The Reactivity of Cellulose: II.WATER Sorption, Heats of Wetting, and the Reactions With Thallous Ethylate in Ether, Nitration Mixtures, and Heavy Water of Cotton Linters Alternately Wetted With Water and Dried

Abstract

Cotton linters dewaxed with benzene and alcohol possess a slightly expanded structure attributed to the swelling effect of the alcohol. Storage causes a partial collapse of the linters especially so when moisture is present. Wetting with water followed by rigorous drying produces a marked reduction in accessibility, but with each additional wetting-drying cycle accessibility of the dried linters increases slightly as measured by reaction with thallous ethylate in ether, a nitration mixture, and in hydrogen-deuterium exchange. Differences in nitration found for limited reaction times are obliterated when these reaction times are extended. Increasing accessibility due to repeated wetting and drying is accon~panied by lower water sorption and smaller heats of wetting. This anomaly is due to the fact that cellulose sanlples obtained by alternately wetting and drying dewaxed linters, when stored with a desiccant, compete for the limited amount of water present and adsorb moisture in proportion to their accessibility. Upon further exposure to water the sample of least accessibility, having adsorbed less water, can now adsorb to a greater extent than do the linters of somewhat greater accessibility.The evidence indicates that the difference in accessibility occasioned by repeated wetting and drying is of a physical rather than chemical nature. INTRODUCTIONThe accessibility of cellulose to reagents is a matter of colisiderable practical and theoretical importance and in recent years has been given a great deal of attention (6,12,16,19,21,28). I t has been shown quite conclusively that this accessibility is influenced by the previous history of the cellulose sufficiently that uniform reactivity is obtained only by the observation of great care in the choice and processing of the raw material (14, 25).The association of cellulose with water throughout most of its history has provoked enquiries regarding the influence that water has upon the properties of cellulose. I t is generally believed that water itself exercises only a swelling effect, producing nothing more than an increase in the amount of accessible cellulose a t the expense of that portion less highly organized. However, recent work indicates that a slight change in dimensions of the unit cell occurs when dry mercerized ramie, spun viscose, or regenerated acetate fibers are wetted (15). Furthermore, lengthy exposure of wet cellulose t o oxygen (air) or ozone is reported to produce some degradation of the macromolecule (3,4). The removal of water from cellulose by direct drying methods is accompanied by a decrease 1 n/Ia?~uscript

The Reactivity of Cellulose: Iii. The Nitration of Cotton Linters Alternately Wetted With Water at Various Temperatures and Dried, and the Probable Distribution of the Nitrate Groups

“…The decreased nitratability occasioned by one wetting a t 0' or 25" (e.g. from 10.36% N to 10.20% N or 10.29% N) has been observed before (4,5) and ascribed to a general collapse of the accessible cellulose from the partly swollen state which might have been attained during the clewaxing process. However, a similar single wetting-drying treatment a t the higher temperatures (50"-100") either maintains the same state or produces more reactive linters as in the case of the 75" series (an increase from 10.36% N to 10.63% N ) .…”

“…The water was then separated from the linters by mild suction and the moist fibers spread out t o dry in air. This preliminary drying was followed by one of greater intensity with phosphorus pentoxide as previously described (5). A sample (1.5-2 g) was retained while the bulk of the linters was again wetted and dried.…”

“…Analysis for nitrogen by the Du Poilt semimicroilitrometer (8) followed the procedure adopted previously (5).…”

“…But, since the reverse was found true (5), small differences in the "bound water" content do not cause the regular variation in nitratability observed. The second factor, that of diffusion of the reagent to the reaction site, probably involving reaction with more resistant ['hydrogen bonded" hydroxyls, appears to be important, since it has been shown that extension of the reaction time of nitration from 30 to 90 minutes obliterated the differences observed (5).…”

“…Highly swollen cotton linters nitrate to a significantly greater extent than do the same linters "collapsed" by drying from a water-soaked state (3). Furthermore, repeated experiments have shown that dewaxed cotton linters, alternately wetted with water a t 25" and dried, exhibit a small increase in accessibility t o thallous ethylate in ether, to a nitration mixture of sulphuric acid, nitric acid, and water, and to deuterium exchange with heavy water (4,5). Thus the extent of reaction and doubtless the distribution of the reacted hydroxyl groups are determined to some extent by the treatment the cellulose has received prior to reaction.…”