Immobilized Cellulose By Modified Alginate Composite Gels

Immobilized enzyme has gained great attention because it can overcomethe shortcomings of free enzyme, such as poor stability, difficult to be separatedand operated. The selection of the carriers is a main factor in determining theproperties of the immobilized enzyme. Due to its good hydrophilicity, biocomp-atibility and network structure, alginate gel has become one of the most commonwater soluble organic carriers for the immobilization of enzyme. With the advantagesof large specific surface, strong adsorption and good mechanical ability, pseudo-boehmite or nano-alumina can be used to prepare composite gels with the alginate.As immobilized enzyme carrier, the composite gels may improve many shortages ofthe alginate gel, such as poor mechanical properties, small lifespan and highmass transfer resistance. The composite gels can provide a suitable micro-environment for enzyme, and improve the performance of immobilized enzyme.Using pseudo-boehmite and nano-alumina as inorganic component respectively,alginate as substrate, three types of composite gels were prepared:(1) two kinds ofadsorption-type composite gels were prepared by doping of pseudo-boehmite (PB) ornano-alumina (NA) into alginate gel.(2) The carboxyl in alginate was activated byEDC and NFS, and crosslinked by KH-550to prepare crosslinking-type compositegel.(3) Coating-type composite gel was prepared through coating the outer surfaceof the alginate beads with pseudo-boehmite gel. Chemical and physical properties,structure and morphology of alginate gel and composite gels were detectedrespectively by FTIR, DMA and BET etc. The swelling mechanism of the alginategel and composite gels was discussed by measuring swelling rate. Diffusionproperties of CMC in the alginate gel and composite gels were determined accordingto the unsteady-state model. The result indicates that anti-swelling abilities, diffusionproperties and storage modulus of the composite gels have been remarkablyenhanced than the alginate gel except diffusion property of coating-type composite gel. According to the effects of different doping amounts on diffusioncoefficient, the best doping amount of inorganic component was obtained,17.5%inadsorption-type composite gel ALG-PB,3g/L in adsorption-type composite gelALG-NA and7g/L in crosslinking-type composite gel.The enzyme loading efficiency, catalytic activities, optimum conditions and theoperational and storage stability of immobilized cellulase were investigated. Loadingefficiency of cellulase in ALG gel was61.4%, while the loading efficiency incomposite gels increased significantly, with the highest loading efficiency incrosslinking-type and coating-type composite gels reaching to85.5%and89.7%. Thecatalytic activity and stability of cellulose in composites was significantly higherthan that in ALG gel due to higher enzyme loading efficiency and improved carriermicroenvironment. Compared to other two types of composites, crosslinking-typecomposite gel showed much better performance due to the more appropriatemicroenvironment for enzyme encapsulation.