Linear viscoelastic behavior of chitosan films as influenced by changes in the biopolymer structure

Films were prepared via solvent casting from different deacetylated and depolymerized chitosans obtained from β‐chitin. The linear viscoelastic behavior of the chitosan films was studied with uniaxial tensile stress–relaxation tests. All stress–relaxation profiles exhibited an asymptotically decaying trend, with a residual value different from zero, thus pointing out a solid‐like, viscoelastic behavior. The decay of the tensile modulus with time was phenomenologically described by a generalized Maxwell model consisting of three exponential functions and an equilibrium elastic modulus. Films prepared from chitosans with higher molecular weights showed higher residual elastic moduli and longer relaxation times. Within the range of the degrees of acetylation analyzed (0–27%), chitosans with the lowest and highest degrees of acetylation exhibited more pronounced solid‐like character. This behavior is explained on the basis of a complex balance between steric effects, types of intermolecular interactions, and aggregation of the chitosan samples. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1907–1915, 2007