Supramolecular Structure Of Cellulose Research Articles

Cellulose is not just cellulose: a review of dislocations as reactive sites in the enzymatic hydrolysis of cellulose microfibrils

Most secondary plant cell walls contain irregular regions known as dislocations or slip planes. Under industrial biorefining conditions dislocations have recently been shown to play a key role during the initial phase of the enzymatic hydrolysis of cellulose in plant cell walls. In this review we chart previous publications that have discussed the structure of dislocations and their susceptibility to hydrolysis. The supramolecular structure of cellulose in dislocations is still unknown. However, it has been shown that cellulose microfibrils continue through dislocations, i.e. dislocations are not regions where free cellulose ends are more abundant than in the bulk cell wall. In more severe cases cracks between fibrils form at dislocations and it is possible that the increased accessibility that these cracks give is the reason why hydrolysis of cellulose starts at these locations. If acid or enzymatic hydrolysis of plant cell walls is carried out simultaneously with the application of shear stress, plant cells such as fibers or tracheids break at their dislocations. At present it is not known whether specific carbohydrate binding modules (CBMs) and/or cellulases preferentially access cellulose at dislocations. From the few studies published so far it seems that no special type of CBM is involved. In one case an endoglucanase was found to preferably bind to dislocations.

Novel insight into cellulose supramolecular structure through 13C CP-MAS NMR spectroscopy and paramagnetic relaxation enhancement

13C CP-MAS NMR and paramagnetic relaxation enhancement provide novel insight into the supramolecular structure of solid cellulose I and II. Separable NMR signals associated with crystalline interiors, solvent accessible and inaccessible surfaces, as well as non-crystalline material are assigned and confirmed. For the first time solvent accessibility is evidenced and monitored through 13C T1 NMR relaxation enhancement in paramagnetic medium. Established NMR signal assignments for cellulose I have been confirmed. Existing cellulose II resonance attributions have been modified and extended. Novel spectral fitting routines for cellulose II allow for the reproducible quantification of separable signal contributions. Results from NMR line shape analyses are straightforwardly introduced into a model for cellulose II supramolecular structure.

Compression molded wood pulp biocomposites: a study of hemicellulose influence on cellulose supramolecular structure and material properties

In this study, the importance of hemicellulose content and structure in chemical pulps on the property relationships in compression molded wood pulp biocomposites is examined. Three different softwood pulps are compared; an acid sulfite dissolving grade pulp with high cellulose purity, an acid sulfite paper grade pulp and a paper grade kraft pulp, the latter two both containing higher amounts of hemicelluloses. Biocomposites based the acid sulfite pulps exhibit twice as high Young’s modulus as the composite based on paper grade kraft pulp, 11–12 and 6 GPa, respectively, and the explanation is most likely the difference in beating response of the pulps. Also the water retention value (WRV) is similarly low for the two molded sulfite pulps (0.5 g/g) as compared to the molded kraft pulp (0.9 g/g). The carbohydrate composition is determined by neutral sugar analysis and average molar masses by SEC. The cellulose supramolecular structure (cellulose fibril aggregation) is studied by solid state CP/MAS 13C-NMR and two forms of hemicellulose are assigned. During compression molding, cellulose fibril aggregation occurs to higher extent in the acid sulfite pulps as compared to the kraft pulp. In conclusion, the most important observation from this study is that the difference in hemicellulose content and structure seems to affect the aggregation behaviour and WRV of the investigated biocomposites.

Cellulose supramolecular structure changes during chemical activation and sulfation 2nd ICC 2007, Tokyo, Japan, October 25–29, 2007

Abstract Cotton cellulose has been sulfated in the presence of organic solvents (methanol, ethanol, iso-propanol and via chlorosulfonic acid-pyridine complex, and a mixture of concentrated sulfuric acid and ethanol) and the effects were studied by polarized light microscopy, electron microscopy, IR spectroscopy, and X-ray diffraction. Sorption-desorption behavior of the sulfonated cellulose was also observed. These processes enhance interfibrillar swelling, weaken intermolecular hydrogen bonds, and loosen the packing density of microfibrils. As a result, the accessibility of esterification reagents was improved depending on the activation method. Microscopic studies showed that the surface of the initial cotton cellulose is wrinkled. The fibrillar structure of the primary fiber wall was not observed. In the case of cotton cellulose, sulfation changed its crimped fibers with different thicknesses, length and defects which were visible in a polarized light as bright luminescence. Fibers become short, thick, and straightened. Moreover, degree of anisotropy and crystallinity of the modified fibers decreased. Their size and degree of crimping are dependent on condition of modification. All pre-activation processes were successful. Thickness of fibers was increased up to 20% and the length was decreased to one-third or one-fourth. The sorption capability of cellulose was increased 2.1–3.4-fold in pre-activated samples, which is due to the increasing specific surface area (45.0–109.1 m2 g-1). Volume and radius of the pores increased up to 0.1164–0.410 m3 g-1 and 36.2–133.3 Å, respectively.

Effect of alkaline treatment on cellulose supramolecular structure studied with combined confocal Raman spectroscopy and atomic force microscopy

The aim of this work was to investigate the morphological and structural changes associated with mercerization of cellulose fibres with combined confocal Raman and atomic force microscopy (AFM). During mercerization the alkali induces a change in polymorphic lattice from cellulose I to II. This was observed by confocal Raman spectroscopy from cellulose samples treated with 10, 15 and 25% aqueous sodium hydroxide solution. AFM images from the same samples illustrated that microfibrils were swollen and more granular in cellulose II than in cellulose I. Raman spectral images in plane and depth directions showed that the polymorphous cellulose structure was uniform throughout the cell wall, whereas the microfibril orientation varied between fibre cell wall layers. The changes in microfibril orientation on the sample surfaces were confirmed by AFM images measured from the same sample position.

Upgrading of paper grade pulps to dissolving pulps by nitren extraction: yields, molecular and supramolecular structures of nitren extracted pulps

Different paper grade pulps were extracted with nitren in order to produce dissolving pulps and polymeric xylan. The yield and molecular structure of the extracted pulps were investigated by carbohydrate analysis and HPSEC combined with fluorescence labelling in order to additionally monitor the carbonyl and carboxyl group profiles of the pulps. The supramolecular structure of selected pulps were further studied by solid state 13C-CP/MAS-NMR and wide-angle X-ray scattering (WAXS). These supramolecular data of nitren extracted pulps were compared to samples extracted with NaOH and a conventional dissolving pulp in order to classify the properties of nitren extracted pulps. Nitren extraction results in selective xylan removal without noticeable degradation or oxidation of the cellulose fraction. The resulting dissolving pulps have high molar masses, a narrow molar mass distribution and the typical contents of carbonyl and carboxyl groups. The supramolecular structure of cellulose is less affected by nitren compared to strong NaOH, and the resultant dissolving pulps still have the cellulose I structure.

Novel Approaches to Metallization of Cellulose by Reduction of Cellulose-Incorporated Copper and Nickel Ions

Summary: Copper and nickel nanoparticles were synthesized in the insoluble microcrystalline cellulose support by reduction of metal ions with several reducers in various media resulting in cellulose-metal nanocomposites. Wide-angle X-ray scattering results showed that supramolecular structure of cellulose did not change. Crystalline Cu2O and Cu0 nanoparticles were prepared with reducers NaBH4 and N2H4 · H2SO4, CuO nanoparticles – with cellulose itself as a reducer. Crystalline Ni0 nanoparticles were synthesized with N2H4 · 2HCl and NaBH4; Ni0 nanoparticles in amorphous form were prepared with KH2PO2 · H2O. SEM revealed large agglomerates of metal particles on the fibre surface. ASAXS and TEM have shown the nanoparticles to be in the range 5–55 nm.

Novel Approaches to Metallization of Cellulose by Reduction of Cellulose‐Incorporated Copper and Nickel Ions

AbstractSummary: Copper and nickel nanoparticles were synthesized in the insoluble microcrystalline cellulose support by reduction of metal ions with several reducers in various media resulting in cellulose‐metal nanocomposites. Wide‐angle X‐ray scattering results showed that supramolecular structure of cellulose did not change. Crystalline Cu2O and Cu0 nanoparticles were prepared with reducers NaBH4 and N2H4 · H2SO4, CuO nanoparticles – with cellulose itself as a reducer. Crystalline Ni0 nanoparticles were synthesized with N2H4 · 2HCl and NaBH4; Ni0 nanoparticles in amorphous form were prepared with KH2PO2 · H2O. SEM revealed large agglomerates of metal particles on the fibre surface. ASAXS and TEM have shown the nanoparticles to be in the range 5–55 nm.

Modifications of the Mesoscopic Structure of Cellulose in Paper Degradation

Paper is the main component of a huge quantity of cultural heritage. It is primarily composed of cellulose that undergoes significant degradation with the passage of time. By using small angle neutron scattering (SANS), we investigated cellulose's supramolecular structure, which allows access to degradation agents, in ancient and modern samples. For the first time, SANS data were interpreted in terms of water-filled pores, with their sizes increasing from 1.61 nm up to 1.97 nm in natural and artificially aged papers. The protective effect of gelatine sizing was also observed.

Changes in cellulose supramolecular structure and molecular weight distribution during steam explosion of aspen wood

We have studied the cellulose supramolecular structure in pulps obtained by steam explosion of aspen wood. The pulps were bleached with hydrogen peroxide in an OQP-sequence and characterised by siz ...

Cellulose Supramolecular Structure Changes During Activation by Organophosphorus Compounds

Cellulose supramolecular structure changes during activation by organophosphorus compounds were studied by electron microscopy, IR spectroscopy, and x-ray diffraction. These processes were shown to enhance interfibrillar swelling, weakening of intermolecular H-bonds between cellulose microfibrils, and loosening of the packing. As a result, the accessibility of esterification reagents to the molecules is improved

Influence of the Alkali Concentration on the Formation of Cellulose II. Study by X-Ray Diffraction and FTIR Spectroscopy

The comparative study shows that the lattice transformation Cellulose I/II as evaluated by X-ray diffraction is reflected in the CH 2 /OH valency vibration range of deconvoluted FTIR spectra. The two methods supplement each other. The phase transition begins with a NaOH concentration of 11-12% and is completed with one of 16.5%. Various changes in the molecular and supramolecular structure of cellulose in this alkali concentration range were identified. The transformation process is determined by splitting and new formation of inter- and intramolecular H-bonds. There is a direct correlation between decrease in crystallinity and H-bond splitting. The conformational variation in the cellulose molecules is the result of the interaction between inter- and intramolecular H-bonds during chain rotation.