Estimation and confirmation of adsorption behavior of acrylic polymer on alumina from a molecular chemistry standpoint of adipic acid adsorption

Abstract

Adsorption of a low molecular carboxylic acid (adipic acid) on alumina was studied at molecular chemistry standpoint to estimate adsorption behavior of an acrylic polymer containing carboxylic acid group in water-base system. By the zeta potential measurement, adipic acid adsorbs on alumina chemically. The maximum amount of adsorption of adipic acid was observed at pH 5, which is close to pKa1 (4.41) and pKa2 (5.28) of adipic acid. In the region over pH 5, the adsorbed amount decreased monotonously with increase of pH. Adsorption behavior of adipic acid is considered by investigating both surface species distribution on alumina (AlOH2+, AlOH, AlO-), and species distribution diagram of adipic acid (H2X, HX-, X2-; X: -OCOC4H8COO-) at various pH. It is supposed that amount of adsorbed adipic acid on alumina is maximum, because the electrostatic attraction between a positive charge of alumina surface and a negative charge of adipic acid is large. By FT-IR analysis of adsorbate, alumina surface reaction with adipic acid produces outer-sphere complex at pH higher than pKa1 of adipic acid. The occupation area of one adipic acid molecule that was calculated from the amount of adsorption agreed with the molecule area estimated by chem-3D simulator. Adipic acid is supposed to be adsorbed on alumina surface perpendicularly in a single molecule layer. Adsorption of acrylic resin on alumina in alkali side was predicted from the knowledge of adsorption behavior of adipic acid. Furthermore, properties of polymer solution, suspension behavior and green sheet were estimated and confirmed. It is found that a molecular chemistry study of adsorption of a low molecular weight carboxylic acid can be adapted to polymer system.