Лако-красочные материалы — производство

Very finely divided fumed silica (pyrogenic silica) is another important inorganic thickener used in the coating industry that

possesses surface hydroxyl groups (silanols) capable of forming a three-dimensional structure via hydrogen bonding to yield incre­ased viscosity. Depending on the system, the thickening effect is determined mainly by the grade and concentration of the pyrogenic silica, system pH, polarity of the medium, degree of dispersion, and presence of other additives.

The hydrogen bonds are relatively weak and get disrupted as soon as light shear forces are applied, with a consequent viscosity red­uction. The three-dimensional silica chain structure reforms upon removal of shear force and thus produces thixotropic consistency in the system (Figure 5.8). The effect is more pronounced in systems without or with low hydrogen bonding capability (such as hydrocar­bons) than in a system capable of hydrogen bond formation (such as water, an alcohol or an amine).