Calcium carbonate is an important chemical raw material with a wide range of uses. As a reinforcing agent and filler, it is widely used in rubber, paper, ink, coating, plastic, food, cosmetics and other industries. 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 prepared by chemical processing methods; heavy calcium carbonate, also known as ground calcium carbonate, is prepared by mechanically directly crushing natural limestone, calcite, chalk, etc.
There are certain differences in the particle size and surface characteristics of heavy calcium carbonate and light calcium carbonate, so there will be differences in use effects.
Nano-calcium carbonate refers to calcium carbonate products with a particle size of 1-100nm, including ultra-fine and ultra-fine calcium carbonate products.
Summary of modification methods
Physical coating modification
The physical coating modification is to mix the modifier and the heavy calcium carbonate in a certain ratio. Under the action of the dispersing force, the modifier is adsorbed on the surface of the heavy calcium carbonate by van der Waals force or electrostatic attraction. Single-layer, double-layer or multi-layer coating.
Surface chemical modification
Surface chemical modification refers to the use of functional groups in the modifier molecule and active points on the surface of the heavy calcium carbonate powder to carry out chemical reactions or chemical adsorption, so that the modifier is coated on the heavy calcium carbonate particles. The surface enhances the compatibility and dispersibility of heavy calcium carbonate with the filled organic matrix, thereby improving the processing performance and physical and mechanical properties of the composite material.
Mechanochemical modification uses mechanical means such as crushing and friction to shift the crystal lattice of heavy calcium carbonate powder and change the crystal form. At the same time, the temperature of the system increases and the internal energy increases.
In the industrial production of heavy calcium carbonate, grinding and surface modification are generally carried out separately. If a modifier is added to modify the surface of heavy calcium carbonate during the crushing process, not only the physical machinery of crushing can be used. Strength to enhance the effect of surface modification, but also to prevent the agglomeration of heavy calcium carbonate particles caused by too fine particles.
Surface deposition modification
Surface deposition modification is to use a suitable method to deposit the modifier on the surface of heavy calcium carbonate. It is one of the most commonly used methods for surface modification of inorganic mineral pigments.
It is suitable for industrialized production, and the process flow is simple. By controlling the reaction conditions, the appropriate particle size and purity can be obtained.
Fatty acid (salt) modification
Stearic acid (salt) is the most commonly used surface modifier for calcium carbonate. The modification process can be dry or wet. Generally, the wet process uses stearates, 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. Studies have shown that after surface modification of calcium carbonate with a special structure of polyphosphate (ADDP), the surface of calcium carbonate particles is hydrophobic and lipophilic, and the average agglomerated particle size in the oil is reduced.
Activated calcium carbonate modified with fatty acid (salt) is mainly used to fill PVC plastics, cable materials, adhesives, inks, coatings, etc.
Coupling agent modification
The coupling agent is an amphoteric structure compound that chemically bonds with the hydroxyl groups on the surface of calcium carbonate through reactive groups. The polar groups of the molecules can react with the functional groups on the surface of calcium carbonate particles to form stable chemical bonds. The other end can be chemically reacted or physically entangled with the organic polymer, so that the two materials with large polarities are closely combined, have good compatibility, and give the composite material better physical and mechanical properties.
According to its structure, it can be divided into silanes, titanates, aluminates, titano aluminates, zirco aluminates and complexes.
Surface modification of calcium carbonate with polymers can improve the stability of calcium carbonate in the organic or inorganic phase (system). These polymers include oligomers, polymers and water-soluble polymers, such as polymethyl methacrylate (PMMA), polyethylene glycol, polyvinyl alcohol, polymaleic acid, polyacrylic acid, alkoxystyrene -Copolymers of styrene sulfonic acid, polypropylene, polyethylene, etc.
Plasma and radiation modification
Using an inductively coupled glow discharge plasma system and using a mixture of argon (Ar) and high-purity propylene (C3H6) as the plasma processing gas to modify the heavy calcium carbonate (1250 mesh) powder by low-temperature plasma. The results show that the Ar- The calcium carbonate filler treated with C3H6 mixed gas has good interfacial adhesion with polypropylene (PP).
Local chemical reaction modification
Local chemical reaction modification is a method in which treatment agents (coupling agents, organic substances, inorganic substances, etc.) are added first, and then the surface functional groups of nano calcium carbonate react with it to achieve the purpose of modification. At present, this method is the most widely used nanometer calcium carbonate surface modification.
There are two main types of local chemical reaction modification processes: dry and wet. The dry method is to add nano calcium carbonate powder and surface modifier to the modifier in sequence to modify the surface. It is suitable for surface modification with coupling agent.
Surface coating modification
A modification method in which the nano calcium carbonate particles and the coating are connected by van der Waals forces or physical methods. The surface modifier or hyperdispersant is added to the preparation solution of the nanometer calcium carbonate, while the nanometer calcium carbonate is produced, the surface modifier is coated on the surface of the calcium carbonate, so that the final product exists in the form of uniform particles.
Master batch filler modification
Masterbatch filler is a new type of filler. By mixing a certain proportion of resin masterbatch, calcium carbonate and surfactant, the masterbatch filler is prepared and the calcium carbonate is surface modified. According to the different matrix resins used, the common masterbatch fillers mainly include polyethylene wax calcium carbonate masterbatch, random 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 rays (such as X-rays, gamma rays, etc.). The surface modification of CaCO3 powder by plasma mainly uses plasma polymerization technology. First, the monomer is activated to generate gas-phase free radicals, which are then adsorbed on the solid surface to become surface free radicals, and then polymerize with the plasma or gas-phase original monomers , A polymer film is formed on the surface of calcium carbonate to achieve modification.
Surface modification is an important means necessary to improve the application performance of calcium carbonate, improve applicability, and expand the market and dosage. The surface-modified calcium carbonate has changed from a traditional filler to a multifunctional modifier, which has a wider application range and is more popular.
In the future, functionalization and specialization will become the main trends in the development of calcium carbonate, and the product structure will also undergo great changes. High-end products such as nanometer calcium carbonate, ultrafine calcium carbonate, medical grade and food grade calcium carbonate; various surface-modified special calcium carbonates, such as natural rubber special, synthetic rubber special, paint special light calcium carbonate, these high additional The market demand for calcium carbonate products will increase, and product quality will surely be the key to the survival and development of enterprises!