Showing papers on "Cellulose published in 1989"

The structure and mechanical properties of sheets prepared from bacterial cellulose

Abstract: A preliminary experiment has shown that a sheet-shaped material prepared from bacterial cellulose has remarkable mechanical properties, the Young's modulus being as high as >15 GPa across the plane of the sheet. The mechanical properties were little affected by the fermentation conditions of pellicles and the preparation conditions of the sheets, i.e. the pressing and drying of pellicles. From structural investigations, the high Young's modulus has been ascribed to the unique super-molecular structure in which fibrils of biological origin are preserved and bound tightly by hydrogen bonds. It has also been found that a “pulp” obtained from bacterial cellulose gives a strong paper and is useful for reinforcing conventional pulp papers and enabling paper-making from some fibrous materials.

Kinetic modelling of the pyrolysis of biomass and biomass components

Abstract: The kinetics of the pyrolysis of lignocellulosic materials was studied with a view of providing simple kinetic models for engineering purposes. Experimental data obtained by means of thermal analysis techniques suggest that the pyrolysis of fine particles (below 1 mm) can be considered to be controlled by pyrolysis kinetics. The rate of pyrolysis of one biomass type can be represented by the sum of the corresponding rates of the main biomass components (cellulose, lignin, hemicellulose). The kinetics of each of these components was simulated by a kinetic scheme capable of predicting the pyrolysis rate and the final weight-loss for a wide range of pyrolysis parameters including various heating conditions.

Tissue biocompatibility of cellulose and its derivatives.

Abstract: Tissue biocompatibility of cellulose and its derivatives was examined in two in vivo tests, one for absorbance by living tissue and one for foreign body reaction. The samples examined were regenerated celluloses and cellulose derivatives: methyl cellulose, ethyl cellulose, aminoethyl cellulose, hydroxyethyl cellulose, and cellulosic polyion complexes. The in vivo absorbance by living tissue was found to depend on the degree of crystallinity and the chemical structure of the sample. The foreign body reaction was relatively mild for all the samples examined, showing that cellulose can be converted to biocompatible materials by physical and/or chemical transformation.

Influence of coupling agents and treatments on the mechanical properties of cellulose fiber–polystyrene composites

Abstract: Wood fibers of aspen in the form of chemithermomechanical pulp (CTMP) and Tembec 6816 have been used as reinforcing fillers in different varieties of polystyrene. The tensile strength, elongation, and energy at maximum point, as well as tensile modulus at 0.1% strain is reported. Also revealed is the optimum condition of compression molding. The influence of different coupling agents, such as poly[methylene(polyphenyl isocyanate)], silanes (A-172, A-174, A-1100), and grating on the mechanical properties of composites is discussed. The extent of increase in mechanical properties depends on the weight percentage of fibers, the concentration of coupling agents, and the grafting level (add-on %). Coating followed by an isocyanate treatment appears to be the best treatment. In addition, the isocyanate treatment and grafting are superior to the silane treatment. Experimental results are explained on the basis of possible interactions among cellulose fiber-coupling agent-polymer in the interfacial area.

Lignin: properties and materials.

Abstract: This books reports on lignins, irregular phenylpropane biopolymers that make up approximately 20-30% of the available polymeric content of hardwood tree stems. In plants, lignin is second in natural abundance only to cellulose. This material offers, therefore, a valuable resource that must be utilized if the full value of harvested tree crops is to be attained. The yearly growth of the world forests is about 7-9 billion cubic meters of biomass. During the production of 140 million tons of cellulose and pulp from a part of this biomass, about 50 million tons of lignin are formed. Over 95% of the lignin is used as an energy source to operate pulping mills.

Future prospects for wood cellulose as reinforcement in organic polymer composites

Abstract: Wood cellulose, a versatile and renewable natural resource, has potential for use as a reinforcement for synthetic organic polymers. During the past 80 years a number of materials using the reinforcing properties of wood cellulose have found major markets. Forms of wood cellulose proposed as reinforcements include: wood fibers, cellulose fibers, microfibillar, and microcrystalline cellulose. Recent attention has been given to them as fillers/reinforcements in thermoplastics and elastomers. Most cellulosic composites derive their existence from their comparatively low materials cost and the filling rather than reinforcing properties of cellulose. However, cellulose chains have a potential stiffness much higher than glass and in the same range as superstiff aramid fibers. This paper examines the state of the art of combining wood cellulose with synthetic organic polymers to from composites and considers new ways for better using cellulose's reinforcing potential.

The role of ester groups in resistance of plant cell wall polysaccharides to enzymatic hydrolysis

Abstract: Xylan backbones in native plant cell walls are extensively acety-lated. Previously, no direct investigations as to their role in cellulolytic enzyme resistance have been done, though indirect results point to their importance. An in vitro deesterification of aspen wood and wheat straw has been completed using hydroxylamine solutions. Yields of 90% acetyl ester removal for both materials have been accomplished, with little disruption of other fractions (i.e., lignin). Apparently, as the xylan becomes increasingly deacetylated, it becomes 5–7 times more digestible. This renders the cellulose fraction more accessible, and 2–3 times more digestible. This effect levels off near an acetyl removal of 75%, where other resistances become limiting.

Pretreatment of cane bagasse with alkaline hydrogen peroxide for enzymatic hydrolysis of cellulose and ethanol fermentation

Abstract: Pretreatment of the agrocellulosic waste, cane bagasse with alkaline hydrogen peroxide greatly enhances its susceptibility to enzymatic cellulolysis and thus the ethanol production from it. Various process conditions have been studied to optimize the enzymate effectiveness. These conditions include the contact time, the hydrogen peroxide concentration and the pretreatment temperature. Results obtained show, that about 50% of lignin and most of hemicellulose content of cane bagasse was solubilized, by 2% alkaline hydrogen peroxide at 30°C within 8 h. The cellulose content was consequently increased from 42% in the orginal cane bagasse to 75% in the oxidized pulp. Saccharification of this pulp residue with cellulase from Trichorderma viride at 45°C for 24 h, yielded glucose with 95% efficiency. The efficiency of ethanol production from the insoluble fraction with S. cervisiae was 90% compared to about 50% for untreated cane bagasse.

Pharmaceutical compositions having good stability

Abstract: A pharmaceutical compositions is provided which has excellent stability, when dispersed in water has a pH of at least about 9, and includes a medicament which is sensitive to a low pH environment such as pravastatin, one or more fillers such as lactose and/or microcrystalline cellulose, one or more binders, such as mirocrystalline cellulose (dry binder) or polyvinylpyrrolidone (wet binder), one or more disintegrating agents such as croscarmellose sodium, one or more lubricants such as magnesium stearate and one or more basifying agents such as magnesium oxide.

Cyclic diguanylic acid and cellulose synthesis in Agrobacterium tumefaciens.

Abstract: The occurrence of the novel regulatory nucleotide bis(3',5')-cyclic diguanylic acid (c-di-GMP) and its relation to cellulose biogenesis in the plant pathogen Agrobacterium tumefaciens was studied. c-di-GMP was detected in acid extracts of 32P-labeled cells grown in various media, and an enzyme responsible for its formation from GTP was found to be present in cell-free preparations. Cellulose synthesis in vivo was quantitatively assessed with [14C]glucose as a tracer. The organism produced cellulose during growth in the absence of plant cells, and this capacity was retained in resting cells. Synthesis of a cellulosic product from UDP-glucose in vitro with membrane preparations was markedly stimulated by c-di-GMP and its precursor GTP and was further enhanced by Ca2+. The calcium effect was attributed to inhibition of a c-di-GMP-degrading enzyme shown to be present in the cellulose synthase-containing membranes.

The effect of enzyme concentration on the rate of the hydrolysis of cellulose.

Abstract: The relationship among extent of hydrolysis, reaction time, and enzyme dosage was investigated. For this, Sigmacell 50 and pretreated poplar wood (20 g/L) was hydrolyzed with varying dosages of cellulases from three different sources (5 to 100 FPU/g) for time periods ranging from 2 to 94 h. It was found that the formation of glucose can be described by summation of two parallel first order reactions. The extent of hydrolysis at fixed time increases with increasing enzyme dosage in a hyperbolic function. From the empirical data it is possible to calculate the fractions of easily and difficult hydrolyzable cellulose and the digestability which could maximally be obtained at infinite enzyme loadings. In the system Sigmacell 50 and Celluclast the easily and difficult hydrolyzable components are 43.0 and 57.0%, respectively, and the maximum digestability at 94 h is 82.6%. Poplar wood, steam treated at 200 degrees , 220 degrees , and 240 degrees C, showed with Celluclast at 24 h a maximum digestability (weight percentage of wood degraded to glucose) of 43.9, 64.9, and 68.0%. The relationships derived from experimental data allow one to compare objectively the effectiveness of different cellulase enzymes and different pretreatments.

Study on the Selectivity of Bleaching with Oxygen-Containing Species

Abstract: In the bleaching of pulp, the term Selectivity is widely used but poorly definedThis work is an attempt to quantify the selectivity of bleaching with Oxygen-containing species by generating hydroxil radicals and measuring their reaction rates with some lignin and carbohydrate models Results of this investigation show that the selectivity factor defined as the ratio of the rate constants for a given pair of lignin and carbohydrate models, lies between 5 and 6

Synergism in Degradation and Utilization of Intact Forage Cellulose, Hemicellulose, and Pectin by Three Pure Cultures of Ruminal Bacteria

Abstract: Pure cultures of ruminal bacteria characterized as using only a single forage polysaccharide (Fibrobacter succinogenes A3c, cellulolytic; Bacteroides ruminicola H2b, hemicellulolytic; Lachnospira multiparus D15d, pectinolytic) were inoculated separately and in all possible combinations into fermentation tubes containing orchard grass as the sole substrate. Fermentations were run to completion, and then cultures were analyzed for digestion of cellulose plus degradation and utilization of hemicellulose and pectin. Addition of the noncellulolytic organisms, in any combination, to the cellulolytic organism F. succinogenes had little effect on overall cellulose utilization. F. succinogenes degraded but could not utilize hemicellulose; however, when it was combined with B. ruminicola, total utilization of hemicellulose increased markedly over that by B. ruminicola alone. L. multiparus was inactive in hemicellulose digestion, alone or in any combination. Although unable to degrade and utilize purified pectin, B. ruminicola degraded and utilized considerable quantities of the forage pectin. In contrast, L. multiparus was very active against purified pectin, but had extremely limited ability to degrade and utilize pectin from the intact forage. Both degradation and utilization of forage pectin increased when F. succinogenes was combined with B. ruminicola. Sequential addition of two cultures, allowing one to complete its fermentation before adding the second, was used to study synergism between cultures on forage pectin digestion. In general, synergistic effects did not appear to be related to a particular sequence of utilization. The ability of F. succinogenes to degrade and B. ruminicola to degrade and utilize forage pectin contradicts both previous and present data obtained with purified pectin. Thus, isolation and characterization of ruminal bacteria on purified substrates may be misleading with regard to their role in the overall ruminal fermentation.

Process for producing solutions of cellulose

Abstract: For producing solutions of cellulose in water-containing tertiary amine oxides from a suspension of cellulose in an aqueous solution of the tertiary amine oxide by supplying heat under reduced pressure, the suspension having a viscosity between 50 and 15,000 Pas.sec, measured in a relative system, is spread as a layer or film over a heating surface and transported until a homogeneous solution of the cellulose is formed, the feeding of the suspension and the take-off of the homogeneous solution being carried out continuously. These solutions can be produced in an indirectly heated vessel which is provided with a stirring device and can be evacuated and which is designed as a cylindrical container (2) with a centrally mounted stirrer shaft (7) and stirrer blades (8) attached thereto, the radial distance (13) of the stirrer blades (8) from the inside wall (1) of the container (2) being at most 20 mm, and an inlet (11) for the cellulose suspension being provided in the upper part of the container and an outlet (12) for the homogeneous cellulose solution being provided at the lower end.

Cellulose fiber-reinforced structure

Abstract: A cellulose fiber-reinforced structure useful for building and construction made from a composition including a water-curable, inorganic binder capable of setting to form a matrix and pulped softwood fibrous material having enhanced levels of summerwood fibers.

Molecular weight distribution of cellulose as its tricarbanilate by high performance size exclusion chromatography

Abstract: Etude de tricarbanilates de celluloses de coton blanchies, d'Avicel PH101, de pâte bisulfite blanchie, de cellulose amorphe et de cellulose II obtenues par reaction avec l'isocyanate de phenyle. Calibration des colonnes en utilisant les echantillons standards. Pyridine meilleur solvant de carbanilation si activation inutile, sinon DMSO meilleur. Meilleure precipitation des CTC en utilisant le melange precipitant eau-methanol a 30-70

Thermal degradation of cellulose‐containing composites during processing

Abstract: The strength properties of composites made of untreated cellulose fibers and linear low density polyethylene were investigated as a function of processing parameters. Studies have shown that the strength properties of composites increase with processing time and temperature. The increase in strength is accompanied by the appearance of new infrared absorption bands at 1718 and 1735 cm−1. A linear relationship between the absorbance and yield strength of composites indicates that oxidation, possibly directly at interfaces, takes place and enhances adhesion between the cellulose and polyethylene.

Assessment of pretreatment conditions to obtain fast complete hydrolysis on high substrate concentrations

Abstract: Steam-heating of aspen wood chips improved the enzymatic digestibility of the cellulose. Scaling up the reaction vessel from 2 to 60 L had virtually no influence on the chemical composition and the accessibility of the lignocellulosic substrate. Over 85% of the cellulose could be hydrolyzed to glucose when an 8% substrate concentration was used. The residual content of alkali-insoluble lignin appeared to control the digestibility of the cellulose. Increased delignification either by prolonged steaming, oxidative posttreatment, or SO2 catalysis improved the accessibility of the cellulose. The use of SO2 as a catalyst also increased the recovery yield of the wood after steam-heating, with more than 70% of the original xylan recovered as monomeric xylose. Conversion yields of above 90% were achieved at low levels of filter paper activity after a relatively short incubation time. Removal of alkali-soluble lignin did not influence digestibility when the enzyme concentration was based on the cellulose content of the substrates.

Degradation and utilization of cellulose and straw by three different anaerobic fungi from the ovine rumen.

Abstract: Three different ruminal fungi, a Neocallimastix sp. (strain LM-1), a Piromonas sp. (strain SM-1), and a Sphaeromonas sp. (strain NM-1), were grown anaerobically in liquid media which contained a suspension of either 1% (wt/vol) purified cellulose or finely milled wheat straw as the source of fermentable carbon. Fungal biomass was estimated by using cell wall chitin or cellular protein in cellulose cultures and chitin in straw cultures. Both strains LM-1 and SM-1 degraded cellulose with a concomitant increase in fungal biomass. Maximum growth of both fungi occurred after incubation for 4 days, and the final yield of protein was the same for both fungi. Cellulose degradation continued after growth ceased. Strain NM-1 failed to grow in the cellulose medium. All three anaerobic fungi grew in the straw-containing medium, and loss of dry weight from the cultures indicated degradation of straw to various degrees (LM-1 greater than SM-1 greater than NM-1). The total fiber component and the cellulose component of the straw were degraded in similar proportions, but the lignin component remained undegraded by any of the fungi. Maximum growth yield on straw occurred after 4 days for strain LM-1 and after 5 days for strains SM-1 and NM-1. The calculated yield of cellular protein for strain LM-1 was twice that of both strains SM-1 and NM-1. The cellular protein yield of strain SM-1 was the same in both cellulose and straw cultures. In contrast to cellulose, straw degradation ceased after the end of the growth phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding-site Analysis of the Ether Linkages between Lignin and Hemicelluloses in Lignin-Carbohydrate Complexes by DDQ-Oxidation

Abstract: Lignin-carbohydrate complexes (LCC; nor-C-1-M, com-C-1-A) isolated from normal and compression woods of Pinus densiflora were hydrolyzed with two types of cellulase preparations, and the hydrolyzates formed were fractionated by adsorption chromatography on polyvinyl gel into water-soluble materials and LCC fragments. To elucidate the binding sites between the lignin and carbohydrate, the cellulase-degraded LCC fragments were subjected to acetylation, and then oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), which was confirmed to oxidatively cleave the benzyl ether linkages between the lignin and carbohydrate. The DDQ-oxidized fraction was then methylated by the method of Prehm, hydrolyzed, reduced and acetylated. A GC-MS analysis of the methylated sugar revealed that alditol acetates from 6-O-methyl mannose, 6-O-methyl galactose, 6-O-methyl glucose and a small amount of their 2-O- or 3-O-methyl isomers existed in both methylated fractions. 2-O-Methyl xylose and 3-O-methyl xylose were also ...