Cellulose Crystals Research Articles

Rheological properties and microstructures of cellulose acetate phthalate/hydroxypropyl cellulose blends

AbstractCellulose acetate phthalate (CAP)/hydroxypropyl cellulose (HPC) blends were investigated by means of attenuated total reflection‐Fourier transform infrared spectroscopy, thermogravimetry/differential thermal analysis, shear viscosity, oscillatory shear tests, and atomic force microscopy (AFM). Effect of solution concentrations in 2‐methoxyethanol, blend compositions, and shear rate on the rheological functions reflects the mobility of the chain segments or their orientation—with thinning behavior in the shear field. Specific interactions, such as the hydrogen bonds between polymer components and 2‐methoxyethanol used in casting solutions of films, influence the resulting morphology. Supernodular aggregates with different intensities and dimensions, which involve the coexistence of an isotropic and an anisotropic phase, typical for lyotropic cellulosic derivative liquid crystals at low concentrations, are evidenced by AFM images. This study is useful for applications of CAP/HPC blends in pharmaceutical domains.POLYM. COMPOS., 33:2072–2083, 2012. © 2012 Society of Plastics Engineers

Dynamics of cello-oligosaccharides on a cellulose crystal surface

Molecular dynamics (MD) simulations were performed to study the dynamics of cello-oligosaccharides on the cellulose crystal surface in the presence of water. In particular, single chains of cello-oligomers containing 2–10 repeat units, i.e. cellobiose, cellotetraose, cellohexaose, cellooctaose as well as cellodecaose—were simulated separately on the (1,0,0) cellulose crystal surface. The dynamics of cello-oligosaccharides were characterized as a function of the distance from the cellulose crystal surface. When the initial location of the cello-oligosaccharides was in the vicinity of the cellulose crystal (separation distance ~4–5A), they exhibited very small changes in their location and conformation. The cello-oligosaccharides with initial positions far from the surface moved either towards or away from the surface, as would be expected for diffusive behavior. However, once these molecules came in contact with the cellulose crystal surface, they became effectively immobile and got adsorbed on the surface. The dynamics of cellodecaose were studied in detail. From several MD trajectories, three stable conformations for the alignment of cellodecaose on the crystal surface were identified. These are: chain axis of cellodecaose is aligned parallel to the axes of the chains on the crystal surface, chain axis is approximately at right angles to the axes of the chains on the surface, and an obtuse angle conformation in which part of the chain is parallel and the other part is at an angle to the axes of the chains on the surface. The mechanism of adsorption of the cellodecaose on the surface was also identified.

Deformation of cellulose nanocrystals: entropy, internal energy and temperature dependence

An in-depth analysis was performed of the molecular deformation mechanisms in cellulose during axial stretching. For the first time, it was demonstrated that entropy affects the stiffness of cellulose nanocrystals significantly. This was achieved through Molecular Dynamics simulations of model nanocrystals subject to constant stress in the axial direction, for nanocrystals of varying lateral dimensions and at different temperatures. The simulations were analyzed in terms of Young’s modulus E, which is a measure of the elastic response to applied stress. A weak but significant temperature dependence was shown, with ∂E/∂T = −0.05 Gpa K−1 at room temperature, in agreement with experimental numbers. In order to analyze the respective contributions from internal energy and entropy, a decomposition of the total response of the free energy with respect to strain was made. It was shown that the decrease in E with increasing T is due to entropy, and that the magnitude of the decrease is 6–9 % at room temperature compared to the value at 0 K. This was also shown independently by a direct calculation of the vibrational entropy of the cellulose crystal. Finally, it was found that internal hydrogen bonds are contributing to the stiffness by 20 %, mainly by stabilizing the cellulose internal structure.

Preparation and Characterization of Nanocomposites of Carboxymethyl Cellulose Reinforced with Cellulose Nanocrystals

AbstractSummary: Cellulose nanocrystals (CNC) were extracted from Kraft pulp of Eucalyptus urograndis. The CNC were isolated by acid hydrolysis with H2SO4 64% (w/w) solution, for 20 minutes at 45 °C. The morphology and crystallinity of the CNC were investigated by atomic force microscopy (AFM) and X‐ray diffraction (XRD), respectively. The AFM image supports the evidence for the development of crystals of cellulose in nanometric scale. These nanoparticles were used as reinforcement material in carboxymethyl cellulose (CMC) matrix. Nanocomposites films were prepared by casting. The nanocomposites were characterized by thermal (TGA) and mechanical (DMA) analyses. A large reinforcing effect of the filler was observed. The tensile strength of nanocomposites was significantly improved by 107%, the elongation at break decreased by 48% and the thermal resistance increased slightly. The improvements in thermo‐mechanical properties suggest a close association between filler and matrix.

Hemicelluloses negatively affect lignocellulose crystallinity for high biomass digestibility under NaOH and H2SO4 pretreatments in Miscanthus

BackgroundLignocellulose is the most abundant biomass on earth. However, biomass recalcitrance has become a major factor affecting biofuel production. Although cellulose crystallinity significantly influences biomass saccharification, little is known about the impact of three major wall polymers on cellulose crystallization. In this study, we selected six typical pairs of Miscanthus samples that presented different cell wall compositions, and then compared their cellulose crystallinity and biomass digestibility after various chemical pretreatments.ResultsA Miscanthus sample with a high hemicelluloses level was determined to have a relatively low cellulose crystallinity index (CrI) and enhanced biomass digestibility at similar rates after pretreatments of NaOH and H2SO4 with three concentrations. By contrast, a Miscanthus sample with a high cellulose or lignin level showed increased CrI and low biomass saccharification, particularly after H2SO4 pretreatment. Correlation analysis revealed that the cellulose CrI negatively affected biomass digestion. Increased hemicelluloses level by 25% or decreased cellulose and lignin contents by 31% and 37% were also found to result in increased hexose yields by 1.3-times to 2.2-times released from enzymatic hydrolysis after NaOH or H2SO4 pretreatments. The findings indicated that hemicelluloses were the dominant and positive factor, whereas cellulose and lignin had synergistic and negative effects on biomass digestibility.ConclusionsUsing six pairs of Miscanthus samples with different cell wall compositions, hemicelluloses were revealed to be the dominant factor that positively determined biomass digestibility after pretreatments with NaOH or H2SO4 by negatively affecting cellulose crystallinity. The results suggested potential approaches to the genetic modifications of bioenergy crops.

Cellulose crystals in fibrovascular bundles of sugarcane culms: orientation, size, distortion, and variability

Cellulose crystals in fibrovascular bundles of sugarcane culms were throughly characterized by X-ray diffraction, with area-detector patterns acquired in fiber geometry. It was observed that microfibril angles are, on average, higher for bundles from pith compared to bundles from intermediate regions and rind, and higher for ratoon canes compared to plant canes. On the other hand, microfibril angles do not differ significantly among sugarcane cultivars, internode positions in the culm, or ratoon cane cut cycles. Broadening analyses of diffraction peaks yield crystal sizes (crystal width from equatorial 200 reflection and apparent crystal lengths from meridional 002 and 004 reflections) similar to other plant species (woods and bamboo). In addition, compared to reference cellulose Iβ, the 200, 110, and 110 diffraction peaks from sugarcane cellulose are notably shifted. These shifts indicate pronounced crystallite distortions, with expanded intersheet spacing d 200 , contracted d 1 1 0 /d 110 , and monoclinic angle γ closer to 90°. Our findings deepen the understanding of the fine structure and variability of sugarcane lignocellulose.

Piezoelectric Effect of Cellulose Nanocrystals Thin Films.

Ultrathin films of aligned cellulose nanocrystals (CNCs) were assembled on mica supports by using electric field-assisted shear. The relationship between polarization gradients and strain mechanics of the obtained films was examined by monitoring their deflection with an atomic force microscope operated in contact mode. The piezoelectric response of the films was ascribed to the collective contribution of the asymmetric crystalline structure of the cellulose crystals. The magnitude of the effective shear piezoelectric constant (d25) of highly ordered CNC films was determined to be 2.1 Å/V, which is comparable to that of a reference film of a piezoelectric metal oxide.

Effects of aging on the vibrational properties of wood

Abstract Vibrational properties of aged wood (121∼296 years old) were compared with those of recently cut “new” wood (8 years old). The aged wood showed higher sound velocity ( V L ) and lower mechanical loss tangent (tan δ L ) than the new wood. The ratio of Young's modulus and shear modulus ( E L / G L ) remained unchanged or increased slightly during the aging period. These results coincide with musicians’ empirical observations that the acoustic quality of wooden soundboards is improved by aging. In addition, the reduced tan δ L of the aged wood indicates the qualitative difference between the naturally aged and heat-treated wood. The experimental results were explained by using a cell wall model when we assumed the following: increase in the volume fraction of cellulosic microfibrils; reduction in the shear modulus of amorphous matrix substances, and; reduction in the loss tangent of the matrix. These assumptions appear reasonable when we consider the crystallization of cellulose, depolymerization of hemicelluloses, and cross-linking in the lignin complex during aging.

Preparation and properties of cellulose‐based nano composites of clay and polypropylene

AbstractComposites of polypropylene (PP) and crystalline cellulose were prepared after modification of the host matrix by reactive extrusion grafting of maleic anhydride. Acid, alkali, and mechanical treatment of wood flour (WF) was conducted to obtain a suspension of micro‐ and nanocrystalline cellulose. Layered silicates (clay) were partially intercalated with cellulose crystals, and the modified layered silicate was used as filler in the PP matrix at various concentrations via a melt‐blending process. The tensile strength of composites prepared from cellulose‐modified clay was greater than that of the PP‐clay and PP‐WF composites at a 5% filler concentration, whereas deterioration of mechanical properties was observed when clay and WF were used alone for reinforcement. The dispersion of the filler in the matrix significantly decreased after clay modification with cellulose at higher concentrations, as shown by X‐ray diffraction (XRD) data and transmission electron microscopy (TEM) images. Thermogravimetric analysis (TGA) showed an increase in the thermal resistance of samples, which was attributed to the presence of clay platelets that dissipated heat by generating torture paths. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Diffraction from nonperiodic models of cellulose crystals

Powder and fiber diffraction patterns were calculated for model cellulose crystallites with chains 20 glucose units long. Model sizes ranged from four chains to 169 chains, based on cellulose Iβ coordinates. They were subjected to various combinations of energy minimization and molecular dynamics (MD) in water. Disorder induced by MD and one or two layers of water had small effects on the relative intensities, except that together they reduced the low-angle scattering that was otherwise severe enough to shift the 1 $$ \bar {1} $$ 0 peak. Other shifts in the calculated peaks occurred because the empirical force field used for MD and minimization caused the models to have small discrepancies with the experimental intermolecular distances. Twisting and other disorder induced by minimization or MD increased the breadth of peaks by about 0.2–0.3° 2-θ. Patterns were compared with experimental results. In particular, the calculated fiber patterns revealed a potential for a larger number of experimental diffraction spots to be found for cellulose from some higher plants when crystallites are well-oriented. Either that, or further understanding of those structures is needed. One major use for patterns calculated from models is testing of various proposals for microfibril organization.

【総説-糖質関連酵素化学シンポジウム-】 分子シミュレーションによる結晶性セルロース基質に対するセロビオヒドロラーゼ糖結合性モジュール基質認識特性の解析

【総説-糖質関連酵素化学シンポジウム-】 分子シミュレーションによる結晶性セルロース基質に対するセロビオヒドロラーゼ糖結合性モジュール基質認識特性の解析

Relationship between wood elastic strain under bending and cellulose crystal strain

Wood is a natural composite material with a complex multi-scale structure. Its stiffness is mainly due to crystalline cellulose fibrils reinforcing the cell walls. In order to quantify the contribution of cellulose to wood elastic properties in both tension and compression, the change in cellulose (0 0 4) lattice spacing (cellulose crystal strain) was measured by X-ray diffraction during a bending test on poplar specimens. A detailed methodology is presented to accurately quantify this cellulose crystal strain. Results show that during elastic loading, cellulose crystal strain is roughly proportional to wood strain. The strain ratio (cellulose crystal strain/wood strain) was close to 0.75, and did not differ significantly in tension and compression. Interpretation of the strain ratio with respect to cellulose orientation shows that part of the wood strain occurs without inducing cellulose crystal strain. This contribution amounts to 10–15% of wood strain, and its possible origin at different levels of wood ultra-structure is discussed.

Production of cellulose nanocrystals using hydrobromic acid and click reactions on their surface

Cellulose nanocrystals (CNCs) were prepared by acidic hydrolysis of cotton fibers (Whatman #1 filter paper). In our efforts to select conditions in which the hydrolysis media does not install labile protons on the cellulose crystals, a mineral acid other than sulfuric acid (H2SO4) was used. Furthermore, in our attempts to increase the yields of nanocrystals ultrasonic energy was applied during the hydrolysis reaction. The primary objective was to develop hydrolysis reaction conditions for the optimum and reproducible CNC production. As such, the use of hydrobromic acid (HBr) with the application of sonication as a function of concentration (1.5–4.0 M), temperature (80–100 °C), and time (1–4 h) was examined. Applying sonic energy during the reaction was found to have significant positive effects as far as reproducible high yields are concerned. Overall, the combination of 2.5 M HBr, 100 °C, and 3 h associated with the sonication during the reaction generated the highest nanocrystal yields. In addition to the optimization study three types of surface modifications including TEMPO-mediated oxidation, alkynation, and azidation were used to prepare surface-activated, reactive CNCs. Subsequently, click chemistry was employed for bringing together the modified nanocrystalline materials in a unique regularly packed arrangement demonstrating a degree of molecular control for creating these structures at the nano level.

Mechanistic understanding of interactions between cellulose and ionic liquids: A molecular simulation study

The interactions between cellulose and ionic liquids (ILs) have been investigated by molecular simulations. A crystalline I β structure is adopted for cellulose and two ILs are considered, namely 1- n-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF 6] and 1- n-butyl-3-methylimidazolium acetate [BMIM][Ac]. The cellulose and ILs are mimicked by the AMBER force field with the atomic charges estimated from quantum chemical calculations. The density, crystalline lattice constants, thermal expansion coefficients and Young’s modulus predicted for the cellulose crystal agree well with experimental data. The Young’s modulus along the chain direction is high due to the strong glycosidic bonds in oligosaccharide chains. Hydrogen-bonding is observed between –OH groups, including the intra-chain O2H2∙∙∙O6 and O3H3∙∙∙O5 and the inter-chain O6H6∙∙∙O3. Upon contact with the two ILs and water, the number of hydrogen-bonds at the cellulose surface decreases, particularly for the inter-chain O6H6∙∙∙O3 in [BMIM][Ac]. The simulation results reveal that solvation leads to the breaking of hydrogen-bonds at the cellulose surface. Among the three solvents, [BMIM][Ac] appears to have the strongest capability to break the hydrogen-bonds in cellulose. This simulation study provides molecular insight into the interactions of cellulose with ILs and suggests that hydrogen-bonding is critical to govern cellulose dissolution.

Manufacture of cellulose nanocrystals by cation exchange resin-catalyzed hydrolysis of cellulose

Cellulose nanocrystals (CNC) were prepared from microcrystalline cellulose (MCC) by hydrolysis with cation exchange resin (NKC-9) or 64% sulfuric acid. The cation exchange resin hydrolysis parameters were optimized by using the Box–Behnken design and response surface methodology. An optimum yield (50.04%) was achieved at a ratio of resin to MCC (w/w) of 10, a temperature of 48°C and a reaction time of 189min. Electron microscopy (EM) showed that the diameter of CNCs was about 10–40nm, and the length was 100–400nm. Regular short rod-like CNCs were obtained by sulfuric acid hydrolysis, while long and thin crystals of cellulose were obtained with the cation exchange resin. X-ray diffraction (XRD) showed that, compared with MCC, the crystallinity of H2SO4-CNC and resin-CNC increased from 72.25% to 77.29% and 84.26%, respectively. The research shows that cation exchange resin-catalyzed hydrolysis of cellulose could be an excellent method for manufacturing of CNC in an environmental-friendly way.

Evolution of cellulose crystals during prehydrolysis and soda delignification of sugarcane lignocellulose

This work investigates the evolution of cellulose crystals from sugarcane lignocellulose (bagasse and leaves) submitted to prehydrolysis (hydrothermal, dilute acid, or steam explosion) and soda delignifications. Raw and treated materials are characterized by X-ray diffraction with modeling of area-detector patterns. Three treatment effects are correlated: increase in cellulose content, quantified by strong acid hydrolysis; increase in average cellulose crystallite width, inferred from sharper 200 diffraction peaks; and decrease in crystallite distortion, evidenced by d 200-spacing approaching reference values. Crystal contents measured according to recent developments (in Driemeier and Calligaris, J Appl Cryst 44:184–192, 2011) are compared to cellulose contents. Limitations for this comparison are discussed. Results are consistent with minimum non-crystalline cellulose in raw lignocellulose, and with partial cellulose decrystallization or more defective crystallites in treated materials.

Natural fibers for biocomposites

Abstract

Characteristics of composite films based on methyl cellulose and poly(N-vinylformamide) prepared from solutions in water and dimethyl sulfoxide

The stress-strain characteristics of composite films based on methyl cellulose and poly(vinylformamide) prepared from solutions of polymer blends in water and dimethyl sulfoxide are studied. The temperature of relaxation transitions in the mixed films and the concentration interval where the polymers are compatible are defined via the thermomechanical method and dynamic mechanical analysis. The effect of the nature of a solvent on the mechanism of crystallization of methyl cellulose, the stress—strain characteristics of the composite films, and the compatibility between the polymers is investigated.

The continuing debate over the structure of cellulose: historical perspective and outlook

The crystalline structure of native cellulose, with its unique microfibrillar morphology resulting from a complex biogenesis mechanism, has not only been the most studied subject in polymer science, but is still generating great interest along with lively debates and controversies. This issue of Cellulose features such a debate in the form of two articles dealing with the conformational analysis of the glucosidic bond in the cellulose chains. This debate is but the latest incident in a long string of events, which represent the foundation of our current understanding of this important material. This makes this an opportune moment to reflect on some of the major milestones in the history of cellulose structure evaluation, which also often involved debates and controversies. It was in 1913, i.e. close to one century ago, that Nishikawa and Ono showed the first diffraction patterns of two cellulose-based plant materials, namely bamboo and hemp, taking advantage of the discovery of the interference phenomena of X-rays reported 1 year earlier by Laue, Friedrich and Knipping. Following this early report, diffraction diagrams of a large number of cellulose materials were duly recorded and subjected to analysis, as it was felt that the knowledge of the crystalline structure of cellulose was of great importance for the development and improvement of cellulose-based products. While recording diffraction patterns of these specimens, it was soon realized that even the X-ray data sets of the most crystalline samples remained limited and it was therefore hard to deduce from them alone the required structural details. It is only when the diffraction data could be complemented by the occurrence of new techniques that substantial advances toward the structural description of cellulose could be made. The sequential emergence of such techniques explains the succession of steps leading to the present understanding. In the progress toward the molecular description of the crystal structure of cellulose from X-ray diffraction data, a first landmark was the incorporation of the stereochemistry of the glucosyl moieties in the molecular models built by, among others, Meyer and Mark (1928), later revised by Meyer and Misch (1937), who presented a model where the crystal of cellulose consisted of two antiparallel chains. This last model, which remained the established standard for at least two decades, was confronted with a series of conflicting data, resulting from new techniques. In 1958, the recording of electron diffraction diagrams of frozen Valonia cell wall fragments allowed Honjo and Watanabe to obtain diffraction data sets far better H. Chanzy—affiliated with the Universite Joseph Fourier and member of the Institut de Chimie Moleculaire de Grenoble.

Cellobiohydrolase Hydrolyzes Crystalline Cellulose on Hydrophobic Faces

Biodegradation of plant biomass is a slow process in nature, and hydrolysis of cellulose is also widely considered to be a rate-limiting step in the proposed industrial process of converting lignocellulosic materials to biofuels. It is generally known that a team of enzymes including endo- and exocellulases as well as cellobiases are required to act synergistically to hydrolyze cellulose to glucose. The detailed molecular mechanisms of these enzymes have yet to be convincingly elucidated. In this report, atomic force microscopy (AFM) is used to image in real-time the structural changes in Valonia cellulose crystals acted upon by the exocellulase cellobiohydrolase I (CBH I) from Trichoderma reesei. Under AFM, single enzyme molecules could be observed binding only to one face of the cellulose crystal, apparently the hydrophobic face. The surface roughness of cellulose began increasing after adding CBH I, and the overall size of cellulose crystals decreased during an 11-h period. Interestingly, this size reduction apparently occurred only in the width of the crystal, whereas the height remained relatively constant. In addition, the measured cross-section shape of cellulose crystal changed from asymmetric to nearly symmetric. These observed changes brought about by CBH I action may constitute the first direct visualization supporting the idea that the exocellulase selectively hydrolyzes the hydrophobic faces of cellulose. The limited accessibility of the hydrophobic faces in native cellulose may contribute significantly to the rate-limiting slowness of cellulose hydrolysis.