Oscillatory rheology of chitosan and calcium chloride crosslinked pectin blend filmogenic solutions and atomic force microscopy of film surface topography

Abstract

This work examines the synergistic interaction between chitosan (CS) and calcium crosslinked pectin (CP) in aqueous solution by small-amplitude oscillatory shear measurements at selected CS/CP blend ratios (1:1, 1:2, 1:3, and 1:4) and compares the surface morphology of cast films of those blends using atomic force microscopy (AFM). A 2% (w/v) pectin solution concentration could not produce a film, which was improved with the addition of 0.18 M calcium chloride solution, and the corresponding dynamic moduli increased by 3 log cycles. The mechanical rigidity of the blends increased with increasing CP contents. The complex viscosity (η*) decreased with increasing temperature due to molecular mobility at higher temperatures and the breaking of the junction between CS and CP. The applicability of the Cole-Cole plot to selected blend ratios demonstrated that only the CS/CP ratio of 1:3 best fitted and established the well-miscibility between the polymers. AFM phase imaging further illustrates the distribution of CS and CP particles in the blended films and provides complementary information to the topography image, revealing the variations in the surface properties of the films. AFM proves to be a powerful tool for investigating microstructural changes in polymer blends and complementing rheological measurements.