Nano-calcium carbonate four types of modification process and characteristics

Compared with ordinary calcium carbonate, nano calcium carbonate has a special crystal structure, surface electronic structure, and has excellent quantum size effect and surface effect, and is widely used in chemical industry, catalysis, optics, magnetism, electricity and other fields. However, nano-calcium carbonate is easy to agglomerate, and its surface is hydrophilic and oleophobic, which limits its application in organisms. Therefore, through surface modification, organic functional groups can be modified or grafted on the surface of nano-calcium carbonate to reduce surface energy and improve its dispersion in organisms. performance.

The nano-calcium carbonate modification process can be divided into four types, namely dry modification, wet modification, in-situ modification and composite modification. The modification process has a huge impact on the modification effect, so it is very important to adopt a suitable modification process for different application fields.

1. Dry modification

Dry modification means that in a dry environment, the high-speed rotating blades in a closed device break up the agglomerated nano-calcium carbonate, and at the same time add the modifier dropwise, and use the mechanical force to coat the modifier on the surface of the nano-calcium carbonate.

The process is simple and efficient, has no pollutant release and waste liquid output, is suitable for large-scale modification, and is widely used in the industry. However, the product modified by this method often cannot be coated uniformly and completely, and is prone to partial coating.

2. Wet modification

Wet modification is to add a certain amount of modifier to the nano-calcium carbonate suspension under stirring, control the stirring speed, temperature and time, and then filter, dry and disperse to obtain modified nano-calcium carbonate.

The modification effect of this process is good, but the investment is relatively large, and the waste liquid needs to be treated. Therefore, general enterprises are unwilling to accept it, and it is difficult to promote and apply it on a large scale.

3. In situ modification

In-situ modification is to simultaneously complete the two steps of nano-calcium carbonate preparation and surface modification in situ, and directly add modifiers to the reaction system for synthesizing nano-calcium carbonate, so that nano-calcium carbonate is modified when it is just generated. Agent coating, effectively inhibit the growth and agglomeration of calcium carbonate, so that calcium carbonate has good dispersibility. In addition, by using different modifiers or controlling the process conditions, the crystal form and particle size of the prepared nano-calcium carbonate are different.

This process represents a new trend in the development of nano-calcium carbonate modification, but it is currently in the basic research stage and it will take some time before it is put into production.

4. Composite modification

At present, compound modification has become the latest attempt in this field. The specific method is to use common modification processes in combination to achieve synergistic effects. Research has proved that compound modification works well. Yan Gancai first used sodium stearate to wet-modify nano-calcium carbonate, then added a dry-modification process, and then filled it into silicone sealant. It was found that the composite modified sample could more effectively improve the sealant Excellent storage stability and water immersion bonding performance.

In addition, some studies have shown that TiO2 can be coated on the surface of calcium carbonate particles by mechanochemical methods, sol-gel methods, hydrophobic polymerization methods, etc., all of which show good hiding power and are widely used in coatings. However, in addition to the hydrophobic polymerization method, the surface of the CaCO3/TiO2 composite material prepared by other methods is hydrophilic, and the CaCO3/TiO2 composite material prepared by the hydrophobic polymerization method has poor compatibility with the organisms in the pigment, so it is usually necessary to treat CaCO3/TiO2 The composite material is organically modified to make it hydrophobic and improve its compatibility with organisms.

The application of nano-calcium carbonate has been very extensive, and the modification methods are also emerging in endlessly. Single modification has gradually failed to meet the high requirements of the application. Studies in recent years have shown that composite modification has a better modification effect and is expected to become a future development trend.