Supramolecular Structure Of Cellulose Research Articles

Enhancing enzymatic conversion of castor stalk through dual-functional ethanolamine pretreatment

Castor stalk from hemp plants is an attractive lignocellulosic feedstock for biomass refining valorization due to its similar chemical composition to hardwoods. In this study, the castor stalk fibers were pretreated with efficient dual-functional ethanolamine to achieve delignification and swelling of the cellulosic fibers, followed by cellulase enzymatic digestion for biomass conversion. Experimental results showed that ethanolamine pretreatment at 160 °C for 1 h effectively removed 69.20 % of lignin and 43.18 % of hemicellulose. In addition to efficient delignification and removal of hemicellulose, the study also revealed that supramolecular structure of cellulose was another major factor affecting enzymatic hydrolysis performance. The lowered crystallinity (60–70 %) and swelled crystal sizes (2.95–3.04 nm) promoted enzymatic hydrolysis efficiency during the heterogeneous reaction process. Under optimal conditions (160 °C, 1 h; enzyme loading: 15 FPU/g substrate), promoted yields of 100 % glucose and over 90 % xylose were achieved, which were significantly higher than those obtained from untreated castor stalk. These findings highlighted the effectiveness of the dual-functional ethanolamine pretreatment strategy for efficient bioconversion of lignocellulosic feedstocks. Overall, this study provides valuable insights into the development of new strategies for the efficient utilization of biomass resources, which is essential for the sustainable development of our society.

Hemicellulose-rich transparent wood: Microstructure and macroscopic properties

Hemicellulose plays a vital role in nature wood matrix. Here, we first demonstrate the significance of hemicellulose for improving the microstructure and macroscopic properties of transparent wood (i.e. wood/polymer composite), an emerging structural material. A delignified basswood templet with high hemicellulose content (~23 wt%) and well-preserved cellulose supramolecular structure was prepared via a peracetic acid-based process. This hemicellulose-rich delignified wood templet possesses nearly intact cell wall structure and sufficient space in the lumen and middle lamella for petroleum-based polymer space-filling. Consequently, the resultant hemicellulose-rich wood/PMMA composite exhibits high optical transmittance (~85 %), medium haze (~72 %), acceptable optical stability as well as excellent mechanical strength (tensile strength of 165.3 MPa and toughness of 1.65 MJ/m3), benefitting from the absence of microstructural defects and heterogeneity in the matrix. It is anticipated that our study would provide new insights into the fabrication of advanced transparent wood material from the point-of-view of wood chemical composition.

Сорбционная способность гель-пленок функционализированной бактериальной целлюлозы по отношению к хлорамфениколу

Due to unique natural characteristics such as biocompatibility, nontoxicity, mechanical stability, and high moisture content, bacterial cellulose can be efficiently used for the production of new medical materials, including various wound dressings. Bacterial cellulose can be produced by bacteria of the genera Gluconaceto-bacter, Aerobacter, Rhizobium and others. Under static cultivation conditions, the producers form gel films of bacterial cellulose, which differ in their properties. Bacterial cellulose does not possess inherent antimicrobial activity; therefore, bacterial cellulose films must be further enhanced before they are used as medical materials. In order to improve the properties of BC, researchers use various modification methods to introduce antimicrobial activity. The main attention is paid to the post-synthetic modification: in this concept, in order to impart antimicrobial properties to bacterial cellulose it is saturated with antibiotics or other antibacterial and antifungal drugs. To improve the sorption properties, successful attempts were made to oxidize BC and then to saturate it with an antibiotic. The introduction of new reactive functional groups to the surface of bacterial cellulose fibers will make it possible to better control the sorption process and increase the saturation of films with antibacterial drugs. The purpose of this work was to determine the effect of bacterial cellulose treatment during oxidation in the TEMPO/NaClO/NaBr system on the properties of oxidized samples, i.e., an increase in the sorption capacity with respect to a biologically active compound. Films were obtained under conditions of stationary cultivation of the strain Gluconacetobacter hansenii GH 1/2008 (VKPM B-10547) on glucose and fructose carbon sources. Chloramphenicol, a broad-spectrum antibiotic, was chosen as a model antibiotic with which the films were saturated. The resulting films did not differ significantly in terms of thickness, water-holding capacity, and dry weight (see Table 1). Derivatives of BC gel films were obtained without destroying the native three-dimensional gel structure using an oxidative process catalyzed by the nitroxyl radical TEMPO (2,2,6,6-tetramethylpiperidin-1-yl)oxyl). Depending on the oxidation conditions, a series of gel films functionalized with carboxyl groups (COOH) were obtained with a total content of COOH groups varying in a wide range from 0.041 to 0.219 mmol/g (see Fig. 2В). It was shown for the first time that the content of COOH groups depends on the quality of films synthesized on various carbon sources: the maximum degree of carboxylation was noted for films synthesized by G. hansenii on fructose, which is apparently associated with differences in the supramolecular structure of cellulose (see Fig.2B and 3). For the obtained gel films, the sorption capacity with respect to the antibacterial drug chloramphenicol (CP) was evaluated. A direct relationship was established between the sorption value and the amount of COOH groups in the films. The amount of sorption of the antibiotic depends on the degree of carboxylation of the sample (see table 3). Thus, the functionalization of the surface of bacterial cellulose gel films with carboxyl groups leads to an increase in their sorption properties. Indeed, the amount of antibiotic absorbed by the oxidized films is several times higher as opposed to the non-oxidized gel films. The obtained results demonstrate the benefits of carrying out the process of oxidation of bacterial cellulose films, increasing the degree of their saturation with antimicrobial agents and the possibility of their further use for medical purposes as a dressing material. The article contains 7 Figures, 3 Tables and 26 References.

Nanopore confinement and fluid behavior in nanocellulose–based hydro- and organogels

The morphology of nanofibrillated cellulose (cellulose nanofibrils or CNF) systems were probed with inorganic water and organic ester as the tracers to determine the porous structure of CNF skeleton. The main novelty of the work was the determined dramatical changes in the gel microscaled porous morphology under replacement of inorganic water by organic ester in the CNF samples of the same origin. For this aim a well-known and well-tested pulsed-field-gradient (PFG) NMR strategy for analyzing mesh size in different porous media was used. For the data analysis the phenomenological scaling approach was applied. It was shown, that the average size of free porous medium dramatically decreases during the transfer of celllose nanofibrils from the inorganic water phase (43 μm) to the organic ester one (1–2 μm). Cooperative analysis of NMR and SEM data for the water and ester CNF-based gels has shown the essential difference in nanoscaled organization of cellulose supramolecular structure. The replacement of water by ester provides the transfer of nanofibrilles to more dispersed state at the nanoscale, which is also confirmed by FTIR experiments.

Influence of Fine Structure on the Variations of Thermal and Mechanical Properties in Flax Fibers Modified with Different Alkaline Treatment Conditions

ABSTRACT The alkaline treatment condition plays a crucial role in governing the ultimate properties of flax fibers. In this study, flax fibers were modified with mild alkalization and severe mercerization conditions to give fundamental insight into how the molecular-scale changes in cell wall fine structure and cellulose supramolecular structure can affect the macroscopic properties of fibers. SEM, FTIR, XRD, TGA, and DSC techniques were employed to characterize the variations in morphology, composition, crystalline structure, and thermal properties of fibers. Also, tensile tests evaluated their reinforcing performance in polypropylene-based composites. The results indicated that alkalization in 5% (w/v) NaOH solution preserved the tensile properties of fibers, shifted their thermal decomposition temperature from 198 to 254°C, and effectively decreased their moisture absorption content by 18%. The improvements primarily originate from the partial removal of noncellulosic constituents and promoted crystallinity of native cellulose Iβ structure. However, mercerization in 20% (w/v) solution significantly reduced the rigidity of fibers in the longitudinal direction. Furthermore, it decreased the moisture absorption only by 6% and shifted the thermal degradation to 275°C. The excessive elimination of noncellulosic constituents and the polymorphic transformation, which led to a weaker hydrogen bonding network in the cellulose II region, accounts for these changes.

DELIGNIFICATION OF PLANT RAW MATERIALS UNDER MICROWAVE IRRADIATION. IR SPECTRA AND ORDERING INDICES OF THE CELLULOSE

The effect of plant raw materials delignification with an 18% solution of peracetic acid under microwave irradiation at a frequency of 2450 MHz on the degree of ordering of the cellulose supramolecular structure was studied. The samples of the obtained cellulose were characterized by FTIR spectroscopy. It was found that microwave heating reduces the rate of ordering of the cellulose supramolecular structure in the process of delignification of wood and straw of annual plants with peracetic acid. In general, the delignification products obtained under microwave irradiation with a treatment time of 30 min are characterized by lower values of the ordering index (0.64–0.79) compared to cellulose samples obtained using heating by thermal conductivity (water bath, 100 °С) at processing time 60 min (0.70–0.86). The IR spectra of cellulose samples obtained with the use of heat conduction heating are characterized by a slightly higher intensity of the band at 1372 cm-1 in comparison with the delignification products obtained under microwave irradiation. It has been shown that the degree of ordering of the cellulose supramolecular structure under the studied delignification conditions is determined by the peculiarities of the composition of the feedstock and the polysaccharides supramolecular organization in the native state. For cellulose obtained from wood and straw, different dependences of the values of the ordering index on the heating method and the residual content of hemicelluloses are characteristic.

Cellulose Structural Changes during Mild Torrefaction of Eucalyptus Wood.

The changes in the cellulose structure of eight Eucalyptus species (E. botryoides, E. globulus, E. grandis, E. maculata, E. propinqua, E. rudis, E. saligna and E. viminalis) in a mild torrefaction (from 160 °C to 230 °C, 3 h) were studied in situ and after cellulose isolation from the wood by solid-state carbon nuclear magnetic resonance (13C NMR), wide angle X-ray scattering (WAXS), Fourier transform infrared spectroscopy (FTIR) and by analytic pyrolysis coupled with gas chromatography and mass spectrometry (Py-GC/MS). Changes in molecular weight were assessed by viscosimetry. A small decrease in cellulose crystallinity (ca. 2%–3%) was attributed to its amorphization on crystallite surfaces as a result of acid hydrolysis and free radical reactions resulting in the homolytic splitting of glycosidic bonds. The degree of the cellulose polymerization (DPv) decreased more than twice during the heat treatment of wood. It has been proposed that changes in the supramolecular structure of cellulose and in molecular weight during a heat treatment can be affected by the amount of lignin present in the wood. The limitations of FTIR and Py-GC/MS techniques to distinguish the minor changes in cellulose crystallinity were discussed.

Cellulose\u2013water system\u2019s state analysis by proton nuclear magnetic resonance and sorption measurements

Most cellulose-based materials’ manufacturing processes include processing this biopolymer in an aqueous medium. Sorption properties depend on cellulose supramolecular structure and nature of its change during moistening. Plenty of researchers’ efforts have been directed to the development of scientifically sound and commercially reliable processes over the past decade for the cellulose fibers’ dispersion in an aqueous medium. Therefore, it needs a more detailed study of the cellulose–water system components’ interaction. This study presents the supramolecular structure and sorption properties of native cotton cellulose research results obtained by 1H NMR relaxation, spectroscopy and sorption measurements. Hydrophilic properties of cellulose as an adsorbent are characterized, taking into account a porous system between its structural elements. We examine in detail water adsorption on the active surface of cellulose Iβ. We also demonstrate the approach for determining the entropy change in the first two layers of adsorbed water and estimate this value increased during adsorption. Cellulose moistening is accompanied by the decomposition of macrofibrils into microfibrils and is manifested in a crystallinity decrease and a specific surface area growth.

Transition of cellulose supramolecular structure during concentrated acid treatment and its implication for cellulose nanocrystal yield

Cellulose nanocrystals with cellulose I and II allomorphs (CNC-I and CNC-II) were prepared from eucalyptus cellulose I substrate by controlling the sulfuric acid hydrolysis conditions, including acid concentration (56–64 wt%), reaction temperature (45 or 60 °C) and time (10–120 min). The crystalline structures were verified by XRD and 13C-NMR. CNC-II only appeared at very restricted reaction conditions. The rapid cellulose supramolecular structure transition under sulfuric acid concentration of around 60 wt% resulted in an abrupt change in CNC yield. A maximal CNC yield of 66.7% was obtained at acid concentration of 58 wt% and reaction temperature of 60 °C. CNC-I exhibited spindle-shape, while CNC-II showed a twisted strip structure. The state of order in cellulose during the acid hydrolysis process has been studied using a coagulation method. A tentative model of CNC-I and CNC-II formation was then proposed. This work provided significant knowledge for the production of CNCs with high yield and controllable allomorph.

Tailored nanocellulose structure depending on the origin. Example of apple parenchyma and carrot root celluloses

Cellulose is the major polysaccharide of cell walls in every plant, making it one of the most abundant natural polymers on Earth. However, despite many decades of investigations, the supramolecular structure of cellulose and especially its variation in the cell walls of different plants have still not been fully revealed. In the present study, cellulose from the parenchymatic tissue of apple fruits and carrot roots was isolated, and nanocellulose was further prepared by high-intensity ultrasonication. AFM revealed that the obtained nanocellulose differed in dimension between the two plant species. Compared with carrot cellulose, whose nanocellulose was obtained in the form of whiskers, apple cellulose had longer and thinner nanofibrils. Both nanocellulose types also differed in terms of their crystalline structure. XRD data indicated that, compared with the apple cellulose, the carrot cellulose had a higher degree of crystallinity and larger crystallites. Moreover, FTIR and Raman spectroscopy revealed differences between the cellulose types in terms of their methine environment, hydroxymethyl conformations and skeletal vibrations. Additionally, with respect to their mechanical properties, the less crystalline apple cellulose and nanocellulose films were more elastic than the stiffer carrot cellulose and nanocellulose films. The possible reason for such differences between the two cellulose types is related to differences in plant tissue morphology and function. During development, apple fruit cell walls must withstand increasing turgor, probably higher that in the case of carrot tissue; therefore, the cellulose scaffolding must be elastic and strong. On the other hand, carrot, a root vegetable, also has to be strong enough to penetrate the soil as well as for its own growth; thus, the cell wall and cellulose scaffold have to be stiff and tough. Thus the structure of nanocellulose depends not only on the treatment but also on the cellulose source.

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.

One-pot construction of cellulose-gelatin supramolecular hydrogels with high strength and pH-responsive properties

Inspired by the supramolecular structure of cellulose, cellulose-gelatin supramolecular hydrogels with high strength and pH-sensitivity were constructed in a basic-based solvent system, ethylene diamine/potassium thiocyanate (EDA/KSCN) with the aid of cyclic freezing-thawing. The investigation on the characteristics of supramolecular hydrogels revealed that repeated freezing-thawing cycles played an important role in the formation of the physical cross-linked supramolecular network structure between cellulose and gelatin. The mechanical properties of supramolecular hydrogels were much higher than pure cellulose and gelatin hydrogel, and the compressive strength was 9.6 times higher than that of pure gelatin hydrogel. The synergistic effect between hydrogen-bonding interaction and the reinforcement of regenerated cellulose nanofibrils (CNF) contributed to the superior mechanical performance. Furthermore, the swelling kinetics tests showed that the supramolecular hydrogels exhibited excellent pH-responsibility, indicating potential applications in biomedical fields. Thus, a straightforward route to construct natural polymer-based hydrogels with supramolecular structure through physical crosslinking strategy without employing hazardous crosslinking agents was developed, paving the way for the design of new types of hydrogels.

КИНЕТИКА НАБУХАНИЯ ДРЕВЕСИНЫ СОСНЫ, МОДИФИЦИРОВАННОЙ АМИНБОРАТАМИ

Wood swells at the contact with capillary and liquid water. This process leads to premature destruction of wood material due to the decrease in its strength characteristics. It is possible to reduce wood swelling in various ways: deep impregnation by hydrophobic reagents, covering the surface with paints and varnishes etc. However, in this case the texture of wood is masked and its unique properties are lost. When modifying wood with amino-borates the supramolecular structure of cellulose is ordered, the specific surface of wood decreases, and its water sorption capacity is reduced. In this regard, we have researched the influence of boron-nitrogenous modifiers of various concentrations on pine wood swelling. The swelling ability of the modified wood was estimated by weight method. As a control sample the samples of unmodified wood were used. On the basis of the obtained experimental data the differential curves of swelling were built and the velocity constants of swelling were determined by a graphic method. As a result of the research it has been established that modifying wood with amino-borates leads to the decrease of equilibrium extent of swelling, and the velocity constant of swelling depends on the nature and concentration of the modifier and its influence on the microstructure of a wood composite.

Unraveling variations of crystalline cellulose induced by ionic liquid and their effects on enzymatic hydrolysis

Ionic liquid (IL) is one of the pretreatment processes gaining considerable interests to remove the native recalcitrance of lignocellulose. But the cellulose crystalline transformation during the pretreatment and their correlations with enzymatic digestibility have not been fully elucidated. Microcrystalline cellulose (Avicel) and holocellulose, which have differential sources and original crystallinity, were respectively pretreated with 1-butyl-3-methylimidazolium chloride ([C4min]Cl). Cellulose crystalline variations as well as chemical and morphological changes were determined. Crystallinity of different materials was proved to influence the effects of pretreatment and following enzymatic digestibility. Recrystallized cellulose Iβ was revealed from slight initial cellulose Iα of Avicel, which was accomplished via formation of intermediate paracrystalline phases. The conversion yield of IL pretreated Avicel displayed no obvious changes, mainly resulted from initial high crystalline order and the recrystallization behavior. Recalcitrance of holocellulose was destroyed during cellulose allomorph transformation and hemicelluloses extraction, contributing to significant increase of glucose yield up to 92.20%. Explicit comprehension on cellulose supramolecular structure may help provide more efficient process for bioconversion after IL pretreatment.

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.

A supramolecular structure insight for conversion property of cellulose in hot compressed water: Polymorphs and hydrogen bonds changes

Waste paper samples with different cellulose supramolecular structure were treated in hot compressed water (HCW) at 375°C and 22.5MPa within 200s to evaluate the specific effect mechanism of cellulose supramolecular structure on the conversion of waste paper to reusable resource. Although the distribution of liquid products and the oligosaccharides were related to reaction time, depolymerization and decrystallization of the cellulose, the characteristics absorption peak of cellulose from FTIR analysis and crystal structure of the cellulose detected in the residues with hydrolysis rate up 96.5% indicated crystal structure was the dominant factor that affect conversion behavior of waste paper. The conversion of cellulose Iβ to cellulose Iα or cellulose I(α+β) in HCW demonstrated that the recrystallization occurred during the decrystallization of cellulose through the rearrangement of hydrogen bonds.

IR absorption spectra of cellulose obtained from ozonated wood

The kinetic curves of ozone absorption by aspen wood were obtained. Processing of wood with peracetic acid gave cellulose samples. The yields of ozonated wood, water-soluble compounds, and cellulose were determined for the samples corresponding to different consumptions of ozone. The IR absorption spectra of wood and cellulose isolated from ozonated wood were analyzed. The supramolecular structure of cellulose can be changed by varying the conditions of wood ozonation.

Investigation of cellulose supramolecular structure changes during conversion of waste paper in near-critical water on producing 5-hydroxymethyl furfural

Waste paper as a kind of biomass contains a great quantity of cellulose which is a renewable energy resource. However, complex cellulose supramolecular structure restricts the conversion of waste paper in near-critical water. This study aimed to investigate the change characteristics of cellulose supramolecular structure (hydrogen bond models and crystallinity) during hydrolysis and its effects on 5-HMF yield. Waste paper has been treated in near-critical water at 375 °C and 22.5 MPa for a reaction time (160–240 s) and correlation between 5-HMF yield and the supramolecular structure of cellulose residues has been built up. The 5-HMF yield was increased with the increase of intermolecular hydrogen bonds content in cellulose residues and was increased first and then decreased with the increase of crystallinity of cellulose residues. The rate of decrystallization was out of sync with that of depolymerization, which also influenced 5-HMF yield. Reaction time can be a macro method to adjust the supramolecular structure of cellulose during the conversion of waste paper to obtain more 5-HMF. It showed that 5-HMF yield reached maximum 9.41% ± 0.47% when the intermolecular hydrogen bonds content of cellulose in residue was 67.77% and the crystallinity of cellulose in residue was 57.14% at 200 s.

Effects of Different Deinking Processes on Fiber Morphology, Hydrogen Bond Models, and Cellulose Supramolecular Structure

Deinked pulp fibers produced by three kinds of deinking processes, alkaline deinking, neutral deinking, and enzymatic deinking, were studied by Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectrometer (FTIR), X-ray Diffraction (XRD), and Cross-Polarization Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance (CP/MAS 13C-NMR). There were remarkable differences in both macroscopic and microscopic structure between the samples. SEM images showed that the effects of deinking processes on fiber morphology were obvious and the influences of alkaline deinking were the most apparent. FTIR analysis indicated that the content of intermolecular hydrogen bonds increased by 22.63%, 9.42%, and 14.40% after the alkaline deinking process, neutral deinking process, and enzymatic deinking process, respectively. XRD revealed that the average width of crystallite size in the (002) lattice plane was decreased after different deinking processes, in accordance with the change tendency of cellulose crystallinity. CP/MAS 13C NMR combined with spectral fitting demonstrated that the content of different cellulose polymorphs changed during deinking processes. The increase of WRV was attributed to changes in the hydrogen bonding patterns and cellulose supramolecular structure.

Supramolecular structure of cellulose as a factor influencing the preparation of its ethers and esters

The change of the degree of crystallinity of mixed cellulose and the influence of this parameter on the reactivity of cellulose during preparation of soluble cellulose xanthogenate were examined based on an evaluation of the x-ray structure characteristics of samples of native cotton and regenerated cellulose. Formulas for calculating the crystallinity index of mixed celluloses and the NaOH concentration of the mercerizing solution that provided the required level of viscose filterability were proposed.