Preliminary Study On Stucture Regulation Of Bacterial Cellulose Nanofibers

The assembly process of bacterial cellulose ribbon is divided into three steps. Firstly, glucose ploymerized into β-1,4-glycoside chains and then chains gathered in to sub-elementary fibers on cellulose synthase sites in bacterial cells. Secondly, sub-elementary fibers discharged from cells and gathered into microfibrils. At last, microfibrils further aggregated to form fiber ribbons. To investigate the influence of various stages on final morphologies of bacterial cellulose, certain methods were used to interfere with the assembling of bacterial cellulose from the second and third stage of fibers’aggregation respectively. In addition, TEMPO-mediated oxidation was also used to separate cellulose ribbons into dispersed bacterial cellulose nanofibers.At the first stage of the aggregation, fluorescent brightener VBL was added to interfere the normal aggregation of sub-elementary fibers. Fibers retains the sub-elementary fibers’structure, so that individual nanofibers were obtained at a diameter about1.5-3nm. After eluting fluorescent brighterners with buffer solution, sub-elementary fibers formed non-fibrous structures by freely assembling. It can be inferred that the aggregation process of bacterial cellulose keeps a close relationship with the life activities of bacterial cells. Bacterial cellulose can’t assemble into three-dimensional nano-network structures without the life activities of bacterial cells.To investigate the impact of microfibrils’aggregation on fibers’structures, biological reducing agents, surefactants, nano-particles and other agents were used in the stage of microfibrils’aggregation. The results showed that regulations of this stage changed the micro structures and crystal structures of bacterial cellulose by adding some additives. However, this process can not fundamentally change the size of bacterial cellulose fibers.The primaty carbon-CH2OH on bacterial cellulose can be oxidized into-COOH by TEMPO-mediated oxidizing. As-COOH increasing the electrostatic repulsion between microfibrils, microfibrils aparted from each others. Individualized bacterial cellulose nanofibers were obtained at a diameter about5-8nm. When bacterial cellulose got a high crystallinity, there might occur nanofibers aggregated by two to three microfibrils in the oxidation products. In this research, the aggregation processes of bacterial cellulose were studied step-by-step. Foundation was laided for further study of assembly machanism of bacterial cellulose.