Water‐sorption properties of poly(ϵ‐lysine): Carboxymethyl cellulose (CMC) dietary complex films

Abstract

AbstractTo investigate the application of supersorbing materials in the food industry, the water sorption of polyion complex films, prepared by solvent‐casting from poly(ϵ‐lysine) (PEL) and carboxymethyl cellulose (CMC), were examined and some physical properties of the hydrogels were studied. Three CMC samples having various degrees of substitution (DS) and molecular weights (MW) were applied to show a variety of water‐sorption behavior and physical properties. The ratio of PEL/CMC was changed from 10/90 to 50/50. Good film swelling in water was achieved when the complex was made from PEL and CMC with a low DS and an appropriate molecular weight, and when the PEL/CMC ratio was low. This indicated that the carboxyl groups in the CMC are not readily dissociated, and that the strength of cationic and anionic interactions affects the film swelling. In line with this view, the addition of electrolytes markedly lowered the film swelling. Nonelectrolytes such as sucrose or urea had no effect. IR and NMR spectra showed that a fraction of the ionic groups in the polyelectrolytes interact. Tensile moduli of complex dry films decreased linearly as the PEL content increased. Compressive moduli of swollen films were affected by neither the degree of swelling nor the molecular weights of CMC. The lower the DS values of CMC, the higher the compressive moduli were. We also examined the relation between the rigidity of polymer component and the ratio of nonfreezable bound water in complex films. On swelling in acetone–water or ethanol–water mixed solvent, expansion–shrinkage transition of the polymer gels occurred at about 20 mol % acetone or ethanol concentrations for every complex film. The overall characterstics of PEL/CMC consisting of a linear polyanionic polypeptide and a chain of cationic rings are reminiscent of polycationic chitosan and polyanionic polyglutamic acid. © 1994 John Wiley & Sons, Inc.