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 approximate to 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 pK(CT) = 6.3 and pK(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. (C) 2009 Elsevier Ltd. All rights reserved.