The aim of this publication is to facilitate the estimation of chitosan molecular weight (MW) in laboratories with no access to sophisticated analytical instruments, by applying the easily accessible and economical capillary viscometry. The procedure of viscosity-average molecular weight (Mv) determination is described in details. The examples provided encompass testing of the experimental procedure for determination of the Mv of chitosan with a low-molecular weight of 7.7 kDa and 88 kDa, after verification with a high-molecular weight polymer (477 kDa). The experimental work demonstrated the importance of the initial concentration of low-MW chitosan for the accurate determination of intrinsic viscosity and, as a consequence, the viscosity-average molecular weight.

Solutions of chitosan (CS) and carboxymethyl chitosan (CMCS) were subjected to irradiation by electron beam in presence of a crosslinking agent (poly(ethylene glycol) diacrylate - PEGDA) in order to produce carboxymethyl chitosan- and chitosan-based hydrogels. PEGDA macromonomer itself undergoes simultaneous polymerization and crosslinking either in neutral water or in acidic medium. Acidic solutions of chitosan of 0.5, 1 and 2% can be effectively crosslinked with PEGDA to form a gel. Although CMCS undergoes radiation-initiated crosslinking only at high concentration in water (over 10%), the presence of PEGDA in solution facilitated hydrogel formation even at lower concentration of CMCS. Formation of CS and CMCS hydrogels required irradiation doses lower than those needed for sterilization, i.e. 25 kGy, in some cases even as low as 200 Gy. Sol-gel analysis revealed relatively high gel fraction of obtained hydrogels, up to 80%, and good swelling ability. Both parameters can be easily controlled by composition of the initial solution and irradiation dose. Possible mechanisms of crosslinking reactions were proposed, involving addition of the polysaccharide macroradicals to a terminal double bond of PEGDA.