The thickening mechanism of cellulose thickeners is that the hydrophobic main chain associates with the surrounding water molecules through hydrogen bonding, which increases the fluid volume of the polymer itself, reduces the free movement space of the particles, and thus increases the viscosity of the system. The viscosity can also be increased by winding the molecular chain, which is manifested as high viscosity in static and low shear, and low viscosity under high shear. This is because at static or low shear speeds, the cellulose molecular chains are in a disordered state and the system exhibits high viscosity; while at high shear speeds, the molecules are arranged in an order parallel to the flow direction, which is easy to slide with each other, so the system Viscosity drops.
The thickening mechanism of polyacrylic acid thickener is that the thickener dissolves in water, and the molecular chain stretches from a spiral to a rod through the homostatic electrostatic repulsion of carboxylate ions, thereby increasing the viscosity of the aqueous phase. In addition, it also forms a network structure by bridging between the latex particles and the pigment to increase the viscosity of the system.
Associated polyurethane thickener A.J. Reuvers made a detailed study on the thickening mechanism of associative polyurethane thickener. The molecular structure of this type of thickener introduces hydrophilic groups and hydrophobic groups to make 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, a molecule has several micelles, which reduces the mobility of water molecules and increases the viscosity of the water phase. This type 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 delamination of the latex.
Bentonite, an inorganic thickener, is a layered silicate. It expands to form a flocculent material after absorbing water. It has good suspendability and dispersibility. It combines with an appropriate amount of water to form a colloidal body. Large system viscosity.
