Classification and selection of dispersants

Dispersant is one of the surfactants commonly used in many industries today, especially in the pigment industry, the application of dispersant is particularly important.

Dispersant can improve the overall luster of the pigment surface, prevent floating color, reduce viscosity, increase pigment load, reduce flocculation, increase color development and many other functions.

Criteria for consideration of dispersant selection

1) Under the conditions, try to choose a dispersant that can improve the energy barrier between particles, increase the repulsive force between particles, so that the particles are fully dispersed.

2) For oxides and hydroxides and materials containing oxidizing groups, attention should be paid to the effect of the pH value of the system on the dispersion of the material in the selection of dispersants, and the appropriate dispersant should be determined according to the range of pH value.

3) Under the particle barrier energy is very low, only by adding a dispersant that can improve the electrostatic repulsion between particles is not possible, should consider the use of polymer dispersants or non-ionic dispersants, using the steric effect to achieve uniform dispersion of materials.

4) A small amount of dispersant with high dispersion efficiency should be selected as far as possible, so as to reduce the pollution of the dispersant on the grading product and reduce the post-processing capacity.

Types and properties of dispersants

1. Inorganic dispersant

Inorganic classes are polyphosphates (sodium pyrophosphate, trisodium phosphate, tetrasodium phosphate, sodium hexametaphosphate), silicates (sodium metasilicate, sodium disilicate).

The adsorption of the inorganic electrolyte dispersant on the particle surface can significantly increase the value of the particle surface potential and produce a strong double electric layer electrostatic repulsion, and the inorganic electrolyte can also enhance the wetting degree of the particle surface, and the adsorption of the inorganic electrolyte on the particle surface can also enhance the surface wettability and increase the strength and thickness of the solvated film, thus enhancing the mutual repulsion of the particles.

2, organic dispersant

Organic category is divided into: anionic, non-ionic, cationic.

Among them, anionic types include alkyl aryl sulfonate, alkyl benzene sulfonate, dialkyl sulfonate, polyglycol alkyl aryl ether sodium sulfonate, non-ionic types include alkyl phenol polyvinyl ether, sorbitan alkyl alkyl phenol ether, polyoxyethylene alkyl phenol ether, and cationic types include alkyl vinylchloride.

The non-polar group length plays a significant role in the modification and dispersion of fine calcium carbonate particles. In water, the dispersion order of surface modification of fine calcium carbonate by different polar groups is as follows :-COONa> -CONHOH > S03H> Titanate > -PO(OH)2= silane.

3, polymer dispersant

Polymers include polycarboxylate, polyacrylic acid derivatives, maleic acid drunk copolymers, non-ionic water-soluble polymers (polyvinylpiroxone, polyether derivatives, polyethylene glycol) and so on.

The dense adsorption film of the polymer dispersant has a very significant effect on the agglomeration and dispersion of the particles.

A large number of polar groups are almost uniformly distributed on the common organic polymer chains. Therefore, the dense adsorption of organic molecules on the particle surface inevitably leads to the hydrophilization of the particle surface and enhances the surface wettability of polar liquid. According to the principle of dispersion regulation, this favours particle dispersion.