Viscoelastic Properties of Crosslinked Chitosan Films

Chitosan films containing citric acid were prepared using a multi-step process called heterogeneous crosslinking. These films were neutralized first, followed by citric acid addition, and then heat treated at 150 degrees C/0.5 h in order to potentially induce covalent crosslinking. The viscoelastic storage modulus, E ', and tan delta were studied using dynamic mechanical analysis, and compared with neat and neutralized films to elucidate possible crosslinking with citric acid. Films were also prepared with various concentrations of a model crosslinker, glutaraldehyde, both homogeneously and heterogeneously. Based on comparisons of neutralized films with films containing citric acid, and between citric acid films either heat treated or not heat treated, it appeared that the interaction between chitosan and citric acid remained ionic without covalent bond formation. No strong evidence of a glass transition from the tan delta plots was observable, with the possible exception of heterogeneously crosslinked glutaraldehyde films at temperatures above 200 degrees C.