ADSORPTION OF CARBOXYMETHYLCELLULOSE ONTO HYDROXYLAPATITE

The effect of sodium salts of carboxymethylcellulose (SCMC) on the stability of aqueous hydroxylapatite (HAP) suspensions, as well as the adsorption isotherms in this system, was investigated. Electron paramagnetic resonance was used both as an analytical tool for the determination of the amounts of adsorbed polymer and as a tool to investigate conformational aspects of polymer adsorbed at the solid/liquid interface. The observed stabilizing effect of SCMC is paralleled by a change in HAP sedimentation volumes. These effects present a saturation at ca. 0.1% SCMC concentration, which corresponds to the beginning of the plateau region in the SCMC/HAP isotherms. Adsorption data fit the Langmuir model. All experimental results can be understood by the assumption that SCMC is spread over the HAP surface, forming small loops not greater than three monomer units, with most of its carboxylate groups bound to surface Ca2+ sites. This model is further supported by the resistance of adsorbed SCMC to cellulase, an enzyme which hydrolyzes SCMC in aqueous solution. © 1991.