Intrinsic viscosity-molecular weight relationship for chitosan

Abstract

The intrinsic viscosity-molecular weight relationship for chitosan was determined in 0.25 M acetic acid/0.25 M sodium acetate. Chitosan samples with a degree of acetylation (DA) between 20 and 26% were prepared from shrimp-shell chitosan by acid hydrolysis (HCl) and oxidative fragmentation (NaNO2). Absolute molecular weights were measured by light scattering and membrane osmometry. Size exclusion chromatography (SEC) was used to determine average molecular weights (Mn, Mv, and Mw) and polydispersity. The following Mark-Houwink-Sakurada equation (MHS) is proposed for chitosan of Mw in the range of 35-2220 kDa: [η] = 1.57×10-4 Mv0.79 = 1.57×10-4 qMHS Mw0.79 = 1.49×10-4 Mw0.79 The value of the MHS exponent a suggests that chitosan behaves as a flexible chain in this solvent. Examination of MHS constants obtained in this work and those available in the literature with other solvents indicates that a and K are inversely related and that they are influenced by DA, and pH and ionic strength of the solvent.