SynopsisRecrystallization of amorphous cellulose prepared by saponification of cellulose triacetate in an non-aqueous medium was found to occur only at very high relative humidities, i.e., near 100%. At lower relative humidities the amount of recrystallization occurring was slight though significant. Correspondingly, the accessibility decreased from 90% (for amorphous cellulose) to a minimum of 79%, the same as that for cellulose 11. The mechanism of recrystallization is discussed in terms of the surface tension, plasticizing action, and the hydrogen bonding ability of the solvent used for bringing about the recrystallieation.It is well known that cellulose can be obtained in an amorphous form by grinding in a vibratory ball mi1l1P2 or by saponification of cellulose acetate in a nonaqueous m e d i~m .~ On immersion in water this amorphous cellulose crystallizes to cellulose II.4 However, little attention has been paid to the details of the crystallization process.The present note describes an attempt to study more elaborately the recrystallization of cellulose by the use of the hydrogen exchange reaction between cellulose hydroxyl hydrogens and water and by x-ray diffraction.The amorphous cellulose used was obtained by treating cellulose triacetate sheets with 1% sodium methylate dissolved in anhydrous methanol. The saponification was allowed to proceed for about 12 hr. The regenerated cellulose thus obtained was neutralized with glacial acetic acid and washed with various alcohols until free of acetic acid. As a control, one sample was also washed in H20. Subsequently the samples were dried in a vacuum desiccator. The following alcohols were used : anhydrous methanol, ethanol, propanol, n-butanol, and isobutanol.In another series of experiments, amorphous cellulose was exposed to water vapor at different relative humidities obtained through the use of various saturated salt solution^.^ The accessibility of all samples was measured by the tritium exchange Kinetic studies of the recrystallization of amorphous cellulose were carried out by an x-ray diffraction method by using a Geiger counter diffractometer. The rate of development of the 107 and 002 peaks was observed at various relative humidities. 2627

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The accessibility of hydrocelluloses and oligosaccharides was measured by hydrogen exchange methods. It is shown that %he accessibility of various celluloses remains constant during prolonged heterogeneous hydrolysis. This is a t variance with the fringed micellar concept of the fine structure of cellulose, on the basis of which a substantial decrease in accessibility would be expected during hydrolysis.Accessibility measurements on amorphous and crystalline oligosaccharides suggest that the accessibility may be related to the perfection of the crystal lattice and does not measure the crystalline-amorphous ratio as previously supposed, Finally, the results are discussed in relation to a recent theory of the fine structure of cellulose. ZUSAMMENFASSUNG:Die Zuganglichkeit (accessibility) von Hydratcellulosen und Oligosacchariden fiir die Wasserstoffaustauschreaktion wurde gemessen. Es zeigte sich, daB die Zuganglichkeit der verschiedenen Celluloscarten wahrend der heterogenen Hydrolyse konstant bleibt. Dieses Ergebnis ist mit dem Strukturmodell der Fransenmizellen, das eine Abnahme der Zuginglichkeit wahrend der Hydrolyse verlangt, nicht zu erkliiren.Die Messungen an amorphen und kristallinen Oligosacchariden lassen vielmehr vermuten, daB die Zuganglichkeit von der Gute des Kristallgitters abhangt; sie ist kein MaO fur das Verhaltnis von kristalliner zu amorpher Phase, wie bisher angenommen wurde.Diese Resultate werden in Zusammenhang mit einer neuen Theorie iiber die Feinstruktur der Cellulose diskutiert.

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