The influence of surface chemical properties of kaolin surfaces on the adsorption of poly(vinyl alcohol)

Changes in the surface chemical properties of kaolin minerals may significantly affect the amounts of poly(vinyl alcohol) (PVOH) and its more hydrophobic analogue, partly hydrolysed polyvinyl acetate (PVOH/Ac), which are adsorbed. It is shown that pre-adsorbed anionic sodium polyacrylate (NaPA) and sodium hexametaphosphate (SHMP) dispersants increase the adsorbed amounts of both PVOH and PVOH/Ac. The mineralogical characteristics of the minerals were found to be even more important for the adsorption process, which is attributed to the larger amounts of PVOH/Ac adsorbed onto kaolin minerals with higher concentrations of montmorillonite contaminants (>1%). Very low affinity was found between the polymers and those kaolin minerals substantially free from montmorillonite. The low affinity of PVOH and PVOH/Ac for a silica surface strongly suggests that the silanol groups located on the basal plane of kaolin particles may not act as main anchor sites for the polymer. This strongly indicates that the non-ionic polymers have a great affinity for the ancillary montmorillonite mineral on the kaolin.