Study On Carboxylation Of Chitosan And Its Ammonia Absorption Property

Chitosan is a linear polysaccharide derived from the deacetylation of chitin. With the excellent properties of non-toxicity, biocompatibility, biodegradation, etc., chitosan and its derivatives have been widely applied in the fields of metal ion adsorption, dye removal, tissue engineering and drug delivery systems. In this thesis, we have focused on the synthesis, characterization and ammonia absorption properties of carboxylated chitosan.Seven N-carboxyethyl chitosans (ACCSs) and seven N-succinyl chitosans (SACSs) with different degree of substitution (DS) via Michael reaction and ring opening acylated reaction were prepared, respectively. The influence of different reaction conditions such as molar ratio, reaction temperature and time on Michael reactions and ring opening acylated reactions were systematically investigated. The results indicated that lower molar ratio, higher reaction temperature and longer time favored higher DS of ACCSs and the results showed that the highest DS of SACS (27.3%) was obtained at the molar ratio (succinic anhydride v.s. chitosan) of 1/3,4 h and 40 ℃. FT-IR and 1H NMR techniques confirmed the Michael reaction and ring opening acylated reaction took place successfully on the amino groups of chitosan. Elemental analysis indicated that the C/N ratio increased after Michael reaction and ring opening acylated reaction, which verified the introduction of acrylic acid and succinic anhydride into chitosan backbone, respectively. The TG analysis confirmed that chitosan decomposed from 215 to 242℃, while the ACCSs decomposed around 206℃ and SACSs decomposed around 203℃,2which indicated the thermal stability of ACCSs and SACSs decreased compared with that of the chitosan. Then the acid-base titration method was used to investigate the ammonia absorption property of ACCS and pH-based method was used to investigate the ammonia absorption property of ACCS and SACS, respectively. The results from the pH-based method indicated that the ACCS and SACS had a certain adsorption effect in ammonia absorption.EDC-catalyzed condensation reaction of succinic acid with the low molecular weight chitosan were performed via at different molar ratios (succinic acid/chitosan is 0.25,0.5 and 1) under 30℃ for 24 h in phosphate buffer solution (pH=6). FT-IR and 1H NMR were used to confirm the structure of chitosan and succinic acid crosslinked chitosan. The results of ’H-NMR indicated that both of the crosslinking degrees of these three chitosan derivatives and the contents of free carboxylic acid group were low. The GPC results showed that, after EDC-catalyzed condensation reaction, the weight average molecular weights of succinic acid crosslinked chitosans increased slightly compared with that of chitosan, which was consistent with the results of 1H NMR. Furthermore, 1H NMR results represented the contents of free carboxylic acid group of these three chitosan derivatives were lower than 9.6%,11.1% and 13.3%, respectively. In this case, the pH-based method was difficult to detect ammonia absorption of resultant products.