Decrystallization Of Cellulose Research Articles

Recovery of Sugars from Ionic Liquid Biomass Liquor by Solvent Extraction

The dissolution of biomass into ionic liquids (ILs) has been shown to be a promising alternative biomass pretreatment technology, facilitating faster breakdown of cellulose through the disruption of lignin and the decrystallization of cellulose. Both biological and chemical catalysis have been employed to enhance the conversion of IL-treated biomass polysaccharides into monomeric sugars. However, biomass-dissolving ILs, sugar monomers, and smaller carbohydrate oligomers are all soluble in water. This reduces the overall sugar content in the recovered solid biomass and complicates the recovery and recycle of the IL. Near-complete recovery of the IL and the holocellulose is essential for an IL-based pretreatment technology to be economically feasible. To address this, a solvent extraction technique, based on the chemical affinity of boronates such as phenylboronic acid and naphthalene-2-boronic acid for sugars, was applied to the extraction of glucose, xylose, and cellobiose from aqueous mixtures of 1-ethyl-3-methylimidazolium acetate. It was shown that boronate complexes could extract up to 90% of mono- and disaccharides from aqueous IL solutions, 100% IL systems, and hydrolysates of corn stover containing IL. The use of boronate complexes shows significant potential as a way to recover sugars at several stages in ionic liquid biomass pretreatment processes, delivering a concentrated solution of fermentable sugars, minimizing toxic byproducts, and facilitating ionic liquid cleanup and recycle.

A new route to high yield sugars from biomass: phosphoric–sulfuric acid

We have developed a simple and effective route for the high yield extraction of sugars from cellulosic based biomass. This process uses a combination of a cellulose decrystallization step with a mixture of phosphoric and sulfuric acid, followed by a hydrolysis step producing sugars (xylose and glucose) with yields of approximately 90%.

The kinetics of cellulose dissolution in sodium hydroxide solution at low temperatures

The dissolution kinetics of cellulose in sodium hydroxide in the presence and absence of urea at low temperature was studied. High molecular weight cotton linter with degree of polymerization of 850 was used for dissolution study. The cotton linter was separated from the dissolution slurry at different dissolution times, and the change of the crystal structure of cotton linter was characterized by Powder X-Ray Diffraction. The rate of decrystallization of cellulose was obtained and the activation energy for cellulose decrystallization in sodium hydroxide solution was derived using Eyring equation. The effect of urea additive was discussed.

A New Route to Improved Glucose Yields in Cellulose Hydrolysis

An unusual inverse temperature-dependent pathway was discovered for cellulose decrystallization in trifluoroacetic acid (TFA). Cellulose was completely decrystallized by TFA at 0 °C in less than 2 hours, a result not achieved in 48 hours at 25°C in the same medium. The majority of TFA used in cellulose decrystallization was recycled via a vacuum process. The small remaining amount of TFA was diluted with water to make a 0.5% TFA solution and used as a catalyst in dilute acid hydrolysis. After one minute, under batch conditions at 185 °C, the glucose yield reached 63.5% without production of levulinic acid. In comparison, only 15.0% glucose yield was achieved in the hydrolysis of untreated cellulose by 0.5% H2SO4 under the same condition. Further improvement of glucose yield is possible by optimizing reaction conditions. Alternatively, the remaining TFA can be completely removed by water while keeping the regenerated cellulose in a highly amorphous state. This regenerated cellulose is much more reactive than untreated cellulose in hydrolysis reactions, but still less reactive than corn starch. The lower temperatures and shorter reaction times with this activated cellulose makes it possible to reduce operating costs and decrease byproduct yields such as HMF and levulinic acid.

Inverse Temperature-Dependent Pathway of Cellulose Decrystallization in Trifluoroacetic Acid

An unusual inverse temperature-dependent pathway was observed during cellulose decrystallization in trifluoroacetic acid (TFA). Decreasing the TFA treatment temperature accelerated the cellulose decrystallization process. It took only 100 min to completely decrystallize cellulose at 0 degrees C in TFA, a result not achieved in 48 h at 25 degrees C in the same medium. There was neither cellulose esterification nor a change of cellulose macrofibril morphology by TFA treatment at 0 degrees C. Our IR data suggest that TFA molecules are present as cyclic dimers when they penetrate into crystalline cellulose regions, transforming crystalline cellulose to amorphous cellulose. On the other hand, the rate of TFA penetration into the cellulose matrix was greatly retarded at higher temperatures where monomeric TFA prevails. At elevated temperatures, esterification of TFA monomers on the external surface of crystalline cellulose, agglomeration of cellulose macrofibrils, as well as water released from the esterification reaction, inhibit the diffusion rate of TFA into the cellulose crystalline region and decrease the TFA swelling capability.

Controlled heterogeneous modification of cellulose fibers with fatty acids: Effect of reaction conditions on the extent of esterification and fiber properties

AbstractThe controlled heterogeneous partial modification of cellulose fibers with fatty acids, partially preserving the fiber structure, was investigated. The effect of reaction conditions, such as reaction time, fatty acid chain length, and solvent types (swelling and non swelling), on the extent of esterification and fiber properties was evaluated by elemental analysis, IR‐ATR, X‐ray diffraction, 13C CPMAS NMR, contact angle measurement, thermogravimetry, and scanning electron microscopy. The degree of substitution (DS) increased with reaction time and with the swelling effect of the reaction medium and decreased with the fatty acids chain length. Higher the DS, higher is the decrystallization of cellulose as a result of the heterogeneous esterification reaction. The esterification with fatty acids enhanced the hydrophobic character of the fibers, but decreased their thermal stability. These properties are not strongly affected by the DS in the range investigated, viz. up to 1.4. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1093–1102, 2006

Influence of the Supramolecular Structure and Physicochemical Properties of Cellulose on Its Dissolution in a Lithium Chloride/N,N-Dimethylacetamide Solvent System

The present work deals with the effects of structural variables of celluloses on their dissolution in the solvent system LiCl/N,N-dimethylacetamide, LiCl/DMAc. Celluloses from fast growing sources (sisal and linters), as well as microcrystalline cellulose (avicel PH-101) were studied. The following structural variables were investigated: index of crystallinity, I(c); crystallite size; polymer porosity; and degree of polymerization determined by viscosity, DPv. Mercerization of fibrous celluloses was found to decrease DPv, I(c), the specific surface area, and the ratio pore volume/radius. The relevance of the structural properties of cellulose to its dissolution is discussed. Rate constants and activation parameters of cellulose decrystallization, prior to its solubilization, have been determined under nonisothermal conditions. The kinetic parameters calculated showed that dissolution is accompanied with small, negative enthalpy and a large, negative entropy of activation.

Comparative study of crude and purified cellulose from wheat straw.

A sequential totally chlorine-free procedure for isolation of cellulose from wheat straw was proposed in this study. The dewaxed straw was pretreated with 0.5 M NaOH in 60% methanol at 60 degrees C for 2.5 h under ultrasonic irradiation for 0-35 min and sequentially posttreated with 2% H(2)O(2)-0.2% TAED at pH 11.8 for 12 h at 48 degrees C, which together solubilized 85.3-86.1% of the original hemicelluloses and 91.7-93.2% of the original lignin, respectively. The yield of crude cellulose ranged between 46.2 and 49.2% on a dry weight basis related to wheat straw, which contained 11.2-12.2% residual hemicelluloses and 2.5-2.9% remaining lignin. Further treatment of the corresponding crude cellulosic preparations with 80% acetic acid-70% nitric acid under the condition given yielded 36.8-37.7% of the purified cellulose, which contained minor amounts of bound hemicelluloses (2.5-2.8%) and was relatively free of associated lignin (0.1-0.2%). The isolated crude and purified cellulose samples were comparatively studied by FT-IR and CP/MAS (13)C NMR spectroscopy, and the relative crystallinity was also estimated. The final stage treatment with 80% acetic acid-70% nitric acid decreased the hemicelluloses and lignin associated in the crude cellulose but led to 3.1-5.4% degradation of the original cellulose; in addition, the purity of the obtained cellulose was high. However, it was found that the final stage treatment is not severe enough to cause decrystallization of cellulose. The thermal stability of the purified cellulose is higher than that of the corresponding crude cellulose.

Properties of wood esterified by fatty-acid chlorides

Lignocellulosic compounds can be esterified through their hydroxyl groups to obtain new materials (plastic films, hydrophobic coatings, etc.). Recently, a new esterification method was developed using wood sawdust and fatty-acid chlorides, avoiding any solvent. The esterified woody materials showed high hydrophobicity properties which increased with using longer fatty-acid chlorides. Cellulose decrystallization was demonstrated by X-ray analysis and was one reason for the thermoplastic properties of the esterified product. The thermal stability of wood was improved after chemical modification.

Phosphoric acid mediated depolymerization and decrystallization of cellulose: Preparation of low crystallinity cellulose — A new pharmaceutical excipient

The reactions of cellulose with phosphoric acid under different temperature conditions were investigated to prepare a new class of cellulose excipients which have controlled, low degrees of crystallinity and reduced levels of polymerization. The results showed the depolymerization of cellulose by phosphoric acid to be a first order reaction with rate constant values corresponding to 4.79 × 10 −3 and 0.314 per hour at 25 and 55°C (after 1 h pretreatment at 22°C), respectively. Products prepared from reactions at 25, 30, 35, 45, and 55°C for 216, 120, 72, 15, and 4.5 h, respectively, exhibited degrees of polymerization values ranging from 64 to 88. The degree of crystallinity of the products prepared at 25, 30, 35, and 45°C ranged from 32 to 45%, whereas that of the product isolated at 55°C was 80%. The activation energy, calculated using the Arrhenius relationship, was 25.3 kcal/mol. A temperature sequencing method, wherein the cellulose is treated at room temperature (22–25°C) for 1–14 h, and then at 50°C for 2–10.5 h, resulted in the preparation of low crystalline cellulose materials with degree of crystallinity and degree of polymerization values ranging between 19–43% and 45–138, respectively.

The effect of N2O4 on the crystalline structure of cellulose

AbstractDepending on reaction conditions, the system cellulose–N2O4 may give two different unstable crystalline compounds, one being an ester (cellulose trinitrite), the second, an adduct of cellulose and HNO3 (the Knecht compound). For these compounds, mechanisms of the formation of the crystalline phase as a result of topochemical reaction and self‐organization are discussed. The different characteristics of structural transformations of the fiber under nitrosation and nitration are noted. The existence of polymorphic forms of the Knecht compound is suggested. These labile nitrogen‐containing compounds make possible the regeneration of cellulose in its various modifications (cellulose I, II, IV, or amorphous cellulose) from the cellulose–N2O4 system. The formation of unstable compounds and their ability to crystallize in the reaction medium allows the passage from amorphous cellulose to its crystalline modifications II or IV under mild conditions. The causes of decrystallization of cellulose by N2O4 are established. © 1993 John Wiley & Sons, Inc.

Studies on the alkaline degradation of cellulose: Part II effect of the supermolecular structure of the pulp

The supermolecular structure of cellulosic pulp plays an important role in its alkaline degradation behaviour. In spite of the well-known compact, ordered and less accessible supermolecular structure of cotton cellulose, it has greater susceptibility to alkaline oxidative degradation than bagasse cellulose. Bagasse kraft pulp undergoes inter-crystalline swelling followed by oxidative degradation which is mostly restricted to the amorphous domains of the fibre. However, in the case of cotton linter the degradation takes place through intracrystalline swelling. In this case the reactant penetrates the crystallites and stronger degradation takes place. The extent of degradation depends upon the structure of the original cellulose. Intracrystalline degradation is more efficient than the intercrystalline degradation in cellulose decrystallization. The purity of the pulp and good hydrolytic attack affect the fibril structure which strongly influences its reactivity towards xanthation.

Pretreatment of lignocellulosic municipal solid waste by ammonia fiber explosion (AFEX)

The Ammonia Fiber Explosion (AFEX) process treats lignocellulose with high-pressure liquid ammonia and then explosively releases the pressure. The combined chemical effect (cellulose decrystallization) and physical effect (increased accessible surface area) dramatically increase lignocellulose susceptibility to enzymatic attack. For example, bagasse digestibility is increased 5.5 times and that of kenaf core is increased 11 times using extracellular cellulases fromTrichoderma reesei. In this study, we applied the AFEX process to mixed municipal solid waste (MSW) and individual components (e.g., softwood newspaper, kenaf newspaper, copy paper, paper towels, cereal boxes, paper bags, corrugated boxes, magazines, and waxed paper). Softwood newspaper proved to be the most difficult component to digest because of its high lignin content. A combination of oxidative lignin cleavage and AFEX was required to increase softwood newspaper digestibility substantially, whereas AFEX alone was able to make kenaf newspaper digestible. Because most MSW components have been substantially delignified in the paper-making process, AFEX only marginally increased their digestibility.

The ammonia freeze explosion (AFEX) process

The Ammonia Freeze Explosion (AFEX) process treats lignocellulose with high-pressure liquid ammonia, and then explosively releases the pressure. The combined chemical effect (cellulose decrystallization) and physical effect (increased accessible surface area) dramatically increase lignocellulose susceptibility to enzymatic attack. There are many adjustable parameters in the AFEX process: ammonia loading, water loading, temperature, time, blowdown pressure, and number of treatments. The effect of these parameters on enzymatic susceptibility was explored for three materials: Coastal bermudagrass, bagasse, and newspaper. Nearly quantitative sugar yields were demonstrated for Coastal bermudagrass and bagasse, using a very low enzyme loading (5 IU/g). Newspaper proved to be much more resistant to enzymatic hydrolysis.

Homogeneous Tritylation of Cellulose in A Sulfur Dioxide – Diethylamine – Dimethyl Sulfoxide Medium

Abstract The present investigation was undertaken to see if a practical method could be developed for homogeneous tritylation of cellulose in a non-aqueous solvent of cellulose. Our new procedure of tritylation of cellulose can easily be carried out under homogeneous conditions by dissolving cellulose in a sulfur dioxide(SO2)-diethylamine (DEA)-dimethyl sulfoxide(DMSO) solvent system, one or the non-aqueous cellulose solvents, followed by addition of trityl chloride and pyridine. This new method can avoid the time consuming pretreatment for the decrystallization of cellulose which has been necessary in the traditional procedure and can lower the reaction temperature. IR spectra of the products indicated the formation of trityl cellulose. Measurements of dielectric properties of the products confirmed that trityl groups were selectively introduced at the primary hydroxyl groups in cellulose. This conclusion was also confirmed by a H-NMR study in which the tritylated products was first acetylated, detrityla...

Some aspects of graft polymerization of vinyl monomers onto cellulose by use of tetravalent cerium. VI

The state of cellulose as defined by its crystallinity, grinding, and average degree of polymerization (D.P.) highly influences the grafting yield. Grinding of cellulose with a Wiley mill results in decreased grafting, while grinding with a ball mill or treatment with ethylenediamine, both of which lead to decrystallization of cellulose, nearly inhibits the grafting reaction from taking place. On the other hand, decreased D.P. leads to increased grafting yield. The governing factor being attributed to the specific surface of the cellulose. Increased specific surface, as decreased D.P., brings about an increase in the active sites formed on the cellulose and hence an increase in the grafting yield. However, this occurs up to a limit beyond which further increase in the specific surface, respectively, the formed active sites, as grinding with a Wiley mill and decrystallization, brings about termination reactions through disproportionation and coupling of the exceedingly increased free radicals, and hence grafting is decreased or nearly inhibited. Drying of cellulose at 105°C resulted in decreased grafting yield. This was attributed to condensation of the cellulose structure. It has been also found that the grafting yield is influenced by the type and origin of cellulose whose reactivities differ for different monomers.

Decrystallization of Cotton Cellulose by Dual Treatments with Benzyltrimethylammonium Hydroxide and Alkali Metal Hydroxides

Kiered, cotton yarns undergo extensive decrystallization when wet in the slack state with 2.1 N aqueous henzyltri methylammonium hydroxide. The decrystallization is temporary, inasmuch as washing and drying cause the yarn to recrystallize to Cellulose I. However, much of the decrystallization can be rendered permanent, if the swollen yarns are aftertreated with aqueous sodium or potassium hydroxide prior to washing and air-drying. The alkali aftertreatment also alters a variety of other physical properties in ways differing from either swelling treatment carried out alone. The effects of concentration and type of alkali metal hydroxides on the decrystallization, lattice conversion, and physical properties of the yarns are reported. The effect of tension applied during various stages of these dual treatments is dis cussed with respect to textile properties of the yarns before and after crosslinking with DMEU, and also with respect to crystallinity, lattice conversion, and orientation imparted.

Decrystallization of cotton cellulose by benzyltrimethylammonium hydroxide followed by polar organic solvents

Decrystallization of cotton cellulose by benzyltrimethylammonium hydroxide followed by polar organic solvents

Supramolecular structure of propionylated cotton cellulose

AbstractHeterogeneous propionylation of cotton cellulose, in the form of yarn, was carried out by reaction with propionyl chloride, in a medium of pyridine and dimethylformamide (DMF). The product was a mixed propionate–α‐propionylpropionate ester of DS varying from 0.24 to 2.94. The supramolecular structure of these esters was studied by kinetic analysis as well as by the measurements of density, refractive index, and x‐ray diffraction. The Sakurada plot of DS against time of reaction showed a discontinuity at a DS of about 2.0, where the x‐ray diffraction pattern shows almost complete loss of crystalline structure. The interpretation, based on the assumption that the Sakurada curve actually represents the sum of two simultaneous rate processes acting in the amorphous phase and at the crystalline surfaces, seems to explain the data adequately. The density showed a continuous decrease, consistent with the idea of continuous destruction of crystalline structure with progressive substitution. Refractive indices showed a continuous decrease with substitution and birefringence was almost absent at complete substitution. The calculated value of molar refraction for the sample of DS 2.94 agreed closely with the experimentally observed value. The x‐ray diffraction intensity traces gave convincing evidence of the progressive decrystallization of cellulose with the degree of substitution. Decrystallization seems to be more or less complete at about a DS of 2.0.

Kinetics of heterogeneous cellulose reactions. II. Reaction with propionyl chloride

AbstractA heterogeneous cellulose reaction was studied by reacting cotton fiber in pyridine medium with propionyl chloride at different initial molar concentrations and at different temperatures. It has been observed that the kinetics of reaction does not follow Sakurada's diffusion equation closely, and the deviation is more noticeable at lower initial concentrations of the reagent and at lower temperatures. A non‐uniform reaction rate is also evident from the time–substitution curve. The rate of substitution changes twice during the reaction, the latter change being associated with the loss of cellulose I crystal structure. In an attempt to treat the data according to simple chemical kinetics, the order has been found to decrease continuously from the beginning, suggesting thereby an autocatalytic type of behavior. However, at the finàl stages of the reaction, when the cellulose I structure was completely lost, the reaction behaved as a pseudo first‐order type. The x‐ray diffractograms of the reacted samples indicate that cellulose I crystallinity decreases from the beginning of the reaction and that a new crystalline lattice develops gradually. The formation of this new crystal lattice is hindered in the cellulose crystalline region due to the lack of freedom of the chains. The diffusion equation has been modified by substituting a crystallinity index for the rate of diffusion of solvent in a solvent–gel system and thus extending Sakurada's equation. A new mechanism has been proposed considering the simultaneous reactions in the amorphous and crystalline regions. This mechanism can explain the deviation of Sakurada's equation. The kinetics expressions are derived, based on the proposed mechanism. The kinetics of decrystallization of cellulose I is also presented. A satisfactory theoretical explanation is given for the fact that the fall of reaction rate occurs at the conclusion of decrystallization of the cellulose I structure.