Preparation Of Magnetic Cellulose Sulfate/Chitosan Composite Microspheres And The Application In Lipase Immobilization

Magnetic microspheres have been a newly developed functional polymer materials in recent years. In this thesis, a new cellulose derivatives cellulose sulfate(CS) was adopted as a raw material to embed Fe3O4 nanoparticles via interactions between CS and chitosan in ionic liquids system. And the CS/chitosan magnetic composite microspheres were prepared by means of microemulsion- coacervation method. The application of lipase immobilization with the obtained microsphere was studied. The main results are as follows:1、Construction of CS- ionic liquid solution system. The CS obtained from sulfation modification of filter paper cellulose for 10 min gained its solubility of 14.7g in ionic liquid [Emim]Ac,which was much higher than that of unmodified cellulose.The rheological properties of CS/[Emim]Ac showed that the solution was characterized by Newton type at low concentration range, and the solution was changed into shear thinning fluid when the mass fraction was higher than 1%. The relaxation time τ and the zero shear viscosity flow activation energy Ea of the system showed that the viscosity of CS/[Emim]Ac was closely related to the mass fraction of CS and the temperature. The rheological behavior of CS/[Emim]Ac was in accordance with the law of Cox-Merz.2、Preparation of magnetic CS/ chitosan composite microspheres by microemulsion-coacervation method. The preparation condition was as follows: the concentration of CS and chitosan composite solution 5%, raw material mass ratio of CS and chitosan 1:4, the water / oil(W/O) ratio 1:6, emulsified 2.5 h based on liquid paraffin, Tween-80 and Span-80 as hybrid emulsification system. With the mentioned conditions, the magnetic CS/ chitosan composite microsphere was obtained with the average particle size of 20-30 μm, and the saturation magnetization of 16 emu/g. In theory, the mechanical stability of the microsphere was maintained throught the electrostatic interactions among CS, chitosan and Fe3O4 nanoparticles.3、 Immobilization of lipase with the CS / chitosan magnetic composite microspheres. With BSA as the model compound of protein, the CS / chitosan magnetic composite microspheres showed excellent adsorption ability for the model protein compound BSA with the maximum adsorption capacity of 780mg/g, much higher than that of similar polymer composite adsorbent material.The optimal conditions for the lipase immobilization with the composite microspheres were as follows: 100 mg magnetic composite microspheres, immobilization time 7 h, amount of lipase 10 mg, pH value 8.0. Under these conditions, the protein solid loading rate was 65%, and the recovery of enzyme activity was 56%. After immobilization, the optimum pH of the lipase increased from 7.0 to 7.5, the optimal reaction temperature increased from 50 ℃ to 55 ℃, thermal stability was better than that of free lipase and has good operation stability.The immobilized lipase retained 63% relative enzyme activity after 10 consecutive operations. The separation and recovery of immobilized lipase and the reuse of the immobilized lipase were achieved.