Effect of dampening on the supramolecular structure of cotton cellulose

Yakunin, N. A.; Zavadskii, A. E.

doi:10.1007/s10692-005-0038-0

Cited by 4 publications

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“…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.…”

Section: And a P Moryganovmentioning

confidence: 99%

“…For this reason, despite the higher error of determination of this parameter, it allows more fully characterizing the change in the accessibility of the crystalline phase with respect to water. Using previously obtained [5] data on the change in quantity (L 002 ) in wetting the investigated sample, a calculated curve (Fig. 1, curve 2) characterizing the change in the content of water-accessible sections as a function of the water vapor activity was plotted.…”

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“…They arise and persist in the polymer only under the effect of internal stresses. In repeated wetting, the structure of the cotton cellulose plasticized with water returns to the equilibrium state during recrystallization [5]. The accessibility of the crystalline phase that arises in drying is correspondingly temporary.…”

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Structural dependence of the features of the sorption behavior of cotton cellulose in reacting with water

2008

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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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Section: And a P Moryganovmentioning

confidence: 99%

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confidence: 99%

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Structural dependence of the features of the sorption behavior of cotton cellulose in reacting with water

2008

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“…The fabric was also used in the form of a set of disks cut with a template. In view of the effect of the moisture content of the cellulose fibres on the diffraction parameters [5,6], the samples were dried at 105°C. The x-ray diffraction analysis was conducted on a DRON-3 diffractometer with the transillumination method with simultaneous rotation of the detector and the sample (θ -2θ scheme), which made it possible to consider the factors that affect absorption and scattering by the samples.…”

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X-ray diffraction method of determining the degree of crystallinity of cellulose materials of different anisotropy

Zavadskii

2004

Fibre Chem

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It is shown that the important change in the x-ray diffraction parameters in preparation of compact products from microcrystalline cellulose and ground cotton fibres by pressing is not due to the amorphous phase of cellulose. A method for determining the degree of crystallinity of cellulose in anisotropic materials using an external standard that ensures spherical scattering symmetry is substantiated. The applicability of the proposed approach for estimating the degree of crystallinity of cellulose fibres directly in fabrics, which reduces the duration of the experimental procedures by 3-4 times, is demonstrated.Pressing is used to increase the compactness and stability of samples for x-ray diffraction analysis of cellulose materials [1][2][3][4]. A drawback of this method is the dependence of the diffraction properties on the type and conditions of formation of the samples (fibre, fabric) due to the features of the texture formed [2,4]. The necessity and possibility of taking this factor into account are valid in solving the problem of determining the polymorphous composition of cotton materials [4]. We will examine the possibility of x-ray diffraction estimation of the degree of crystallinity of cellulose materials of different anisotropy prepared by pressing in different conditions.Bleached cotton fabric and fibres separated from the fabric and ground into 0.2-0.5 mm fragments were investigated. Microcrystalline cellulose (MCC) obtained by hydrolysis of cotton fibres in 2.5 N solution of HCl at 100°C and powdered amylopectin of the same chemical composition as cellulose were also used. Flat samples of constant diameter were prepared by pressing in the 0 to 400 MPa pressure range in a special mold. The fabric was also used in the form of a set of disks cut with a template. In view of the effect of the moisture content of the cellulose fibres on the diffraction parameters [5,6], the samples were dried at 105°C. The x-ray diffraction analysis was conducted on a DRON-3 diffractometer with the transillumination method with simultaneous rotation of the detector and the sample (θ -2θ scheme), which made it possible to consider the factors that affect absorption and scattering by the samples. CuKα radiation separated by balanced Ni and Co filters was used. The samples were placed in a hermetically sealed cell with polyester film windows and placed in a holder that made it possible to average the diffraction intensity by rotating the objects. The background was taken into account by separately scanning an empty cell with the sample placed in front of the detector.The intensity of scattering by the samples I sam (2θ) at diffraction angles 2θ was determined with consideration of the background and use of differential filters based on the equations from [6]. The integral value of scattering by the samples A sam in the given range of angles ∆2θ was found with the equationwhere A exp t(∆2θ) is the experimental integral value of scattering by the sample, pulses; A b (∆2θ) is the integral value of the background, pulse.Ivanov...

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“…The diffraction parameters were calculated taking into account the background and differential filtration of the radiation [10,11]. The diffraction intensities of the studied samples were normalized to the scattering intensity of an external standard and the experimentally determined optical density of the samples in order to adjust the measurements to a single scale [7].…”

Section: X-ray Analysis Of Polypropylene Thread Crystallization Durinmentioning

confidence: 99%

X-Ray Analysis of Polypropylene Thread Crystallization during Spinning

2015

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The need to account for the anisotropy of compact samples pressed from ground polypropylene (PP) fibers was demonstrated during a determination of the degree of polymer crystallinity using x-ray structure analysis. The destruction of the spherical scattering symmetry of x-rays by PP fiber samples was proven to be unrelated to the polymer amorphous phase. A method for calculating the degree of crystallinity of fiber composites from the normalized intensity of the diffuse halo of the studied composites and standard powdered PP samples was proposed. It was found that the degree of spinneret drawing of PP composite threads had practically no effect on the degree of polymer crystallinity whereas the simultaneous effects of temperature and orientation factors during solid-state drawing increased the fiber crystallinity by 1.15-1.17 times with degree of drawing 4.2-5.6, which was one of the reasons for the increased thread strength.Polypropylene composite threads (PCT) are produced by spinning from the melt followed by oriented drawing at elevated temperature. Studies of fine-structure formation of elemental threads at various spinning stages are very important for predicting the properties of finished threads and optimizing the processing schemes.It was established previously that the practically complete conversion of lamellar stacked crystallites into fibrillar crystallites of elongated chains that was observed during oriented drawing of PCT in the range 4.2-5.6 with heating increased significantly the tensile strength of the threads [1]. Furthermore, it was shown the increasing the number of preliminary drawings of PCT, which reduced considerably the possibility of forming a*-oriented stacked lamellae in which the molecular chains were perpendicular to the thread axes, produced much stronger threads [1, 2].These features of fiber crystallization during various stages of PCT spinning should affect the degree of polymer crystallinity and largely determine the physicomechanical properties of the fibrous materials [3,4]. Therefore, the goal of the present work was to study the effects of spinneret drawing and subsequent deformation of PCT on their crystallinity.One of the basic methods for determining the degree of crystallinity of polypropylene (PP) is x-ray diffraction structure analysis (XSA) [5,6]. It is important to note that, as a rule, quantitative determination of this parameter for polymeric materials by XSA requires the use of isotropic samples that provide spherical scattering symmetry [3]. This problem for fibers with texture is usually solved by grinding them to produce powdered samples. However, it was shown using cellulose materials as an example that even the very small forces required to prepare compact samples from ground fibers caused texturing of the samples because the fragments became oriented as the result of clearly pronounced anisotropy [7]. The destruction of the spherical scattering symmetry because of this complicated severely the analysis of the crystallinity of fibrous materials. Therefor...

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Effect of dampening on the supramolecular structure of cotton cellulose

Cited by 4 publications

References 3 publications

Structural dependence of the features of the sorption behavior of cotton cellulose in reacting with water

Structural dependence of the features of the sorption behavior of cotton cellulose in reacting with water

X-ray diffraction method of determining the degree of crystallinity of cellulose materials of different anisotropy

X-Ray Analysis of Polypropylene Thread Crystallization during Spinning

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