Study On The New Homogeneous Synthesis Method Of N-Acyl Chitosan In Ionic Liquids

Chitosan and its modified products have been widely used in papermaking, food additives and biomaterials, etc because of their excellent properties. The acyl-chitosan is one of the important modified products. It is traditionally manufactured in acetic acid homogeneous system. However, the shortcomings of these processes include long reaction time, gelatin, complicated separation procedures, and the disadvantages of conventional solvents such as high volatility, severely contaminated, strongly causticity and the degeneration of chitosan. Therefore, it is important to find a new green solvent for improvement the acylation reaction of chitosan.According to the excellent property of ionic liquid in cellulose, ionic liquid was introduced in the homogeneous reaction of acyl-chitosan. Four kinds of ionic liquids: [Gly]Cl, [Pro]Cl, [Lys]Cl and [Pro] [ClCH₂COO]were prepared based on standard literature method. Their structures were characterized by FTIR and NMR. N-acetylated chitosan, N-maleyl chitosan and N-succinyl chitosan were synthesized in homogeneous system of ionic liquid aqueous solution and chitosan. The results showed [Gly]Cl was of better solubility performance than the other three ionic liquids. The influences of reaction time, temperature and the mole ratio of reactants on the degree substitution of the above three acyl-chitosan were investigated respectively in the homogeneous system of which weight percentage is 2%. The repeating usage of ionic liquid was also discussed. The optimum conditions were obtained as follows: n(acetic anhydride): n(chitosan)=2.75, reaction temperature 60℃and reaction time 5h, the degree substitution of N-acetylated chitosan was 93.8%. n(maleic anhydride): n(chitosan)=2.5, reaction temperature 60℃and reaction time 5h, the degree substitution of N-maleyl chitosan was 90.4%. n(succinic anhydride): n(chitosan)=2.75, reaction temperature 40℃and reaction time 4h, the degree substitution of N- succinyl chitosan was 91.1%. [Gly]Cl could be reused 3 times without any disposal and the degree substitution was still above 89%. Their structures were characterized by XRD and FTIR.The products have good water-solubility, moisture-absorption and moisture-retention capacity. Furthermore, moisture-absorption capacity was better than the moisture-absorption capacity of glycerol. The post-disposal was treated with simple techniques. The reaction conditions were mild. Therefore, an environment friendly process of the synthesis of N-acyl chitosan is provided.