Physicochemical behaviour of chitin gels

Syneresis of chitin gels formed in the course of N-acetylation of chitosan in hydroalcoholic media has been studied. A critical cross-linking density related to a critical acetylation degree for which the gel undergoes weak s yneresis and swells in water was shown (degree of acetylation (DA) 88%). Ab ove this value, the weight loss during syneresis increases with DA. Convers ely, syneresis decreases on increasing the polymer concentration, but disap pears at a macroscopic level for a polymer concentration close to the criti cal concentration of entanglement in the initial solution. An increase in t emperature favours the formation of hydrophobic interactions and new inter- and intramolecular hydrogen bondings. Due to the weak polyelectrolyte char acter of chitin, the weight of the gel depends on the pH and ionic strength of the media. Swelling-deswelling experiments show that the swelling of th e gel is not fully reversible in relation with the formation of new cross-l inks during the depletion of the network. Our results reveals that the bala nce between segment-segment and segment-solvent interactions as well as the molecular mobility play the major role. (C) 2000 Elsevier Science Ltd. All rights reserved.