Morphological studies on precipitated cellulose

Abstract

In connection with the problem of biosynthesis of cellulose, it is of fundamental importance to decide whether the crystal structure and morphological features of the native fibriles are also genetically determined through some kind of matrix mechanism, or are simply the end result of a spontaneous crystallization process.The recently reported observationl) that fibrils showing native structure (unit cell I) and morphology can precipitate spontaneously from dilute solutions of native cellulose seems to favor the latter interpretation. The precipitated cellulose was found to consist of a small proportion of fhrils and a large proportion of morphologically undefined aggregates. These results are the more remarkable in view of the fact that the fibrilar morphology was invariably found t o be associated with the crystal structure of cellulose I while the aggregates possess the structure of cellulose 11.In order to establish a clear-cut experimental evidence as t o whether the structure and morphology of the precipitated fibrils could in any way be a consequence of the structure of the original material, we have now carried out a series of precipitation experiments employing mercerised cellulose (unit cell 11) as starting material.The mercerised cellulose was prepared by treating native cotton fibers (m = 13.000) with a 20% solution of NaOH in water a t O°C under an atmosphere of nitrogen for 2 hrs. Solutions of mercerised cellulose in cuoxam (ammoniacal copper hydroxyd) a t a concentration of 0.Z.10-3 g/ml were prepared by shaking the components under an atmosphere of nitrogen. The precipitation was effected by slow dialysis of the solution against cuoxam solvent progressively diluted with water. Suitable specimens for comparative X-ray and electron-dif fraction investigations were prepared by dispersion of both mercerised and precipitated cellulose in a high speed (48.000 rpm) homogenizer at about -7 O O C .The electron-diffraction experiments were conducted with a Philips EM-ZOO electron microscope. The X-ray powder photographs were taken with a DEBYE-SCHERRER camera employing CuKa radiation (Ni filter).

Influence of substitution of direct dye having biphenylenebis(azo) skeletal structure on nascent cellulose produced byacetobacter xylinum [II]

“…2,3 This result supports the concept of cellulose I microfibrils crystallization without the direct involvement of living cells. 4,5 Using A. xylinum, a bacterium that synthesizes a highly crystalline ribbon of cellulose I, Kai et al 3,6,7 and Haigler and coworkers. 8,9 have demonstrated that fluorescent brightening agents and direct dyes that bind to cellulose in vivo can separate glucan chain polymerization from microfibril crystallization.…”

4. Cellulose

“…4-26). Fibrils with the lattice of cellulose I could be precipitated from cuoxam solution (Macchi, Palma 1969). Fibrils with the lattice of cellulose I could be precipitated from cuoxam solution (Macchi, Palma 1969).…”