The effect of polymer molecular weight in the adsorption process

Abstract

The stability of pigment dispersions, which governs most of the film properties of paints, depends on the type and the extent of polymer species adsorbed by a pigment. The adsorption dependency with respect to molecular weight of the polymer and concentration of its solution was studied using epoxy esters of different molecular weights as adsorbates and anatase titanium dioxide as adsorbent. The amount of polymer adsorbed was determined by infrared spectroscopy. The type of molecular weight species adsorbed from unfractionated binder, the competitive adsorption in presence of more than one molecular weight species, and displacement of one molecular weight species by the other at different concentrations of the resin solutions were followed by gel permeation chromatography. The hiding power of paint and the gloss of the paint film, which are dependent on the degree of dispersion, were examined and the results correlated with the types of molecular weight species used in paint formulations. The type of molecular weight species adsorbed was found to be concentration dependent: the lower the concentration, the higher the molecular weight species adsorbed. The dispersions of pigment in the solution of higher-molecular-weight species were found to be more stable than those derived from lower-molecular-weight resin solutions. The TiO 2 paint derived from higher-molecular-weight epoxy resins had better gloss and hiding power.