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 dioxi de had a high positive surface charge, no difference in bleeding was o bserved in comparison to lake dye suspensions at the same pH. The degr ee of bleeding was directly related to the magnitude of the negative s urface charge of the titanium dioxide. It is hypothesized that negativ ely charged titanium dioxide accelerates bleeding of aluminum lake dye s because of surface acidity. The concentrations of aluminum cation an d dye in solution in mixed suspensions were initially higher than in c ontrol suspensions containing only the aluminum lake dye. The concentr ation of dye in solution increased with time in both the mixed and con trol suspensions. The concentration of aluminum cation in solution inc reased 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 ne gatively charged titanium dioxide particles. Evidence in support of th is hypothesis is the change in the electrophoretic mobility of the mix ed suspension from negative to positive with time. (C) 1994 Academic P ress. Inc.