Source Lei little knowledge, the type of nano calcium carbonate modifier.
The surface modification of nano-calcium carbonate can not only increase the interfacial affinity between calcium carbonate and polymer, but also qualitatively adsorb on the surface of nano-calcium carbonate to form charge repulsion, which makes it difficult to polymerize and has better stability, wettability and dispersibility.
The mechanism of surface modification lies in the influence of the internal structure and composition of calcium carbonate, as well as the number, type and activity of calcium carbonate surface groups, and the way of surface treatment, the type of surface treatment agent and the activation process also play a certain role.
At present, the commonly used surface modifiers of nano-calcium carbonate mainly include: coupling agents, polymers, surfactants, inorganic substances and composite use of inorganic and organic substances.
surface active agent
(1) Titanate coupling agent
Titanate coupling agent is divided into single alkoxide type, and coordination type and chelating type, in order to improve the uniformity of the reaction, the need to use inert solvent for dissolution and dilution, and then in the form of spray surface modification machine, can be better with calcium carbonate particles for dispersion and surface chemical coating.
The modification effect of titanate is good, but because its color is brown, the whiteness of the product will be affected after modification, and the price is expensive, which may endanger human health.
(2) aluminate coupling agent
The calcium carbonate modified by aluminate ester can be well dispersed in organic media, the mechanical properties are improved, and the physical and mechanical properties and processing performance of the product can be improved. It is widely used in filled plastics and other products.
Aluminate has the characteristics of light color, non-toxic, high thermal decomposition temperature, low price, convenient packaging and transportation, but it is easy to hydrolyze and cannot be used in wet surface modification process.
(3) borate coupling agent
Borate ester coupling agent has the advantages of non-toxic, antibacterial, excellent coupling function, good thermal stability and good hydrolysis resistance. Therefore, boric acid ester is not only used for dry surface modification process, but also can be used for wet modification treatment.
(4) Fatty acid (salt)
The nano-calcium carbonate modified by fatty acid has high dispersibility and good compatibility with organic polymer materials. Stearic acid (salt) is the most commonly used and very cheap surface modifier for calcium carbonate modification.
(5) Phosphate esters (salts) and condensed phospholipids
The application of nano-calcium carbonate modified with phosphate ester in composite materials can not only improve the processability and mechanical properties of the materials, but also improve the acid resistance and flame retardancy.
The surface modification of calcium carbonate powder with condensed phosphoric acid (metaphosphoric acid or pyrophosphoric acid) can overcome the shortcomings of poor acid resistance and high surface pH. The pH of the modified product is 5.0~8.0 (the pH before modification is 9.0~10.5), which is difficult to dissolve in weak acids such as acetic acid and has good acid resistance.
(6) Quaternary Ammonium Salts
Quaternary ammonium salt is a kind of cationic surfactant, one end of its molecule can be crosslinked with polymer materials, and the other end can be charged with positive electrostatic adsorption on the surface of calcium carbonate.
(7) reactive monomers, active macromolecules
The small molecule carboxylic acid with unsaturated bond in the reactive monomer can interact with nano-calcium carbonate to disperse nano-calcium carbonate, and its reactivity (unsaturated bond) can be used to graft with polyolefin to form a graft to strengthen the interface between nano-calcium carbonate and polymer.
The macromolecules in the active macromolecules can act on the surface of calcium carbonate to improve its affinity and dispersion with organic polymer materials.
Commonly used polymers are mainly oligomers, polymers and water-soluble polymers. The polymer can carry out directional adsorption on the surface of calcium carbonate, so that calcium carbonate has charge characteristics and forms a physical or chemical adsorption layer on the surface of calcium carbonate particles, increases the distance between particles, prevents adhesion and agglomeration between calcium carbonate particles, and improves dispersibility.
Hyperdispersant is mainly composed of solvent segment and anchoring segment, the anchoring segment is generally a polar group, which can be closely combined with the particle surface in the form of single-point anchoring or multi-point anchoring; the solvent segment has different polarity and is suitable for polymer modification with different polarity.
Inorganic modifier can improve the dispersion and acid resistance of nano calcium carbonate, commonly used mainly metaphosphoric acid (salt), polyphosphoric acid (salt), aluminic acid (salt), alum, barium salt and so on.
Inorganic electrolyte adsorbed on the surface of calcium carbonate particles, on the one hand, can improve the potential value of the surface and induce steric hindrance effect, resulting in double layer electrostatic repulsion, thus improving the dispersion of particles; on the other hand, due to steric hindrance, hydrogen ions can not contact the inner calcium carbonate particles, significantly improving its acid resistance.
The hydrophilic polar groups in the coupling agent can react with various groups such as hydroxyl groups on the surface of calcium carbonate, such as hydroxyl groups on the surface of calcium carbonate, forming strong chemical bonds, while other hydrophobic non-polar groups can chemically react with polymers, or physically entangle, relying on the bridging effect of the monomolecular layer of the coupling agent, or wrapping it on the surface of calcium carbonate, making it show lipophilic characteristics, thus, two very different substances, minerals and organisms, are firmly bound together.
At present, the coupling agents used in the surface modification of nano calcium carbonate mainly include silane coupling agent, titanate coupling agent and aluminate coupling agent.
There are roughly two mechanisms for surface modification of calcium carbonate with polymers: one is that monomers form a very thin polymer film by polymerization reaction and adsorb it on the surface of calcium carbonate; The second is to coat the surface of calcium carbonate with a polymer dissolved in a certain solvent to prevent the solvent from preferentially forming a coating on the surface, and to form a protective layer on its surface through physical and chemical adsorption to prevent calcium carbonate particles from agglomerating and improving its dispersion performance.
Alkaline calcium carbonate is easy to be decomposed in acidic environment, which greatly limits its application. In order to expand its application range, calcium carbonate is often treated with acid-resistant inorganic substances such as condensed phosphoric acid, sodium aluminate and silicon dioxide. Adsorption of nano-calcium carbonate by inorganic electrolyte dispersant can not only significantly increase the absolute value of the surface potential of nano-calcium carbonate, but also produce a strong electrostatic repulsion effect. In addition, the strong spatial repulsion effect produced by the adsorption layer will also contribute to the subsequent compatibility with the matrix. And the inorganic electrolyte effectively suppresses agglomeration of the filler in water by enhancing the affinity of the filler surface to water.
Compound of different modifiers
When using two kinds of modifiers for compounding, it is necessary to consider the compounding ratio of the two modifiers, so that they have a synergistic effect on the calcium carbonate coating, so as to achieve the best modification effect.
Species, calcium carbonate, surface, modification, coupling agent, nano, polymer, action, modifier, formation
Kaolin is a non-metallic mineral, which is a kind of clay and clay rock mainly composed of kaolinite clay minerals. Because it is white and delicate, also known as white earth. It is named after Gaoling Village, Jingdezhen, Jiangxi Province.
Barium sulfate is based on barite as the main raw material, through beneficiation, ore washing, crushing and other processes. Barium sulfate has a hardness of 3~3.5 (Mohs) and a specific gravity of 4.3~4.7. It has the characteristics of high specific gravity, low hardness and brittleness. Barite is almost insoluble in water, ethanol and acid, soluble in hot concentrated sulfuric acid. With the development of some high-performance barium sulfate products, the application field of barium sulfate is constantly expanding.