[Influence of culture mode on bacterial cellulose production and its structure and property]

Acetobacter xylinum NUST4.2 has been applied in the studies to examine the production, structure and thermal property of bacterial cellulose (BC) produced in stationary culture and in the stirred tank reactor. These differences are as follows: BC yield reached 7.5 g/L in stationary culture for 6 days and its productivity was 0.052 g/L/h. BC production reached 3.13 g/L in the stirred tank reactor for 72h and its productivity was 0.043 g/L/h. SEM showed that there was almost no difference between network structure built of entangled cellulose ribbons produced in static culture and in the reactor. But the cellulose ribbons produced in static culture were a much more entangled and denser network with curved and overlapping cellulose ribbons in comparison with that one produced in the stirred tank reactor. Also the thickness of the cellulose ribbons seems to differ between the two BC samples, with the one from static culture distinguished by the slightly thinner ribbons. FT-IR revealed that there was no effect of stirring on the chemical structure of BC, but intermolecular hydrogen bond of cellulose was weakened. Furthermore, BC synthesized in static culture displayed I(alpha)-rich cellulose. XRD results indicated that no remarkable change in the cellulose crystallographic form of the BC samples. Nevertheless, BC produced in static culture was characterized by a higher crystallinity, higher I(alpha) content and higher crystalline size than cellulose that was produced in the reactor. All of these results revealed that stirring in the reactor interfere strongly in the process of nascent microfibrils crystallization, favoring the formation of smaller size microfibrils and increased I(beta), the more stable allomorph. Compared with cotton cellulose, the changes of thermal decomposition behavior in the BC samples were that BC produced in static culture displayed better thermal stability, but BC produced in the stirred reactor displayed better flame retarding.