Conductimetric study of the interpolyelectrolyte reaction between chitosan and pectin

Abstract

The study of the interpolymer reaction between two natural polelectrolytes, chitosan, a cationic polysaccharide,
and pectin a polysaccharide of anionic nature is undertaken. The interpolyelectrolyte reaction was followed by monitoring
the variation of the conductivity of a pectin solution (2.03 · 10-4 equiv · L-1) resulting from the addition of a chitosan
hydrochloride solution (3.55 · 10-3 equiv · L-1) due to the formation of a polyelectrolyte complex (PEC). The appearance of
a slight turbidity in the solution during titration evidenced the formation of the insoluble PEC. The slope change in the
titration curve after the equivalence point indicates that the interpolyelectrolye reaction has been completed. Therefore,
it was possible to determine the stoichiometry of the complex, Z ([Chitosan]/[Pectin]), which turned out to be Z = 0.89.
The extent of the reaction or degree of complexation, θ, was evaluated as a function of the [Chitosan]/[Pectin] ratio. It
remained close to unity throughout the whole [Chitosan]/[Pectin] interval studied, evidencing that the reaction is highly
cooperative. The highest degree of complexation was obtained with the first additions of chitosan hydrochloride to the
sodium pectinate solution. From then on θ decreases reaching a minimum value (θ = 0.94) at Z ≈ 0.6 and then increases
again to almost unity ( = 0.99) at Z = 0.83.