of calcium carbonate. Research has shown that after surface modification of calcium carbonate with a special structure of polyphosphate ester (ADDP), the surface of calcium carbonate particles becomes hydrophobic and oleophilic, and the average agglomerated particle size in oil decreases.

Activated calcium carbonate modified with fatty acids (salts) is mainly used for filling PVC plastics, cable materials, adhesives, inks, coatings, etc.

Coupling agent modification

Coupling agents are amphoteric compounds that chemically bond with hydroxyl groups on the surface of calcium carbonate through reactive groups. The polar groups of their molecules can react with the functional groups on the surface of calcium carbonate particles to form stable chemical bonds. The other end can undergo chemical reactions or physical entanglement with organic polymers, thereby tightly bonding two materials with large polarity differences and having good compatibility, endowing the composite material with good physical and mechanical properties.

Modification method of nano calcium carbonate

Localized chemical reaction modification

Localized chemical reaction modification is a method in which a treatment agent (coupling agent, organic compound, inorganic compound, etc.) is first added, and then the surface functional groups of nano calcium carbonate react chemically with it to achieve the purpose of modification. At present, this method is the most widely used for surface modification of nano calcium carbonate.

There are mainly two types of local chemical reaction modification processes: dry and wet. Dry method involves sequentially adding nano calcium carbonate powder and surface modifier to the modifier for surface modification. Suitable for surface modification with coupling agents.

Surface coating 

A modification method in which nano calcium carbonate particles are connected to the coating material through van der Waals forces or physical methods. Add surface modifiers or hyperdispersants to the preparation solution of nano calcium carbonate. While producing nano calcium carbonate, coat the surface modifiers on the surface of the calcium carbonate to ensure that the final product exists in the form of uniform particles.

Modification of masterbatch filler

Masterbatch filler is a new type of filler, which is prepared by mixing a certain proportion of resin masterbatch, calcium carbonate, and surfactant to modify the surface of calcium carbonate. According to the different matrix resins used, common masterbatch fillers mainly include polyethylene wax calcium carbonate masterbatch, irregular polypropylene calcium carbonate masterbatch (APP masterbatch), and resin calcium carbonate masterbatch fillers.

High performance surface modification

A method of modification using plasma or high-energy radiation (such as X-rays, gamma rays, etc.). The surface modification of CaCO3 powder by plasma is mainly achieved through plasma polymerization technology. Firstly, the monomers are activated to generate gas-phase free radicals, which are then adsorbed on the solid surface to become surface free radicals. Then, they undergo polymerization reaction with the plasma or gas-phase original monomers to form a polymer film on the surface of calcium carbonate, achieving modification.