Cellulose Crystallites Research Articles

Cross-polarization dynamics and conformational study of variously sized cellulose crystallites using solid-state 13C NMR

Cellulose forms crystalline fibrils, via biosynthesis, that can be just a few nanometers wide. The crystallinity is a structural factor related to material performance. Recently, many routes to isolate these fibrils as nanocellulose have been developed, and there exist various types of nanocellulose with different crystallinities. Quantitative assessment of the crystallinity of nanocellulose is thus essential to advance knowledge in the high performance and functionality of such materials. Solid-state 13C cross-polarization/magic-angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy is a strong tool to investigate the structural features and dynamics of solid cellulose. The crystallinity is often evaluated by using the NMR signal ratio of the C4 crystalline and noncrystalline regions as a crystallinity index (CI) value. To calculate the CI value, it is necessary to examine the dependence of the contact time (CT) for CP on the signal intensity and set the optimum CT at a maximum of the signal intensity. However, the dependence has not been investigated for evaluation of the CI value of various cellulose samples with different crystal sizes. Here, we optimized the CT for evaluation of the CI value of cellulose with different crystal sizes. The error in the CI at the optimized CT was ~ 3%. At the optimized CT, the structural change after surface modification by TEMPO-oxidation was also analyzed from the NMR spectra of the C6 region. The relationship between the CI value and the degree of oxidation shows that it is possible to evaluate the degree of oxidation from the NMR spectra irrespective of the crystallinity of cellulose. Furthermore, the C4-based CI value was linearly correlated with the C6-based trans-gauche (tg) ratio, which is approximated by a function, CI = 0.9 tg ratio.

Fabrication of oxidized bacterial cellulose by nitrogen dioxide in chloroform/cyclohexane as a highly loaded drug carrier for sustained release of cisplatin

Carboxylated bacterial cellulose (OBC) was fabricated by oxidation with nitrogen dioxide in chloroform/cyclohexane and employed as a carrier for sustained release of antitumor substance cisplatin (CDDP). The influence of removing water method, solvent used in the synthesis, concentration of N2O4, and duration of the oxidation on content of carboxyl groups in reaction products was established. Due to the possibility of nitrogen dioxide to penetrate into cellulose crystallites, the carboxyl group content of the OBC reaches high values up to 4 mmol/g. In vitro degradation of OBC was determined under simulated physiological conditions. The immobilization of CDDP on OBC was studied in detail. The initial burst release of the drug from the polymer was depressed. The cytotoxicity of CDDP-loaded OBC was evaluated with HeLa cells. The unique structure and properties of OBC make it a great candidate as drug delivery carrier.

High acoustic absorption properties of hackberry compared to nine different hardwood species: A novel finding for acoustical engineers

Wood is one of the most usable natural composite. Noise pollution from the various sources affect the human health and environment worldwide. How to reduce noise pollution has become a major issue? Hence, finding the proper sound absorbing wood is necessary for improved acoustic environment. In the present work, we choose most useful ten different hardwood species. Analysis of basic properties, surface morphology by HR-FESEM, elemental analysis using EDAX, cellulose crystallites by XRD, air permeability by a capillary flow porometer, sound absorption coefficient and sound transmission loss by microphones transfer function method using impedance tube is discussed in detail. The Hackberry wood shows better sound absorption coefficient (0.640 at 4000 Hz), sound transmission loss (15.23 at 4000 Hz) due to the higher value of Darcy permeability constant (9.78), porous surface morphology and lower cellulose crystallites (16.6%). These results became extremely important to the engineers for designing good acoustic housing environment.

Effect of Degradation on Wood Hygroscopicity: The Case of a 400-Year-Old Coffin

The hygroscopicity and thermodynamic properties of Pinus sylvestris L. wood from a coffin allegedly holding the remains of famous Spanish author Miguel de Cervantes Saavedra (1547–1616) were studied using the 15 °C and 35 °C isotherms fitted to the Guggenheim–Anderson–de Boer model and comparing them with the isotherms of recently felled wood of the same species. In addition, using infrared spectroscopy (FTIR-ATR) and X-ray diffractograms, the functional groups were determined and the crystallinity and organization of the cell wall components were analyzed. The absence of the 1740 cm−1 group indicates hemicellulose degradation in the archaeological wood, and the X-ray diffractograms show a considerable decrease in cellulose crystallinity and disorganization of the cellulose crystallites. The greater availability of active –OH groups means that the archaeological wood isotherms are above the juvenile and mature wood isotherms, and therefore the thermodynamic balance in the sorption of the archaeological wood is greater.

Features of the Structural Organization and Sorption Properties of Cellulose

An improved model of the layered structure of cellulose microfibrils is proposed, taking into account the presence of slit-like pores between its structural elements. The scheme of the formation of donoracceptor intramolecular, intermolecular and interlayer hydrogen bonds of one glucopyranose unit in the cellulose crystallite is presented. The mechanism of specific adsorption interactions of water molecules in a monolayer with active centers located on the hydrophilic surfaces of elementary fibrils is described. The energy of dipole-dipole interactions was calculated depending on the distance between the active center and the adsorbate water molecule. The thermodynamic parameters characterizing the state of the adsorbate in the adsorption layers are determined by the proton magnetic relaxation method and sorption measurements. The possibility of determining the net heat of adsorption in a bilayer taking into account the Arrhenius nature of the correlation times of the thermal molecular motions of the adsorbate was established. An increase in the entropy of adsorbed water during the adsorption process was revealed. It was found that during adsorption, a part of the inner regions of crystallites transitions to their surface with the participation of cellulose hydroxyl groups, and during desorption, the reverse process is observed.

Cellulose derived nitrogen and phosphorus co-doped carbon-based catalysts for catalytic reduction of p-nitrophenol

The cellulose, which is one of the most abundant solid by-products of agriculture and forestry industry, has been successfully tested for the synthesis of nitrogen and phosphorus co-doped carbon-based metal-free catalysts (NPC) via freeze-drying the mixture of cellulose crystallite and ammonium phosphate, followed by annealing of the hydrogel under nitrogen atmosphere at 800 °C for 2 h. Different techniques including TEM, SEM, FTIR and XPS spectroscopy have been applied to characterize the as-prepared NPC, which presents flake-like morphology with N and P doping levels of 4.3 atom% and 10.66 atom%, respectively. The NPC exhibits excellent catalytic activity for the reduction of p-nitrophenol (p-NP). The turnover frequency (TOF) of the reduction of p-NP is as high as 2 × 10−5 mmol·mg−1·min−1 and the apparent kinetic rate constant was calculated as 0.0394 min−1 at room temperature. The catalytic mechanism is proposed by combining the density functional theory calculation and analysis of the experimental results. These findings open up new possibilities of valorization for cellulose-based by-product and treatment of p-NP-based wastewater.

Even Visually Intact Cell Walls in Waterlogged Archaeological Wood Are Chemically Deteriorated and Mechanically Fragile: A Case of a 170 Year-Old Shipwreck.

Structural and chemical deterioration and its impact on cell wall mechanics were investigated for visually intact cell walls (VICWs) in waterlogged archaeological wood (WAW). Cell wall mechanical properties were examined by nanoindentation without prior embedding. WAW showed more than 25% decrease of both hardness and elastic modulus. Changes of cell wall composition, cellulose crystallite structure and porosity were investigated by ATR-FTIR imaging, Raman imaging, wet chemistry, 13C-solid state NMR, pyrolysis-GC/MS, wide angle X-ray scattering, and N2 nitrogen adsorption. VICWs in WAW possessed a cleavage of carboxyl in side chains of xylan, a serious loss of polysaccharides, and a partial breakage of β-O-4 interlinks in lignin. This was accompanied by a higher amount of mesopores in cell walls. Even VICWs in WAW were severely deteriorated at the nanoscale with impact on mechanics, which has strong implications for the conservation of archaeological shipwrecks.

Deterioration of the cell wall in waterlogged wooden archeological artifacts, 2400 years old

ABSTRACT The relationship between the cell wall ultrastructure of waterlogged wooden archeological artifacts and the state of water bound to cell walls and free in voids is fundamental to develop consolidating and drying technologies. Herein, a lacquer-wooden ware and a boat-coffin dating 4th century BC were selected as representative artifacts to study. Wood anatomy results indicated that they belonged to Idesia sp. and Machilus sp., respectively. They exhibited a typical spongy texture, as revealed by SEM observations, and their water contents had increased significantly. Solid state NMR, Py-GC/MS, imaging FTIR microscopy and 2D-XRD results demonstrated that the deterioration resulted from the partial cleavages of both polysaccharide backbones and cellulose hydrogen-bonding networks, almost complete elimination of acetyl side chains of hemicellulose, the partial depletion of β-O-4 interlinks, as well as oxidation and demethylation/demethoxylation of lignin. These further caused the disoriented arrangement of crystalline cellulose, and the decrease in cellulose crystallite dimensions and crystallinity. In consequence, mesopores and macropores formed, and the number of moisture-adsorbed sites and their accessibility increased. Moreover, results on free water deduced by the changes of pore structure and the maximum monolayer water capacity achieved by the GAB model indicated that water in waterlogged archeological wooden artifacts was mainly free water in mesopores.

Assessment of Sisal Fiber Integrity as a Reinforcing Element in MgO-Based Cement Matrices

The aim of this work is to evaluate the effects of sisal fiber exposure to cement matrices with different alkalinity in order to assess their viability as reinforcing elements in cementitious composites. To improve sisal fiber durability, this study introduces the use of a different calcium (Ca)-free cement binder based on MgO and SiO2. Sisal fibers were exposed to both MgO–SiO2 and conventional Portland cement to compare chemical interactions before and after different aging conditions by TGA, XRD and SEM/EDS analysis. MgO–SiO2 cement removes the amorphous phases of sisal fibers similarly to NaOH treatments used for polymeric composites. Contrarily for cements with high Ca(OH)2 concentration, MgO–SiO2 cement promotes the hydrolysis of the fibers only in the amorphous phase, while the cellulose content and crystallite size was hardly modified. Sisal fibers exposed to MgO–SiO2 cement do not present any extra crystalline phase related to the cement hydration products. Thus, fiber mineralization process is avoided, whereas good adherence is promoted between M-S-H gel and fibers.

The Effects of the Blending Condition on the Morphology, Crystallinity, and Thermal Stability of Cellulose Microfibers Obtained from Bagasse

In this study, cellulose microfibers were isolated from bagasse fibers in three stages. Initially, the fibers were treated with 5 wt.% NaOH solution followed by bleaching with 5 wt.% H2O2 in an alkali condition (pH 11) to remove hemicelluloses and lignin. Whole cellulosic fibers were obtained by mechanically separating the fibers using a modified kitchen blender to produce cellulose microfibers. Morphological (Scanning Electron Microscopy (SEM)) and structural analysis of the treated fiber was performed using Fourier Transformed Infrared (FTIR) spectroscopy and X-ray Diffraction (XRD). Morphological characterization identified that the diameter of the fibers varied between 20 nm to 20 µm and the FTIR analysis demonstrated that the treatments resulted in the gradual removal of lignin and hemicelluloses from the fiber. Furthermore, the XRD studies revealed that the combination of the chemical and mechanical treatment is an effective way to increase purity of cellulose (removal of amorphous lignin and hemicellulose) and break down the microfiber into shorter crystalline parts with higher crystallinity (77.25%) than raw bagasse (40.54%). Accordingly, changing the agitation time revealed that the cellulose crystallite size in the sample varied slightly with agitation time by using a blender (3.35 nm). Finally, the higher crystallinity and crystallite size improved the thermal stability of the cellulose microfiber confirming their suitability in the manufacturing biomaterial composites.

Moisture-activated dynamics on crystallite surfaces in cellulose

The structural basis of the interdependence between moisture content and activation of cooperative dynamics in natural cellulose is explored using a solid state NMR experiment which is able to localize these motions to cellulose chains on the surface of the unitary crystallite. Making assumptions based on current knowledge of biosynthesis of cellulose and the dipolar line widths of H spectra in solids, it is shown that the sorption of moisture causes the activation of cooperative motion of cellulose chains on the surface of the cellulose crystallite in a manner which is related to the moisture content. An important implication for these results is that densification of cellulose and associated changes in the water sorption isotherm, is possible by structural relaxation on the nano, or unitary crystallite scale. The result is also discussed in term of the evolving and modern picture of cellulose.

A novel method for preparing microcrystalline cellulose from bleached chemical pulp using transition metal ions enhanced high temperature liquid water process

A novel method for preparing microcrystalline cellulose (MCC) from bleached chemical pulp based on the transition metal ion-enhanced high temperature liquid water (HTLW) process was established in this study. Transition metal ions (Fe3+, Cu2+ or Cr3+) were used to enhance the depolymerization effect of HTLW treatment on fibers. Hemicelluloses are selectively removed, resulting in an increase in the α-cellulose content; cellulose undergoes hydrolytic degradation, causing a significant decrease in the average degree of polymerization (DP). SEM images indicated that the as-prepared MCC had granular or rod-like shape. The repose angle results showed a desirable fluidity of obtained MCC. The copper number results showed an increase in the reducing end groups of the obtained MCC. The XRD analysis indicated that the cellulose crystallite exhibited negligible changes, and the crystallization index (CI) increased. However, a very high concentration of transition metal ions lowered the CI. The transition metal ion-enhanced HTLW treatment provides an acid free method for preparing MCC.

Impact of hydrothermal and alkaline treatments of birch kraft pulp on the levelling-off degree of polymerization (LODP) of cellulose microfibrils

The levelling-off degree of polymerization (LODP) is typically considered an apodictic number of each cellulosic source that relates to the length of its cellulose crystallites. In this study, we have performed hydrothermal and alkaline treatments on bleached birch kraft pulp to adjust the xylan content, and the resulting pulps have been subjected to acid hydrolysis to determine their LODP. The results show that hydrothermal treatments promote longitudinal alterations in the supramolecular structure of cellulose, represented by a linear decrease in the LODP with lowering the xylan content in the pulp. Moreover, a decrease in LODP is also observed after alkaline extraction of the birch kraft pulp, but the decrease as a function of xylan content differs from that observed after hydrothermal treatments. The results appear to indicate that the LODP is rather an artifact introduced during processing of the material than a true measure of the length of the crystallites in the native cellulose source.

Microstructural characterization and evaluation of certain important physical properties of thuja burl wood

This investigation aimed to characterize certain important anatomical, chemical and physical properties of Tetraclinis articulate (Thuja) burl wood from Morocco. Anatomical properties and constituent structure were analysed using image analysis system, environmental scanning electron microscope (ESEM) and powder x-ray diffraction techniques. A few important physical properties of Thuja burl wood such as density, specific gravity, equilibrium moisture content (EMC), total swelling and water absorption characteristics were evaluated. Real-time water absorption and swelling profiles were recorded electronically using a digital force sensor and linear variable differential transformers (LVDTs) respectively. Microscopic structure observed on fractured surfaces showed very compact and thread-like fibers. Average crystallinity index and diameter of cellulose crystallite was found to be 0.35±0.03 and 36.00±5.58 A respectively. The average values of air-dry density and the EMC of Thuja burl wood were 932.67±50.57 kg/m3 and 10.19±1.43% respectively. Swelling profile as a function of the water immersion duration followed a curvilinear variation with maximum swelling coefficient of 2.9±0.43% after 24 hour from oven-dry condition. The suitability of this wood for decorative and handicraft items is attributed mainly to its dense microstructure, higher dimensional stability, lower water absorption, random grain texture, dark brownish with intense and pleasant smell.

Effects of ageing on the cell wall and its hygroscopicity of wood in ancient timber construction

An important traditional load bearing member in oriental ancient timber structure buildings, i.e. Huagong (flower arm), was selected to explore the alterations in cell wall components and hygroscopic properties of wood during long time ageing. This archaeological poplar (Populus spp.) wood with cal. BP 690: BP 790 was studied from the wood surface and inwards by means of imaging FTIR spectroscopy, X-ray diffraction and dynamic vapour sorption. The deterioration of the archaeological wood mainly displayed a depolymerization of glucomannan and lignin as well as a hydrolysis of the glucuronic acid of xylan and of the aromatic C–O groups in the condensed lignins or lignin–carbohydrate complexes. Furthermore, the degradation promoted the rearrangement of the cellulose molecules in adjacent microfibrils. The cellulose crystallites in the archaeological wood were therefore packed more tightly and had larger diameter. The structural alterations of wood cell wall components and a decrease in crystallinity contributed to an increase in the number of moisture bonding sites and led to an increase in both the equilibrium moisture content of the archaeological wood in the entire RH range as well as an increase in hysteresis.

ANALYSIS OF STRUCTURAL CHANGES OF CELLULOSE COMPONENT IN PROCESS OF ELEMENTARIZATION OF FLAX FIBERS

The comparative research of composition and supramolecular structure of the flax fibers received by methods of a cottonization and a mechanical elementarization under the influence of the cyclic deforming loadings was conducted. It was shown that under the influence of cyclic loadings removal of a considerable part of impurity with the increase in content of cellulose to 80.1% is reached. At the same time, division of complexes onto elementary filament provides the increase in the total surface of material and, as a result, to availability of fibers to the reagents at the subsequent alkaline boiling. X-ray analysis of flax samples with a method of comparison of the normalized parameters of diffraction by crystalline regions of cellulose allowed to establish that degree of crystallinity of a cellulose component of fibers remains constant even at deep purification of raw materials under the influence of cyclic deformations and subsequent boiling. The research of the oriented fibers by X-ray diffraction method has shown that removal of impurity from flax in the course of an elementarization has only weak influence on the sizes of crystallites of cellulose. The increase in the cross sizes of crystallites by 4 – 6% was observed at deep purification of fibers due to the boiling. This phenomenon can be connected with the decrease in influence of a diffraction maximum from impurity on half-width of the equatorial reflex 200 for cellulose Iβ. It should be noted that the longitudinal sizes of crystallites at the same time do not change. It was suggested on possible influence of decrease in content of impurity on supramolecular structure of an amorphous phase of cellulose and as a result on the observed growth of sorption and mechanical properties of flax fibers at an elementarization by method of cyclic deformation.Forcitation:Zavadskii A.E., Stokozenko V.G., Moryganov A.P., Larin I.Yu. Analysis of structural changes of cellulose component in process of elementarization of flax fibers. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 6. P. 102-108.

Monitoring the Crystalline Structure of Sugar Cane Bagasse in Aqueous Ionic Liquids

The use of aqueous ionic liquids as a pretreatment for enhancing enzymatic saccharification of lignocellulosic biomass is well-known, with a focus on lignin and hemicellulose removal. However, in-depth knowledge of changes in cellulose crystallinity during the pretreatment is limited. To this effect, detailed Fourier transform infrared (FT-IR) spectroscopy, cross-polarized magic angle spinning 13C nuclear magnetic resonance (CP/MAS 13C NMR), and X-ray diffraction (XRD) studies on sugar cane bagasse that has been pretreated with aqueous ionic liquids is presented. Secondary derivatives of FT-IR spectra and Gauss deconvolution of XRD patterns were applied to give a detailed understanding of the crystalline changes in sugar cane bagasse cellulose upon pretreatment. The results showed that aqueous ionic liquid pretreatment destroys the semicrystalline region of sugar cane bagasse cellulose, thus disordering the orientation of the cellulose crystallites.

Pyrolysis of cellulose in aromatic solvents: Reactivity, product yield, and char morphology

Aromatic solvents are known to stabilize levoglucosan (1,6-anhydro-β-d-glucopyranose), the major pyrolysis intermediate of cellulose, against thermal degradation including char formation. In this article, pyrolysis of cellulose, a crystalline component of biomass, was investigated in the aromatic solvents 1,3-diphenoxybenzene, diphenyl sulfide, and benzophenone under nitrogen at 280°C. Thermal degradation of cellulose (Whatman filter paper) was markedly delayed in the aromatic solvents and gave thin film-like char after the removal of unreacted cellulose through hydrolysis. The yields of levoglucosan and 5-hydroxymethylfurfural were greatly enhanced in the aromatic solvents. These observations are discussed at the molecular level in terms of the interactions of cellulose crystallites and the pyrolysis products with the aromatic solvents. A possible char formation mechanism via 5-hydroxymethylfurfural involving the ultrastructure of the cell wall is also discussed. This study provides insight into the molecular-based cellulose pyrolysis mechanisms and efficient and selective thermochemical production of bio-based materials and chemicals.

Analysis of Structural Changes in Jute Fibers after Peracetic Acid Treatment

Peracetic acid (PAA) is one of the most commonly used bleaching agents in the textile industry. The structural changes of jute fibers after PAA treatment are important in creating industrial applications. An investigation was carried out to determine the structural changes resulting from the removal of noncellulosic materials from jute fibers by PAA. The surface features of jute fiber were studied using a scanning electron microscope. PAA was effective in separateingindividual cellulose fibers from raw jute. However, fibers were damaged when the treatment time reached 80 minutes, PAA concentration was 10 wt. % and the pH was in the 4~5 range. The delignification by PAA treatment was confirmed by Fourier transform infrared spectroscopy. CP/MAS13C-NMR spectroscopy showed that the PAA did cause some macromolecular structure changes in the cellulose fibers. X-ray diffraction technique demonstrated that there were four stages of crystallinity change, due to the removal of noncellulosic materials. These four stages include attack at the surfaces of cellulose crystallites, the dissolution of amorphous zones, attack of the inner cellulose crystallite and oxygen interference, respectively.

An NMR relaxation and spin diffusion study of cellulose structure during water adsorption

The goal of this paper is a systematic investigation of changes in the supramolecular structure of cellulose during its water uptake. The main attention is concentrated on the analysis of the mechanism of dispersion of microfibrils by proton NMR relaxation techniques. Spin diffusion NMR experiments made it possible to estimate the linear dimensions of the surface thickness of cellulose crystallites and the average depth of micropores that are formed between elementary fibrils, as well as the character of the filling of micropores during adsorption. It has been shown that when the relative water content gradually increases to 7–8%, water molecules occupy the space between cellulose microfibrils, which is accompanied by an increase in the pore sizes and their specific surface area and a simultaneous decrease in the degree of crystallinity. Upon acquiring a free induction decay signal, a magic sandwich echo sequence was used, due to which the accuracy and information value of the results were considerably improved.