Cellulose Crystals Research Articles

Cellulose structure and lignin distribution in normal and compression wood of the Maidenhair tree (Ginkgo biloba L.).

We studied in detail the mean microfibril angle and the width of cellulose crystals from the pith to the bark of a 15-year-old Maidenhair tree (Ginkgo biloba L.). The orientation of cellulose microfibrils with respect to the cell axis and the width and length of cellulose crystallites were determined using X-ray diffraction. Raman microscopy was used to compare the lignin distribution in the cell wall of normal/opposite and compression wood, which was found near the pith. Ginkgo biloba showed a relatively large mean microfibril angle, varying between 19° and 39° in the S2 layer, and the average width of cellulose crystallites was 3.1-3.2 nm. Mild compression wood without any intercellular spaces or helical cavities was observed near the pith. Slit-like bordered pit openings and a heavily lignified S2L layer confirmed the presence of compression wood. Ginkgo biloba showed typical features present in the juvenile wood of conifers. The microfibril angle remained large over the 14 annual rings. The entire stem disc, with a diameter of 18 cm, was considered to consist of juvenile wood. The properties of juvenile and compression wood as well as the cellulose orientation and crystalline width indicate that the wood formation of G. biloba is similar to that of modern conifers.

Endo-β-1,4-glucanases impact plant cell wall development by influencing cellulose crystallization.

Cell walls are vital to the normal growth and development of plants as they protect the protoplast and provide rigidity to the stem. Here, two poplar and Arabidopsis orthologous endoglucanases, which have been proposed to play a role in secondary cell wall development, were examined. The class B endoglucanases, PtGH9B5 and AtGH9B5, are secreted enzymes that have a predicted glycosylphosphatidylinositol anchor, while the class C endoglucanases, PtGH9C2 and AtGH9C2, are also predicted to be secreted but instead contain a carbohydrate-binding module. The poplar endoglucanases were expressed in Arabidopsis using both a 35S promoter and the Arabidopsis secondary cell wall-specific CesA8 promoter. Additionally, Arabidopsis t-DNA insertion lines and an RNAi construct was created to downregulate AtGH9C2 in Arabidopsis. All of the plant lines were examined for changes in cell morphology and patterning, growth and development, cell wall crystallinity, microfibril angle, and proportion of cell wall carbohydrates. Misregulation of PtGH9B5/AtGH9B5 resulted in changes in xylose content, while misregulation of PtGH9C2/AtGH9C2 resulted in changes in crystallinity, which was inversely correlated with changes in plant height and rosette diameter. Together, these results suggest that these endoglucanases affect secondary cell wall development by contributing to the cell wall crystallization process.

Exploring the nature of cellulose microfibrils.

Ultrathin cellulose microfibril fractions were extracted from spruce wood powder using combined delignification, TEMPO-catalyzed oxidation, and sonication processes. Small-angle X-ray scattering of these microfibril fractions in a "dilute" aqueous suspension (concentration 0.077 wt %) revealed that their shape was in the form of nanostrip with 4 nm width and only about 0.5 nm thicknesses. These dimensions were further confirmed by TEM and AFM measurements. The 0.5 nm thickness implied that the nanostrip could contain only a single layer of cellulose chains. At a higher concentration (0.15 wt %), SAXS analysis indicated that these nanostrips aggregated into a layered structure. The X-ray diffraction of samples collected at different preparation stages suggested that microfibrils were delaminated along the (11̅0) planes from the Iβ cellulose crystals. The degree of oxidation and solid-state (13)C NMR characterizations indicated that, in addition to the surface molecules, some inner molecules of microfibrils were also oxidized, facilitating the delamination into cellulose nanostrips.

Rheo-NMR study of water-based cellulose liquid crystal system at high shear rates

Since long ago cellulosic lyotropic liquid crystals were thought as potential materials to produce fibers competitive with spidersilk or Kevlar, yet the processing of high modulus materials from cellulose-based precursors was hampered by their complex rheological behavior. In this work, by using the Rheo-NMR technique, which combines deuterium NMR with rheology, we investigate the high shear rate regimes that may be of interest to the industrial processing of these materials. Whereas the low shear rate regimes were already investigated by this technique in different works [1–4], the high shear rates range is still lacking a detailed study. This work focuses on the orientational order in the system both under shear and subsequent relaxation process arising after shear cessation through the analysis of deuterium spectra from the deuterated solvent water. At the analyzed shear rates the cholesteric order is suppressed and a flow-aligned nematic is observed which for the higher shear rates develops after certain time periodic perturbations that transiently annihilate the order in the system. During relaxation the flow aligned nematic starts losing order due to the onset of the cholesteric helices leading to a period of very low order where cholesteric helices with different orientations are forming from the aligned nematic, followed in the final stage by an increase in order at long relaxation times corresponding to the development of aligned cholesteric domains. This study sheds light on the complex rheological behavior of chiral nematic cellulose-based systems and opens ways to improve its processing.

Effects of polymorphs on dissolution of cellulose in NaOH/urea aqueous solution

This study focused on the effect of cellulose crystal type on the dissolution of cellulose in aqueous NaOH/urea. Cellulose I, II, IIII, and IVI were prepared and characterized. Subsequently, the solubility of these cellulose samples in aqueous NaOH/urea was tested and the mechanism was determined by a combination of 1H NMR spectroscopy and differential scanning calorimetry (DSC). The results indicated that, compared with the degree of polymerization (DP) and crystallinity index of cellulose, the cellulose crystal type had greater impact on cellulose dissolution. Specially, the solubility of the cellulose I, II, and III was progressively decreased, probably due to different hydrogen bond network and packing energy in it. The ability of cellulose I, II, III, and IV to form hydrogen bonds with sodium hydroxides was nearly the same, while gradually increased when cellulose preparations were associated with urea. Moreover, all the cellulose solutions showed good thermal stability.

Vibrational spectral signatures of crystalline cellulose using high resolution broadband sum frequency generation vibrational spectroscopy (HR-BB-SFG-VS)

Both the C–H and O–H region spectra of crystalline cellulose were studied using the sub-wavenumber high-resolution broadband sum frequency generation vibrational spectroscopy (HR-BB-SFG-VS) for the first time. The resolution of HR-BB-SFG-VS is about 10-times better than conventional scanning SFG-VS and has the capability of measuring the intrinsic spectral lineshape and revealing many more spectral details. With HR-BB-SFG-VS, we found that in cellulose samples from different sources, including Avicel and cellulose crystals isolated from algae Valonia (Iα) and tunicates (Iβ), the spectral signatures in the O–H region were unique for the two allomorphs, i.e. Iα and Iβ, while the spectral signatures in the C–H regions varied in all samples examined. Even though the origin of the different spectral signatures of the crystalline cellulose in the O–H and C–H vibrational frequency regions are yet to be correlated to the structure of cellulose, these results lead to new spectroscopic methods and opportunities to classify and to understand the basic crystalline structures, as well as variations in polymorphism of the crystalline cellulose.

Comprehensive analysis of cellulose content, crystallinity, and lateral packing in Gossypium hirsutum and Gossypium barbadense cotton fibers using sum frequency generation, infrared and Raman spectroscopy, and X-ray diffraction

The mesoscale packing and crystal structure of cellulose microfibrils as well as temporal changes in cell wall composition and hydration during the development of cotton fibers from two species, Gossypium hirsutum and G. barbadense were studied using vibrational sum frequency generation (SFG), attenuated total refection infrared (ATR-IR), Fourier transform Raman (FT-Raman) spectroscopy and X-ray diffraction (XRD). The developmental stages analyzed (13–60 days post anthesis) included primary wall synthesis, transitional cell wall remodeling, secondary wall thickening via synthesis of nearly pure cellulose, and fiber maturation. ATR-IR and FT-Raman combined with principle component analysis revealed that fibers of both species undergo abrupt changes in the cellulose and matrix polymer contents during the transition to secondary cell wall synthesis. XRD revealed that cellulose crystal size and crystallinity increase similarly over time in both species. SFG analysis of fibers from un-opened bolls, which were stored in water then air dried, showed subtle differences between two species in the mesoscale ordering of cellulose microfibrils in the maturing secondary walls. In the samples of mature fibers dried on the plant after the boll split opened naturally, the difference in SFG spectra between species was negligible. Collectively, the results show that (a) SFG can uniquely reveal differences in cellulose fibril ordering in maturing cotton fibers before boll opening; and (b) illustrate the comparative usefulness of other commonly used spectroscopic analytical methods for cotton fiber analysis.

Extraction of cellulose nanocrystals from plant sources for application as reinforcing agent in polymers

In the last few decades, the usages of plant sources-based stiff fillers as reinforcement material in polymer composites have attracted significant interests of researchers. The crystalline part of the semicrystalline cellulose chains as found in the plant cell walls represents the most highly potential reinforcing agents for polymer. This review systematically covers the extraction of nano-sized cellulose crystals from plant cell wall which involving the applications of several highly effective techniques. The topic about the derivation of products functionality at each stage as well as their influences on the final reinforcing capability is also covered. Apart from these, a detailed overview of current knowledge on the surface modification of nanocellulose has been provided also. Inasmuch, this paper is desired to encourage the emergence of preparation of cellulose derivative nanocrystals with controlled morphology, structure and properties, so that enable positive development of biocompatible, renewable and sustainable reinforcing materials for polymer composites field.

Role of bound water on structural change of water insoluble polysaccharides

In terms of the functionalities of polysaccharides, water molecules play a crucial role. Two kinds of bound water, freezing bound water and non-freezing water have been classified based on the phase transition of water restrained by hydrophilic polymers. In this study, conversion of bound water accompanied with the structural change of two kinds of water insoluble polysaccharides, cellulose and curdlan, is investigated. It was found that bound water is involved in reversible and irreversible structural change of both cellulose and curdlan. Bound water contributes to the reversible structural change of natural cellulose, whose mechanical properties increase in the presence of water. In water-induced crystallization of amorphous cellulose, bound water is excluded from molecular chains and the crystalline region is irreversibly established. Transformation of freezing bound water to non-freezing water was observed when gelation mechanism of curdlan is changed from reversible to irreversible state. Quantification of bound water involved in the above process is described based on the melting enthalpy of ice restrained by cellulose and curdlan.

Use of alginate, chitosan and cellulose nanocrystals as emulsion stabilizers in the synthesis of biodegradable polymeric nanoparticles

Biopolymeric nanoparticles (NPs) based on a biodegradable poly(dl-Lactide-co-Glycolide) PLGA copolymer matrix combined with alginate, chitosan and nanostructured cellulose crystals as three different natural emulsion stabilizers, were synthesized by a double emulsion (water/oil/water) method with subsequent solvent evaporation. The morphological, thermal, chemical and rheological properties of the novel designed NPs and the effect of the different emulsion stabilizers used during the synthesis were deeply investigated in order to optimize the synthesis procedure and the development of biodegradable nanoparticles coated with natural polymers.The morphological analysis of the produced nanoparticles showed that all the different formulations presented a spherical shape with smooth surface. Infrared spectroscopy investigations showed that the PLGA copolymer maintained its backbone structure and confirmed the presence of chitosan, alginate and cellulose nanocrystals (CNC) on the nanoparticle surface. The obtained results suggest that PLGA nanoparticles with CNC as emulsion stabilizer might represent promising formulations opening new perspective in the field of self-assembly of biodegradable nanomaterials for medical and pharmaceutical applications.

The Arabidopsis COBRA Protein Facilitates Cellulose Crystallization at the Plasma Membrane

Mutations in the Arabidopsis COBRA gene lead to defects in cellulose synthesis but the function of COBRA is unknown. Here we present evidence that COBRA localizes to discrete particles in the plasma membrane and is sensitive to inhibitors of cellulose synthesis, suggesting that COBRA and the cellulose synthase complex reside in close proximity on the plasma membrane. Live-cell imaging of cellulose synthesis indicated that, once initiated, cellulose synthesis appeared to proceed normally in the cobra mutant. Using isothermal calorimetry, COBRA was found to bind individual β1-4-linked glucan chains with a KD of 3.2 μm. Competition assays suggests that COBRA binds individual β1-4-linked glucan chains with higher affinity than crystalline cellulose. Solid-state nuclear magnetic resonance studies of the cell wall of the cobra mutant also indicated that, in addition to decreases in cellulose amount, the properties of the cellulose fibrils and other cell wall polymers differed from wild type by being less crystalline and having an increased number of reducing ends. We interpret the available evidence as suggesting that COBRA facilitates cellulose crystallization from the emerging β1-4-glucan chains by acting as a "polysaccharide chaperone."

Molecular deformation mechanisms of the wood cell wall material

Wood is a biological material with outstanding mechanical properties resulting from its hierarchical structure across different scales. Although earlier work has shown that the cellular structure of wood is a key factor that renders it excellent mechanical properties at light weight, the mechanical properties of the wood cell wall material itself still needs to be understood comprehensively. The wood cell wall material features a fiber reinforced composite structure, where cellulose fibrils act as stiff fibers, and hemicellulose and lignin molecules act as soft matrix. The angle between the fiber direction and the loading direction has been found to be the key factor controlling the mechanical properties. However, how the interactions between theses constitutive molecules contribute to the overall properties is still unclear, although the shearing between fibers has been proposed as a primary deformation mechanism. Here we report a molecular model of the wood cell wall material with atomistic resolution, used to assess the mechanical behavior under shear loading in order to understand the deformation mechanisms at the molecular level. The model includes an explicit description of cellulose crystals, hemicellulose, as well as lignin molecules arranged in a layered nanocomposite. The results obtained using this model show that the wood cell wall material under shear loading deforms in an elastic and then plastic manner. The plastic regime can be divided into two parts according to the different deformation mechanisms: yielding of the matrix and sliding of matrix along the cellulose surface. Our molecular dynamics study provides insights of the mechanical behavior of wood cell wall material at the molecular level, and paves a way for the multi-scale understanding of the mechanical properties of wood.

Isolation of micro- and nano-crystalline cellulose particles and fabrication of crystalline particles-loaded whey protein cold-set gel

Micro- and nano-crystalline cellulose (MCC and NCC, respectively) particles isolated from cellulose filter papers via acid digestion were characterised and loaded into a heat-denatured whey protein isolate (WPI) solution which was subsequently cold-set-gelled. Both the MCC and NCC particles were rod-shaped and had higher crystallinity degrees than had the cellulose source they were isolated from. The hydrodynamic diameter of NCC particles was ≈15nm. Fourier transform infrared (FTIR) spectroscopy suggested more surface hydroxyl groups on the NCC than the MCC particles and complete digestion of hemicellulose on the cellulosic substrate by acid. MCC- and NCC-loaded WPI gel matrices were topographically less uniform and contained many more undulations in comparison to the crystal-free counterpart. It was found, using dynamic rheometry and penetration tests, that the crystal loading into WPI gels weakened the texture. Non-covalent interactions between the cellulose crystals and whey protein strands were proposed in the gel structure according to FTIR results.

Water structuring over the hydrophobic surface of cellulose.

Many important biological solutes possess not only polar and hydrogen-bonding functionalities but also weakly hydrating, or hydrophobic, surfaces. While the aggregation of these hydrophobic surfaces has been shown to play an important role in the aggregation of individual chains of cellulose, it is not known whether the water structuring imposed by these hydrophobic surfaces more closely resembles that associated with small hydrophobic solutes like methane and fats or more closely resembles that associated with extended hydrophobic surfaces like mica or waxy planes. By using molecular dynamics simulations to characterize the water molecule orientations over different regions of the 100 surface of cellulose in contact with water, it was found that the hydrophobic strips of the cellulose crystal are sufficiently narrow that they hydrate like a fatty acid chain, rather than like a more extended surface, suggesting that their aggregation would be dominated by entropy rather than enthalpy.

Characterization of cellulose and other exopolysaccharides produced from Gluconacetobacter strains

This study characterized the cellulosic and non-cellulosic exopolysaccharides (EPS) produced by four Gluconacetobacter strains. The yields of bacterial cellulose and water-soluble polysaccharides were dependent on both carbon source and Gluconacetobacter strain. The carbon substrate also affected the composition of the free EPS. When galactose served as an exclusive carbon source, Gluconacetobacter xylinus (G. xylinus) ATCC 53524 and ATCC 700178 produced a distinct alkaline stable crystalline product, which influenced the crystallization of cellulose. Gluconacetobacter hansenii (G. hansenii) ATCC 23769 and ATCC 53582, however, did not exhibit any significant change in cellulose crystal properties when galactose was used as the carbon source. Microscopic observation further confirmed significant incorporation of EPS into the cellulose composites. The cellulosic network produced from galactose medium showed distinctive morphological and structural features compared to that from glucose medium.

Characterization of water-soluble exopolysaccharides from Gluconacetobacter xylinus and their impacts on bacterial cellulose crystallization and ribbon assembly

Gluconacetobacterxylinus has the ability to produce different types of water soluble exopolysaccharides (EPS). Those EPS have different levels of association to bacterial cellulose (BC). At least a portion of the EPS can be released from the BC by 0.1 to 4 M NaOH solution treatments. Hard to extract EPS (HE-EPS) released by 4 M NaOH solutions have been characterized and contain approximately 75 % mannose and 25 % glucose. To study the effect of the EPS on BC synthesis, purified EPS were added to the medium at the start of cultivation and the BC produced was characterized. Results showed that the presence of HE-EPS in the culture medium interfered with the alignment of the BC crystals, but did not reduce crystal size. This is in contrast to similar studies performed using xyloglucan, xylan and glucomannan. The width of the average ribbon increased by 60 % when HE-EPS levels increased in the medium, which indicated that the HE-EPS could also modulate the bundling of cellulose ribbons. Based on the data we propose a mechanism for how HE-EPS alters cellulose formation and assembly. The addition of HE-EPS disturbs the preferential crystal orientation and increases the spacing of cellulose microfibrils without affecting crystallization by associating with ordered cellulose prior to physical aggregation or bundling.

Theoretical study of the structural stability of molecular chain sheet models of cellulose crystal allomorphs.

The structural stabilities of the molecular chain sheets constituting the crystal structures of the cellulose allomorphs Iα, Iβ, II, and IIII were investigated by density functional theory (DFT) optimization of the isolated chain sheet models with finite dimensions. The DFT-optimized chain sheet models of the two native cellulose crystals developed a right-handed twist with a similar amount of twisting. The DFT-optimized cellulose II (010) and (020) models twisted in opposite directions with right- and left-handed chirality, respectively. The cellulose IIII (1-10) model retained the initial flat structure after the DFT-optimization. The structural features of the DFT-optimized chain sheet models were reflected in the structures of the parent crystal models observed in solvated molecular dynamics (MD) simulations. The minor conformations of the hydroxymethyl groups proposed in the real crystal structures were detected in the MD crystal models and the DFT-optimized (010) model of cellulose II. The crystal chain packing and crystal conversions are interpreted in terms of principal chain sheet stacking.

Nanocellulose in polymer composites and biomedical applications

Nanocellulose materials are nano-sized cellulose fibrils or crystals produced by bacteria or derived from plants. These materials exhibit exceptional strength characteristics, light weight, transparency, and excellent biocompatibility. Compared with some other nanomaterials, nanocellulose is renewable and less expensive to produce, and a wide range of applications for nanocellulose has been envisioned. The areas most extensively studied include polymer composites and biomedical applications. Cellulose nanofibrils and nanocrystals have been used to reinforce both thermoplastic and thermoset polymers. Given the hydrophilic nature of these materials, the interfacial properties with most polymers are often poor; thus, various surface modification procedures have been adopted to improve the interaction between polymer matrix and cellulose nanofibrils or nanocrystals. The applications of nanocellulose as a biomaterial also have been explored, including wound dressing, tissue repair, and medical implants. Nanocellulose materials for wound healing and periodontal tissue recovery have become commercially available, demonstrating the great potential of nanocellulose as a new generation of biomaterials.

From Cellulosic Based Liquid Crystalline Sheared Solutions to 1D and 2D Soft Materials.

Liquid crystalline cellulosic-based solutions described by distinctive properties are at the origin of different kinds of multifunctional materials with unique characteristics. These solutions can form chiral nematic phases at rest, with tuneable photonic behavior, and exhibit a complex behavior associated with the onset of a network of director field defects under shear. Techniques, such as Nuclear Magnetic Resonance (NMR), Rheology coupled with NMR (Rheo-NMR), rheology, optical methods, Magnetic Resonance Imaging (MRI), Wide Angle X-rays Scattering (WAXS), were extensively used to enlighten the liquid crystalline characteristics of these cellulosic solutions. Cellulosic films produced by shear casting and fibers by electrospinning, from these liquid crystalline solutions, have regained wider attention due to recognition of their innovative properties associated to their biocompatibility. Electrospun membranes composed by helical and spiral shape fibers allow the achievement of large surface areas, leading to the improvement of the performance of this kind of systems. The moisture response, light modulated, wettability and the capability of orienting protein and cellulose crystals, opened a wide range of new applications to the shear casted films. Characterization by NMR, X-rays, tensile tests, AFM, and optical methods allowed detailed characterization of those soft cellulosic materials. In this work, special attention will be given to recent developments, including, among others, a moisture driven cellulosic motor and electro-optical devices.

Isolation and characterization of cellulose nanocrystals from garlic skin

For the value-added utilization of underutilized agricultural by-products, garlic skin obtained abundantly in the food processing industry has been tested as a new source of cellulosic materials. Cellulose microfibers (CMF) and cellulose nanocrystals (CNC) were isolated from garlic skin fibers by alkali treatment and acid hydrolysis. The crude fiber, CMF, and CNC of garlic skin were characterized by Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Transmission electron microscopy (TEM). Most of the lignin and hemicellulose was removed after the chemical treatment, and the degree of crystallinity of the CMF and CNC was increased compared with the crude fiber. The degree of crystallinity was 35%, 45%, and 63% for the crude fiber, CMF, and CNC, respectively. The cellulose nanocrystals exhibited spherical in shape with the size of 58–96 nm. The thermal stability of the CMF increased significantly, but that of CNC decreased slightly due to the introduction of sulfate groups into the cellulose crystals during acid hydrolysis. The nanocrystals had a high potential to be used as reinforcing filler for the preparation of bionanocomposites.