On the phase structure of cellulose
Authors: Mikhailov N. V. 
Published: April 2003

Earlier in our work with Kargin we expressed for the first time the assumption concerning the amorphous structure of cellulose. This assumption was proved in the case of partially oriented fibers and films of hydrated cellulose on the basis of structural mechanical data. A perfect reversibility of the orientation of these fibers was clear from these data as well as a far‐reaching analogy between the x‐ray diagram of isotropic cellulose and similar diffraction diagrams of amorphous rubber and low molecular weight liquids. At present this conclusion is recognized by many research workers and there are no serious objections to it. It was, however, not clear whether it is possible to apply this statement to “perfectly oriented” hydrated cellulose. There had already been obtained textures with a similar or even higher degree of orientation than with native ramie cellulose. The influence of the orientation on the crystallinity of the fibers of hydrated cellulose in the entire range of extension up to 200% was therefore studied. The x‐ray investigation of these fibers according to the criteria of Katz showed that the structure of fibers of hydrated cellulose similar to ramie cellulose as determined from the Debye diagram did not differ significantly from the Debye diagrams of the initially isotropic fibers. From this it necessarily follows that during the orientation of the fibers new elements of symmetry do not arise in their structure. Further x‐ray research was directed to studying the differences of the phase structure of hydrated cellulose and its structural modification prepared according to the method of Meyer and Badenhützen by heating completely oriented fibers of hydrated cellulose in a polar liquid. At the same time it was found that the transition of hydrated cellulose to its modification, native cellulose is thermodynamically reversible and that it can be repeated many times. The direct transition of native cellulose to hydrated cellulose occurs spontaneously and is connected only with a decrease of the force acting between the molecules as a result of swelling. The reverse transition, however, requires an increase of the value of kT. This is required only by the differing flexibility of the chains of these modifications of cellulose caused by their differing configuration and not at all by a change of the phase structure of the cellulose.

Since the structural criterion is not adequate for the definitive derivation of the phase structure of cellulose, we determined the integral heat of solution of cellulose fibers of differing structure and molecular weight in an aqueous solution of the quaternary ammonium base (C2H5)3NC6H5OH in an adiabatic calorimeter with sufficiently high precision. The results obtained show that the heat content of hydrated cellulose does not change over a wide range of orientation of the fibers and that it does not depend on the molecular weight of cellulose nor on the history of the fiber. The absolute values of the corresponding quantities for native cellulose differ only slightly. They change continuously and without breaks on transforming native cellulose to hydrated cellulose by often repeated xanthogenation and regeneration under the action of mineral acids, without damaging the fiber structure. At the same time this rules out phase differences in the structure of both modifications, hydrated cellulose and native cellulose.