What effects does the pH have in a waterborne coating?
The pH will have a major effect on several properties of a coating. Most waterborne coatings are formulated at a pH between 7.5 and 9, though some systems can be on the acidic side, such as 4. The specific target needs to be maintained for the additives, pigments and resins to work together. The first, and probably the most obvious effect, is on the viscosity. Many thickeners are based upon carboxylic acid-containing polymers or polymers that interact with the hydronium ion or hydroxide. The ionic interactions along the polymer chain, either by having the ionic groups as a part of the chain or associated with the chain, cause the chain to become elongated, which increases the viscosity. Any change in the pH can result in an increase or decrease in viscosity in these systems. A second area is pigment dispersion stability. The point of zero charge on pigments is the pH at which the surface of the particle has no charge. When the pH is increased above this value it is usually negatively c
