The molecular mass of Sodium Polyacrylic Acid used as a dispersant is generally controlled at 3000-5000. It is a water-soluble polymer polyelectrolyte. When Sodium Polyacrylic Acid is dissolved in water, it is ionized in water, and the degree of ionization is large, forming a polymer Anions and many small molecular ions (Na+). Polymer anions and small molecular ions are firmly adsorbed on the surface of the dispersed particles, so that the ions have the same charge, and the oppositely charged ions (Na+) freely diffuse into the surrounding liquid medium, forming a stable diffusion layer of charged ions , the electric double layer. Since the ions with the same charge repel each other, the formation of electrostatic repulsion can prevent particles such as pigments from flocculating in the aqueous medium, so as to achieve the purpose of dispersion. At the same time, due to the steric hindrance effect of the polymer, it can also prevent the particles doing Brownian motion from approaching, resulting in composite stabilization.
If, when the molecular weight of Sodium Polyacrylic Acid is relatively large (above 104), the excessively long molecular chain will cause the particles to become larger and precipitate through bridging between the particles. At the same time, the negative charge of the acid radical on the macromolecular chain is combined with the particles in the water through adsorption, so that flocculation occurs between the particles due to aggregation. This is also the mechanism of action of the large molecular weight Sodium Polyacrylic Acid as a flocculant. Therefore, polyacrylic acid It is very important to control the molecular weight of sodium, otherwise it will have a completely different effect.