Interfaces study of all-polysaccharide composite films

Abstract

Films made of xylan (X) and quaternized chitosan (QC) were prepared and the interactions of the polysaccharides on interfaces were discussed. According to elemental analysis, the X film contained also cellulose (31%) which could not be separated from the water suspension. The QC sample was soluble in water due to the presence of quaternized glucosamine units (4%) despite the presence of equal amounts of chitosan (CS, 48%) and chitin (CT, 48%). According to mechanical tests on QC/X = 1/3 composite film, the modulus and tensile strength values were the best from all mixtures measured, but still not better than on the film from X. We assume this is due to the sorption of xylan onto the surface of insoluble cellulose fibrils in the X film. Cyclic voltammetry indicates that the incorporation of X into the QC film decreases the overall positive charge provided by the QC. The X composite with net negative charge is indeed a barrier against the diffusion of ferricyanide anions. Based on TG/DTG/DTA analysis, the onset temperatures (OT) are decreasing with increasing X content in the blended films. X and QC films exhibited the highest OT values in comparison with the blended samples. The lowest OT temperature was observed at QC/X = 1/3. We think it is due to the thermocatalytic effect of the 4-O-methyl-D-glucuronate in X and the QC quaternary groups on the thermolysis–thermo-oxidation mechanism. According to AFM, the QC/X = 1/3 film exhibited the largest roughness values on both sides of the films, likely due to having the highest density of electrostatic interactions. XRD profiles of the films indicate some crystalline residues of cellulose in the xylan component as well as some chitin in the QC component. We assume that the properties are the result of the combination of the electrostatic interactions of carboxyl and quaternary groups of the soluble components of X and QC bonded to the surface of insoluble cellulose fibrils by hydrogen bonds. This probably results in both synergistic and antagonistic effects expressed by the improved or diminished values of determined properties.