![]() Rietveld peak fitting XRD cellulose crystallinity rationality reproducibility. At the same time, the optimized fitting method is adopted to calculate the content of cellulose I and II, which can be used to guide the selection of alkali concentration and alkali treatment time in the spinning process of native cellulose. Moreover, the reproducibility and precision of the crystallinity of three kinds of natural cellulose are tested under the optimized conditions. Then, three evaluation indexes (Rwp, FWHM, and RSD) are used to evaluate the rationality of crystallinity calculation results. Through limiting the convergence conditions of fitting functions, we firstly discuss the effects of peak shape functions, scanning range, and the positions of amorphous peaks on crystallinity determination, which helps to reduce the randomness of XRD in solving crystallinity of cellulose and improve the precision of calculation. Due to the special crystal structure of natural cellulose and the characteristics of crystallinity determination by peak separation method, the XRD Rietveld fitting method is adopted to determine the crystallinity of native cellulose. Therefore, when calculating the crystallinity of natural cellulose by fitting the peaks, only relying on the single evaluation factor of Rwp (R-weighted Pattern) may lead to great randomicity of calculation results. Four digital X-ray diffraction pattern simulations for four independent determinations of ammonia cellulose, each pattern is clearly distinguishable from the others. The diffraction peaks of the crystalline phase largely coincide with those of the amorphous phase of cellulose, leading to the low resolution. 6 (111), 55-60 (2010).Full width at half maximum (FWHM) of diffraction peaks of native cellulose is larger than 1°. Solov’mev, Computational Chemistry, SOLON-Press, Moscow, 2005, 536 pp.Ĭ. Stan Tsai, An Introduction to Computational Biochemistry, Wiley-Liss, New York, 2002, 368 pp. Orenburgskii Univ., Orenburg, 2004, 150 pp.Ĭ. Kobzev, Application of Non-empirical and Semi-empirical Methods in Quantum-Chemical Calculations: Student Aide, Gos. Warren, X-ray Diffraction, Addison-Wesley Publ. Melekh, “X-ray Structural Studies of Celluloses and Lignins of Various Origins,” Candidate Dissertation, PetrGU, Petrozavodsk, 2008, 166 pp.ī. A cluster consisted of 16 cellulose chains ~52 Å in length. The distribution of atoms in the short-range ordered region was modeled using molecular dynamics and corresponded to a disordered cellulose II cluster with dimensions along the crystallographic axes of 2a, 2b, and 5c (15, 16, and 52 Å). Differences in the coordination numbers were due to structural differences in the short-range order. The calculated coordination-sphere radii for lyophilized hydrogels corresponded to analogous data for cellulose II. Super-swelled and lyophilized hydrogels from the cellulose solutions gave diffuse diffraction patterns characteristic of amorphous materials. It was found that flax cellulose was characterized by a higher degree of crystallinity and larger transverse cross section and monofilament length than deciduous cellulose. Three-dimensional models of atomic positions in the short-range order of amorphous hydrogels were constructed. Structural characteristics were calculated. Cellulose powders from flax fiber and deciduous wood and hydrogels regenerated from DMA/LiCl solutions of them were studied using x-ray diffraction. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |