Effects of pH and salt concentration on the formation and properties of chitosan-cellulose nanocrystal polyelectrolyte-macroion complexes.

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.