Showing papers on "Cellulose published in 2000"

Comparison of model surfaces for cellulose interactions: elevated pH

Abstract: Two different substrates have been used to measure interaction forces between cellulose and between cellulose and glass at normal and high pH. Forces between microspheres of cellulose (r = 20–30 μm) have been measured using the colloidal probe atomic force microscopy technique. Interactions between Langmuir—Blodgett cellulose films on a hydrophobised mica substrate and a glass sphere have been determined with the noninterferometric surface force apparatus. Also, the interaction between two identical Langmuir—Blodgett cellulose films determined with the interferometric surface force apparatus is given for comparison. At low pH (5.5–6) the interaction at large separations in both systems is characterised by a double-layer repulsion with an electrosteric contribution dominating the shorter-range regime. At pH 10, the Langmuir—Blodgett cellulose film swells considerably, which generates a long-range steric repulsion. In many cases several inward steps have been observed in the force—distance curves. We attribute this to a sudden partial collapse of the swollen cellulose film. After initial compression of the steric layer (upon consecutive force runs) the long-range interaction is again dominated by a double-layer force. In contrast, measurements between two cellulose spheres have shown no excessive swelling. Only a limited increase (from about 10 nm to about 20 nm per surface) of the range of the electrosteric repulsion has been found at pH 10. The force at longer distances is in good agreement with the Poisson—Boltzmann theory, with the surface potential increasing with pH as expected.

Dissolution and Hydrolysis of Cellulose in Subcritical and Supercritical Water

Abstract: Decomposition experiments of microcrystalline cellulose were conducted in subcritical and supercritical water (25 MPa, 320−400 °C, and 0.05−10.0 s). At 400 °C hydrolysis products were mainly obtained, while in 320−350 °C water, aqueous decomposition products of glucose were the main products. Kinetic studies of cellulose, cellobiose, and glucose at these conditions showed that below 350 °C the cellulose decomposition rate was slower than the glucose and cellobiose decomposition rates, while above 350 °C, the cellulose hydrolysis rate drastically increased and became higher than the glucose and cellobiose decomposition rates. Direct observation of the cellulose reaction in high-temperature water at high-pressure conditions by using a diamond anvil cell (DAC) showed that, below 280 °C, cellulose particles became gradually smaller with increasing reaction time but, at high temperatures (300−320 °C), cellulose particles disappeared with increasing transparency and much more rapidly than expected from the lowe...

Plasticized Starch/Tunicin Whiskers Nanocomposites. 1. Structural Analysis

Abstract: Nanocomposite materials were obtained using glycerol plasticized starch as the matrix and a colloidal suspension of cellulose whiskers as the reinforcing phase. The cellulose whiskers, prepared from tunicin, consisted of slender parallelepiped rods with a high aspect ratio. After mixing the raw materials and gelatinization of starch, the resulting suspension was cast and evaporated under vacuum. The composites were conditioned at various moisture contents in order to evaluate the effect of this parameter on the composite structure. The resulting films were characterized using scanning electron microscopy, differential scanning calorimetry, water absorption experiments, and wide-angle X-ray scattering. An accumulation of plasticizer in the cellulose/amylopectin interfacial zones was evidenced. The specific behavior of amylopectin chains located near the interface in the presence of cellulose probably led to a transcrystallization phenomenon of amylopectin on cellulose whiskers surface.

PROCUSTE1 Encodes a Cellulose Synthase Required for Normal Cell Elongation Specifically in Roots and Dark-Grown Hypocotyls of Arabidopsis

Abstract: Mutants at the PROCUSTE1 (PRC1) locus show decreased cell elongation, specifically in roots and dark-grown hypocotyls. Cell elongation defects are correlated with a cellulose deficiency and the presence of gapped walls. Map-based cloning of PRC1 reveals that it encodes a member (CesA6) of the cellulose synthase catalytic subunit family, of which at least nine other members exist in Arabidopsis. Mutations in another family member, RSW1 (CesA1), cause similar cell wall defects in all cell types, including those in hypocotyls and roots, suggesting that cellulose synthesis in these organs requires the coordinated expression of at least two distinct cellulose synthase isoforms.

Cellulose microfibrils from potato tuber cells: Processing and characterization of starch–cellulose microfibril composites

Abstract: The ultrastructure and morphology of potato (Solanum tuberosum L.) tuber cells were investigated by optical, scanning, and transmission electron microscopies. After removal of starch granules, pectins and hemicelluloses were solubilized under alkaline conditions. The alkaline insoluble residue consisted mainly of primary cell wall cellulose, which can be disintegrated under shearing to produce a homogenized microfibril suspension, as reported in a previous work.40 Composite materials were processed from this potato cellulose microfibril suspension, gelatinized potato starch as a matrix and glycerol as a plasticizer. After blending and casting, films were obtained by water evaporation. The mechanical properties and water absorption behavior of the resulting films were investigated, and differences were observed depending on the glycerol, cellulose microfibrils, and relative humidity content. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 2080–2092, 2000

Pretreatment of wheat straw using combined wet oxidation and alkaline hydrolysis resulting in convertible cellulose and hemicellulose.

Abstract: The wet oxidation process of wheat straw has been studied as a pretreatment method to attain our main goal: To break down cellulose to glucose enzymatic, and secondly, to dissolve hemicellulose (e.g., for fermentation) without producing microbial inhibitors. Wet oxidation combined with base addition readily oxidizes lignin from wheat straw facilitating the polysaccharides for enzymatic hydrolysis. By using a specially constructed autoclave system, the wet oxidation process was optimized with respect to both reaction time and temperature. The best conditions (20 g/L straw, 170 degrees C, 5 to 10 min) gave about 85% w/w yield of converting cellulose to glucose. The process water, containing dissolved hemicellulose and carboxylic acids, has proven to be a direct nutrient source for the fungus Aspergillus niger producing exo-beta-xylosidase. Furfural and hydroxymethyl-furfural, known inhibitors of microbial growth when other pretreatment systems have been applied, were not observed following the wet oxidation treatment.

Multiple cellulose synthase catalytic subunits are required for cellulose synthesis in Arabidopsis.

Abstract: The irregular xylem 1 (irx1) mutant of Arabidopsis has a severe deficiency in the deposition of cellulose in secondary cell walls, which results in collapsed xylem cells. This mutation has been mapped to a 140-kb region of chromosome 4. A cellulose synthase catalytic subunit was found to be located in this region, and genomic clones containing this gene complemented the irx1 mutation. IRX1 shows homology to a previously described cellulose synthase (IRX3). Analysis of the irx1 and irx3 mutant phenotypes demonstrates that both IRX1 and IRX3 are essential for the production of cellulose in the same cell. Thus, IRX1 and IRX3 define distinct classes of catalytic subunits that are both essential for cellulose synthesis in plants. This finding is supported by coprecipitation of IRX1 with IRX3, suggesting that IRX1 and IRX3 are part of the same complex.

Two-stage dilute-acid pretreatment of softwoods.

Abstract: Whole treechips obtained from softwood forest thinnings were pretreated via single-and two-stage dilute-sulfuric acid pretreatment. Whole-tree chips were impregnated with dilute sulfuric acid and steam treated in a 4-L steam explosion reactor. In single-stage pretreatment, wood chips were treated using a wide range of severity. In two-stage pretreatment, the first stage was carried out at low severity tomaximize hemicellulose recovery. Solubilized sugars were recovered from the first-stage prehydrolysate by washing with water. In the second stage, water-insoluble solids from first-stage prehydrolysate were impregnated with dilute sulfuric acid, then steam treated at more severe conditions to hydrolyze a portion of the remaining cellulose to glucose and to improve the enzyme digestibility. The total sugar yields obtained after enzymatic hydrolysis of two-stage dilute acid-pretreated samples were compared with sugar yields from single-stage pretreatment. The overall sugar yield from two-stage dilute-acid pretreatment was approx 10% higher, and the net enzyme requirement was reduced by about 50%. Simultaneous saccharification and fermentation using an adapted Saccharomyces cerevisiae yeast strain further improved cellulose conversion yield and lowered the enzyme requirement.

Changes of crystallinity in wood cellulose by heat treatment under dried and moist conditions

Abstract: The different effects of heat treatment on wood, especially on the cellulose crystallites of wood under ovendried and highly moist conditions, were investigated by X-ray diffractometer. Heat was found to increase significantly the crystallinity of wood cellulose; moreover, almost twice as much crystallization was observed after heat treatment of spruce and buna under a highly moist condition than under the oven-dried condition. In pure cellulose almost the same crystallization was observed under both the conditions, whereas more crystallization occurred in wood cellulose than in pure cellulose. Absolute crystallization was observed for the wood species and pure cellulose under both conditions, considering the thermal decomposition of the amorphous region in addition to crystallization. Our results suggested that other components accomparying wood cellulose were involved in the increase of crystallinity by heat treatment, and that wood cellulose contained more quasicrystalline regions than pure cellulose. Moreover, calculated apparent activation energies revealed that crystallization and decrystallization in pure and wood cellulose under heat treatment of highly moist condition were some-what easier than those under the oven-dried condition. The behavior of the piezoelectric modulusd′ 25 almost paralleled that of crystallinity.

Factors affecting cellulose hydrolysis and the potential of enzyme recycle to enhance the efficiency of an integrated wood to ethanol process

Abstract: Past technoeconomic modeling work has identified the relatively large contribution that enzymatic hydrolysis adds to the total cost of producing ethanol from lignocellulosic substrates. This cost was primarily due to the high concentration of enzyme and long incubation time that was required to obtain complete hydrolysis. Although enzyme and substrate concentration and end-product inhibition influenced the rate of hydrolysis, the effect was less pronounced during the initial stages of hydrolysis. During this time most of the cellulases were adsorbed onto the unhydrolyzed residue. By recycling the cellulases adsorbed to the residual substrate remaining after an initial 24 h, a high rate of hydrolysis, with low overall residence time and minimal cellulase input, could be achieved for several rounds of enzyme recycle. A comparison of the front end (pretreatment, fractionation, and hydrolysis) of a softwood/hardwood to ethanol process indicated that the lignin associated with the softwood-derived cellulose stream limited the number of times the cellulose containing residue could be recycled. (c) 1996 John Wiley & Sons, Inc.

Virus-Induced Silencing of a Plant Cellulose Synthase Gene

Abstract: Specific cDNA fragments corresponding to putative cellulose synthase genes (CesA) were inserted into potato virus X vectors for functional analysis in Nicotiana benthamiana by using virus-induced gene silencing. Plants infected with one group of cDNAs had much shorter internode lengths, small leaves, and a “dwarf” phenotype. Consistent with a loss of cell wall cellulose, abnormally large and in many cases spherical cells ballooned from the undersurfaces of leaves, particularly in regions adjacent to vascular tissues. Linkage analyses of wall polysaccharides prepared from infected leaves revealed a 25% decrease in cellulose content. Transcript levels for at least one member of the CesA cellulose synthase gene family were lower in infected plants. The decrease in cellulose content in cell walls was offset by an increase in homogalacturonan, in which the degree of esterification of carboxyl groups decreased from ∼50 to ∼33%. The results suggest that feedback loops interconnect the cellular machinery controlling cellulose and pectin biosynthesis. On the basis of the phenotypic features of the infected plants, changes in wall composition, and the reduced abundance of CesA mRNA, we concluded that the cDNA fragments silenced one or more cellulose synthase genes.

A rapid and simple method to isolate pure alpha-cellulose.

Abstract: A protocol is described to isolate small quantities of highly purified cellulose for isotopic analysis of 10–100 mg samples of secondary (Pinus sylvestris L.) and primary (Rubus idaeus L.) plant cell wall material. Elemental analysis of 350 cellulose samples isolated from pine wood samples estimated the relative carbon content to be ca. 43.7% ± 1.2%. This value indicates that the cellulose quality is high and that the protocol is highly reproducible. High-performance anion exchange chromatography with pulsed amperometric detection of hydrolysis products quantified the purity of the cellulose as ca. 99% for wood cellulose and primary cell wall cellulose. DRIFT spectroscopy corroborated this purity and found no evidence of cellulose degradation. Carbon isotopic composition of the purified cellulose using mass spectrometry was measured with an accuracy of 0.11‰ (standard deviation). The method is rapid (56 samples may be routinely processed within 8 h) and requires only standard laboratory equipment and chemicals. Copyright © 2000 John Wiley & Sons, Ltd.

Effective preparation of cellulose derivatives in a new simple cellulose solvent

Abstract: Full Paper: Ceflulore with a degree of polymerization up to 650 can be dissolved in dimethyl sulfoxide containing 10 to 20% (w/v: tetrabutylammonium floride trihydrate without any pretreatment within15 min at room temperature. The new solvent can be classified as a non-derivatizing one as concluded from 13 C NMR measurements. The solvent can be used as reaction medium for the homogeneous functionalization of the polymer. Cellulose esters are prepared very effective by transesterification reactions. The functional groups are deistributed in the order expected for a homogeneous conversion, i. e., a preferred reaction at the primary hydroxyl groups occurs. Moreover, carboxymethyl cellulose with a preferred functionalization at the primary hydroxyl groups and a nonstatic content of the different repeating units was accessible.

The mechanical properties and molecular dynamics of plant cell wall polysaccharides studied by Fourier-transform infrared spectroscopy.

Abstract: Polarized one- and two-dimensional infrared spectra were obtained from the epidermis of onion (Allium cepa) under hydrated and mechanically stressed conditions. By Fourier-transform infrared microspectroscopy, the orientation of macromolecules in single cell walls was determined. Cellulose and pectin exhibited little orientation in native epidermal cell walls, but when a mechanical stress was placed on the tissue these molecules showed distinct reorientation as the cells were elongated. When the stress was removed the tissue recovered slightly, but a relatively large plastic deformation remained. The plastic deformation was confirmed in microscopic images by retention of some elongation of cells within the tissue and by residual molecular orientation in the infrared spectra of the cell wall. Two-dimensional infrared spectroscopy was used to determine the nature of the interaction between the polysaccharide networks during deformation. The results provide evidence that cellulose and xyloglucan associate while pectin creates an independent network that exhibits different reorientation rates in the wet onion cell walls. The pectin chains respond faster to oscillation than the more rigid cellulose.

Cellulose and Hemicellulose Hydrolysis Models for Application to Current and Novel Pretreatment Processes

Abstract: Acids catalyze the hydrolysis of cellulose and hemicellulose to produce sugars that organisms can ferment to ethanol and other products. However, advanced low- and no-acid technologies are critical if we are to reduce bioethanol costs to be competitive as a pure fuel. We believe carbohydrate oligomers play a key role in explaining the performance of such hydrolysis processes and that kinetic models would help us understand their role. Various investigations have developed reaction rate expressions based on an Arrhenius temperature dependence that is first order in substrate concentration and close to first order in acid concentration. In this article, we evaluate these existing hydrolysis models with the goal of providing a foundation for a unified model that can predict performance of both current and novel pretreatment process configurations.

Imaging the enzymatic digestion of bacterial cellulose ribbons reveals the endo character of the cellobiohydrolase Cel6A from Humicola insolens and its mode of synergy with cellobiohydrolase Cel7A.

Abstract: Dispersed cellulose ribbons from bacterial cellulose were subjected to digestion with cloned Cel7A (cellobiohydrolase [CBH] I) and Cel6A (CBH II) from Humicola insolens either alone or in a mixture and in the presence of an excess of beta-glucosidase. Both Cel7A and Cel6A were effective in partially converting the ribbons into soluble sugars, Cel7A being more active than Cel6A. In combination, these enzymes showed substantial synergy culminating with a molar ratio of approximately two-thirds Cel6A and one-third Cel7A. Ultrastructural transmission electron microscopy (TEM) observations indicated that Cel7A induced a thinning of the cellulose ribbons, whereas Cel6A cut the ribbons into shorter elements, indicating an endo type of action. These observations, together with the examination of the digestion kinetics, indicate that Cel6A can be classified as an endo-processive enzyme, whereas Cel7A is essentially a processive enzyme. Thus, the synergy resulting from the mixing of Cel6A and Cel7A can be explained by the partial endo character of Cel6A. A preparation of bacterial cellulose ribbons appears to be an appropriate substrate, superior to Valonia or bacterial cellulose microcrystals, to visualize directly by TEM the endo-processivity of an enzyme such as Cel6A.

Solubility of Cellulose in NaOH/Urea Aqueous Solution

Abstract: NaOH/urea aqueous solution as solvent of cellulose including cotton linter, bagasse, alkali-soluble cellulose and Bemliese® was studied by solubility analysis, viscometry and light scattering. The addition of 2—4 wt% urea significantly improved the solubility of cellulose in 6—8 wt% NaOH aqueous solutions, and moderate urea plays a role in improving solubility and avoiding the formation of cellulose gel. Celluloses I with viscosity-average molecular weight (Mη) of 6.7×104 were completely dissolved in 6 wt% NaOH/4 wt% urea aqueous solution. Cellulose dissolved in 6 wt% NaOH/4 wt% urea aqueous solution degraded slowly with storage time, and Mη of cellulose in the solution decreased 20% after storage for 100 days. The stability of cellulose solution was higher than cellulose cuoxam. A regenerated cellulose membrane having the tensile strength of 88.7MPa and breaking elongation of 11% was successfully prepared by coagulating 4 wt% Bemliese® solution in 6 wt% NaOH/4 wt% urea with 5 wt% CaCl2 then 1.3 wt% HCl aqueous solution as coagulate at 20°C.

Birefringent Glassy Phase of a Cellulose Microcrystal Suspension

Abstract: We prepared a stable and highly viscous suspension of cellulose microcrystals by postsulfating the HCl-hydrolyzed cellulose microcrystals. The neutralized suspension was isotropic and showed flow birefringence at low solid content (ca. <1%). At a solid content of approximately 2−3%, the suspension was still flowing but showed intricate birefringent patterns, which remained after the flow had ceased. At high solid content (7.1%), the suspension became too viscous to flow and showed a frozen-in birefringent pattern with a microscopic crosshatch texture. These features show that this postsulfated suspension forms a “birefringent glassy phase”, similar to that observed for a boehmite rod suspension, being distinctly different from the behavior of the suspension prepared by direct hydrolysis of cellulose with concentrated sulfuric acid.

Fractionation of carbohydrates in Arabidopsis root cell walls shows that three radial swelling loci are specifically involved in cellulose production.

Abstract: Three non-allelic radial swelling mutants (rsw1, rsw2 and rsw3) of Arabidopsisthaliana L. Heynh. were shown to be specifically impaired in cellulose production. Fractionation methods that identify, characterise and quantify some of the major cell wall polysaccharides in small quantities of seedlings demonstrated that changes in the production of cellulose are much more pronounced than changes in the production of non-cellulosic polysaccharides. A crude cell wall pellet was sequentially extracted with chloroform methanol (to recover lipids), dimethyl sulphoxide (starch), ammonium oxalate (pectins) and alkali (hemicelluloses). Crystalline cellulose remained insoluble through subsequent treatments with an acetic/nitric acid mixture and with trifluoroacetic acid. Cetyltrimethylammonium bromide precipitation resolved neutral and acidic polymers in the fractions, and precipitation behaviour, monosaccharide composition and glycosidic linkage patterns identified the major polysaccharides. The deduced composition of the walls of wild-type seedlings and the structure and solubility properties of the major polymers were broadly typical of other dicots. The three temperature-sensitive, radial swelling mutants produced less cellulose in their roots than the wild type when grown at their restrictive temperature (31 °C). There were no significant differences at 21 °C where no radial swelling occurs. The limited changes seen in the monosaccharide compositions, glycosidic linkage patterns and quantities of non-cellulosic polysaccharides support the view that the RSW1, RSW2 and RSW3 genes are specifically involved in cellulose synthesis. Reduced deposition of cellulose was accompanied by increased accumulation of starch.

Effect of substrate and cellulase concentration on simultaneous saccharification and fermentation of steam‐pretreated softwood for ethanol production

Abstract: Economic optimization of the production of ethanol by simultaneous saccharification and fermentation (SSF) requires knowledge about the influence of substrate and enzyme concentration on yield and productivity. Although SSF has been investigated extensively, the optimal conditions for SSF of softwoods have yet not been determined. In this study, SO2-impregnated and steam-pretreated spruce was used as substrate for the production of ethanol by SSF. Commercial enzymes were used in combination with the yeast Saccharomyces cerevisiae. The effects of the concentration of substrate (2% to 10% w/w) and of cellulases (5 to 32 FPU/g cellulose) were investigated. SSF was found to be sensitive to contamination because lactic acid was produced. The ethanol yield increased with increasing cellulase loading. The highest ethanol yield, 68% of the theoretical based on the glucose and mannose present in the original wood, was obtained at 5% substrate concentration. This yield corresponds to 82% of the theoretical based on the cellulose and soluble glucose and mannose present at the start of SSF. A higher substrate concentration caused inefficient fermentation, whereas a lower substrate concentration, 2%, resulted in increased formation of lactic acid, which lowered the yield. Compared with separate hydrolysis and fermentation, SSF gave a higher yield and doubled the productivity.

Fundamental Aspects of Dilute Acid Hydrolysis/Fractionation Kinetics of Hardwood Carbohydrates. 1. Cellulose Hydrolysis

Abstract: Previous kinetic modeling and bench-scale demonstration efforts using batch, percolation, or plug-flow reactors for the dilute sulfuric acid hydrolysis of cellulose have concluded that glucose yields above 70% of theoretical were not possible. This has been explained to be a result of reactions involving glucose or the cellulose itself in a destructive manner, as well as hydrolyzed soluble oligomers which have been modified chemically so as not to release glucose. However, recently, we have demonstrated that near-quantitative yields of glucose from cellulose can indeed be obtained using a bench-scale shrinking-bed percolation reactor in which an internal spring compresses the biomass as the reaction progresses. The present study was initiated to gain a fundamental understanding of the kinetic sequences involved in these high yields. Three reactor configurations (batch, percolation, and shrinking-bed percolation) were studied using similar hydrolysis severities to begin addressing chemical, physical, and h...