This leads to changes in macro, micro, and supramolecular assemblies and consequently to alterations in physical properties. Oxidation of polysaccharides originating from forests often features oxidation of structures rather than liberated molecules. Periodate-oxidized materials can be subjected to thermal transitions that differ from the native cellulose. Fibers, fibrils, crystals, and molecules originating from forests that have been subjected to periodate oxidation can be crosslinked with other entities via the generated aldehyde functionality, that can also be oxidized or reduced to carboxyl or alcohol functionality or used as a starting point for further modification. This review summarizes the research on this topic. read more read lessĪbstract: Periodate oxidation of polysaccharides has transitioned from structural analysis into a modification method for engineered materials. Experimental patterns from cellulose are never ideal, so Rietveld analyses can compensate for the varied unit cell dimensions, inevitable preferred orientation, A. (2002) to calculate a diffraction pattern for an ideal crystalline powder. The Rietveld method uses the x-, y-, and zcoordinates of the atoms in the crystal structure unit cell such as from Nishiyama et al. It also disqualifies a fourth method, ‘‘amorphous subtraction’’ (Thygesen et al. The interpretation that the intensity between peaks results from peak overlap, particularly in the region that Segal attributed to only amorphous intensity, casts doubt on the Segal method as a ‘‘crystallinity’’ determination (French and Santiago Cintrón 2013). When the sharp and separated calculated peaks are broadened to mimic the peaks that arise from model crystals of a size similar to most cellulosic samples (a few nanometers), it appears that much of the intensity formerly attributed to ‘‘background’’ or ‘‘amorphous scatter’’ is just the overlapped intensity from adjacent crystalline peaks (French 2014). Paul Scherrer (1918) showed that peaks are sharp when crystals are large, and broad when crystals are small. These smaller peaks can be visualized by calculating a diffraction pattern for an unrealistically large (100 nm) model cellulose crystal. Unlike peak deconvolution, the Rietveld method includes the smaller peaks that are lost in what appears to be the background or amorphous scattering. The Rietveld method also optimizes variables to fit a diffraction pattern, but it uses all of the diffraction peaks. A third method (Rietveld 1969 (16,400 citations) Young 1995) is used for general molecular structure determination of powders as well as occasionally for cellulose crystallinity. Typically, general purpose curve-fitting software is used. At present, conventional peak deconvolution involves curve fitting to the observed pattern with the individual visible peaks plus a very broad, but simple, e.g., Gaussian, peak for the amorphous material. Perhaps Hermans and Weidinger (1948) were first to suggest that the area under diffraction peaks be divided by the total area. Another approach, peak deconvolution, is more effort to carry out and to attribute. It had 4871 citations as of this writing, despite frequent use with no attribution or with only citations of secondary publications. The most prevalent, and by far the simplest, is the Segal peak height method (Segal et al. Several diffraction methods are used to analyze cellulose crystallinity (Thygesen et al. First, a brief review of diffraction crystallinity methods. Two papers in this issue mark a transition in general understanding of cellulose crystallinity analysis. Abstract: Crystallinity analysis is important for practical reasons and related research can offer information on the nature of amorphous cellulose.
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