Amino Acid Ionic Liquid System Under Electro-catalytic Degradation Of Chitosan Research

Low molecular weight chitosan which has unique physical activities and functional properties is widely used in pharmaceutical, food, agriculture, cosmetics and other fields. However, chitosan generally has high molecular weight which greatly limits its application. Therefore, the degradation of chitosan is of great significance. At present, many low boiling acids (such as hydrochloric acid, acetic acid, etc.) are used for the degradation of chitosan, which recycled difficultly and polluted the environment. Therefore, to find an environmentally friendly solvent instead of these traditional ones is very important. Amino acid ionic liquids (AAILs) make full use of natural resources, can dissolve many polar or non-polar polymer materials, wide liquid rang, high electric conductivity, non-pollution, recyclablility and known as "environmentally friendly green solvents".In this study amino acid ionic liquid was chosen because of its solubility and electrolyte. The degradation process was reacted based on Ti/TiO2-R.uO2 electrode in glycine hydrochloride ionic liquid solution and then had explored the impact of different factors on the degradation, analysed the structure change of degradated produces, and studied the mechanism and kinetic of the electro-catalytic degradation of chitosan. Meanwhile, the reuse performance of the ionic liquid was studied. Main research results are as follows:(1) The molecular weight of chitosan decreased apparently after the electro-catalytic degradation. The effect of chitosan degradation increased with the current density, reaction temperature and molecular weight of original chitosan increased, decreased with the initial concentration of chitosan increased, and increased firstly and then decreased with the ionic liquid concentration increased.The chemical structure and degree of deacetylation of degraded chitosan was not obviously modified besides the new formed carboxylic or carboxyl side groups. The crystallinity and thermal stability of degradation products was slightly lower than that of original chitosan; After degradated, the ionic liquid could be used repeatedly, which effectively implemented recycling.(2) The degradation process obeyed the zeroth-order reaction kinetics under the experimental conditions examined. The activation energy(Ea=19.1kJ/mol) of the degradation process was significantly lower than that of that for H2O2 degradation(Ea=88.5 kJ/mol) and nitrous acid hydrolysis of chitosan(Ea=87.1 kJ/mol).The apparent rate constant increased with the current density and reaction temperature increased, decreased with the initial concentration of chitosan increased, while increased firstly and then decreased when the ionic liquid concentration increased;(3) Combined with FT-IR and UV characterization results, the degradation mechanism of chitosan by electro-catalytic process under the amino acid ionic liquid solution was present as follow:Firstly, the physically adsorbed hydroxyl radicals, MOx [·OH] and chemisorbed oxygen in the oxide lattice, MOx+i generated at the electrode surface; Secondly, these radicals attacked theβ-(1,4) glycosidic bonds of chitosan chain, lead to chain scission of chitosan.