Two potential applications of bacterial cellulose produced by A. xylinum
Creators: name: Vallejo-Cordoba, Belinda
Publisher: name: University of British Columbia
Year: 2010

description: The focal point of this research project was the development of two applications of cellulose produced from bacterial cultures of Acetobacter xylinum. The first part of this study relates to the culture method. Selection of influential factors for maximum cellulose production in defined medium was carried out by using Taguchis' L₂₇ (3¹³) Fractional Factorial Design. Sucrose and peptone concentrations and pH were found to be significant sources of variation on cellulose yields. Stability of three strains of A. xylinum were assessed over serial transfers of static and swirled cultures. It was concluded that all the strains tested were unstable under swirled conditions, ATCC 14851 being the most stable of the three when grown under static conditions. Growth curves of the three strains were studied and cellulose yields, pH values, sugar utilization, sugar conversion and nitrogen content in dry cellulose were determined over a 4-0 day incubation period. Comparison of the growth curves of A. xylinum strains showed that this organism varied widely in its efficiency of converting sugar to cellulose. The degree of polymerization (D.P.) values of the cellulose synthesized by two of the strains were followed over an incubation period of 32 days. The D.P. values of both strains appeared to decrease with incubation time. The second aspect of this study was to develop a process that integrates cellulose fibrils into a cotton-like fibre. Since A. xylinum naturally produces cellulose in the form of highly fibrillar ribbons, a process was devised to mechanically direct bacterial cells to spin these ribbons into oriented parallel filaments by cultivating the organisms in a straight-line flow path. Aeration rates in the system appeared to influence growth and cellulose yields. Flow mode (intermittent and continuous) and A. xylinum strain were shown to be highly significant sources of variation on the tensile strength of fibres. Optimum conditions for the mercerization treatment of fibres for achieving maximum tensile strength were determined by using a mapping super simplex optimization technique. Tensile properties of mercerized and unmercerized fibres were studied by conducting load-elongation tests to specimen failure. Light and electron microscopy were employed to observe the fine fibre structure. Finally, the third aspect of this study consisted of the development of a process for the purification and hydrolysis of A. xylinum cellulose for the manufacture of microcrystalline cellulose (MCC). Chemical composition and physical properties of the spray dried MCC were determined. The flow behaviour of A. xylinum MCC dispersions was examined and compared to commercial Avicel PH-101 MCC. Rheograms of both MCC dispersions displayed non-Newtonian pseudoplastic behaviour. A. xylinum MCC dispersions were found to have rheological behaviour of the thixotropic type, that is, there was a reversible change in viscosity with time at a constant rate of shear. Results of this study indicated that it is technically feasible to produce synthetic cotton-like fibres by stimulating A. xylinum cells to extrude their cellulose ribbons in a parallel fashion A. xylinum cellulose appeared to be a good source of raw material in the manufacture of microcrystalline cellulose because it is a highly purified form of cellulose which can be made available all year around at any location.