Yuan Lei's Little Knowledge | Nano Calcium Carbonate Surface Modification Technology
Nano-calcium carbonate is a new type of ultrafine solid powder material developed in the 1980 s, and its particle size is between 0.01 and 0.1μm. Due to the ultrafine of nano-calcium carbonate particles, the crystal structure and surface electronic structure change, resulting in the quantum size effect, small size effect, surface effect and macroscopic quantum effect that ordinary calcium carbonate does not have.
Due to the hydrophilic, oleophobic and high surface energy characteristics of the surface of nano-calcium carbonate particles, it is easy to agglomerate, which makes the dispersion of nano-calcium carbonate in the organic matrix such as plastic is uneven, thus affecting its application effect in the organic matrix such as plastic. Therefore, before nano-calcium carbonate is used as a filling material for organic substrates such as plastics, surface modification must be carried out to improve its application effect.
1. dry modification
Dry modification refers to the high-speed mixing of the modifier and the nano-calcium carbonate powder in a dry environment, and under the action of mechanical force, the modifier forms a thin layer uniformly coated on the surface of the nano-calcium carbonate particles, and the modified nano-calcium carbonate can be used directly without post-treatment. The commonly used surface modifier is a coupling agent, which forms a molecular bridge between the surface of nano-calcium carbonate and the organic polymer material by means of the coupling agent, so that their compatibility is greatly improved; in addition, the use of the coupling agent can also increase the amount of filler and improve the rheological properties of the system.
Dry surface modification is characterized by simple process and flexible formulation; calcium carbonate surface treatment and downstream processes are connected in series, with high production efficiency, low cost and easy transportation, but there are defects such as uneven modification, poor modification effect and high requirements for modified equipment, and it is difficult to achieve industrialization.
Precautions for dry surface modification: rapid stirring is required to quickly coat each calcium carbonate particle with the coupling agent; the modification temperature should be appropriate to facilitate the coating reaction; the source of hydroxyl group, if the water content in calcium carbonate is high, the coupling agent will first react with water instead of hydroxyl group on the surface of calcium carbonate, which cannot achieve the purpose of surface modification. Therefore, it is necessary to ensure the three basic conditions of rapid distribution, suitable temperature and no moisture, in order to play the role of coupling agent.
2. wet modification
Wet modification is to add water-soluble modifier to the nano calcium carbonate suspension at a certain temperature for water bath heating and stirring modification, so that it is fully contacted and mixed evenly, and then washed, dried and dried to obtain modified nano calcium carbonate.
The calcium carbonate is more easily dispersed in liquid phase than in gas phase, and the dispersion effect is better after adding dispersant, so that the effect of calcium carbonate particles and surface modifier molecules is more uniform.
The surface energy of calcium carbonate particles is reduced after wet modification treatment, and even if secondary particles are formed after pressure filtration and drying, only soft agglomeration with weak binding force is formed, which effectively avoids the hard agglomeration phenomenon caused by the formation of chemical bond oxygen bridge in dry modification. The wet modification process is more complex than the dry modification process, and the amount of surface modifier is slightly higher, but it has obvious advantages in terms of quality.
3. in situ surface modification
In-situ surface modification means that the two steps of preparation and surface modification of nano calcium carbonate are simultaneously completed in situ. That is, the surface modifier is added to the chemical synthesis solution system, the modifier is introduced before the formation of nanoparticles, and in the process of growing up of nano-calcium carbonate particles, sufficient force is provided to inhibit their growth, and at the same time, it can also play a role in preventing particle agglomeration, and finally obtain modified nano-calcium carbonate. In-situ surface modification can effectively improve the problem of particle agglomeration, and the modifier as an organic substance not only changes the surface properties of nano-calcium carbonate, but also regulates the nucleation and growth of nano-calcium carbonate.
4.New Technology of Surface Modification of Nano Calcium Carbonate
1. Masterbatch filler modification
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, the common masterbatch fillers mainly include polyethylene wax calcium carbonate masterbatch, irregular polypropylene calcium carbonate masterbatch (APP masterbatch) and resin calcium carbonate masterbatch fillers.
2. High energy surface modification
A method of modification using plasma or high-energy rays (e. g., X-rays, gamma rays, etc.). Plasma on the surface of CaCO3 powder modification is mainly the use of plasma polymerization technology, first of all, the monomer activation gas phase free radicals, and then adsorbed on the solid surface to become surface free radicals, and then with the plasma or gas phase of the original monomer polymerization reaction, the formation of polymer film on the surface of calcium carbonate, to achieve modification.
Modified, calcium carbonate, surface, nano, modifier, filler, particle, coupling agent, dry process
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