RU2570092C2 - Methods of detecting differences in cellulose structural condition - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: samples of cellulose objects are produced in form of flatly-parallel plates or pressed tablets and installed in holder in such a way that in geometry for reflection axes of fibres are parallel to reflection planes, and in geometry for translucence - perpendicular, which makes it possible to determine width and length of elementary fibrilla respectively. To determine degree of crystallinity selected is area of scattering angles, in which maximum, corresponding to scattering of amorphous component, is registered completely, pneumonogram in the area is separated into peaks, corresponding to scattering of amorphous component and refractions from crystallographic planes, which belong to the same range of angles. By integral widths of refractions sizes of crystallites in specified crystallographic directions are determined. To determine periods and angles of elementary cell applied is additional holder, which makes it possible to realise rotation of sample in its plane, diffractogram is registered in the entire interval of scattering angles with minimally possible step by angle, and then analysed, applying structural characteristics if different polymorphous modifications of cellulose.

EFFECT: provision of possibility of complex research of changes in the structure of amorphous-crystalline celluloses, which occur at the atomic, molecular and supramolecular levels with simultaneous reduction of time spent on each research, as well as increased accuracy of determination of elementary cell periods to the fourth sign after comma.

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Description

The invention relates to the field of physics, namely to the study of the ultrafine structure of a substance in its initial state and under the influence of various physicochemical effects using x-ray diffraction, and can be used for appropriate control in the production of modified cellulosic materials and creating the physical foundations of an industrial technology for cellulosic materials with specific properties.

Physico-chemical effects, such as defibration, exposure to high temperatures, oxidizing agents, soda (sulfate or craft) or acid (sulfite, bisulfite) cooking, mercerization, regeneration, bleaching, enzymatic destruction, etc. lead to a change in the atomic, molecular and supramolecular structure of cellulosic materials. To assess the structural state of such a complex multicomponent natural object with various polymorphic modifications, one research technique is not enough and an integrated approach to its study using a combination of sequentially applied techniques is needed.

Cellulose is a two-phase material, the crystalline and amorphous regions of which do not have clear boundaries: the transition from an ordered to an amorphous state occurs gradually. To study the structural state of such objects at all levels (atomic, molecular and supramolecular), it is necessary to determine the following characteristics:

- the value of the relative content of the crystalline part in the material is the degree of crystallinity;

- the value characterizing the supramolecular structure of the crystalline component of cellulose is the size of the coherent scattering regions, called crystallinity regions;

- parameters describing the atomic-molecular structure of crystallinity regions — periods and angles of the unit cell and the nature of the packing of the molecules in the cell.

Separate methods for studying the structural state of materials are known in the literature, which make it possible to determine the degree of crystallinity, crystallite sizes, periods and unit cell angles.

The Ruland-Wonka method [1] is known, according to which the degree of crystallinity is calculated as the ratio of the integrated scattering intensity of the crystalline phase to the sum of the integrated scattering intensities of the crystalline and amorphous phases. To calculate the scattering intensity of the amorphous component, the use of a standard is required.

However, this method allows us to determine only the only characteristic of the structure of materials - the degree of crystallinity - as the ratio of the number of structural fragments in an ordered state and their total number in the material and is unsuitable for determining the complex parameters of the structure of cellulose.

There is a known method for estimating the sizes of coherent scattering regions (a certain characteristic region of a crystal scattering X-rays independently of other similar regions) using the Scherrer formula [2], according to which the CSR size in the direction of the normal to the reflecting planes with indices (hkl) is calculated as the ratio of the product of length x-ray waves and a constant depending on the CSR shape and the product of the physical broadening of β _hkl reflection with indices (hkl) and the cosine of the Bragg angle θ _hkl .

From the experiment, the integral reflection widths (B _hkl ) of the material are calculated, which are equal to the ratio of the area under the maximum (integrated intensity) of the corresponding line of the sample to its height. Corrections for instrumental broadening (b _hkl ), defined as the ratio of the integrated intensity of the corresponding standard line to its height, must be introduced into the integral widths of reflections. The physical broadening β _{hkl of the} reflection with indices (hkl) is calculated either as the difference between the reflection width B _hkl and the instrumental broadening b _hkl , or as the square root of the difference in their squares.

However, this method allows you to determine only the only characteristic of the structure of materials - the sizes of the ordered regions of the crystalline component - and is unsuitable for determining the complex parameters of the structure of cellulose.

The following methods are known for determining and refining unit cell periods.

1. The method of indicating radiographs. If the unit cell is unknown, the Lipson method [3] is used for indication. Next, the periods and the monoclinic angle of the unit cell are calculated using quadratic crystal forms.

However, to determine the periods and the angle of monoclinicity of the unit cell using this method, at least 4 well-resolved intense reflexes are required, which is difficult in the study of cellulosic materials, since the X-ray diffraction patterns of the celluloses are blurred, the reflections overlap and the determination of their indices is often ambiguous.

2. The method of full-profile analysis (Rietveld method) is based on minimizing the difference between the theoretical and experimental profiles of the x-ray [4]. The periods and angles of the unit cell are then specified as profile parameters of the radiograph.

The use of the method of full-profile analysis as applied to cellulosic materials requires the development of a specific refinement strategy and in this form cannot be used to determine the parameters of cellulose.

A known method for determining the residual stresses in products from single-crystal materials by the X-ray method, in which to determine the residual stresses in the selected and perpendicular to the selected directions, such crystallographic planes are used, the reflections from which are in the precision region and whose normal projections onto the surface of the controlled product have a minimum angle of deviation from selected direction. Then, the selected planes are alternately brought into the reflecting position by rotating and tilting the sample, acting on a controlled product in parallel with an X-ray beam, recording reflections from the selected planes, processing reflections to determine the angular positions, determining the true periods of the crystal lattices of each phase, undistorted by residual stresses, and then determine the residual stress [5].

This method allows you to determine only the residual stresses, as well as the true periods of the crystal lattice of single crystals and is not intended to determine the structural characteristics of amorphous-crystalline cellulose materials.

Thus, these known methods do not allow to determine the structural characteristics of cellulosic materials (periods and unit cell angles, crystallinity and crystallite sizes) at all levels - atomic, molecular and supramolecular.

The technical result of the invention is to enable comprehensive studies of changes in the structure of amorphous crystalline celluloses occurring at the atomic, molecular and supramolecular levels, by increasing the number of studied parameters of cellulose, while reducing the time spent on each study, and increasing the accuracy of determining the periods of the unit cell to the fourth decimal place.

The technical result is achieved by the fact that the samples of cellulose objects are made in the form of plane-parallel plates or pressed tablets and installed in the holder in series in two mutually perpendicular directions relative to the incident beam, in the reflection geometry the sample is installed in the holder so that the fiber axes are parallel to the reflecting planes, and the thickness of the elementary fibril is determined, then in geometry the sample is set to the light so that the fiber axes are perpendicular to the reflection length of the elementary fibril, determine the length of the elementary fibril, to determine the degree of crystallinity, choose the region of scattering angles in which the maximum corresponding to the scattering of the amorphous component is completely recorded, then this region is divided into peaks corresponding to the scattering of the amorphous component and reflections from crystallographic planes falling into the same the very range of angles, and by the ratio of the integrated scattering intensities, the degree of crystallinity is established, and by the integrated reflection widths the crystallite sizes are adjusted in the given crystallographic directions, then, to determine the periods and angles of the unit cell, the sample is removed from the holder and mounted on the diffractometer in an additional holder that allows the sample to rotate in its plane, the diffraction pattern is recorded over the entire range of scattering angles with the smallest possible angle step and The obtained diffraction pattern is analyzed using the structural characteristics of various polymorphic modifications of cellulose. The invention is illustrated in Table 6, Figure 4.

A method for detecting differences in the structural state of cellulose includes the following operations:

- the manufacture of samples of cellulose objects in the form of plane-parallel plates or pressed tablets;

- installation of the sample in the holder sequentially in two mutually perpendicular directions relative to the incident beam;

- irradiation of the sample with monochromatic x-ray radiation;

- registration of diffraction patterns in different ranges of diffraction angles in the form of an intensity profile of diffracted x-ray radiation, in a geometry in which the x-ray quantum counter moves at a speed twice that of the sample, which in reflection geometry is mounted in the holder so that the fiber axes are parallel reflecting planes, and determine the thickness of the elementary fibrils, then in geometry the clearance of the sample is set so that the fiber axes are perpendicular to the reflecting planes, determine the length of the elementary fibrils;

- the choice on the obtained x-ray of the region of scattering angles, in which the maximum corresponding to the scattering of the amorphous component is completely recorded, and the division of this region into peaks corresponding to the scattering of the amorphous component and reflections from crystallographic planes falling within the same range of angles;

- an estimate of the degree of crystallinity by the ratio of the integrated intensities of scattering;

- an estimate of the integrated widths of reflections of crystallite sizes in predetermined crystallographic directions;

- removing the sample from the holder;

- installation of an additional holder on the diffractometer, allowing rotation of the sample in its plane;

- installation of the extracted sample in an additional holder;

- registration of the diffraction pattern in the entire range of scattering angles with the minimum possible step in the angle;

- analysis of the obtained diffraction pattern using the structural characteristics of various polymorphic modifications of cellulose.

A method for detecting differences in the structural state of cellulose is carried out using an automated X-ray diffractometer, including an X-ray source, a goniometer with a sample holder, an X-ray detector and a system for recording diffraction spectra with program-oriented complexes for processing and analysis of diffraction patterns.

Samples of fibrous technical cellulose and wood are in the form of plane-parallel plates. For this, powder samples are placed in a cuvette with a weak bond in the form of a solution of glue, for example, BF-2 in alcohol, or pressed in the form of thin plane-parallel plates or tablets.

Samples are placed in the holder, making it possible to register diffraction patterns in transmission geometries (in the light), so that the fiber axes are perpendicular to the reflecting planes, and to the x-ray reflection, so that the fiber axes are parallel to the reflecting planes, with the sample rotating in its plane and without rotation.

A beam of monochromatized x-ray radiation is sent to the sample. Using the X-ray detector, the intensity distribution of the diffracted radiation is recorded as a function of the diffraction angle — the diffraction pattern (x-ray) of the sample — with the intensity recorded in a file at each step (the scanning step of the x-ray diffraction is selected depending on the degree of diffusion). An X-ray diffraction pattern is recorded over the entire range of scattering angles, the value of which is determined by the characteristics of the equipment used.

To determine the degree of crystallinity and CSR sizes, the intensity maxima corresponding to X-ray diffraction on the atomic planes of the crystal lattice and the intensity maximum corresponding to diffuse scattering from the amorphous component are distinguished on the diffractogram. The scattering angles 2θ corresponding to the positions of the maxima, interplanar distances, areas under these maxima (integral intensities) and the integral width of all maxima are calculated. The CSR sizes, determined from the width of the reflections with different indices (hkl), allow us to characterize the shape of the coherent scattering regions (crystallites) of cellulose, in particular, to determine the thickness and length of elementary fibrils.

By the method of full-profile analysis using the entire x-ray, the periods and angles of the unit cell are specified and the model of molecular packing is selected. The main selection criteria are the minimum values of the profile and Bragg factors of uncertainty.

To determine the degree of crystallinity in the claimed method for detecting differences in the structural state of cellulose, the modified Ruland-Wonka method [1] was used, which does not require the use of a standard to calculate the scattering intensity of the amorphous component. The essence of the method is that the position of the amorphous maximum is determined as the position of the minimum between the reflections (110) and (200), then the integral intensities of the amorphous and crystalline components are calculated by varying the position of the peaks, their maximum intensity and width, similar to how this is done in the Rietveld method.

)), 2 - направление короткой диагонали элементарной ячейки ([110]), 3 - направление диагонали прямоугольника, состоящего из двух элементарных ячеек по оси Z ([102]), 4 - направление вдоль периода а элементарной ячейки ([100]) и 5 - направление вдоль периода с элементарной ячейки ([001]).To estimate the size of crystallinity regions in the claimed method for detecting differences in the structural state of cellulose, the Scherrer formula was used [2], and the size of CSR was calculated for several crystallographic directions in order to provide an opportunity to characterize the crystallite shape of cellulosic materials. Figure 1 shows in a unit cell with periods a, b, and c the crystallographic directions along which the CSR sizes were calculated, where X, Y, Z are the coordinate axes along which the unit cell periods are plotted; 1 - direction of the long diagonal of the unit cell (normal to the reflecting plane with indices ( $$\overline{\mathrm{one}}10$$

)), 2 - the direction of the short diagonal of the unit cell ([110]), 3 - the direction of the diagonal of the rectangle, consisting of two unit cells along the Z axis ([102]), 4 - the direction along the period a of the unit cell ([100]) and 5 is a direction along a period from a unit cell ([001]).

The calculation of the periods and the angle of the unit cell, as well as the establishment of a model of the atomic structure in the claimed method for detecting differences in the structural state of cellulose, was carried out using a full-profile analysis (Rietveld method) [4]. The complexity of applying the Rietveld method to the analysis of amorphous-crystalline celluloses is associated with the smearing of their diffraction patterns. Therefore, the following calculation strategy was developed.

When refining the structure of cellulose I, the characteristics of each of the four currently known models of the structure of cellulose obtained for single crystals: Iα, Iβ with parallel up, down, and antiparallel chain orientations were used as initial data [6]. The variant of the structure for which the values of the factors of uncertainty were the smallest was considered the closest to the structure of a real cellulose object, even if visually the quality of coincidence of the theoretical and experimental profiles was the best for any other model with large values of the factors of uncertainty.

After clarification of the scale factor, background polynomial coefficients, characteristics determining the counter zero shift, eccentricity of the sample and absorption of rays in the sample, refinement of the parameters of the peak profile function and unit cell parameters, the U, V, W values describing the reflection width Hm (Hm ² = Utg ² θ + Vtgθ + W [4]), were selected by trial and error. In this case, the reliability criteria, as usual, were the values of the profile and Bragg factors R _p and R _b . Further refinement concerned the texture and asymmetry of the maxima, after which the whole procedure was repeated from the very beginning to achieve a stable result.

During the verification of the proposed method for detecting differences in the structural state of cellulose, it was possible to detect changes in the structural state of cellulose-containing materials depending on their native nature, the method for producing fibrous technical cellulose I and materials obtained on their basis after physicochemical exposure, for example, finely divided cellulose materials.

1. Identification of the dependence of structural characteristics on the native nature of cellulose

Figure 2 shows the x-ray (converted into electronic units) of native cellulose-containing materials of various origin: early (a) and late (b) pine wood (solid line in the geometry for reflection, dotted line in the geometry for light); cotton (dotted line) and brown algae (c); radial cut of pine wood (g) in geometry for reflection (1) and clearance (2).

As can be seen from figure 2, natural cellulose objects of different origin are characterized by significantly different from each other (both in terms of the nature of the distribution of intensity and degree of blur) diffraction patterns. At the same time, the same materials give diffractograms of different degrees of blur, captured in different geometries (Fig. 2, a, b, d). Brown algae and radial cut of pine wood, captured in the geometry for the passage of x-rays, are characterized by diffuse radiographs, i.e. have an amorphous structure.

Table 1 shows the characteristics of the supramolecular structure of the crystalline component of natural cellulose objects: the degree of crystallinity and CSR sizes calculated for five different directions in the unit cell indicated in Fig. 1.

Table 2 shows the characteristics of the atomic-molecular structure of native cellulose-containing materials: periods and unit cell angles, as well as the model of molecular packing: Iβ, antip. - monoclinic cell, antiparallel packing, Iβ down and Iβ up - monoclinic cells with parallel packing, Iα - triclinic single-stranded cell.

Table 1 Crystallinity (k) and crystallite sizes of natural cellulosic materials Sample k,% The crystallite size, D _hkl (Å), in the directions:

][ $$\overline{\mathrm{one}}10$$

] [110] [102] [one hundred] [001] Cotton pulp 64 43 43 43 43 47 Flax pulp 78 43 43 37 43 34 Early pine wood 63 24 49 49 27 92 Late pine wood 36 29th 44 - 29th 46 Radial pine cut on reflection 77 26 43 - 29th 94 Δk = ± 5%, ΔD = 5 ÷ 10Å

table 2 Models of native cellulose, periods and unit cell angles, values of profile and Bragg factors of uncertainty Sample model a, Å b, Å c, Å γ, ° R _p ,% R _b % Cotton pulp Iβ, antip. 7.94 8.16 10.34 96.4 12.60 6.70 Flax pulp Iβ, antip. 7.96 8.17 10.31 96.6 10.9 3.45 Early pine wood Ib down 7.91 8.17 10.34 97.0 10.99 2.83 Late pine wood Iβ, antip. 8.09 8.17 10.34 96.4 10.99 5.04 Radial pine cut on reflection Iα ∗ 6.74 5.93 10.36 81.3 10/18 12.40 ∗ angles: α = 117 °, β = 113 ° Δa = Δb = ± 0.01 Å, Δc = ± 0.01 Å, Δγ = ± 0.2 °

From table 1 it can be seen that the largest SC has a radial cut sample of pine and flax cellulose, the most amorphous in structure is late wood.

], совпадающем с длинной диагональю базисной плоскости элементарной ячейки, и составляют в среднем 4 элементарных ячейки. В направлении [110], совпадающем со второй, более короткой, диагональю, размеры ОКР примерно в 1.5-2 раза выше. Размер ОКР в направлениях [100] и [001] фактически соответствует толщине и длине упорядоченных областей элементарных фибрилл. Как видно, толщина их составляет 3-4 элементарных ячейки, а длина - 5-9 ячеек.Cotton cellulose samples are characterized by almost spherical CSR; the diameter of the spheres is on average 45 Å. Flax cellulose also has the same CSR size in three crystallographic directions. For other materials, crystallites are anisotropic: their sizes are minimal in the direction [ $$\overline{\mathrm{one}}10$$

], which coincides with the long diagonal of the basal plane of the unit cell, and comprise an average of 4 unit cells. In the [110] direction, which coincides with the second, shorter diagonal, the CSR sizes are approximately 1.5–2 times higher. The CSR size in the [100] and [001] directions actually corresponds to the thickness and length of the ordered regions of elementary fibrils. As you can see, their thickness is 3-4 unit cells, and the length is 5-9 cells.

From table 2 it is seen that natural cellulosic materials of various origins have a different type of unit cell and a different nature of the packing of molecules in it (parallel and antiparallel). The most low-symmetric triclinic cell is characteristic of a radial cut of pine wood, the remaining samples are characterized by a monoclinic cell. The largest difference in the values of the unit cell period is observed for period a .

Thus, the inventive method allows to detect changes in the content of the crystalline part, to characterize the shape of the regions of coherent scattering (crystallites), as well as to establish the nature of the packing of molecules and to reveal changes in the atomic structure of crystallites depending on the native nature of the cellulosic material.

2. Identification of the dependence of structural characteristics on the method of producing fibrous technical pulp I

Figure 3 shows the x-ray (converted into electronic units): a) unbleached (1) and bleached (2) sulfate coniferous celluloses; b) bleached sulfate hardwood pulp.

Table 3 presents the characteristics of the supramolecular structure of these technical celluloses: the degree of crystallinity and the size of the CSR, calculated for five different directions in the unit cell.

Table 3 The degree of crystallinity (k) and crystallite sizes of technical pulps Sample k,% The crystallite size, D _hkl (Å), in the directions:

][ $$\overline{\mathrm{one}}10$$

] [110] [102] [one hundred] [001] Unbleached sulfate coniferous 75 29th 44 87 43 49 Coniferous bleached sulphate 76 28 43 - 44 42 Bleached Sulphate Deciduous 79 28 57 57 43 59 Δk = ± 5%, ΔD = 5 ÷ 10 Å

Table 4 shows the characteristics of the atomic-molecular structure of these technical celluloses: periods and unit cell angle, as well as a model of molecular packing.

Table 4 Models of technical celluloses, periods and unit cell angles, values of profile and Bragg factors of uncertainty Sample model a, Å b, Å c, Å γ, Å R _p ,% R _b % Unbleached sulfate coniferous Iα ∗ 6.72 5.97 10.37 81.8 10.00 2.39 Coniferous bleached sulphate Iα ∗ 6.74 5.94 10.36 81.3 10.00 2.50 Bleached Sulphate Deciduous Iβ up 8.04 8.17 10.44 96.5 9.13 4.66 ∗ angles: α = 117 °, β = 113 ° Δa = Δb = ± 0.01 Å, Δc = ± 0.01 Å, Δγ = ± 0.2 °

An analysis of the data given in Table 3 shows that the supramolecular structure of industrial celluloses depends more on the type of wood (coniferous or deciduous) than on bleaching used in the technological process: bleached and unbleached sulfate celluloses differ only in the length of ordered regions of elementary fibrils. Bleached sulfate conifers and deciduous differ in this parameter more noticeably and are characterized, in addition, by different CSR sizes in the [110] direction.

As follows from Table 4, the structures of bleached and unbleached sulfate coniferous celluloses are characterized by a triclinic unit cell and differ mainly in the value of period b and angle γ. The structure of bleached sulfate hardwood pulp is described by a monoclinic cell with parallel packing of molecules.

Thus, the claimed method allows to identify the dependence of the features of the atomic-molecular structure on the method of producing fibrous technical cellulose I.

3. Identification of the dependence of structural characteristics on the method of obtaining fine cellulose materials.

Fine cellulose materials include powdered cellulose (PC) and microcrystalline cellulose (MCC). MCC was obtained by hydrolytic treatment of cellulose in a 10% solution of sulfuric acid at a boiling point of a liquid for 120 minutes. Microcrystalline cellulose obtained in accordance with the method of "classical" hydrolysis was used as a reference sample. PCs were prepared using an anhydrous technology using solutions of Lewis acids: titanium chlorides (TiCl ₄ ) and aluminum (AlCl ₃ ), highly effective catalytic reagents capable of exerting not only destructive, but also modifying effects on cellulose macromolecule. To study the changes occurring in the structure of materials obtained in an unconventional way, we used the integrated approach described in paragraphs 1, 2.

Figure 4 shows the distribution curves of the scattering intensity of bleached sulphate hardwood pulp (1), as well as powder pulps obtained on its basis using different Lewis acids (2): treated with a solution of TiCl ₄ in C ₆ H ₁₄ (a) and treated with a solution of AlCl ₃ in CCl ₄ (b).

Table 5 shows the characteristics of the supramolecular structure of the initial bleached sulfate hardwood pulp, PC and MCC: the degree of crystallinity and CSR sizes calculated for the directions in the unit cell shown in figure 1.

Table 5 The degree of crystallinity (k) and crystallite sizes of powdered cellulose and MCC (sample No. 6) Sample Destruction agent Processing time k,% The crystallite size, D (Å), in pressures:

][ $$\overline{\mathrm{one}}10$$

] [110] [102] [one hundred] [001] Feedstock - 79 28 57 57 43 59 one 1.5% 30 minutes 67 31 76 55 43 60 TiCl ₄ in C ₆ H ₁₄ 2 0.1% 30 minutes 74 36 62 56 43 123 AlCl ₃ to CCl ₄ 3 0.1% 30 min warm up 74 34 57 43 43 72 AlCl ₃ to CCl ₄ four 0.1% 30 minutes 75 38 57 43 43 59 TiCl ₄ to CCl ₄ 5 0.1% 30 min warm up 68 36 74 56 43 80 TiCl ₄ to CCl ₄ 6 10% 120 min 88 26 69 58 49 60 H ₂ SO ₅ Δk = ± 5%, ΔD = 5 ÷ 10, Å

Table 6 shows the characteristics of the atomic-molecular structure of bleached sulfate hardwood pulp, PC and MCC: periods and unit cell angle, as well as a molecular packing model.

As follows from table 5, the degree of crystallinity of the PC and MCC for a number of samples differs from the similar characteristics of the initial bleached sulfate hardwood pulp. The greatest difference (~ by 12%) was noted for two samples: obtained during the processing of cellulose in a solution with the highest concentration of titanium tetrachloride (sample No. 1) and in a solution with a lower concentration of TiCl ₄ , but with additional heating (sample No. 5). The highest degree of crystallinity (88%) is in the MCC sample (sample No. 6), which is 10–20% higher than in the PC samples.

Table 6 Models of powder pulp and MCC (Sample No. 6), periods and unit cell angles, values of profile and Bragg factors of uncertainty Sample Destruction agent Processing time a, Å b, Å s, Å γ, ° R _p ,% R _b % Model Feedstock 8.04 8.17 10.44 96.5 9.13 4.66 Iβ up one 1.5% TiCl ₄ in C ₆ H ₁₄ 30 minutes 8.04 7.62 10.96 96.4 6.98 4.60 antip. 2 0.1% AlCl ₃ in CCl ₄ 30 minutes 7.98 8.03 10.34 96.4 11.60 3.50 antip. 3 0.1% AlCl ₃ in CCl ₄ 30 min warm up 8.04 7.96 10.34 96.4 9.83 4.90 antip. four 0.1% TiCl ₄ in CCl ₄ 30 minutes 7.99 7.91 10.85 96.6 9.03 3.61 Ib down 5 0.1% TiCl ₄ in CCl ₄ 30 min warm up 8.09 8.18 10.61 96.7 10.37 4.64 Iβ up 6 10% H ₂ SO ₅ 120 min 7.97 8.18 10.35 96.4 9.81 4.95 antip. Δa = Δb = Δс = ± 0.01 Å, Δγ = ± 0.2 °

The largest difference in the sizes of crystallinity regions is observed for crystallographic directions [110] and [001]. The latter fact indicates a noticeable spread in the length of the ordered sections of elementary fibrils in finely dispersed samples, depending on the used Lewis acid solution and processing conditions.

An analysis of the data shown in Table 6 shows that the unit cell periods of the initial bleached sulfate cellulose also noticeably change when it is converted into a powder form, either by conventional hydrolysis or using Lewis acid solutions. The observed increase in the period from the unit cell and the decrease in periods a and b during treatment in TiCl ₄ solutions in C ₆ H ₁₄ and CCl ₄ (without heating) indicate that a structural modification occurs, which consists in straightening the cellulose unit (increasing the bond angle between anhydroglucose residues), which can be explained by the formation of complexes of the donor-acceptor type “Lewis acid - cellulose” [7, 8, 9].

Subsequent heating of the samples leads to the fact that the periods tend to return to their original values due to the removal of distortions, but this process does not occur to the end. When processing cellulose AlCl ₃ solution in CCl ₄ as a result of warm-up period and only returns to its original value. When exposed to this solution, as well as a solution of TiCl ₄ in hexane, a phase transition occurs from a structure with a parallel to a structure with antiparallel orientation of the chains.

Thus, the inventive method for detecting differences in the structural state of cellulose allows you to identify changes that occur at the atomic-molecular and supramolecular levels, depending on the method of producing finely divided cellulose materials both by traditional hydrolysis and using anhydrous technologies.

The inventive method for detecting differences in the structural state of cellulose was tested using an automated X-ray diffractometer DRON-6, manufactured by NPP Burevestnik, St. Petersburg. The instrument uses Bragg-Brentano focusing, BSV-27 tubes with Cu-Kα (0.154178 nm) and Fe-Kα (0.193728 nm) anodes, the minimum scanning step of the device is 0.002 °, voltage U = 40 kV, are used as X-ray sources. current I = 25 mA, pulse count error 0.4%. Data collection and processing of measurement results is carried out under the control of a PC with OS Windows XP.

The proposed method for detecting differences in the structural state of cellulose, in contrast to the known methods for determining the structure of materials, allows us to trace changes in the complex at all levels of the structural state of cellulose, including determining the type of molecular packing and characterizing the shape of crystallinity regions.

Information sources

1. Thygesen A., Oddershede J., Lilholt H., Thomsen A.V., Ståhl K. On the determination of crystallinity and cellulose content in plant fibers // Cellulose. 2005. No. 12. S.563-576.

2. Speakman S.A. Estimating Crystallite Size Using XRD // MITCenter for Materials Science and Engineering. 2005. P. 105.

3. Lipson G., Steeple G. Interpretation of powder x-ray. M.: Mir, 1972. P.152.

4. Young R.A. The Rietveld method. Oxford University Press, 2002. 308 p.

5. Patent RU No. 2427826 C1. A method for determining residual stresses in products from single-crystal materials by the X-ray method. Date of commencement of the term of validity of the patent: 05/11/2010.

6. Aleshina L.A., Melekh H.V., Fofanov A.D. Study of the structure of celluloses and lignins of various origin // Chemistry of plant raw materials. 2005. No3. S.31-59.

7. Frolova S.V. The structure and physicochemical properties of cellulose degraded by Lewis acids. Diss. ... cand. Chem. sciences. Ivanovo: IHR RAS, 2009.150 s.

8. Frolova S.V., Demin V.A. The destruction of cellulose by Lewis acids in order to obtain cellulose powders // Journal of Applied Chemistry. 2008.V. 81. Issue 1. No. 1. S.152-156.

9. Frolova S.V., Demin V.A. The structure and properties of cellulose powder materials obtained in anhydrous organic media // Mater. III Vseros. scientific conf. Prince 3. Barnaul, 2007. With 247.

Claims (1)

A method for detecting differences in the structural state of cellulose, including installing a sample in a holder, irradiating a sample with monochromatic x-ray radiation, recording diffractograms in different ranges of diffraction angles in the form of an intensity profile of diffracted x-ray radiation, in a geometry in which the x-ray quantum counter moves at a speed twice that than a sample, characterized in that the samples of cellulose objects are made in the form of plane-parallel plates or pressed x tablets and are installed in the holder sequentially in two mutually perpendicular directions relative to the incident beam, in the geometry of reflection, the sample is mounted in the holder so that the fiber axes are parallel to the reflecting planes, and the thickness of the elementary fibril is determined, then in the geometry of the light the sample is set so that the fiber axes were perpendicular to the reflecting planes, and the length of the elementary fibril was determined; to determine the degree of crystallinity, the region of scattering angles was chosen, in which the maximum corresponding to the scattering of the amorphous component is completely recorded, then this region is divided into peaks corresponding to the scattering of the amorphous component and reflections from crystallographic planes falling in the same range of angles, and the degree of crystallinity is established by the ratio of the integral scattering intensities, and by the integrated reflection widths set the size of crystallites in the given crystallographic directions, then to determine the periods and angles of the unit cell brazets removed from the holder and mounted on the diffractometer in a further holder to allow for the rotation of the specimen in its plane diffractogram recorded in the entire range of scattering angles with the smallest possible pitch angle and of the resulting diffraction pattern was analyzed using the structural characteristics of the different polymorphic modifications of cellulose.

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