In Situ crystallization of bacterial cellulose I. Influences of polymeric additives, stirring and temperature on the formation celluloses I ? and I ? as revealed by cross polarization/magic angle spinning (CP/MAS)13C NMR spectroscopy

Abstract

To obtain further information about the formation of cellulose Iα and Iβ, cross polarization/magic angle spinning (CP/MAS)13C NMR spectroscopy was used to study the effects of polymeric additives, stirring and culture temperature on the Iα When xyloglucan (XG) or carboxymethyl cellulose sodium salt (CMC) was added to the incubation medium, the amount of cellulose Iα decreased markedly, from a normal level of 64% to as low as 30%, with the most additive giving the lowest levels of Iα. Moreover, stirring causes mixtures containing even small amounts of XG to have a large effect. These results suggest that CMC or XG interferes with the aggregation of fibrillar units into the normal ribbon assemblies. It may be that there is a strain associated with this aggregation that results in the higher-energy Iα form. Thus, cellulose Iβ may grow preferentially when the strain caused by aggregation is not present. Lower temperatures (36–10 °C) gave an increase in Iα (from 56 to 72%).