Effects of pH and Salt Concentration on the Formation and Properties of Chitosan–Cellulose Nanocrystal Polyelectrolyte–Macroion Complexes

Abstract

This study examines the effects of pH and salt concentration on the formation and properties of chitosan-cellulose nanocrystal (CNC) polyelectrolyte-macroion complexes (PMCs). The components' pK values, determined by potentiometric titration, were 6.40 for chitosan and 2.46 for the CNCs. The turbidity of PMC particle suspensions was measured as a function of chitosan-CNC ratio, pH, and salt concentration. The maximum turbidity values in titrations of a chitosan solution with a CNC suspension and vice versa occurred at charge ratios of 0.47 ± 0.11 (SO(3)(-)/NH(3)(+)) and 1.16 ± 0.06 (NH(3)(+)/SO(3)(-)), respectively. A pH increase caused a turbidity decrease due to shrinking of the PMC particles upon changes in their components' degrees of ionization. An increase in salt concentration caused a decrease in turbidity due to charge-screening-related shrinking of the PMC particles. The effects of pH and salt concentration on particle size were confirmed by scanning electron microscopy.