Cellulose Orientation Research Articles

Impact of coagulation solvent interactions on porous morphology evolution in cellulose xerogels

The role of coagulation solvent interactions on the pore formation mechanism in cellulose xerogels was investigated using single-step coagulation baths. A series of cellulose xerogels were fabricated from cotton yarns partially dissolved in ionic liquid (i.e., 1-ethyl-3-methylimidazolium acetate) and then immersed in one of seven different coagulation baths. These samples were evaluated using N2 physisorption, inverse gas chromatography, and X-ray photoelectron spectroscopy. The regenerated cellulose orientation and resultant surface hydrophilicity was found to be dependent on solvent solubility interactions with an emphasis on polar interaction and dispersion force strength. More importantly, the xerogel specific surface area dramatically decreased from 100 m2g−1 to 0.278 m2g−1 with increasing hydrophilicity, confirming the importance of controlled cellulose orientation during the coagulation step of cellulose xerogel fabrication. These results have been used to propose a new pore formation mechanism in cellulose xerogels and provide recommendations towards the development of controllable porosity during xerogel fabrication.

Synchrotron X-ray measurements of cellulose in the cell wall of aged wood under uniaxial loading

Abstract The purpose of this study is to examine the effect of wood aging on the mechanical behavior at the cell-wall level. Synchrotron X-ray diffraction (XRD) measurements were performed to investigate the mechanical behavior of cellulose in the S2 layer of aged wood from a 250-year-old attic cabin beam. XRD measurements under uniaxial loading were performed on the cellulose (004) plane; the results were compared with those of recent wood. The cellulose in aged wood exhibited a delayed response to both tensile and compressive loading compared with recent wood. Under compressive loading, cellulose showed an increase in maximum strain and a significant increase in the variation of cellulose orientation angle, indicating that it may exhibit buckling-like meandering behavior. These results could be explained based on the decrease in hemicellulose content in the cell wall due to wood aging. In other words, the results suggested that an amorphous material in the cell wall affected the mechanical behavior of wood at the cell-wall level.

In situ infrared imaging of the local orientation of cellulose fibrils in plant secondary cell walls.

The mechanical and chemical properties of plant cell walls greatly rely on the supramolecular assembly of cellulose fibrils. To study the local orientation of cellulose in secondary plant cell walls, diffraction limited infrared (IR) micro-spectroscopic mapping experiments were conducted at different orientation of transverse leaf section of the grass Sorghum bicolor with respect to the polarization direction of the IR radiation. Two-dimensional maps, based on polarization-sensitive absorption bands of cellulose were obtained for different polarization angles. They reveal a significant degree of anisotropy of the cellulose macromolecules as well as of other biopolymers in sclerenchyma and xylem regions of the cross section. Quantification of the signals assigned to polarization sensitive vibrational modes allowed to determine the preferential orientation of the sub-micron cellulose fibrils in single cell walls. A sample of crystalline nano-cellulose comprising both a single microcrystal as well as unordered layers of nanocrystals was used for validation of the approach. The results demonstrate that diffraction limited IR micro-spectroscopy can be used to study hierarchically structured materials with complex anisotropic behavior.

Detecting the orientation of newly-deposited crystalline cellulose with fluorescent CBM3

Cellulose microfibril patterning influences many of the mechanical attributes of plant cell walls. We developed a simple, fluorescence microscopy-based method to detect the orientation of newly-synthesized cellulose microfibrils in epidermal peels of onion and Arabidopsis. It is based on Alexa Fluor 488-tagged carbohydrate binding module 3a (CBM3a) from Clostridium thermocellum which displayed a nearly 4-fold greater binding to cell walls at pH 5.5 compared with pH 8. Binding to isolated cellulose did not display this pH dependence. At pH 7.5 fibrillar patterns at the surface of the epidermal peels were visible, corresponding to the directionality of surface cellulose microfibrils, as verified by atomic force microscopy. The fibrillar pattern was not visible as the labeling intensity increased at lower pH. The pH of greatest cell wall labeling corresponds to the isoelectric point of CBM3a, suggesting that electrostatic forces limit CBM3a penetration into the wall. Consistent with this, digestion of the wall with pectate lyase to remove homogalacturonan increased labeling intensity. We conclude that electrostatic interactions strongly influence labeling of cell walls with CBM3 and potentially other proteins, holding implications for any work that relies on penetration of protein probes such as CBMs, antibodies, or enzymes into charged polymeric substrates.

Effects of microwave-assisted drying on the drying shrinkage and chemical properties of bamboo stems

This study aimed to evaluate changes in the microwave-assisted drying shrinkage and chemical properties of a bamboo stem treated by microwave-assisted drying. The result showed that the bamboo stem treated via microwave-assisted drying exhibited a wall thickness shrinkage rate of 3.88 %，which was lower than that of natural bamboo (4.36 %). A sizable number of C-C bonds and C–O bonds were formed while the carbonyl and hydroxyl groups were reduced on the surface of the treated bamboo. This observation indicates that the treated bamboo stem showed an altered chemical bond location on the surface. Meanwhile, microwave-assisted drying partly degraded polysaccharides from hemicellulose and lignin, oxidizing the methoxyl and aromatic hydroxyl groups in lignin, and increasing the absorption peak at 148 ppm. The treated samples had a decreased amorphous region near the fiber surface and hemicellulose content and increased secondary crystalline fibers. In addition, the hydroxyl groups on the cell surface underwent a condensation reaction via microwave irradiation, and intramolecular hydroxyl groups were formed in the amorphous region, increasing the consistent arrangement of cellulose and lignin. The parenchyma cells were largely deformed, decreasing the orientation of cellulose and lignin on the cell surface, as well as reducing the absorption peak.

The spatial orientation and interaction of cell wall polymers in bamboo revealed with a combination of imaging polarized FTIR and directional chemical removal

The mechanical and physical properties of lignocellulosic materials are closely related to the orientation and interaction of the polymers within cell walls. In this work, Imaging Polarized FTIR, combined with directional chemical removal, was applied to characterize the spatial orientation and interaction of cell wall polymers in bamboo fibers and parenchyma cells from two bamboo species. The results demonstrate the cellulose in bamboo fibers is nearly axially oriented whereas it is almost transversely arranged in parenchyma cells. Xylan and lignin are both preferentially oriented alongside cellulose, but with less orientation degree in the parenchyma cells. After lignin removal, the average orientation of xylan and cellulose is little affected, suggesting a strong interaction between cellulose and xylan. However, the alkaline treatment significantly weakens the orientation of lignin in both fibers and parenchyma cells, and more significant for the latter, indicating the easy-degradable nature of lignin in parenchyma cells. Additionally, it seemed the lignin and xylan in fibers were more difficult to remove as compared to parenchyma cells, supporting the assumption that stronger interaction exists between lignin and xylan in the fibers. In a word, it is believed parenchyma cells are more suitable for biorefinery owing to their less ordered and relatively loose molecular assembly, as compared to fibers.Graphical abstract

Detecting the Orientation of Newly-Deposited Crystalline Cellulose with Fluorescent Cbm3

Detecting the Orientation of Newly-Deposited Crystalline Cellulose with Fluorescent Cbm3

Local Variations in Carbohydrates and Matrix Lignin in Mechanically Graded Bamboo Culms.

The mechanical performance of bamboo is highly dependent on its structural arrangement and the properties of biomacromolecules within the cell wall. The relationship between carbohydrates topochemistry and gradient micromechanics of multilayered fiber along the diametric direction was visualized by combined microscopic techniques. Along the radius of bamboo culms, the concentration of xylan within the fiber sheath increased, while that of cellulose and lignin decreased gradually. At cellular level, although the consecutive broad layer (Bl) of fiber revealed a relatively uniform cellulose orientation and concentration, the outer Bl with higher lignification level has higher elastic modulus (19.59–20.31 GPa) than that of the inner Bl close to the lumen area (17.07–19.99 GPa). Comparatively, the cell corner displayed the highest lignification level, while its hardness and modulus were lower than that of fiber Bl, indicating the cellulose skeleton is the prerequisite of cell wall mechanics. The obtained cytological information is helpful to understand the origin of the anisotropic mechanical properties of bamboo.

Gradient Diffusion Anisotropic Carboxymethyl Cellulose Hydrogels for Strain Sensors.

Recently, because of the unique properties of anisotropic and isotropic structures, there are more research studies on anisotropic hydrogels. We prepared a gradient anisotropic carboxymethyl cellulose hydrogel (CMC-Al3+) by directionally diffusing aluminum chloride solution. The orientation of carboxymethyl cellulose (CMC) chains is perpendicular to the direction of aluminum ion diffusion. The degree of cross-linking and orientation gradually decrease along the direction of aluminum ion diffusion. Compared with anisotropic hydrogels prepared by other methods, the hydrogels prepared by directionally diffusing aluminum ion solution have a gradient lamellar structure. Because of the large amount of aluminum ions in CMC-Al3+, the hydrogel shows good sensing performance. CMC-Al3+ is packaged with PVC electrical flame retardant tape to produce a strain sensor used to detect human tiny movements, which can accurately and stably monitor tiny movements. Hydrogel-based strain sensors can be widely used in the fields of human-computer intelligence, human-computer interaction, and wearable devices in the future.

Functional modification of cellulose by chitosan and gamma radiation for higher grafting of UV protective natural chromophores

This study demonstrated a green functionalization process of a cellulose substrate by combining the chitosan treatment and gamma radiation. To impart the UV protection characteristics in the cellulosic structure, natural chromophores derived from Banana floral stem (BFS) was grafted in the functionalized cellulose surface. Phytochemical screening was performed to confirm the types of UV protective natural chromophores (UVPNCs) presented in BFS. The result exhibited the presence of condensed tannin, flavonoids, anthocyanin, betacyanin, and anthraquinone as the major UVPNC components in BFS. The optimum conditions for maximum sorption of UVPNCs into the functionalized cellulose matrix were recorded at 80°C for 60 min. The cationic biopolymer chitosan (2 g/L), different gamma absorbs doses (2, 4, and 6 kGy), and combined chitosan and gamma treatment into cellulose resulted around 15–23%, 44%, and 41–64% improved absorption of UVPNCs, respectively, as demonstrated by the change in color strength (K/S) compared to unmodified cellulose matrix. The concurrent treatments greatly improved the total crystallinity index (TCI), hydrogen bond intensity (HBI), hydrogen bonding energy (EH), hydrogen bonding distance (R) and asymmetric factor (AF) from 1.358 to 1.363, 0.971 to 0.988, 27.15 kJ–27.40 kJ (at 3274 cm−1), 2.766 Å to 2.764 Å (at 3274 cm−1) and 0.47 to 0.10, respectively. For gamma treatment, 6 kGy irradiation dose provided the best result for improved molecular orientation of cellulose and in combination of chitosan the substrate attained a maximum K/S of 1.98 after UVPNCs grafting. It was found that the UV protection factor (UPF) rating has a linear relationship with the UVPNCs absorption (K/S) and a maximum four-fold increase in UPF (165–506) was evident. The excellent bonding durability of the UVPNCs grafted samples was further ensured in terms of several colorfastness properties. This sustainable functionalization of cellulose with high UPF offers a great promise for applications in health care and photodegradation protection.

Preferred crystallographic orientation of cellulose in plant primary cell walls

Cellulose, the most abundant biopolymer on earth, is a versatile, energy rich material found in the cell walls of plants, bacteria, algae, and tunicates. It is well established that cellulose is crystalline, although the orientational order of cellulose crystallites normal to the plane of the cell wall has not been characterized. A preferred orientational alignment of cellulose crystals could be an important determinant of the mechanical properties of the cell wall and of cellulose-cellulose and cellulose-matrix interactions. Here, the crystalline structures of cellulose in primary cell walls of onion (Allium cepa), the model eudicot Arabidopsis (Arabidopsis thaliana), and moss (Physcomitrella patens) were examined through grazing incidence wide angle X-ray scattering (GIWAXS). We find that GIWAXS can decouple diffraction from cellulose and epicuticular wax crystals in cell walls. Pole figures constructed from a combination of GIWAXS and X-ray rocking scans reveal that cellulose crystals have a preferred crystallographic orientation with the (200) and (110)/(1bar 10) planes preferentially stacked parallel to the cell wall. This orientational ordering of cellulose crystals, termed texturing in materials science, represents a previously unreported measure of cellulose organization and contradicts the predominant hypothesis of twisting of microfibrils in plant primary cell walls.

Preparation of Cellulose Insulating Paper with Low Dielectric Constant by BTCA Esterification Crosslinking

AbstractThis study aims to decrease the dielectric constant of kraft paper by 1,2,3,4‐butanetetracarboxylic acid (BTCA) esterification crosslinking. Kraft paper samples are treated with various concentrations of BTCA to prepare modified paper with different reaction degrees. Morphology and surface chemical composition are characterized. The dielectric constant and loss of the plain and modified paper are also investigated. Results show that esterification occurs successfully between cellulose molecular chain and BTCA. The intrinsic dielectric constant and loss of 6 g L−1 BTCA‐treated paper decrease by 23.5% and 36.3%, respectively, at 50 Hz. The esterification can reduce the hydroxyl amounts on cellulose. The formed crosslinking network between the cellulose chains restricts the cellulose orientation polarization, thereby reducing cellulose polarizability. The electrical strength, mechanical properties, and thermal behavior of the samples are explored to evaluate comprehensively the modifying effect. BTCA esterification crosslinking proves to be a promising method for decreasing the dielectric constant of kraft paper.

Wood cell wall ultrastructure The key to understanding wood properties and behaviour

ABSTRACT In the last 100 years, major advances have been made in understanding wood cell wall ultrastructure in tracheids, fibres, vessels and parenchyma and its relationship with xylem function and wood properties. This review will focus on how the development of imaging techniques and their application to wood cell walls has led to an understanding of cell wall organisation and the relationship between micro and macro scale properties in wood and wood-based materials. Topics such as wood formation, wood chemistry and reaction wood have recently been reviewed elsewhere and are considered only briefly in this review. Two features of wood cell walls have dominated the literature; orientation and layering of cellulose which determines the longitudinal stiffness of wood, and the distribution (topochemistry) of lignin which determines compression strength and pulping properties.

Significant influence of lignin on axial elastic modulus of poplar wood at low microfibril angles under wet conditions.

Wood is extensively used as a construction material. Despite increasing knowledge of its mechanical properties, the contribution of the cell-wall matrix polymers to wood mechanics is still not well understood. Previous studies have shown that axial stiffness correlates with lignin content only for cellulose microfibril angles larger than around 20°, while no influence is found for smaller angles. Here, by analysing the wood of poplar with reduced lignin content due to down-regulation of CAFFEOYL SHIKIMATE ESTERASE, we show that lignin content also influences axial stiffness at smaller angles. Micro-tensile tests of the xylem revealed that axial stiffness was strongly reduced in the low-lignin transgenic lines. Strikingly, microfibril angles were around 15° for both wild-type and transgenic poplars, suggesting that cellulose orientation is not responsible for the observed changes in mechanical behavior. Multiple linear regression analysis showed that the decrease in stiffness was almost completely related to the variation in both density and lignin content. We suggest that the influence of lignin content on axial stiffness may gradually increase as a function of the microfibril angle. Our results may help in building up comprehensive models of the cell wall that can unravel the individual roles of the matrix polymers.

Structural organization of the cell wall polymers in compression wood as revealed by FTIR microspectroscopy.

Glucomannan was more strongly oriented, in line with the orientation of cellulose, than the xylan in both compression wood and normal wood of Chinese fir. Lignin in compression wood was somewhat more oriented in the direction of the cellulose microfibrils than in normal wood. The structural organization in compression wood (CW) is quite different from that in normal wood (NW). To shed more light on the structural organization of the polymers in plant cell walls, Fourier Transform Infrared (FTIR) microscopy in transmission mode has been used to compare the S2-dominated mean orientation of wood polymers in CW with that in NW from Chinese fir (Cunninghamia lanceolata). Polarized FTIR measurements revealed that in both CW and NW samples, glucomannan and xylan showed a parallel orientation with respect to the cellulose microfibrils. In both wood samples, the glucomannan showed a much greater degree of orientation than the xylan, indicating that the glucomannan has established a stronger interaction with cellulose than xylan. For the lignin, the absorption peak also indicated an orientation along the direction of the cellulose microfibrils, but this orientation was more pronounced in CW than in NW, indicating that the lignin is affected by the orientation of the cellulose microfibrils more strongly in CW than it is in NW.

Highly Stretchable, Transparent, and Conductive Wood Fabricated by in Situ Photopolymerization with Polymerizable Deep Eutectic Solvents.

The rational design of high-performance, flexible, transparent, electrically conducting sensor attracts considerable attention. However, these designed devices predominantly utilize glass and plastic substrates, which are expensive and not environmentally friendly. Here, novel transparent and conductive woods (TCWs) were fabricated by using renewable wood substrates and low-cost conductive polymers. Polymerizable deep eutectic solvents (PDES), acrylic-acid (AA)/choline chloride (ChCl), were used as backfilling agents and in situ photopolymerized in the delignified wood, which endowed the materials with high transparency (transmittance of 90%), good stretchability (strain up to 80%), and high electrical conductivity (0.16 S m-1). The retained cellulose orientation and strong interactions between the cellulose-rich template and poly(PDES) endow TCWs with excellent mechanical properties. Moreover, TCWs exhibited excellent sensing behaviors to strain/touch, even at low strain. Therefore, these materials can be used to detect weak pressure such as human being's subtle bending-release activities. This work provides a new route to fabricate functional composite materials and devices which have promising potential for electronics applications in flexible displays, tactile skin sensors, and other fields.

High-Density Molded Cellulose Fibers and Transparent Biocomposites Based on Oriented Holocellulose.

Ecofriendly materials based on well-preserved and nanostructured wood cellulose fibers are investigated for the purpose of load-bearing applications, where optical transmittance may be advantageous. Wood fibers are subjected to mild delignification, flow orientation, and hot-pressing to form an oriented material of low porosity. The biopolymer composition of the fibers is determined. Their morphology is studied by scanning electron microscopy, cellulose orientation is quantified by X-ray diffraction, and the effect of beating is investigated. Hot-pressed networks are impregnated by a methyl methacrylate monomer and polymerized to form thermoplastic wood fiber/poly(methyl methacrylate) biocomposites. Tensile tests are performed, as well as optical transmittance measurements. Structure-property relationships are discussed. High-density molded fibers from holocellulose have mechanical properties comparable with nanocellulose materials and are recyclable. The thermoplastic matrix biocomposites showed superior mechanical properties (Young's modulus of 20 GPa and ultimate strength of 310 MPa) at a fiber volume fraction of 52%, with high optical transmittance of 90%. The study presents a scalable approach for strong, stiff, and transparent molded fibers/biocomposites.

Self-Assembly of Cellulose in Super-Cooled Ionic Liquid under the Impact of Decelerated Antisolvent Infusion: An Approach toward Anisotropic Gels and Aerogels.

Assembly of (bio)polymers into long-range anisotropic nanostructured gels and aerogels is of great interest in advanced material engineering since it enables directional tuning of properties, such as diffusivity, light, heat, and sound propagation, cell proliferation, and mechanical properties. Here we present an approach toward anisotropic cellulose II gels and aerogels that employs specific diffusion and phase separation phenomena occurring during decelerated infusion of an antisolvent into isotropic supercooled solutions of cellulose in an ionic liquid to effectuate supramolecular assembly of cellulose in anisotropic colloidal network structures. At the example of the distillable ionic liquid 1,1,3,3-tetramethylguanidinium acetate, the antisolvent ethanol, and spherocylindrical porous molds, we demonstrate that the proposed facile, environmental-benign and versatile route affords gels and aerogels whose specific anisotropic nanomorphology and properties reflect the preferred supramolecular cellulose orientation during phase separation, which is perpendicular to the direction of antisolvent diffusion. Comprehensive X-ray scattering experiments revealed that the (aero)gels are composed of an interconnected, fibrous, highly crystalline (CrI ≈ 72%), cellulose II with a cross-sectional Guinier radius of the struts of about 2.5 nm, and an order parameter gradient from about 0.1 to 0.2. The obtained gels and aerogels feature high specific surface areas (350-630 m2 g-1) and excellent mechanical properties like high toughness (up to 471 kJ m-3 for a 60% compression, ρB = 80 mg cm-3) and resilience (up to 13.4 kJ m-3, ρB = 65 mg cm-3).

Anisotropic growth is achieved through the additive mechanical effect of material anisotropy and elastic asymmetry.

Fast directional growth is a necessity for the young seedling; after germination, it needs to quickly penetrate the soil to begin its autotrophic life. In most dicot plants, this rapid escape is due to the anisotropic elongation of the hypocotyl, the columnar organ between the root and the shoot meristems. Anisotropic growth is common in plant organs and is canonically attributed to cell wall anisotropy produced by oriented cellulose fibers. Recently, a mechanism based on asymmetric pectin-based cell wall elasticity has been proposed. Here we present a harmonizing model for anisotropic growth control in the dark-grown Arabidopsis thaliana hypocotyl: basic anisotropic information is provided by cellulose orientation) and additive anisotropic information is provided by pectin-based elastic asymmetry in the epidermis. We quantitatively show that hypocotyl elongation is anisotropic starting at germination. We present experimental evidence for pectin biochemical differences and wall mechanics providing important growth regulation in the hypocotyl. Lastly, our in silico modelling experiments indicate an additive collaboration between pectin biochemistry and cellulose orientation in promoting anisotropic growth.

TRM4 is essential for cellulose deposition in Arabidopsis seed mucilage by maintaining cortical microtubule organization and interacting with CESA3.

Summary The differentiation of the seed coat epidermal (SCE) cells in Arabidopsis thaliana leads to the production of a large amount of pectin‐rich mucilage and a thick cellulosic secondary cell wall. The mechanisms by which cortical microtubules are involved in the formation of these pectinaceous and cellulosic cell walls are still largely unknown.Using a reverse genetic approach, we found that TONNEAU1 (TON1) recruiting motif 4 (TRM4) is implicated in cortical microtubule organization in SCE cells, and functions as a novel player in the establishment of mucilage structure. TRM4 is preferentially accumulated in the SCE cells at the stage of mucilage biosynthesis. The loss of TRM4 results in compact seed mucilage capsules, aberrant mucilage cellulosic structure, short cellulosic rays and disorganized cellulose microfibrils in mucilage. The defects could be rescued by transgene complementation of trm4 alleles. Probably, this is a consequence of a disrupted organization of cortical microtubules, observed using fluorescently tagged tubulin proteins in trm4 SCE cells. Furthermore, TRM4 proteins co‐aligned with microtubules and interacted directly with CELLULOSE SYNTHASE 3 in two independent assays.Together, the results indicate that TRM4 is essential for microtubule array organization and therefore correct cellulose orientation in the SCE cells, as well as the establishment of the subsequent mucilage architecture.