Powder diffraction has been a convenient and widely used way to study cellulosic materials since the late 1950s. The diffraction pattern reveals information on numerous traits of cellulose samples, including purity and history as indicated by one of at least five different crystal forms. It is important in many projects because it demonstrates that the starting material is what is described. For instance, workers may believe that they have a pure cotton fabric that they received from a textile mill, but the X-ray diffraction pattern might reveal a polyester component, or some sharp peaks can indicate the presence of calcium oxalate. Perhaps the biggest question is “how crystalline is my sample”, broken down into how much crystalline material is present vs. the amount of non-crystalline material. The widely used Segal method and the “peak deconvolution” method have disqualifying problems, leaving the Rietveld method as the only hope for a quantitative answer. Nanocellulose from wood in an ISO method development study and some similar samples from cotton gin motes were compared along with a microcrystalline cellulose sample created from cotton fiber were studied using similar procedures and the MAUD Rietveld software. Factors considered included variation in unit cell dimensions, preferred orientation, crystallite dimensions, and environmental background. In most cases, the analyses could be considered as over-fitted, as the number of observations per variable parameter is less than one. At the current state of the art, it may be that the effective crystallite widths can be determined.

Rietveld XRD studies of nanocellulose crystallinity

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