| Magnetic starch have been prepared by corn starch and waxy corn starch desporting or embedding Fe3O4, the optimum synthesis condition and main influence factors of magnetic starch were investigated, and the parts of properties, structure, magnetic effects of magnetic starch were also studied in this paper. The single factor experiments were carried out selecting the amount of Fecl2, the amount of starch, pH and reaction temperature as main influencing factors andχm and particle size as indexs. Based on the results of single factor experiments, using waxy corn starch as materials, response surface experiments and analysis was carried out. The results showed:the optimal condition for magnetic waxy corn starch synthesis were:the amount of Fecl2 20.4g, the amount of starch 14.4g, pH 11.2, reaction temperature 70℃. The effecting significance sequence of the factors was:the amount of Fecl2>pH>the amount of starch>reaction temperature. There were certain interactions between the amount of Fecl2 and reaction temperature, the amount of starch and reaction temperature, pH and reaction temperature, the amount of starch and pH. While the interactions between the amount of Fecl2 and the amount of starch, the amount of Fecl2 and pH were not significant.The properties such as mass susceptibility(χm), particle size, infrared absorption spectra, magnetic domain structure, crystal structures, surface structure and morphology, thermal stability of magnetic waxy corn starch were determined and analyzed. Mass susceptibility of magnetic waxy corn starch was more than zero, which explained it was paramagnetic material. MFM found that the samples prepared in the optimum condition were full of even granular or strip shaped magnetic domain. Infrared absorption spectra showed that magnetic waxy corn starch contained Fe3O4 crystal, meanwhile, enriched in hydroxy and Carboxyl groups. X-Ray Diffractomet showed that magnetic waxy corn starch crystal spike diffraction characteristic of starch weakened and dispersion diffraction characteristic enhanced, meanwhile, crystal characteristic peak of Fe3O4 was found as compared with common waxy corn starch. SEM found surface structure of magnetic waxy corn starch was distinctly different from that of common waxy corn starch, but particle morphology almost kept invariant, based mainly on circular and polygon. The particle size analysis showed the average size of magnetic starch was 15.8μm, slightly larger than common waxy corn starch. Thermogravimetric analysis showed that thermal stability of magnetic waxy corn starch was higher than common waxy corn starch.Lipase had been immobilized onto magnetic starch microspheres by crosslinking with gultaraldehyde. Parts of properties of immobilized lipase were different from free lipase. Enzyme activity of immobilized lipase was 35% of that of free enzyme. Immobilized lipase had wider range of pH than free lipase. The optimal catalysis temperature of free lipase was 40℃, the optimal catalysis temperature of immobilized lipase was 45℃,5℃more than free lipase, which explained that heat resistance of immobilized lipase was higher than that of free lipase.
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