Recrystallization of amorphous cellulose

Abstract

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

In vitro synthesis of cellulose II from a cytoplasmic membrane fraction of Acetobacter xylinum

“…Noncrystalline cellulose in an aqueous solvent can crystallize into cellulose II during removal of water; therefore, it is important to establish that the cellulose II pattern observed is not a consequence of drying (22). Water-washed never-dried as well as organicsolvent-exchanged in vitro product also gave a cellulose II pattern.…”

“…USA 84 (1987) 6987 washed with water three times, and packed without drying directly into a glass capillary tube. (B) Never-dried in vitro product was subjected to organic solvent exchange by washing three times with methanol followed by three washes with n-pentane (22). The organic solvent-exchanged in vitro product suspended in n-pentane was then dried over P205 in a vacuum desiccator.…”

Prospects for Maintaining Strength of Paper and Paperboard Products While Using Less Forest Resources: A Review

“…It is likely that the opportunities for formation of crystallites in the zone of adhesion between adjacent fibers is limited by the presence of materials other than pure cellulose at the surfaces of the adjacent fibers, and also the stringent requirements for alignment in order for adjacent crystallites to "heal together," forming a single unit (Wool 2008). Much more extensive formation of crystallites might be possible if a fully amorphous cellulose, which has to be carefully prepared in the laboratory, were placed in water (Wadehra and Manley 1965). Work by Kontturi et al (2011) showed, however, that certain amorphous cellulose materials can resist conversion to a crystalline form even when they are exposed to water.…”

Deuterium and Cellulose: A Comprehensive Review

“…The amorphous films revealed an interesting behavior in that they did not undergo H/D exchange to a full extent. Although Wadehra [39] and Jeffries [40] had already reported that the materials could probably recrystallize upon D 2 O vapor exposure, Kondo and colleagues argued differently. One of their arguments was that, upon recrystallization, the H/D exchange rate changed significantly, as well as the absorption band of the νOH vibrations.…”