Separation And Selection Of Bacterial Cellulose Strain And Research On Phosphorylated Modification

Bacterial cellulose(BC) is a kind of nano-fiber synthesized by microbial. It has many perfect characteristics, such as high crystallinity, high purity, good mechanical properties, and high water content and so on, and it is widely used in food, medicine, papermaking, grade acoustics equipment, etc. But BC also has some defects. For example, it is difficult to be dissolved and processed due to its high crystallinity; its functions were limited because of its onefold functional group, etc. Therefore, modification researches on BC have become an important direction in the field of application.To select and identify cellulose-producing strains, homemade persimmon vinegar with BC membrane was used as raw material in this research. BC was also modified by phosphorylated, and PBC’s adsorption ability on heavy metal ions like Pb2+, Cd2+, Cr3+ and Hg2+ was tested. Then the structure and property of BC and PBC were determined. The main results were got as follows:(1) Four strains with high yield and stable heritability relatively were isolated from persimmon vinegar. Based on apparent observation and physical and biochemical analysis, the strains T621 and T651 were identified as Gluconobacter, T631 and T641 were identified as Acetobacter aceti;(2) Phosphorylated bacterial cellulose(PBC) was obtained by modification of BC, and the best synthetic condition which got by single factor test and orthogonal test were as follows: homogeneous pressure was 0 MPa, phosphoric acid was 20 g, urea was 40 g, reaction time was 4 h, temperature was 130℃. Under this condition, the phosphorylation degree of PBC was up to 75.93%;(3) By the adsorption experiment of PBC on Pb2+, Cd2+, Cr3+ and Hg2+, I concluded that PBC has strong adsorption ability on four metal ions, and the adsorption pecking order is Cd2+>Cr3+>Hg2+>Pb2+; The adsorption ability was strengthened with the increase of phosphorylation degree of PBC and initial concentration of the metal ions; The optimal PBC usage was 2 g/L; The optimal pH values of adsorption on the four metal ions were Pb2+ 5.0, Cd2+ 5.5, Cr3+ 2.0, Hg2+ 4.5, respectively; The equilibrium adsorption time for Pb2+, Cd2+ and Hg2+ was 60 min, while Cr3+ was 120 min;(4) Water content of PBC was about half of BC, while its ash content was about twice of BC; By atomic force microscopy chart, we could see that BC had a loose three-dimensional network structure, the microfibril gathered into a bundle by way of parallel or spiral, while the fibrils of PBC gathered more closely; By FTIR spectra, BC had vibration peaks of-OH,-CH2, and C-O-C from glycosidic unit and β-(1,4)-glycosidic bond, PBC also had vibration peaks of P-H, P=O, P-OH, P-O-C in addition to those of BC, and these peaks were strengthened by the increase of the phosphorylation degree of PBC, which indicated that PBC was synthesized; By the XRD spectra and thermal properties analysis, the result showed that when PBC was processed, the ultrapure network structure, crystallization and thermal stability of BC were destroyed, so the crystallinity and thermal degradation of stability of PBC were lower than that of BC.