Synthesis And Characterization Of Aliphatic Polyester Grafting Chitosan In Ionic Liquid

As the development and use of natural polymers gradually become a research focus due to overuse of the synthetic polymers and the gradual exhaustion of the nonrenewable resource such as oil. Chitosan is a fully or partly deacetylated product of chitin, which is the second most abundant natural resource next to cellulose. Recently, chitosan has attracted much attention for its favorable properties such as good biocompatibility, biodegradability and antibacterial activity. Unfortunately, the application of chitosan suffers greatly from many drawbacks such as poor solubility (low solubility in aqueous and insolubility in common organic solvents) and processability (nonthermal plasticity), resulting from the strong intramolecular and intermolecular hydrogen bonds between hydroxyl groups and amino groups.Ionic liquids (ILs), as a new generation of green recyclable solvents, have attracted increasing attention recently owing to their low vapor pressure and tunable solvability by varying the structure of cations and anions and provide a possible way to solve the problems about the weak solubility of chitosan. It was also reported that ionic liquid can be used as a plasticizer of polysaccharide to improve the processing performance of chitosan. In this research, we use the ionic liquid in which chitosan dissolved well as the homogeneous reaction medium of modifying chitosan. Also, we used the ionic liquid as the plasticizer of chitosan, and mixed it with chitosan by the thermo-mechanical treatment to improve the processing performance of chitosan. The conclusions are as follow.We used the (1-sulfobutyl-3-methylimidazolium trifluoromethanesulfonate, BSMIM·CF3SO3) aqueous solution as the green homogeneous solvent of the reaction that the water-soluble polyester grafting onto chitosan. Then, we obtained a lot of CS-g-PBT with different degree of substitution. The 1H NMR and ATR-FTIR confirmed that the polyester grafted onto chitosan successfully. WAXD test shows that the crystallinity of the products decreases obviously. It was deduced that the rigid structure and the regularity of chitosan chains stabilized by hydrogen bonds were drastically destroyed by the grafted PBT segments. And the chitosan derivatives can be soluble in neutral water. Then, we used the (1-propylene-3-methylimidazolium chloride) AMIMC1 to mix it with chitosan, as the plasticizer of chitosan. Bythermal-mechanical treatment, we obtained the mixtures which are melt-processable. It was confirmed that the mixtures had lower crystallinity by WAXD analysis, and the thermal stability were higher with the ionic liquid introduced. The tensile strength decreased obviously and the elongation at break increased slightly. Last but not least, the electrical conductivity of the mixtures is significantly increased.