Adsorption of polyvinylalcohol onto Fuller's earth surfaces

The adsorption of polyvinyl alcohol (PVA) onto Fuller's earth surfaces has been studied at fixed pH (4.8) and ionic strength of the medium. The adsorption isotherm obtained resembles with LIII type of isotherm, which indicates that multilayer formation of polymer chains begins after a certain time period when the monolayer formation is complete. The study of concentration effect and kinetics of adsorption process enabled in evaluating various adsorption and kinetic parameters such as the adsorption coefficient, modified Freundlich adsorption isotherm constants, distribution coefficient and rate constants for adsorption and desorption. A plausible mechanism of adsorption process was suggested according to which the adsorption was predominantly due to the formation of hydrogen bonds between the OH groups of PVA and aluminols, silanols and carboxylate ions of the organic matter of the Fuller's earth. The proposed mechanism was further confirmed by the IR spectral analysis of native and PVA-adsorbed clay. The adsorption was appreciably affected by the pH, presence of salts, organic solvents, solid to liquid ratio and temperature of the adsorption medium. The study of temperature effect was quantified by calculating various thermodynamic parameters such as Gibb's free energy, enthalpy and entropy. The results obtained in the study helped in formulating a mechanism of interaction between PVA and Fuller's earth surfaces. (C) 2003 Elsevier Science B.V. All rights reserved.