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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Cellulose crystallinity index: measurement techniques and their impact on interpreting cellulase performance

Lignins are complex natural polymers resulting from oxidative coupling of, primarily, 4-hydroxyphenylpropanoids. An understanding of their nature is evolving as a result of detailed structural studies, recently aided by the availability of lignin-biosynthetic-pathway mutants and transgenics. The currently accepted theory is that the lignin polymer is formed by combinatorial-like phenolic coupling reactions, via radicals generated by peroxidase-H2O2, under simple chemical control where monolignols react endwise with the growing polymer. As a result, the actual structure of the lignin macromolecule is not absolutely defined or determined. The ``randomness'' of linkage generation (which is not truly statistically random but governed, as is any chemical reaction, by the supply of reactants, the matrix, etc.) and the astronomical number of possible isomers of even a simple polymer structure, suggest a low probability of two lignin macromolecules being identical. A recent challenge to the currently accepted theory of chemically controlled lignification, attempting to bring lignin into line with more organized biopolymers such as proteins, is logically inconsistent with the most basic details of lignin structure. Lignins may derive in part from monomers and conjugates other than the three primary monolignols (p-coumaryl, coniferyl, and sinapyl alcohols). The plasticity of the combinatorial polymerization reactions allows monomer substitution and significant variations in final structure which, in many cases, the plant appears to tolerate. As such, lignification is seen as a marvelously evolved process allowing plants considerable flexibility in dealing with various environmental stresses, and conferring on them a striking ability to remain viable even when humans or nature alter ``required'' lignin-biosynthetic-pathway genes/enzymes. The malleability offers significant opportunities to engineer the structures of lignins beyond the limits explored to date.

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Lignins: Natural polymers from oxidative coupling of 4-hydroxyphenyl- propanoids

Crystalline structure analysis of cellulose treated with sodium hydroxide and carbon dioxide by means of X-ray diffraction and FTIR spectroscopy.

Effects of short-time vibratory ball milling on the shape of FT-IR spectra of wood and cellulose

Valorization of native birch wood lignin into monomeric phenols over nickel-based catalysts has been studied. High chemoselectivity to aromatic products was achieved by using Ni-based catalysts and common alcohols as solvents. The results show that lignin can be selectively cleaved into propylguaiacol and propylsyringol with total selectivity >90% at a lignin conversion of about 50%. Alcohols, such as methanol, ethanol and ethylene glycol, are suitable solvents for lignin conversion. Analyses with MALDI-TOF and NMR show that birch lignin is first fragmented into smaller lignin species consisting of several benzene rings with a molecular weight of m/z ca. 1100 to ca. 1600 via alcoholysis reaction. The second step involves the hydrogenolysis of the fragments into phenols. The presence of gaseous H2 has no effect on lignin conversion, indicating that alcohols provide active hydrogen species, which is further confirmed by isotopic tracing experiments. Catalysts are recycled by magnetic separation and can be reused four times without losing activity. The mechanistic insights from this work could be helpful in understanding native lignin conversion and the formation of monomeric phenolics via reductive depolymerization.

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Lignin depolymerization (LDP) in alcohol over nickel-based catalysts via a fragmentation–hydrogenolysis process

A modified acetyl bromide procedure is proposed for the spectrophotometric determination of lignin in herbaceous plants. The digestion with 25 % acetyl bromide (AcBr) in acetic acid at 70°C is improved by including 4 % perchloric acid in the digesting solutions. This allows for more rapid, complete digestion and the use of coarser samples. On the basis of infrared spectra and nitrobenzene oxidation data for milled sample lignins, the value of 20.0 g−1 litre cm−1 for the specific absorption coeficient of AcBr-treated lignins of herbaceous plant samples gave lignin values which were consistent with nitrobenzene oxidation data, but were higher than those obtained by the acid detergent lignin method and the earlier AcBr method proposed for grasses. The lower lignin values obtained in the latter methods are considered to be due to partial lignin solubilisation in the sulphuric acid digestion.

Determination of lignin in herbaceous plants by an improved acetyl bromide procedure

The equation suggested in the standard method SCAN C15:62 for the estimation of the degree of polymerization (DP) of a cellulose sample from its intrinsic viscosity ([η]) in cupriethylenediamine hydroxide (cuene) solution, P0.905 = 0.75 [η]/mL g−1, where P is an indeterminate average DP, is incorrect. Although differences between the experimental results from several laboratories need to be resolved, a tentative replacement (PV = 1.65 [η]) is suggested, based upon the pooled data and a conversion from the intrinsic viscosity of cellulose tricarbanilate (CTC) in tetrahydrofuran (THF) to that of cellulose in cuene. The treatment of statistical errors in Mark–Houwink–Sakurada parameters, and the nonlinearity of the log[η]−log Pv correlation are discussed.

Cellulose molecular weights determined by viscometry

Changes in cellulose crystallinity during kraft pulping were investigated by analysing a series of kraft pulps with yields between 96 and 47% using X-ray diffraction and infrared (IR) spectroscopy. The results were compared with those obtained for the same set of samples using solid state 13 C nuclear magnetic resonance (NMR) spectroscopy. All three methods indicated that the degree of crystallinity of the cellulose increased as kraft pulping proceeded due to preferential removal of the less ordered carbohydrates. Both X-ray and IR analyses indicated that the amount of crystalline cellulose remaining in the fibre stayed nearly constant as pulping proceeded. NMR spectroscopy, on the other hand, showed some increase in the amount of crystal interior cellulose in the early stages of pulping and evidence for damaged cellulose at yields below 57 %. The differences between the results obtained using the three methods are discussed.

Changes in Cellulose Crystallinity During Kraft Pulping. Comparison of Infrared, X-ray Diffraction and Solid State NMR Results

The polysaccharides in a series of Eucalyptus globulus and E. nitens woods, and E. globulus pulps, were analysed by high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD), following hydrolysis with sulfuric acid. The technique was evaluated as a small-scale method for characterising mltiple samples of eucalyp woods. Acetyl groups and 4-0-methylgluronic acids (MeGUAs) associated with the hemicellulose, fraction were removed during acid hydrolysis and were determined separately. Acetyl and MeGUA results were combined with the hydrolysis results to enable calculation of cellulose and hemicelluloses contents for each sample. The cellulose content of the wood samples varied over the range 41-50% (E. globulus) and 36-44% (E. nitens), although the range of total polysaccharide contents was similar for both woods. Analysis of the pulp polysaccharides after enzymic hydrolysis showed that the pulps contained hexenuronic acids. The analyses for cellulose and hemicellulose content showed satisfactory precision, and gave values similar to those associated with gravimetric determination of cellulose and hemicelluloses. The hydrolysis-HPAECPAD method for carbohydrates is proposed as a better alternative to gravimetric techniques for exploring the relationship between the chemical composition of plantation eucalypt woods and their pulp yields and papermaking properties.

Chemical analysis of polysaccharides in plantation eucalypt woods and pulps

Etude de tricarbanilates de celluloses de coton blanchies, d'Avicel PH101, de pâte bisulfite blanchie, de cellulose amorphe et de cellulose II obtenues par reaction avec l'isocyanate de phenyle. Calibration des colonnes en utilisant les echantillons standards. Pyridine meilleur solvant de carbanilation si activation inutile, sinon DMSO meilleur. Meilleure precipitation des CTC en utilisant le melange precipitant eau-methanol a 30-70

Adrian F. A. Wallis

Papers

Determination of lignin in herbaceous plants by an improved acetyl bromide procedure

Cellulose molecular weights determined by viscometry

Changes in Cellulose Crystallinity During Kraft Pulping. Comparison of Infrared, X-ray Diffraction and Solid State NMR Results

Chemical analysis of polysaccharides in plantation eucalypt woods and pulps

Molecular weight distribution of cellulose as its tricarbanilate by high performance size exclusion chromatography