Cellulose crystallinity index: measurement techniques and their impact on interpreting cellulase performance
TL;DR: Four different techniques incorporating X-ray diffraction and solid-state 13C nuclear magnetic resonance (NMR) were compared using eight different cellulose preparations and it was found that the simplest method, which is also the most widely used, and which involves measurement of just two heights in the X- Ray diffractogram, produced significantly higher crystallinity values than did the other methods.
Abstract: Although measurements of crystallinity index (CI) have a long history, it has been found that CI varies significantly depending on the choice of measurement method. In this study, four different techniques incorporating X-ray diffraction and solid-state 13C nuclear magnetic resonance (NMR) were compared using eight different cellulose preparations. We found that the simplest method, which is also the most widely used, and which involves measurement of just two heights in the X-ray diffractogram, produced significantly higher crystallinity values than did the other methods. Data in the literature for the cellulose preparation used (Avicel PH-101) support this observation. We believe that the alternative X-ray diffraction (XRD) and NMR methods presented here, which consider the contributions from amorphous and crystalline cellulose to the entire XRD and NMR spectra, provide a more accurate measure of the crystallinity of cellulose. Although celluloses having a high amorphous content are usually more easily digested by enzymes, it is unclear, based on studies published in the literature, whether CI actually provides a clear indication of the digestibility of a cellulose sample. Cellulose accessibility should be affected by crystallinity, but is also likely to be affected by several other parameters, such as lignin/hemicellulose contents and distribution, porosity, and particle size. Given the methodological dependency of cellulose CI values and the complex nature of cellulase interactions with amorphous and crystalline celluloses, we caution against trying to correlate relatively small changes in CI with changes in cellulose digestibility. In addition, the prediction of cellulase performance based on low levels of cellulose conversion may not include sufficient digestion of the crystalline component to be meaningful.
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01 Jan 1954
6,295 citations
TL;DR: In this paper, an empirical method for determining the crystallinity of native cellulose was studied with an x-ray diffractometer using the focusing and transmission techniques, and the influence of fluctuations in the primary radiation and in counting and recording processes have been determined.
Abstract: An empirical method for determining the crystallinity of native cellulose was studied with an x-ray diffractometer using the focusing and transmission techniques. The influence of fluctuations in the primary radiation and in the counting and recording processes have been determined. The intensity of the 002 interference and the amor phous scatter at 2θ = 18° was measured. The percent crystalline material in the total cellulose was expressed by an x-ray "crystallinity index." This was done for cotton cellulose decrystallized with aqueous solutions containing from 70% to nominally 100% ethylamine. The x-ray "crystallinity index" was correlated with acid hydrolysis crys tallinity, moisture regain, density, leveling-off degree of polymerization values, and infrared absorbance values for each sample. The results indicate that the crystallinity index is a time-saving empirical measure of relative crystallinity. The precision of the crystallinity index in terms of the several crystallinity criteria is given. Bas...
6,189 citations
"Cellulose crystallinity index: meas..." refers methods in this paper
...It should be remembered that Segal and coworkers only intended this method to be used as a 'time-saving empirical measure of relative crystallinity' [19]....
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...First, CI was calculated from the height ratio between the intensity of the crystalline peak (I002 - IAM) and total intensity (I002) after subtraction of the background signal measured without cellulose [17-19] (Figure 1a)....
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...Method 1: the XRD peak height method This method, developed by Segal and coworkers [19], examined the changes in XRD spectra during decrystallization of cotton cellulose by chemical and mechanical methods....
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TL;DR: It is suggested that it is timely to revisit and reinvigorate functional modeling of cellulose hydrolysis and that this would be highly beneficial if not necessary in order to bring to bear the large volume of information available on cellulase components on the primary applications that motivate interest in the subject.
Abstract: Information pertaining to enzymatic hydrolysis of cellulose by noncomplexed cellulase enzyme systems is reviewed with a particular emphasis on development of aggregated understanding incorporating substrate features in addition to concentration and multiple cellulase components. Topics considered include properties of cellulose, adsorption, cellulose hydrolysis, and quantitative models. A classification scheme is proposed for quantitative models for enzymatic hydrolysis of cellulose based on the number of solubilizing activities and substrate state variables included. We suggest that it is timely to revisit and reinvigorate functional modeling of cellulose hydrolysis, and that this would be highly beneficial if not necessary in order to bring to bear the large volume of information available on cellulase components on the primary applications that motivate interest in the subject.
1,852 citations
"Cellulose crystallinity index: meas..." refers background in this paper
...Decoupling CI from changes in other properties has proven extremely difficult [62]....
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TL;DR: A review of the information gathered on cellulose structure over the last few decades can be found in this paper, where the authors attempt to bring together basic and complex information which has been gathered on the structure of native cellulose.
Abstract: This article attempts to bring together basic and complex information which has been gathered on cellulose structure, principally that of native cellulose, over the last few decades. Even though advances have been made in the field of crystallography, powder crystallography cannot yield a definitive cellulose structure and single crystal diffraction is not possible due to the lack of suitable crystals. Knowledge obtained on the biosynthesis of native cellulose and on the polymorphy of cellulose and its derivatives help our understanding of ultrastructure. Many inconsistencies between early crystallographic studies of native cellulose have been clarified by the discovery that two polymorphs (α and β) of cellulose I exist. Models of the possible ultrastructural arrangements within native cellulose have been put forward over the decades; with advancement in technology, computer simulations of small and large systems are being created to test the viability of these ultrastructural models. It is hoped that this review will aid in the understanding of the complexity and uncertainties that still exist in this subject
1,460 citations