Structural features and properties of BC em meio agitado

Structural features and properties of BC em meio agitado

(Parte 3 de 3)

Viscosity (Pa

. s)

FIGURE 6. Apparent viscosity of suspension containing disintegrated bacterial cellulose. s, Agitated culture; d, static culture.

196 WATANABE ET AL.

suspension. Higher WHC of disintegrated Ag-BC may relate to higher suspension viscosity (Fig. 6).

It is also thought that WHC and suspension viscosity relate not only to the size but also to the morphology of the individual particles in disintegrated Ag-BC or St-BC. However, as shown in Fig. 9, it is dif®cult to analyse quantitatively the morphology of each ®bril. Further investigation will be necessary to clarify the morphology of the disintegrated product. The disintegration conditon in this study did not affect DP, crystallinity, or content of cellulose Iá (data not shown). Therefore, the above results suggest that the inherent disordered structure of Ag-BC, such as lower DP, lower crystallinity, smaller size of crystallites and lower content of cellulose Iá leads to smaller particles of Ag-BC than those of St-BC after disintegration, although the location of the disordered region on the cellulose ®bril is not clari®ed.

Table 2 also presents the ®ller retention aid function and emulsion stability index. As reported previously, the disintegrated Ag-BC has higher retention aid function in the papermaking process (Hioki et al., 1995) and higher emulsion stabilizing effect (Ougiya et al., 1997). The value of the retention aid function is de®ned as the amount of calcium carbonate ®ller particles ®xed in a paper by bacterial cellulose. The more dispersed and smaller particles of disintegrated Ag-BC were more ef®cient than those of St-BC in retaining ®ller granules because the particles of disintegrated Ag-BC have a wider accissible surface area during the ®ltration process in papermaking (Hioki et al., 1995). In the case of an emulsion stabilizer, the more dispersed and smaller particles of disintegrated Ag-BC seemed to cover the wider surface area of oil droplets and, as a

Disintegration time (min)

Particle size ( µ m)

FIGURE 7. Particle size of disintegrated bacterial cellulose as a function of the disintegration time. s, Agitated culture; d, static culture.

STRUCTURE AND PROPERTIES OF BACTERIAL CELLULOSE 197

result, the emulsion containing disintegrated Ag-BC may become stable (Ougiya et al., 1997).

Thus, it is expected that Ag-BC exhibits more suitable properties with regard to various industrial applications in the wet state and in the disintegrated form than St-BC. The knowledge obtained by our investigation will become useful for the structural design of bacterial cellulose in future. In addition, the agitated culture in the production system has an advantage for supplying a large amount of bacterial cellulose which is required for developing practical applications as a commodity material.

FIGURE 8. Polarized optical micrographs of bacterial cellulose after the 10 min disintegration. (a) Agitated culture; (b) static culture. Scale bar 0:4m m

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The authors are most grateful to Professor Fumitaka Horii of the Institute for Chemical Research, Kyoto University, for performing the NMR analysis, for valuable advice and for critical reading of the manuscript. The authors are also indebted to Professor Takeshi Okano of Faculty of Agriculture, the University of Tokyo, and the Professor Junji

FIGURE 9. Scanning electron micrographs of bacterial cellulose after the 10 min disintegration. Scale bar 500 ìm (a1, b1), 10 ìm (a2, b2) 5 ìm (a3, b3). a1, a2, a3, Agitated culture; b1, b2, b3, static culture.

STRUCTURE AND PROPERTIES OF BACTERIAL CELLULOSE 199

Sugiyama of the Wood Research Institute, Kyoto University, for performing X-ray analysis and for fruitful discussion in our study. The authors also thank Mr Tahara for measuring CMCase activity. Thanks are also due to Mr Hiroshi Toyosaki, Mr Takaaki Naritomi and Mr Akira Shibata in Bio-bolymer Research Co. Ltd. for perparing cellulose samples and for technical assistance.

Ben-Bassat, A., Burner, R., Shoemaker, S., Aloni, Y., Wong, H., Johnson, D. C. and Neogi, A. (1986)

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Horii, F., Hirai, A. and Kitamaru, R. (1982) Polym. Bull. 8, 163±170. Kouda, T., Yano, H. and Yoshinaga, F. (1997) J. Ferment. Bioeng. 83, 371±376. Kuga, S., Muton, N., Usuda, M. and Brown, Jr., R. M. (1989) In Cellulose: Structural and Functional

Okiyama, A., Motoki, M. and Yamanaka, S. (1992) Food Hydrocoll. 6, 479±487. Ougiya, H., Watanabe, K., Morinaga, Y. and Yoshinaga, F. (1997) Biosci. Biotech. Biochem. 62, 1541±1545.

Toyosaki, H., Naritomi, T., Seto, A., Matsuoka, M., Tsuchida, T. and Yoshinaga, F. (1995) Biosci.

T. (1994) Proceedings of '94 Cellulose R&D, 1st Annual Meeting of the Cellulose Society of Japan (Cellulose Society of Japan, ed.) Tokyo, p. 45±50.

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