The thermodynamics study on the dissolution mechanism of cellobiose in NaOH/urea aqueous solution

NaOH/urea aqueous solution is a novel, green solvent for cellulose. To explain why cellulose just be dissolved in this solvent under ?13 °C, we studied and discussed the dissolving process of cellobiose in water, urea solution, NaOH solution and NaOH/urea aqueous solution. Dissolving cellobiose in water and the urea solution absorb heat, which is an entropy-driven process. Dissolving cellobiose in NaOH solution and mixed NaOH/urea solution is exothermic, which is an enthalpy-driven process. OH^? plays an important role in the dissolving process by forming a hydrogen-bonding complex. From the thermodynamic point of view, negative entropy can well interpret why cellulose must be dissolved in cold NaOH/urea aqueous solution.     

Alkaline steeping of dissolving pulp. Part I: cellulose degradation kinetics

The production of cellulosic man made fibres by the viscose process has been known for more than 120 years now, but still some aspects are not sufficiently understood in detail. The carbohydrates in the pulp are exposed to varying conditions during the manufacturing process. In the first production step of steeping, the strong alkaline treatment leads to undesirable loss reactions of the cellulose. In this study, a comprehensive kinetic model was developed for process simulation of cellulose degradation for the fist time comprising primary and secondary peeling, stopping and alkaline hydrolysis. A total chlorine free bleached beech sulfite pulp was treated with 18 % sodium hydroxide at 40, 50 and 60 °C for time periods up to 80 h. The corresponding reaction rates, activation energies and frequency factors for all reaction steps were calculated. The peeling-off reaction was of great significance for the cellulose yield loss, due to a contribution of the secondary peeling after random chain scission. The moderate decrease of the intrinsic viscosity and the changes in molar mass distribution indicated the validity of the assumption. Further, a reduction of the carbonyl and an increase of the carboxyl groups in the cellulose were observed due to the formation of the stable metasaccharinic acid at the reducing ends of the molecules. The fibre morphology was investigated by SEM measurements. Already short alkaline treatment times favored the dissolution of fibril fragments from the fibre surface leading to a smooth fibre surface.     

Reaction pathway to CZTSe formation in CdI2

The thermal decomposition of cotton and hemp fibers was studied after mild alkaline treatments with tetramethyl-, tetraethyl- and tetrabutylammonium hydroxides with the goal of modeling the chemical activation during carbonization of cellulosic fibers. The thermal decomposition was studied by thermogravimetry/mass spectrometry and pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS). The treated samples decomposed in two temperature ranges during heating in the thermobalance. At lower temperature, tetraalkylammonium hydroxides (TAAH) ionically bonded to the cellulose molecules were decomposed; moreover, the alkaline agents initiated the partial decomposition of cellulose. Those fiber segments, which were not accessible for TAAH, decomposed at similar temperatures as the original cotton and hemp samples. It is known that quaternary ammonium hydroxides swell the cellulosic fibers; however, the results of this study proved that there was a chemical interaction between the alkaline swelling agents and cotton or hemp fibers at rather low temperatures (200–300 °C). The evolved products indicated that the alkaline chemicals reacted with the cellulose molecules and alkylated compounds were formed. This observation was confirmed by thermochemolysis experiments carried out by Py–GC/MS using tetramethylammonium hydroxide reagent. The thermochemolysis experiments under mild conditions resulted in the methylation of the glucoside units and levoglucosan, and no peeling reactions of the sugar units were observed as during strong alkaline conditions described in the literature.

     

Direct carbamation of cellulose fiber sheets

The paper is on introducing carbamate groups in sheets of cellulose fiber assemblies by pad-dry-cure treatments with aqueous solutions of polyethylene glycol, amide and salt. The effects of process variables—on carbamation levels and on mechanical properties of the substrate—are reported. Depending on treatment conditions, the nitrogen contents in substrates are in the range 0.668–2.252 wt%, corresponding to nominal degrees of carbamate group substitution of 0.08–0.28. The carbamation is initiated at 140 °C curing, and the levels rise with temperature up to 220 °C, but decrease at higher temperatures. The duration of curing also exerts an influence. There is a catalytic effect of sodium acetate on the carbamation, but the salt also induces a brown coloration in samples, which is likely a result of Maillard-type reactions. The treatments cause hydrolytic degradation in substrates, but there are options to adjust treatment conditions and minimize damage. Pad-dry-cure treatments are a common operation in the textile and paper industries, and the process may be adopted in commercial-scale operations to create derivatized paper or fabrics (woven, knitted or non-woven) for utilization in applications such as adsorbents for heavy metals from waste water, in hygiene products, in the creation of flame retardant products, or in creating all-cellulose composites by further treatment with alkali.     

The influence of alkaline reserve on the aging behavior of book papers

Degradation of cellulose under alkaline conditions is involved either involuntarily or deliberately in many different cellulose processing steps, such as pulping, bleaching, or aging within the viscose process, and the underlying chemistry has been the topic of numerous studies. When it comes to aging under alkaline conditions—either natural or accelerated (artificial)—the degradation processes are by far less investigated and understood. A prominent example of moderately alkaline cellulosic material is deacidified book paper from libraries which had undergone a mass-deacidification treatment. We studied their aging behavior under accelerated conditions in comparison to non-deacidified duplicates in order to better understand how the alkaline reserve, which was introduced by the deacidification treatment, affects the stability of the books on the long run. GPC analysis of cellulose and determination of carbonyl functionalities were performed, which were critical parameters to achieve a deeper insight into hydrolytic and oxidative changes of cellulose structure upon deacidification treatment and subsequent aging. Also, model book papers impregnated with different amounts of alkaline reserve were used to support the findings from the original book samples. Hydrolytic degradation rates of the original book papers were significantly reduced after mass deacidification compared to the non-deacidified duplicates. The beneficial effect of mass deacidification on cellulose stability was found to be strongly related to the amount of alkaline reserve deposited, independent of varying parameters of book papers. Although some indication of alkali-induced β-elimination was found (a minor decrease of the along-chain carbonyl content in the original deacidified book papers during aging), it did not occur to an extent that significantly influenced the molar mass of cellulose. The beneficial effect of retarded hydrolytic degradation by mass deacidification thus clearly outweighed possible negative alkalinity effects of the deposited alkaline reserve.     

Dissolving-grade birch pulps produced under various prehydrolysis intensities: quality,structure and applications

Aqueous-phase prehydrolysis followed by alkaline pulping is a viable process to produce wood-based dissolving pulps. However, detailed characterisation of the achievable pulp quality, performance and cellulose structure is yet lacking. In this study, the production of hemicellulose-lean birch soda-anthraquinone pulps after prehydrolysis under various intensities was investigated. Increasing prehydrolysis intensity resulted in pulps of higher purity but lower cellulose yield and degree of polymerisation. Higher cellulose yield by using sodium borohydride during pulping was achieved at the expense of reducing pulp purity. Cellulose crystallinity was similar in all pulps indicating simultaneous degradation of both crystalline and amorphous cellulose regions. Reinforced prehydrolysis seemingly increased the cellulose crystal size and the interfibrillar distances. Moderate intensity prehydrolysis (170 °C) resulted in a pulp well suited for viscose application, whereas reinforced prehydrolysis favoured the production of acceptable cellulose triacetate dope. The performance of the pulps in viscose and acetate applications was strongly related to the chemical and structural properties.     

Synthesis of diblock copolymers with cellulose derivatives. 1. Model study with azidoalkyl carboxylic acid and cellobiosylamine derivative

The basic strategy to make a well-defined A-block-B type cellulose derivative consisting of cellulose and a hydrophobic part was established. The model experiments using cellobiose derivatives play an important role in an actual synthesis of A-block-B type copolymer consisting of cellulose and a hydrophobic part with well-controlled length. A new hydrophobic building block, 15-azidopentadecanoyl chloride, was converted from a commercially available15-hydroxypentadecanoic acid. The novel hydrophobic linker, 15-azidopentadecanoyl chloride, was twice introduced into the reducing end of the cellobiosylamine derivative. The structures of the model compounds for A-block-B type copolymer consisting of sugar and non-sugar blocks were characterized by use of nuclear magnetic resonance (NMR) spectroscopy and Matrix Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS).     

Grafting and initiation reactions

Grafting of acrylic monomers onto cellulose substrates in acid aqueous medium using complex of Mn³⁺ ions as a redox initiator is described. Assuming that the /Mn³⁺/ ions react with aldehydes and vicinal diols, the rate of these reactions has been measured spectroscopically. (ESR and visible light) using model compounds. It is concluded that the /Mn³⁺/ grafting onto cellulose is a radical reaction initiated mainly by oxidation of aldehydes at reducing end groups and C-C bond scission of vicinal diols at the end groups and along the cellulose chains. The initiation rates of the Ce⁴⁺, /Mn³⁺/ and VO₂²⁺ redox ions are related to their oxidation potential.     

13C CPMAS NMR investigations of cellulose polymorphs in different pulps

In order to obtain information about the crystallinity and polymorphs of cellulose, and the occurrence of hemicelluloses in pulp fibers, wood cellulose, bacterial cellulose, cotton linters, viscose, and celluloses in different pulps were investigated by solid state ¹³C CPMAS NMR spectroscopy. A mixed softwood kraft pulp and a dissolving-grade pulp were treated under strongly alkaline and acidic conditions and the effect on cellulose crystallinity was studied. The presence of different crystalline polymorphs of cellulose and the amounts of hemicelluloses are considered.     

Nitrogen-Containing Hydrochar: The Influence of Nitrogen-Containing Compounds on the Hydrochar Formation

Hydrothermal carbonization (HTC) of fructose and urea containing solutions was conducted at 180 °C to study the influence of nitrogen-containing compounds on the conversion process and HTC products properties. The concentration of fructose was fixed, while the concentration of urea was gradually increased to study its influence on the formation of nitrogen-containing hydrochar (N−HC). The degradation of urea has an important influence on the HTC of fructose. The Maillard reaction (MR) promotes the formation of N−HC in acidic conditions. However, in alkaline conditions, MR promotes the formation of bio-oil at the expense of N−HC. Alkaline conditions reduce N−HC yield by catalyzing fragmentation reactions of fructose and by promoting the isomerization of fructose to glucose. The results showed that adjusting the concentration of nitrogen-containing compounds or the pH value of the reaction environment is important to force the reaction toward the formation of N−HC or N-bio-oil.     

Increasing softwood kraft pulp yield using sodium methyl mercaptide

Cellulose - The objective of this work was to determine the effect of sodium methyl mercaptide (SMM) on the minimization of peeling reactions of southern pine chips in the kraft pulping process....     

Cellobiose as a model compound for cellulose to study the interactions in cellulose/lithium chloride/<Emphasis Type="Italic">N</Emphasis>-methyl-2-pyrrolidone systems

To investigate the solvent/solute interactions that take place during the dissolution of cellulose, cellobiose was employed as a model of the longer-chain cellulose molecule in a dissolution study of the cellobiose/LiCl/N-methyl-2-pyrrolidone (NMP) system, conducted using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), ¹³C, ³⁵Cl, and ⁷Li NMR spectroscopy, and conductivity measurements. For the LiCl/NMP system, FTIR and ¹³C NMR analyses of the NMP carbonyl moiety showed a strong dependence on the LiCl concentration, which suggested an association between the Li⁺ cations and the carbonyl groups of NMP. As the cellobiose molecules are dissolved in the LiCl/NMP solvent, the Li⁺–Cl^? ion-pairs in LiCl/NMP are dissociated. Strong hydrogen bonds are then formed between the hydroxyl groups of cellobiose and the Cl^? anions, resulting in breakage of the intermolecular hydrogen bonds of cellobiose. Meanwhile, the Li⁺ cations are further associated with the extra free NMP molecules. However, the NMP molecules do not directly interact with the dissolved cellobiose. Based on these results, we propose that our study is conducive to a more in-depth comprehension of the dissolution mechanism of cellulose in LiCl/NMP.     

Use of Cellulase Inhibitors to Produce Cellobiose

The economics driving biorefinery development requires high value-added products such as cellobiose for financial feasibility. This research describes a simple technology for increasing cellobiose yields during lignocellulosic hydrolysis. The yield of cellobiose produced during cellulose hydrolysis was maximized by modification of reaction conditions. The addition of an inhibitor from the group that includes glucose oxidase, gluconolactone, and gluconic acid during cellulase hydrolysis of cellulose increased the amount of cellobiose produced. The optimal conditions for cellobiose production were determined for four factors; reaction time, cellulase concentration, cellulose concentration, and inhibitor concentration using a Box-Behnken experimental design. Gluconolactone in the cellulase system resulted in the greatest production of cellobiose (31.2%) from cellulose. The yield of cellobiose was 23.7% with glucose oxidase, similar to 21.9% with gluconic acid.     

Direct characterization of hydrogen peroxide bleached thermomechanical pulp using spectroscopic methods

The effects of thermomechanical pulp (TMP) bleaching with hydrogen peroxide under acidic and alkaline conditions were studied using different spectroscopic analytical methods. The results of hydroxyl radical determination in bleaching solutions, analyses of carbonyl and carboxyl groups contents in the pulp, and the cellulose fiber surface analysis by X-ray photoelectron spectroscopy (XPS) elucidate the chemistry of the hydrogen peroxide treatment. Diffuse reflectance laser flash photolysis (DRLFP) method showed the differences in the photochemical behavior that reflect the changes of the chromophoric system after the preliminary peroxide bleaching stage under acidic conditions. Fourier transform infrared (FTIR) spectroscopy confirmed the non-delignifying character of the bleaching process. Suppression of carbonyl and formation of carboxyl groups in the case of the two-stage peroxide bleaching performed in the presence of catalysts and stabilizers was also confirmed. FT-Raman studies showed the removal of coniferaldehyde groups after treatment under acidic and alkaline conditions.     

Mass spectrometric study of glucose and cellobiose produced during enzymatic hydrolysis of α‐cellulose extracted from oak late‐wood annual rings

We present the first results concerning interannual variations in concentrations of glucose and cellobiose, obtained through enzymatic hydrolysis of α‐cellulose. The α‐cellulose was extracted from late‐wood of oak. The tree‐ring chronologies, wood components and their physical and chemical properties provide information about the ecosystem in which the tree grew, and thus information regarding climate variability and the impact of human activity in the past. The large molecular size and insolubility make it difficult to determine precisely the chemical and physical properties of the intact cellulose polymer. Enzymatic hydrolysis is the principal method of degradation of cellulose. In this study the feasibility has been examined of characterizing α‐cellulose through analysis by mass spectrometry (MS) of the degradation products from hydrolysis. Degradation of α‐cellulose was possible without using alkaline or acid buffers. Analysis by MS provided the opportunity to obtain information on the biodegradation of saccharides. The presence of cellobiose and glucose in the degradation product was evidenced by the mass spectra. We have compared the abundances of these glucose and cellobiose ions with carbon isotope ratios, the efficiency of extraction of α‐cellulose from the wood and tree‐ring width indices. The challenge is to establish, with respect to climate changes and environmental conditions, the significance of the variations from one year to another in the observed abundances of glucose and cellobiose ions. Copyright © 2009 John Wiley & Sons, Ltd.     

Viscometric determination of dialdehyde content in periodate oxycellulose. Part I. Methodology

Periodate oxycellulose was subjected to alkaline hydrolysis at room temperature in both homogeneous (cupriethylenediamine) and heterogeneous (sodium hydroxide) medium, and the degradation kinetics was followed for nearly three months. By comparing the obtained results with the degradation kinetics of both hydrocellulose and periodate oxycellulose reduced with tert-butylamine borane, it was demonstrated that the -alkoxy fragmentation of oxidised sites is a very fast reaction, which reaches completeness during the preparation of samples for viscometric analyses. The subsequent degradation is due to other mechanisms, such as autoxidation and peeling. A comparison between the degrees of polymerisation of periodate oxycellulose before and after its reduction allows the quantitative determination of dialdehyde groups, without the interference of reducing end groups. Although this technique might not be valid for other kinds of oxycellulose, it supplies a simple and fast method for the analysis of mildly oxidised cellulose.     

Determination of reducing carbonyl groups in cellulose in the solvent system LiCl/N,N-dimethylacetamide

 The 2,3,5-triphenyltetrazolium chloride (TTC) method for the determination of reducing carbonyl groups in cellulose in water suspensions has been thoroughly evaluated. By reduction of TTC in alkaline medium, triphenylformazane (formazane) is produced. It is thermally unstable and an unavoidable loss results in a relatively high detection limit for the determination of reducing carbonyl groups in most celluloses with a low content of such groups. Besides, oxidized cellulose is unstable in the alkaline media in which the reaction is performed. The determined content of reducing groups has also been shown to be affected by the amount of sample, indicating that absorption of triphenylformazane takes place. A new method for determination of reducing carbonyl groups in cellulose in homogeneous medium has been developed. Cellulose is dissolved in the solvent system LiCl/N,N-dimethylacetamide and reacts with TTC in the presence of tert-butylamine at 75 ^°C for 10 min and formazane is subsequently determined spectrophotometrically at 524 nm. None of the systematic errors inherent in the “aqueous” suspension method can be defined. The new procedure is also more reproducible and has a lower detection limit of 7 nmol reducing groups in a given mass of sample. The two procedures have been tested on five differently oxidised cellulose samples and the difference in the determinations are discussed. Received: 4 March 1996/Revised: 21 May 1996/Accepted: 25 May 1996     

The role of salt on cellulose dissolution in ethylene diamine/salt solvent systems

Ethylene diamine (EDA)/salt solvent systems can dissolve cellulose without any pretreatment. A comparison of the electrical conductivity of different salts in EDA was made at 25 °C, and conductivity decreased in the order of KSCN>KI>NaSCN at the same molar concentration. Among the salts tested, potassium thiocyanate (KSCN) was capable of dissolving both high molecular weight (DP>1000) and low molecular weight (DP = 210) cellulose, and this was confirmed by polarized light microscopy. ³⁹K and ¹⁴N NMR experiments were conducted at 70 °C as a function of cellobiose concentration with EDA/KSCN as the solvent. The results showed that the K⁺ ion interacts with cellobiose more than the SCN⁻ ion does. Recovered cellulose was studied by infrared spectroscopy (FTIR) and wide angle X-ray diffraction (WAXD). Changes in the FTIR absorption bands at 1,430 and 1,317 cm⁻¹ were associated with a change in the conformation of the C-6CH₂OH group. The changes in positions and/or intensities of absorption bands at 2,900, 1,163, and 8,97cm⁻¹ were related to the breaking of hydrogen bonds in cellulose. X-ray diffraction studies revealed that cellulose, recovered by precipitating cellulose solutions with water, underwent a polymorphic transformation from cellulose I to cellulose II.     

Study of cellulose/ethylene diamine/salt systems

To better understand the complex interactions leading to dissolution of cellulose in ethylene diamine (EDA)/salt solvents, studies of interactions in sub systems of solution components and a model system based on cellobiose were conducted. Interaction between EDA and salt cation was investigated through comparison of solvation of K⁺, Na⁺ and Li⁺ in the EDA/H₂O binary solvent system. The least degree of solvation of K⁺ in EDA increased its availability for direct interaction with cellulose. Wide angle X-ray diffraction was utilized to study the interaction between EDA and cellulose. The effect of various solvents on cellulose crystalline polymorph was compared. The results indicated that cellulose was easily accessible to EDA and 1,3-diaminopropane, but was not affected by water or ethanolamine. The effect of salt concentration was investigated using cellobiose as a model compound through HSQC (Heteronuclear Single Quantum Coherence) NMR spectroscopy. Solid state CP/MAS (cross polarization/magic angle spinning) ¹³C NMR spectroscopy was employed to characterize changes in the conformation of the CH₂OH group of cellulose during dissolution. A mechanism scheme of cellulose dissolution in EDA/KSCN systems was proposed based on the information gathered.     

Production of succinate from glucose, cellobiose, and various cellulosic materials by the ruminai anaerobic bacteriaFibrobacter succinogenes andRuminococcus flavefaciens

The production of organic acids by two anaerobic ruminal bacteria,Fibrobacter succinogenes S85 andRuminococcus flavefaciens FD-1, was compared with glucose, cellobiose, microcrystalline cellulose, Walseth cellulose (acid swollen cellulose), pulped paper, and steam-exploded yellow poplar as substrates. The major end product produced byF. succinogenes from each of these substrates was succinate (69.5–83%), the principal secondary product was acetate (16–30.5%). Maximum succinate productivity ranged from 14.1 mg/L · h for steam-exploded yellow Poplar to 59.7 mg/L · h for pulped paper. ForR. flavefaciens, the major end product from cellobiose, microcrystalline cellulose, and acid-swollen Walseth cellulose was acetate (39–46%), pulped paper and steam-exploded yellow poplar yielded succinate (42–54%) as the major product. Maximum succinate productivity byR. flavefaciens ranged from 9.21 mg/L · h for cellobiose to 43.1 mg/L · h for pulped paper. In general, much less succinate was produced at a lower maximum productivity byR. flavefaciens than byF. succinogenes under similar fermentation conditions. The maximum succinate productivities by these two organisms are comparable to the previously reported value of 59 mg/L · h forAnderobiospirillum succiniciproducens grown on glucose and corn steep liquor.