Extraction Of Chitin From Lobster Shells By Deep Eutectic Solvents And Preliminary Study On Chitosan Hydrogels

Chitin/chitosan has been widely used in medicine,environmental protection,food and many other fields due to its excellent biological properties.It has important economic and social value.In this thesis,the extraction process of chitin from lobster shells as raw materials using four kinds of deep eutectic solvents(DES)was studied.Then chitosan was prepared by the deacetylation of chitin with the highest purity,and chitosan hydrogels were prepared with glutaraldehyde as the cross-linker.The feasibility of the extraction process with low production cost and low environmental pollution and product application was explored by analyzing the properties and structure of chitin,chitosan and chitosan hydrogels.The details are as follows:(1)Four kinds of DES consisting of choline chloride(CC)with thiourea(T),urea(U),glycerol(G)and malonic acid(MA)were prepared at different molar ratio and synthesis temperature.They were labeled as CCT DES,CCU DES,CCG DES,and CCMA DES,respectively.Through the determination of their physical properties,it was found that the optimal preparation conditions for four kinds of DES were: the molar ratio of 1:1,1:2,1:2,1:2,and the synthesis temperature of 90°C,90°C,100°C,100°C.Four kinds of DES prepared under these conditions had short synthesis time,low freezing point and convenient storage at room temperature.(2)The extraction process of chitin from lobster shells using four kinds of DES(CCT DES,CCU DES,CCG DES and CCMA DES)prepared under the optimum condit ions and product structure were studied.It was found that when hydrogen bond acceptors were all choline chloride and hydrogen bond donors were changed,the process conditions of chitin extraction by different DES differed greatly and the extraction results were completely different.For the CCMA DES system,when the solid-liquid ratio was 7%,the extraction temperature was 50°C,and the time was 2 h,the sample MA-S(67.2 ± 0.9%)and the sample MA-P(80.6 ± 0.8%)with different crystallinity could be obtained simultaneously,and they also had two kinds of thermal stability.The total yield of the extracted chitin was 20.63 ± 3.30%,which was higher than that(16.53 ± 2.35%)of the chitin extracted by the acid-alkali method.The purity of chitin could reach the national standard GB/T 29941-2013,and was similar to that of the chitin extracted by the acid-alkali method and commercial chitin.They were all present in stable structure of ?-chitin.In addition,chitin extracted from lobster shells had porous structure.(3)Two kinds of chitin(MA-S and MA-P)extracted by CCMA DES with different crystallinity were deacetylated to obtain two kinds of chitosan(CS-S and CS-P),which were compared with that(CS-AA)prepared from the chitin(AA)extracted by the acid-alkali method.The effect of solid-liquid ratio,reaction temperature and reaction time on the degree of deacetylation and viscosity of chitosan was investigated.It was found that when the reaction time was 5 h and the solid-liquid ratio was 1:100,the reaction temperature of chitosan prepared from the chitin MA-S and MA-P could be reduced from 120°C to 80°C compared with that of chitosan prepared from the chitin AA.The degree of deacetylation was close to each other and could reach the requirement of more than 85%.The viscosity was also high.By FTIR and XRD analysis,the chitosan CS-S,CS-P,CS-AA and commercial chitosan had the same structure.(4)Four kinds of chitosan hydrogels(CH-S,CH-P,CH-AA and CH-C)were prepared using four kinds of chitosan(CS-S,CS-P,CS-AA and commercial chitosan)as raw materials and glutaraldehyde as the cross-linker.Through the analysis of their performance and structure,it was found that due to different degree of deacetylation and molecular weight of four kinds of chitosan,the equilibrium swelling ratio of four kinds of chitosan hydrogels was: CH-S>CH-AA>CH-P>CH-C.In addition,four kinds of chitosan hydrogels using different chitosan as raw materials were more sensitive to the acidic solvent.By FTIR,XRD and SEM analysis,the chitosan hydrogel CH-S,CH-P,CH-AA and CH-C had the same structure.Their crystallinity was close,and their surface had holes with different sizes.However,the surface of the chitosan hydrogel CH-C was relatively flat with only a small number of small pores.