Full width at half maximum (FWHM) of diffraction peaks of native cellulose is larger than 1°. The diffraction peaks of the crystalline phase largely coincide with those of the amorphous phase of cellulose, leading to the low resolution. 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. 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. 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. Then, three evaluation indexes (Rwp, FWHM, and RSD) are used to evaluate the rationality of crystallinity calculation results. Moreover, the reproducibility and precision of the crystallinity of three kinds of natural cellulose are tested under the optimized conditions. 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.

天然纤维素衍射峰的半峰全宽(FWHM)大于1°。纤维素结晶相的衍射峰与非晶相的衍射峰大部分重合，导致分辨率较低。因此，在通过峰拟合计算天然纤维素的结晶度时，仅依靠Rwp（R-weighted Pattern）单一评价因子可能会导致计算结果的随机性很大。由于天然纤维素特殊的晶体结构以及峰分离法测定结晶度的特点，采用XRD Rietveld拟合法测定天然纤维素的结晶度。通过限制拟合函数的收敛条件，首先讨论了峰形函数、扫描范围、非晶峰位置等对结晶度测定的影响，有助于减少XRD求解纤维素结晶度的随机性，提高测定的精度。计算。然后，利用三个评价指标（Rwp、FWHM和RSD）来评价结晶度计算结果的合理性。此外，在优化条件下测试了三种天然纤维素结晶度的重现性和精密度。同时采用优化拟合方法计算出纤维素I和II的含量，可用于指导原纤维素纺丝过程中碱浓度和碱处理时间的选择。