In situ crystallization of bacterial cellulose .2. Influences of different polymeric additives on the formation of celluloses I-alpha and I-beta at the early stage of incubation

Effects of polymeric additives with different degrees of polymerization (DP) or substitution (DS) on the crystallization of celluloses I-alpha and I-beta have been examined at an early stage of the incubation of Acetobactor xylinum by using newly developed FT-IR spectroscopy. It was found that the mass fraction of cellulose I-alpha is greatly decreased with increasing concentrations of carboxymethyl cellulose sodium salt (CMC) or xyloglucan (XG) in the incubation medium. Such a decrease in the mass fraction of cellulose I-alpha, which corresponds to the enhanced crystallization of cellulose I-beta, is more prominent for CMC or XG with lower DPs, but the additives with too low DPs are not so effective probably due to higher solubility and the lower adhesion on the surface of microfibrils. Moreover, the mass fractions of celluloses I-alpha and I-beta are highly correlated with the crystallite size of microfibrils, indicating that I-alpha is crystallized in larger-size microfibrils while I-beta is produced in smaller-size microfibrils. On the basis of these experimental results, the mechanism of the crystallization of celluloses I-alpha and I-beta is discussed in the Acetobactor xylinum system.