A Study of the Amorphous Portion of Dry, Swollen Cellulose by an Improved Thallous Ethylate Method1,2

Hydration and Sorption Properties of Raw and Milled Flax Fibers

The physicochemical and hydration properties of mechanically modified flax fibers (FFs) were investigated herein. Raw flax fibers (FF-R) were ball-milled and sieved through mesh with various aperture sizes (420, 210, and 125 μm) to achieve modified samples, denoted as FF-420, FF-210, and FF-125, respectively. The physicochemical and hydration properties of FF-R with variable particle sizes were characterized using several complementary techniques: microscopy (SEM), spectroscopy (FT-IR, XRD, and XPS), thermoanalytical methods (DSC and TGA), adsorption isotherms using gas/dye probes, and solvent swelling studies in liquid H₂O. The hydration of FF biomass is governed by the micropore structure and availability of active surface sites, as revealed by the adsorption isotherm results and the TGA/DSC profiles of the hydrated samples. Gravimetric water swelling, water retention values, and vapor adsorption results provide further support that particle size reduction of FF-R upon milling parallels the changes in surface chemical and physicochemical properties relevant to adsorption/hydration in the modified FF materials. This study outlines a facile strategy for the valorization and tuning of the physicochemical properties of agricultural FF biomass via mechanical treatment for diverse applications in biomedicine, energy recovery, food, and biosorbents for environmental remediation.

HYDROGEN EXCHANGE BETWEEN CELLULOSE AND WATER: I. MEASUREMENT OF ACCESSIBILITY

Estimates of the extent of the hydrogen exchange reaction between cellulose and water vapor determined by an improved method using tritiated water and by the use of heavy water were usually in good agreement. With certain samples, surface roughness had a small effect upon the measurement of tritium radioactivity in cellulose.The accessibility or limiting extent of the exchange increased slightly with relative humidity in the range 20 to 100% and was attributed to the reduction of crystalline order reported recently in similar experiments.In contrast to cellulose whose accessibility corresponds approximately to the amorphous fraction, a partially crystalline amylose was 100% accessible while an amorphous xylan was 52% accessible, indicating that in these substances the accessibility and the fraction of amorphous material are not identical.

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

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 accompanied by lower water sorption and smaller heats of wetting. This anomaly is due to the fact that cellulose samples 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.