Surface chemical studies on the competitive adsorption of poly(acrylic acid) and poly(vinyl alcohol) onto alumina

Abstract

The adsorption of poly(acrylic acid) (PAA) and poly(vinyl alcohol) (PVA) onto alumina has been studied as a function of pH, both individually and in the presence of each other. The adsorption density of PAA is found to decrease with an increase of pH while that of PVA shows the opposite trend. In a binary system containing PAA and PVA, the presence of PVA does not affect the adsorption of PAA onto alumina, but the addition of PAA diminishes the adsorption of PVA in the pH range investigated. The adsorption isotherm of PAA at acidic pH exhibits high-affinity Langmuirian behavior. The isotherms for PVA appear rounded and are of the low-affinity type. Once again the adsorption isotherms of PAA remain unaltered in the presence of PVA whereas those of PVA are significantly affected resulting in a lowering of the adsorption density consequent to PAA addition. A variation in the sequence of addition of PAA and PVA does not affect the adsorption behavior of either of the polymers. The electrokinetic behavior of alumina with PAA is hardly influenced by the addition of PVA. On the other hand, the electrophoretic mobility of alumina in the presence of PVA is significantly altered in the presence of PAA and closely resembles the trend observed with PAA alone. Desorption studies reveal that over 80% of PVA could be desorbed in the pH range 3-9 whereas in the case of PAA, the percent desorption increases from 20 to about 70% as the pH is increased from about 3 to 8. Solution conductivity tests confirm interaction of aluminum species and PAA in the bulk solution. FTIR spectroscopic data provide evidence in support of hydrogen bonding and chemical interaction in the case of the PAA-alumina system and hydrogen bonding with respect to the PVA-alumina interaction.