Relation between Change in Morphology and Crystallization of Cellulose Gels Produced by Acetobacter xylinum

Abstract

Relation between change in the morphology and the crystallization of cellulose gels produced by Acetobacter xyilnum has been studied from the aspects of the resistance of the never-airdried cellulose gels to alkali. The yield of cellulose was determined as the function of time of incubation and the observation of fibrils was carried out by an electron microscope. The never-air-dried cellulose gels from the glucose medium incubation for 5 hours at 28°C consisted of about 30 wt% of microscopic fibrils and about 70 wt% of fibrils without microscopic fibrils. The fraction of microscopic fibrils increased to 80 wt% when incubation was continued for 12 hours. The never-air-dried cellulose gels from the complex medium incubation in exponential bacteria growth stage consisted of about 40 wt% of fibrils without microscopic fibrils and about 60 wt% of microscopic fibrils and these values were independent of the incubation period.
X-ray diffraction and IR results showed that, when the concentration of NaOH was higher than 11 wt%, the resistance of the never-air-dried cellulose gels from glucose and complex medium to alkali was equivalent to that of purified and dried sample. However, when the concentration of NaOH was lower than 11 wt%, the absorbance of the 1430 cm^-1 band in IR spectrum of the alkali-treated sample made from the never-air-dried cellulose gels of the short incubation time was lower than that of the purified and dried sample. X-ray photographs of all the never-air-dried samples treated with 11 wt% NaOH showed the diffraction of Cellulose I but not that of Cellulose II.
It was concluded that the microscopic fibril formed from the initial fibril later had Cellulose I crystal already. It is assumed that the fibrils before transforming into microscopic fibrils have Cellulose I crystals already or the structure which is easily to be converted into Cellulose I crystals.