Comparative analysis of the characteristics of supramolecular structures of dry and swollen cotton fibers makes it possible to differentiate structural regions accessible to water. The revealed features of water desorption from cotton cellulose (exceptionally low rates at the final stages, presence of residual moisture) are related to the removal of water, which is localized in the regions of the crystalline phase disorganized upon drying. The fact of incomplete moisture removal from cotton fibers at T < 325 K is interpreted from the stand point of the frozen molecular mobility in the microsurroundings of sorption sites, which are located at the defects of crystallites, at the final stage of the desorption process. A marked contribution from the recrystal lization of disorganized regions in the surface layer of crystallites to the thermal effect of the interaction between water and cotton cellulose at low water content is established.

547.458.81X-ray structural analysis showed that both the crystallite content and the degree of perfection of their surface layer increase during dampening of cotton cellulose. The maximum structural ordering of cellulose is attained at a fibre moisture content ≥14.8%. The determining role of the absorption mechanism of dissolution of water in amorphous regions of cellulose is confirmed by a quantitative estimation of the X-ray diffuse scattering parameters for cotton with different moisture contents.In contrast to most natural and chemical fibres, the breaking load of cotton increases significantly in dampening, which is usually attributed to the morphological features of its structure [1]. A hypothesis was also advanced concerning the correlation of this event with the supramolecular structure of cotton fibres [2]. This hypothesis is in agreement with the quantitative x-ray diffraction data on the effect of moisture on the crystalline [3] and amorphous [4] phases of cotton cellulose. For this reason, it is useful to examine the structural transformations in cotton cellulose during sorption of water within the framework of the unique amorphous-crystalline structure of the polymer. Our study analyzed the effect of the moisture content of cotton fibres on the x-ray diffraction parameters of crystallite regions and the amorphous phase of cellulose.We investigated scoured and bleached cotton cloth with a moisture content (ω) of 0 to 19.4%, attained by holding the sample at 20°C in desiccators above solutions of sulfuric acid of different concentration.The x-ray structural analysis was conducted on a DRON-3 diffractometer using CuKα radiation separated by balanced Ni and Co filters. The transillumination scheme with simultaneous rotation of sample and detector was used. The flat sample placed in a hermetically sealed cell was prepared by pressing disks of fabric cut out with a template at a pressure of 400 MPa, which ensured maximum orientation of the fibres in the preparation and stability of its shape [5]. The sample scattering parameters were quantitatively estimated according to [4,6] using the diffractometers computer system. The diffraction characteristics were normalized with the scattering intensity of an external standard and the optical densities of the sample and the cellulose component [3,4].The curves of the normalized x-ray scattering intensity I n s (2θ) for dry and dampened (ω = 19.4%) cotton fibres are shown in Fig. 1 as an example.The integral scattering value in the range of ∆2θ = 18.5-2.65°, corresponding to the intensity distribution for maximum reflection 002, was used in assessing the changes in the crystalline phase of the fibres as a result of dampening (see Fig. 1). The intensity of reflections 002 and 040 caused by the transverse and longitudinal ordering of cellulose I were also analyzed [5]. The values of the halfwidth of these reflections, determined with consideration of the instrumental factor [3], were used to calculate the longitudinal and transverse crystallite size.Separation of dif...

and A. P. MoryganovIt was shown that the increase in the accessibility of cotton cellulose to water in drying is due to perturbations of the long-range order in the surface layer of crystallites. The necessity of quantitatively considering the structural changes in calculations of sorption values was demonstrated. The correlation of some features of the sorption behavior of cellulose materials in processes that include frequently repeated wetting and drying operations with the probable character of formation of accessible sections in the surface layer of the crystalline phase was noted.Studying the cellulose-water system has sustained continuous interest for many years. Information on this is important not only because of its theoretical value, but it also has direct practical significance, since cellulose materials are in close contact with aqueous and water-vapor media, primarily with atmospheric moisture, in all stages of production, processing, and use. Valuable information on the reaction of the components of the system is obtained in analyzing the water-vapor sorption isotherms for cellulosic materials [1]. Calculations of the different sorption characteristics using these isotherms usually assume constancy of the content of sorbing regions in the cellulose during water absorption. Moreover, the effect of a change in the supramolecular structure of different cellulosic materials during wetting has been reliably established with different methods of investigation (x-ray structural analysis, IR spectroscopy, dilatometry) [1][2][3][4]. The important effect of the moisture content on the ratio of amorphous and crystalline phases in cellulose should undoubtedly be reflected in the equilibrium and kinetic characteristics of its reaction with water. In this research, we established the cause of the dependence of these features of the sorption behavior of cotton cellulose which are related to the structural rearrangements that take place when the moisture content changes.The sorption measurements were performed by vacuum gravimetry using a quartz spring. We investigated scoured and bleached cotton fabric; samples of this fabric had previously been used in x-ray diffraction studies [4,5]. This make it possible to use the established parameters of the supramolecular structure in calculations of the sorption characteristics.The reaction of oxidation of cellulose with atmospheric oxygen at 150°C was also used to study the character of the structural changes that take place when cotton cellulose is wet and dried. The degree of thermooxidative degradation of the samples of cotton fabric was evaluated with the yellowness parameter, defined as coordinate b of the color field of the CIE Lab colorimetric system. It was calculated with the spectral reflection curve of thermooxidized samples taken on a reflection spectrophotometer in the 400-700 nm wavelength range.The water-vapor sorption isotherm for the investigated fabric sample at 20°C is shown in Fig. 1. In determining such a sorption value as the average hydration numbe...

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