EFFECT OF TITANIUM-DIOXIDE ON THE BLEEDING OF ALUMINUM LAKE DYES

An increase in the rate of bleeding of aluminum lake dyes was observed in mixed suspensions containing both titanium dioxide and an aluminum lake dye when pH conditions caused the titanium dioxide to have a net negative surface charge. In mixed suspensions in which titanium dioxide had a high positive surface charge, no difference in bleeding was observed in comparison to lake dye suspensions at the same pH. The degree of bleeding was directly related to the magnitude of the negative surface charge of the titanium dioxide. It is hypothesized that negatively charged titanium dioxide accelerates bleeding of aluminum lake dyes because of surface acidity. The concentrations of aluminum cation and dye in solution in mixed suspensions were initially higher than in control suspensions containing only the aluminum lake dye. The concentration of dye in solution increased with time in both the mixed and control suspensions. The concentration of aluminum cation in solution increased with time in the control suspension but decreased in the mixed suspension. It is believed that aluminum cations which are solubilized by the surface acidity of the titanium dioxide are adsorbed by the negatively charged titanium dioxide particles. Evidence in support of this hypothesis is the change in the electrophoretic mobility of the mixed suspension from negative to positive with time. (C) 1994 Academic Press. Inc.