Protonation behavior of cotton fabric with irreversibly adsorbed chitosan: A potentiometric titration study

The protonation of cotton fabric with irreversibly adsorbed medical chitosan (CO–CT) was measured in aquatic medium at 0.1 M ionic strength by means of potentiometric titrations, and compared with the results obtained for pure cotton and chitosan. For CO–CT, the charging isotherm exhibits a charge reversal around pH ≈ 6.0 , which is identified as the point of zero charge (PZC). The pure chitosan and the acid fraction that is present in cotton, protonate according to the one-pK model, with p K CT = 6.3 and p K CO = 4.7 , respectively. At pH > PZC , the charge of the acid fraction in CO–CT is negative and constant, and the proton binding is attributed purely to the adsorbed chitosan. On the other hand, the cotton-bound acid exhibits a more complex protonation mechanism in CO–CT than in the pure fabric, which is evidenced as an excess positive charge at pH < PZC and a deviation from the one-pK behavior.