Why should nano-calcium carbonate be surface modified?

Nano-calcium carbonate refers to a functional inorganic filler with a particle size of 1-100nm.
Ultra-fineness makes its crystal structure and surface electronic structure change.
It has quantum size effect, small size effect, surface effect and macro quantum effect, and is widely used rubber, plastics, paper, chemical building materials, inks, coatings, sealants and adhesives, and other fields
.
? Why should nano-calcium carbonate be modified? ? Nano calcium carbonate has excellent properties due to the nanometerization of its particles, but there are two major defects in its application in organic media: First, nano calcium carbonate is an inorganic material with hydrophilic and oleophobic surface, and its dispersion in polymers is poor.
Poor affinity with organisms, easy to form agglomerates, direct application effect is not good, resulting in material performance degradation;? Second, nano calcium carbonate has a small particle size, a large number of surface atoms, large surface energy, and strong interaction between particles, which is easy Agglomeration of nano calcium carbonate powder is formed
.
With the increase in the amount of nano-calcium carbonate used, these defects become more obvious, and excessive filling will make the material unusable
.
? Therefore, it is necessary to adopt effective modification methods and processes to modify the surface of nano-calcium carbonate to reduce the surface energy, increase the dispersibility, and make the surface lipophilic to become active nano-calcium carbonate
.
? Nano calcium carbonate modification method? At present, the main methods used for nano calcium carbonate surface modification are: surface coating modification, microemulsion modification, high-energy surface modification, mechanochemical modification and local chemical reaction modification and so on
.
? (1) Surface coating modification? Surface coating modification means that the surface modifier has no chemical reaction with the surface of nano calcium carbonate.
It is a kind of physical coating modification.
The modifier and the particles rely on physical methods or van der Waals.
Strength and connection modification method
.
Firstly, a surfactant is added to the solution for preparing the nanometer calcium carbonate.
When the nanometer calcium carbonate is formed, the surface active agent is coated on the surface to form uniform nanoparticles
.
(2) Microemulsion modification? The microemulsion modification method is to coat the surface of nano calcium carbonate with a film of other substances to change the characteristics of the particle surface.
The difference from surface coating modification is that the coated film is uniform Of
.
? Ke Changmei and others used nanometer polyacrylate microemulsion and acrylate emulsion to modify the surface of nanometer calcium carbonate, and characterize the structure and performance of the modified active nanometer calcium carbonate
.
It is found that the modified nano-calcium carbonate has reduced oil absorption value, greatly enhanced lipophilicity, and significantly improved dispersibility in non-polar media
.
? (3) Mechanochemical modification method? Mechanochemical modification is the use of ultrafine crushing and other strong mechanical forces to purposefully activate the surface of calcium carbonate particles to change the surface crystal structure and physical and chemical structure of calcium carbonate to make carbonic acid The displacement of the molecular lattice in calcium enhances its reactivity with organic or other inorganic substances, including ball milling, bead milling, and ultrasound
.
The mechanochemical modification method is more effective for large particles of calcium carbonate.
Because the nanometer calcium carbonate has a small particle size, the effect of mechanical crushing and grinding is not significant
.
However, this method can increase the active sites and active groups on the surface of nano calcium carbonate, and enhance its effect with organic surface modifiers.
Therefore, if it can be used in combination with other modification methods, it can also effectively change the surface of nano calcium carbonate.
Nature
.
? (4) Local chemical reaction modification? Local chemical reaction modification mainly uses the chemical reaction between the functional groups on the surface of nano calcium carbonate and the modifier to achieve the purpose of modification
.
Local chemical reaction modification is mainly divided into two processes: wet modification and dry modification
.
? Wet modification is generally to put the modifier directly into the nano calcium carbonate suspension, mix the modifier and nano calcium carbonate powder uniformly at a certain temperature, and form the surface modifier coated nano calcium carbonate powder after the reaction The double-membrane structure is filtered, dried and sieved to obtain surface-modified active nano-calcium carbonate
.
? Water-soluble surfactants are more suitable for the wet modification process, because the surfactants have both a hydrophilic group and a lipophilic group.
There is affinity between the hydrophilic group and the nano calcium carbonate, and the lipophilic group It has affinity with rubber.
When the surfactant is between nanometer calcium carbonate and rubber, the two are tightly combined.
Such water-soluble surfactants are mainly higher fatty acids and their salts
.
? Dry modification is to directly add nano calcium carbonate powder and modifier directly into a high-speed kneader for kneading, which is simple and convenient.
It can be directly packaged after discharging, and it is easy to transport and discharge
.
The surface of the nano calcium carbonate powder obtained by this method is not uniform, which is suitable for occasions where the requirements are not high, but the processing method is simple to operate, so it is widely used
.
? (5) High-energy surface modification? High-energy surface modification includes high-energy rays (γ-rays, X-rays, etc.
), plasma treatment and other methods
.
The radiation treatment modification method uses high-energy radiation generated by an electron accelerator to activate the calcium carbonate surface, and then reacts the powder with active points on the surface with the monomer to form an organic coating layer on the surface of the calcium carbonate particles, thereby Improve the surface properties of the filler and its compatibility with polymer materials to achieve the purpose of modification
.
? The plasma modification method mainly uses a glow discharge plasma system, and uses one or more gases as the plasma processing gas
.
The surface modification of calcium carbonate powder by plasma mainly uses plasma polymerization technology
.
Plasma polymerization technology is to activate the monomers of organic compounds to form free radicals in the gas phase.
When the gas phase free radicals are adsorbed on the surface of calcium carbonate, surface free radicals are formed.
The surface free radicals are generated in the original monomer or plasma in the gas phase.
The derivatized monomer polymerized on the surface of calcium carbonate to form a polymer film with a large molecular weight to coat the surface of calcium carbonate, thereby changing the surface properties of calcium carbonate and achieving the purpose of modification
.
? However, the high-energy modification method has relatively complicated technology, high cost, low production capacity, and unstable modification effect, so the application is relatively small
.