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

Abstract

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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