| Chitosan is the only cation polymer existent in nature. It-and its decompositionproducts are non-poisonus. Besides, theproperties of chitosan are easy to be modified,and it possesses good biocompatibility and biodegradation, thus attracting scientists'much attention. Chitosan hydrogel can be synthesized in acetic acid solution withchitosan using glutaraldehyde as crosslinker. The hydrogel are well sensitive to pHand ion, but its swelling properties, mechanical properties and thermal stability are notgood, which restricts the wide application of chitosan hydrogel.This dissertation discusses ways to synthesize chitosan hydrogel,chitosan-polyether hydrogel, chitosan-polyvinyl alcohol hydrogel, chitosan-acrylicacid hydrogel and chitosan-acrylic acid-hydroxyethyl methacrylate hydrogel by usingchitosan, polyether, polyvinyl alcohol, acrylic acid and hydroxyethyl methacrylate asthe chief materials and glutaraldehyde as the crosslinker through the aqueous way,based on the design theory of polymer molecule. In this study, the process conditionsto produce chitosan-based hydrogels were optimized, and the optimized processvariables was determined by orthogonal experiments. The relevant theories andvarious factors affecting the swelling properties, mechanical properties and stability ofchitosan hydrogel were investigated. Moreover, the relationship between the structureand performances of chitosan-basecl hydrogels, its shaping and processing, itsapplication in beer brewing as the carrier materials for immobilization and so on. Themain contents of this dissertation are as follows:(1) The quality analytiedal results of chitosan are as follows: water for 15.205%;degree of deacetylation 92.671%; the weight average relative molecular weight ofchitosan 195900; the viscosity average relative molecular weight of chitosan 194100;and the decomposing temperature 298℃. The infrared ray IR spectra of chitosanshows that the feature-absorbing band of chitosan amido was 1601cm-1, that ofβ-indican bond was 986cm-1. The results of the X-ray diffraction of chitosan indicatesthat its degree of deacetylation and degree of crystal are both big.When the concentration of chitosan is 2.0%(g/mL), concentration of glutaraldehydeis 0.213mol/L, and gelatin temperature is 45℃, the swelling ratio of chitosan hydrogelis the biggest; When the concentration ofchitosan is 3.0%(g/mL), concentration ofglutaraldehyde is 0.426mol/L, and gelatin temperature is 55℃, its hardness is thehighest. The synthesis conditions have great impact on its swelling ratio and hardness.Among them, concentration of glutaraldehyde and chitosan is the main factoraffecting the swelling ratio and hardness of chitosan hydrogel. Dry chitosan hydrogel can no longer absorb water to swell. It is typically pH-sensitive and ion-sensitive, andits sensitivity is closely related to the amido on the molecular chain of chitosan.(2) The results of orthogonal experiments showed that when the gelatin temperaturewas 45℃, the mass ratio of polyether and chitosan was 0.4, the concentration ofglutaraldehyde was 0.213mol/L, the swelling ratio of chitosan-polyether hydrogel isthe biggest. When the gelatin temperature was 45℃, the mass ratio of polyether andchitosan was 0.6, the concentration of glutaraldehyde was 0.426mol/L, its hardness isthe highest. The relative molecular weight of chitosan, polyether, and the type andconcentration of crosslinker are the main factors affecting the swelling ratio andhardness of chitosan hydrogel. Among them concentration of glutaraldehyde not onlyaffects the structure and property of chitosan hydrogel, but also affects its kinds ofswelling kinetics. Chitosan hydrogel is pH-sensitive and ion-sensitive, and itssensitivity is closely related to the amido on the molecular chain of chitosan, but it isirrelevant to polyether, which is hydrophilic yielding macromolecule polymer.Polyether and chitosan form hydrogel of semi-interpenetrating polymernetworks(semi-IPN), and the swelling properties of dry hydrogel are excellent.(3) The best conditions for making high swelling ratio chitosan-polyvinyl alcoholhydrogel are as follows: the mass ratio of polyvinyl alcohol and chitosan 2; volume ofacetic acid 100.0mL; concentration of glutaraldehyde 0.213mol/L and concentrationof formaldehyde 1.086mol/L. However, the best conditions for making hard hydrogelare as follows: the mass ratio of polyvinyl alcohol and chitosan 6; the volume ofacetic acid 80.0mL; the concentration of glutaraldehyde 0.426mol/L andconcentration of formaldehyde 1.086mol/L.Polyvinyl alcohol possesses excellent mechanical properties. If it formssemi-interpenetrating polymer networks hydrogel with chitosan, the hydrogel will bestronger. As a fore-crosslinker, formaldehyde can improve the crosslinking effect ofchitosan-polyvinyl alcohol hydrogel. The freeze-thaw cycle made the molecule ofpolyvinyl alcohol to formed physical crosslink, resulting in increase in hardness of thehydrogel due to increase in crosslink density. Because of amido of chitosan chitosan-polyvinyl alcohol hydrogel is well sensitive to pH and the concentration ion. However,the above fact is irrelevant to polyvinyl alcohol.(4) Cerium ammouium nitrate is the initiator which makes chitosan ring openingand grafting. When 3.0mL 3.0mmol/L cerium ammouium nitrate was added, theconcentration of acrylic acid was 5.080mol/L, and grafting condition was 2.5h at60℃, its grafting yield was the highest. The grafting yield had great effect on thestructure and properties of chitosan-acrylic acid hydrogel. When the concentration of acrylic acid was 5.805mol/L, the volume of ceriumammouium nitrate was 4.0mL, the concentration of glutaraldehyde was 0.213mol/L,the temperature of gelation was 50℃, the swelling ratio of chitosan-acrylic acidhydrogel was the highest. When the concentration of acrylic acid was 3.628mol/L, thevolume of cerium ammouium nitrate was 2.0mL, the concentration of glutaraldehydewas 0.426mol/L, gelation at 45℃, the hardness of chitosan-acrylic acid hydrogelwas the highest. The synthesis conditions are the main factors affecting the swellingratio and hardness of Chitosan-acrylic acid hydrogel. The amido of Chitosan and thecarboxyl of acrylic acid made Chitosan-acrylic acid hydrogel pH-sensitive andion-sensitive.(5) The results of orthogonal experiments showed that when the concentration ofacrylic acid was 5.805mol/L, the concentration of glutaraldehyde was 0.213mol/L,3.0mL of cerium ammouium nitrate and 20.0mL of hydroxyethyl methacrylate wereadded, the swelling ratio of the hydrogel was the best. When the concentration ofacrylic acid was 2.903mol/L, the concentration of glutaraldehyde was 0.426mol/L,2.0mL of cerium ammouium nitrate and 40.0mL of hydroxyethyl methacrylate wereadded, the hardness of the hydrogel was the highest. The concentration of acrylic acidand glutaraldehyde and the amount of cerium ammouium nitrate and hydroxyethylmethacrylate added had great effect on the swelling ratio and hardness of the hydrogel.The structure of the hydrogel will change with time and it will become compact andordered. In other words, it will become transparent, lustrous and much harder. Thehydrogel will swell rapidly in the solution of sodium hydroxide, and the water in it isnon-freezing water (bond water) and freezing water (free water and intermediatewater). The results of thermal analysis showed that the water exists in different states-freezing and non-freezing.(6) Studies on the structures and properties of chitosan-based hydrogels performedwith the help of such devices as Texture Aualyser, FTIR, XRD, SEM, DSC,DSC-TGA showed that the properties of chitosan-based hydrogels were determinedby its structures.As the carrier for immobilization of beer yeast, chitosan-based hydrogels can beused in beer brewing. Among these chitosan-based hydrogels, chitosan-polyvinylalcohol hydrogel is regarded as valuable carrier material for immobilization, and thechitosan-acrylic acid-hydroxyethyl methacrylate hydrogel has some incomparableadvantages over other hydrogels in structure and properties.
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