Effect of layer charge and charge distribution on the formation of chitosan - smectite bionanocomposites.

Chitosan-clay bionanocomposites were prepared from chitosan biopolymer solutions and four different smectites (SAz-1 and SWy-2 montmorillonites, SBId-1 beidellite and NAu-1 nontronite), and the effect of layer charge and charge distribution on the formation of bionanocomposites was examined. The intercalation of the chitosan in the homoionic Na+-smectite samples showed that all samples produced chitosan-smectite nanocomposites even at the lowest chitosan-clay ratios. The adsorption isotherms of chitosan by the smectites were classified as L- type isotherms. The equilibrium data were fitted to Langmuir and Freundlich isotherms and the equilibrium adsorption was best described by the Langmuir isotherm model for SWy-2 and SBId-1 while the Freundlich model achieved a better description for SAz-1 and NAu-1 for the higher chitosan concentrations. The adsorption of chitosan exceeded the CEC in the montmorillonites (SWy-2 and SAz-1) whereas in SBId-1 and NAu-1 with tetrahedral charge it either reached or it was lower than the CEC showing that layer charge and charge localization may hinder chitosan adsorption. Unlabelled Image • Chitosan-smectite bionanocomposites were produced even at the lowest chitosan-clay ratios. • Adsorption isotherms follow the Langmuir and the Freundlich model. • The increase of Δ d L spacing is in full accordance with adsorption isotherms. • Adsorption of chitosan in excess of the CEC is evident in smectites with octahedral charge. • Layer charge and charge localization influence chitosan adsorption and formation of bionanocomposites. [ABSTRACT FROM AUTHOR]