FORMATION AND CHARACTERIZATION OF A PHYSICAL CHITIN GEL

The formation of N-acetyl chitosan gels in an acetic acid-water-propan ediol solution was studied. Side reactions arising from the esterifica tion of 1,2-propanediol by acetic anhydride, and hydrolysis of acetic anhydride were studied, as well as their possible role on the gel form ation. The gels were studied by FTIR and H-1 NMR spectroscopy. Indepen dently of the initial acetylation degree of chitosan, a minimal acetyl ation degree is required for gelation (80%). The final acetylation deg ree of the gels increases with the molar ratio acetic anhydride/amine, but does not reach 100%. An increase in temperature favours the molec ular mobility, inter-and intra-molecular hydrogen bondings and hydroph obic interactions, responsible for gelation which appears to depend on two parameters: a critical acetylation degree and a critical molecula r weight allowing the aggregation of the polymer chains. The nature of the solvent used to avoid chitosan side reactions during gelation (et hanol or propanediol) does not influence the chemical structure of the gel but only the kinetics of gelation. (C) 1997 Elsevier Science Ltd.