Commercial chitosan is purified in the neutral form and as chitosan acetate and chitosan hydrochloride. These samples were characterized and compared with respect to solubility, hydrophilicity, surface's morphology and crystallinity. Commercial chitosan and its neutral purified form present similar characteristics and properties but the saline purified forms, mainly the chitosan hydrochlorides, are quite different from them. The surface morphologies of the former samples are similar but that of the lyophilized chitosan hydrochloride presents pores which are not observed in the other samples. Commercial chitosan and its neutral purified form are not soluble in pure water but chitosan acetate is partially soluble. These samples present similar hydrophylicities and crystallinities but in the cases of the chitosan hydrochlorides the presence of charges and of counter ions from a strong acid enhances the hydrophilicity, promotes solubility in water and significantly alters the interactions inter and intrachains, modifying the packing in the solid state and drastically reducing the crystallinity. In the case of chitosan acetate it is observed that the crystallites are smaller probably due to the partial protonation of amine groups and to the presence of acetate anions.
Chitosan; purification; chitosan acetate; chitosan hydrochloride
