Low molecular weight sodium polyacrylate paper coating dispersant

With the introduction of high concentration coating machines and the development of copperplate paper, the demand for dispersants is increasing. Dispersants are a very delicate part of coating components. The first step in coating preparation is to suspend pigment particles in water, but the particles must be dispersed due to van der Waals attraction. However, inorganic dispersants have many disadvantages in use, such as relatively low solid content in the dispersed liquid, easy hydrolysis causing pigment flocculation, poor dispersion time stability, etc., which further reflect the advantages of organic dispersants. Low molecular weight sodium polyacrylate, as an organic dispersant in the papermaking industry, can produce coatings with low viscosity and high solid content compared to most pigments. It can improve the fineness of pigments, the stability of dispersion systems, and the softness, strength, whiteness, and water retention of paper. It is also soluble in water, not easily hydrolyzed, non flammable, non-toxic, and non corrosive, making it a promising dispersant in the papermaking industry. This dispersant can be used alone or in combination with inorganic phosphate dispersants. Experimental results have shown that combination use is more effective than individual use. In addition, it has a good dispersion effect on kaolin, barium sulfate, calcium carbonate and their mixtures.

Dispersion mechanism of low molecular weight sodium polyacrylate paper coating dispersant

The process of dispersant acting on pigment particles is a chemical process. Firstly, the dispersant dissolves in water and generates ionization, with a high degree of ionization, forming a large anion and a small cation with an equal amount of heterogeneous charges. The positive and negative ions firmly adhere to the surface of pigment particles, giving them the same charge. Ions with opposite charges freely diffuse into the surrounding liquid medium, forming a diffusion layer of charged ions, known as a double layer. The potential difference between the two layers of ions from the surface of the pigment to the farthest point of the diffusion layer (where opposite charges are zero) is called the zeta potential. Due to the repulsion of ions with the same charge, electrostatic repulsion is formed, which can prevent the pigment from flocculation in aqueous media and achieve dispersion.

In the presence of electric repulsion, dispersants must have high ionization properties. The greater the degree of ionization, the greater the affinity of ions adsorbed on the surface of pigment particles, and the more effective the dispersion effect. Polyelectrolytes are ideal substances with such ionic activity. The characteristic of polyelectrolytes is the presence of a large ion skeleton (a single large ion with many similar charged groups connected by chemical bonds) and a small and independent equilibrium ion with opposite charges. The representative polyelectrolyte is sodium polyacrylate.

If the amount of dispersant is just enough to isolate pigment particles with the repulsive force between the same charges, the optimal dispersion state is achieved. When the amount of dispersant is small, particles that are not encapsulated by the dispersant tend to agglomerate due to electrical attraction and produce precipitation. When the dosage of dispersant is too large, excessive dispersant will destroy the formed double layer, causing an unbalanced distribution of charges and resulting in precipitation. It can be seen that the optimal dosage of dispersant must be selected.

Sodium polyacrylate has a wide range of uses, but its use is closely related to its molecular weight. Low molecular weight sodium polyacrylate paper coating dispersant can reduce the viscosity of high concentration coatings in the papermaking industry, resulting in good rheological properties. As a dispersant for coating, it has good effects, and the products synthesized by the new process have good quality, low cost, and strong market competitiveness. Therefore, low molecular weight sodium polyacrylate will have better prospects for promotion and application in papermaking.