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Common surface modifier and process of ultrafine barium sulfate

time:2021/5/19 9:30:00    Views:

As a high-quality barium sulfate product, ultra-fine barium sulfate has the advantages of non-toxic, tasteless, small particle size and so on. It is widely used in various fields. However, there are two key problems in the ultrafine barium sulfate products:

On the one hand, the ultrafine barium sulfate particles have small particle size, large specific surface area and high surface energy, so it is easy to agglomerate among particles, which makes the particle size become larger and the morphology is irregular.

On the other hand, the surface polarity of ultrafine barium sulfate is strong, and the particles are hydrophilic and oleophobic, with poor compatibility with organic materials and poor affinity with organic polymers, which affects the properties of composites and limits their application.

In order to restrain the agglomeration between particles and stabilize the dispersion system; In order to improve the organic compatibility of barium sulfate and the properties of composite materials, it is necessary to modify the surface of barium sulfate to make its surface hydrophilic and hydrophobic, so as to broaden its application.

1, barium sulfate commonly used surface modifier

The surface polarity of ultrafine barium sulfate particles is strong, and it is easy to dissociate the water adsorbed on the surface of barium sulfate particles to generate hydroxyl groups, which provides the possibility for the surface modification of barium sulfate. The surface modifier should first have hydrophilic polar group and oil-philic non-polar groups, which can be adsorbed on the surface of barium sulfate particles to form a firm adsorption layer; Secondly, the electrostatic force on the surface of the particles can be changed or the steric hindrance effect can be generated to make the ultrafine barium sulfate particles disperse and stabilize and inhibit their agglomeration. At the same time should also have acid resistance, alkalinity and weather resistance.

(1) coupling agent

The surface coating of superfine barium sulfate with coupling agent is simple, but it is widely used. The surface modification of superfine barium sulfate with coupling agent as the filler of coating can improve the mechanical properties of composite coating, such as shock resistance, impact resistance, strength and stiffness.

Various interfacial coupling agents such as titanium (aluminum) ester, stearic acid and silane can be selected according to different matrix materials.

(2) Superdispersant

Super dispersant is a new kind of water-soluble polymer dispersant, with barium sulfate particles surface hydroxyl by hydrogen bonding into or physical adsorption layer wrapped in barium sulfate particles surface, reduce the particle surface tension and surface energy, which changes on particle size of the electrostatic force resulted from space steric effect or disperse system is stable, the inhibitory effect of intergranular, improve the reunion between the particles. Commonly used super dispersant: polyester dispersant, low polymer soap dispersant, water soluble polymer dispersant, etc.

(3) Organic silicon

Polymer organosilicon is a kind of polymer with Si-O-Si bond chain (Si-O-Si) as skeleton and organic functional groups connected on silicon atoms. The structure stability of the inorganic skeleton in the polymer organosilicon is very high, and the organic functional groups outside the inorganic skeleton determine the surface properties of the polymer organosilicon.

Ultrafine barium sulfate modified by organosilicone can be widely used in coating industry. It can react with some components of coating materials to improve the fluidity of composite materials and solve problems such as agglomeration and dust. Common silicone modifier: silane coupling agent, silicon surfactant, liquid silicone rubber, silicone resin, etc.

2. Barium sulfate surface modification process

(1) Dry modification

Dry modification is achieved by dispersing friction between the modifier and barium sulfate particles during grinding. A certain proportion of modifier and product will be taken to wrap the modifier on the surface of barium sulfate particles in the process of stirring or grinding, so as to achieve the modification effect. This method is simple, easy to operate, low cost, but the modifier coverage is not uniform, weak binding force, the modification effect is not good. It can be used as an auxiliary modification method in actual industrial production.

(2) in situ modification

In situ modification refers to the two processes of particle synthesis and modification are completed simultaneously during the reaction, namely in situ modification of barium sulfate, which not only completes the synthesis of barium sulfate, but also includes the modification of barium sulfate. Due to the characteristics of in-situ modification, the modifier not only binds to barium sulfate particles, but also binds to free Ba2+ in solution, so that the modifier is not only wrapped on the surface of barium sulfate particles, but also exists between particles, which inhibits the agglomeration and growth of particles, and improves the dispersion and hydrophobicity of ultrafine particles.

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