Thickening mechanism of thickener

The thickening mechanism of cellulose thickeners is that the hydrophobic main chain associates with the surrounding water molecules through hydrogen bonds, which increases the fluid volume of the polymer itself, reduces the space for particles to move freely, and thus increases the viscosity of the system. The viscosity can also be increased by the entanglement of molecular chains, which is characterized by high viscosity under static and low shear, and low viscosity under high shear. This is because, at static or low shear speed, the cellulose molecular chain is in a disordered state, which makes the system highly viscous; while at high shear speed, the molecules are arranged in an orderly parallel to the direction of flow and are easy to slide with each other, so the system The viscosity drops. 

The thickening mechanism of polyacrylic acid thickeners is that the thickener dissolves in water, and through the same-sex electrostatic repulsion of carboxylate ions, the molecular chain stretches from a spiral to a rod shape, thereby increasing the viscosity of the water phase. In addition, it also increases the viscosity of the system by bridging the latex particles and the pigment to form a network structure.

Associative polyurethane thickener A.J. Reuvers has detailedly studied the thickening mechanism of associative polyurethane thickener. Hydrophilic groups and hydrophobic groups are introduced into the molecular structure of this type of thickener, making it exhibit certain surfactant properties. When the concentration of its aqueous solution exceeds a certain concentration, micelles are formed, and the micelles and polymer particles associate to form a network structure, which increases the viscosity of the system. On the other hand, one molecule carries several micelles, which reduces the mobility of water molecules and increases the viscosity of the water phase. This kind of thickener not only affects the rheology of the coating but also interacts with adjacent latex particles. If this effect is too strong, it will easily cause latex delamination. The inorganic thickener bentonite is a layered silicate, which expands to form a flocculent substance after absorbing water. It has good suspension and dispersibility. It combines with an appropriate amount of water to form a colloid, which can release charged particles in the water and increase Large system viscosity. The characteristics of various thickeners and their choice. Cellulosic thickeners have high thickening efficiency, especially for thickening the water phase; there are few restrictions on coatings and coatings, and they are widely used; and applicable The pH range is large. However, there are disadvantages such as poor leveling, more splashes during roll coating, poor stability, and susceptibility to microbial degradation. Because it has low viscosity under high shear and high viscosity under static and low shear, the viscosity increases rapidly after the coating is completed, which can prevent sagging, but on the other hand, it causes poor leveling. Studies have shown that as the relative molecular weight of thickeners increases, the splashing properties of latex coatings also increase.