Sorption and desorption studies on chitin gels

Abstract

The aim of this work was to study various transport phenomena in chitin gels obtained by N-acetylation of chitosan in a water–alcohol mixture. Three kinds of transport were investigated: the sorption of solutes interacting with chitin, the desorption of solutes without significant interaction with the polymer, and osmosis phenomena. In the case of interactive sorption, dyes having different chemical structures such as C.I. Acid Blue 74, C.I. Reactive Violet 5 or C.I. Direct Red 28 were tested. Sorptions of C.I. Acid Blue 74 and C.I. Reactive Violet 5 depend on the charge density of the polymer network and, as a consequence, on DA, pH and the dielectric constant of the media. This result reveals the importance of electrostatic interactions. On the other hand, the sorption of C.I. Direct Red 28 is mainly due to hydrophobic interactions and H-bonding, it is limited to the extreme surface of the gel. Concerning the non-interactive desorption, solutes of different steric hindrance such as PP vitamin, B1 vitamin and caffeine exhibit similar diffusion coefficients located within 3.7–5.6×10 −6 cm 2 s −1. Finally, the osmotic behaviour of the gel immersed in a concentrated solution of gelatine allows us to multiply by 25 the concentration of chitin in the gel without any penetration of gelatine.