Molecular Weight Distribution Of Cellulose Research Articles

Progress in improving the properties of dissolving pulp by enzymes

Dissolving pulp consists of high purity cellulose and is widely used to as raw materials for the production of regenerated cellulose fiber, cellulose ester and cellulose ether. The characteristic of dissolving pulp affects greatly the production and processing performance of subsequent products. The α-cellulose content, hemicellulose content, pulp viscosity, ash, transition metal ion content, fiber morphology, molecular weight distribution of cellulose and the reactivity are the important properties. Because of its green, mild and high efficiency, the application of enzymes in improving the properties of dissolving pulp has a promising application prospect and has been researched significantly. In this review, the main properties of dissolving pulp are presented first, followed by a recommendation of the enzymes to improve these properties. The application and current research of cellulase and xylanase in improving the properties of dissolving pulp are emphasized. The main problems and the future research areas in improving the properties of dissolving pulp by enzymes are revealed. Finally, the technology prospects in this field are proposed.

Non-woven fabrics of fine regenerated cellulose fibers prepared from ionic-liquid solution via wet type solution blow spinning

A wet type solution blow spinning system with a water-mist coagulation chamber was developed to spin fine regenerated cellulose fibers from the non-volatile ionic liquid solvent 1-ethyl-3-methylimidazolium diethyl phosphate. The molecular weight distribution of cellulose, and the rheological properties and spinnability of its spinning solution were evaluated. Scanning electron microscope observations indicated that the fine water mist/vapor was important for efficient coagulation of the stretched solution jets. Under optimized spinning parameters, a non-woven fabric was obtained consisting of fine fibers with an average diameter of 0.98 ± 0.62 μm. The tensile strength of the samples was greatly influenced by the fabric structure formed upon regeneration of cellulose from solution. X-ray diffraction and polarized optical microscopy measurements revealed that the prepared cellulosic non-woven fabric was highly crystalline and had a well-defined molecular orientation, respectively, which might have contributed to the increased tensile strength.

Effects of Caustic Extraction on Properties of Viscose Grade Dissolving Pulp

Viscose, a cellulose-based commodity fibre, is produced by pulping and bleaching of wood, yielding a high quality “dissolving pulp” which is then spun. During pulping and bleaching, effective hemicellulose extraction is required to allow fibre production. We present a design of experiments (DoE) approach to optimise caustic extraction in a total chlorine free (TCF) bleaching sequence (O-CE-Z-P) of beech wood sulphite pulp. Temperature and sodium hydroxide concentration were varied to identify highest xylan extraction yield, and a maximum xylan removal of 83% was achieved at 20 °C and 120 g/L NaOH. Additionally, caustic extraction conditions were derived from the DoE model that led to pulps with high yield, high alpha cellulose content or uniform cellulose molecular weight distribution. Pulps from verification experiments exhibited good reactivity in viscose application tests. Hence, the presented O-CE-Z-P bleaching sequence can be considered as suitable for integrated viscose fibre production. We assume that the presented caustic extraction model will be useful for pulp and biorefinery researchers who work on caustic biorefinery processes involving hardwood feedstocks.

Population balance based modeling of changes in cellulose molecular weight distribution during ageing

Ageing is an important processing step in viscose fiber production. The degree of polymerization of viscose solution is controlled by ageing of alkali cellulose for desired fiber properties. In this work, alkali cellulose was treated under typical ageing conditions for different time periods. The changes in the molecular weight distribution due to the ageing reactions were analyzed by size exclusion chromatography with multi-angle laser light scattering detection. Furthermore, a population balance based approach to model the evolution of the molecular weight distribution during cellulose ageing is introduced. Several scission rate models capable of predicting the evolution of the molecular weight distribution are proposed and evaluated against the experimental data. The comparison of results from different models revealed that the scission rate of polymers is a function of the degree of polymerization and ageing time period. This modelling approach provided the possibility of more accurate and efficient solution than the previous similar models.

Direct HPILC analysis of cellulose depolymerisation in ionic liquids

Changes of average molecular weight and molecular weight distribution of cellulose in a polar ionic liquid (IL) were analysed with high performance liquid chromatography using a polar IL as an eluent (HPILC). 1-Ethyl-3-methylimidazolium methylphosphonate was used as the polar IL. As a model of partly depolymerised cellulose, a mixed sample composed of cellulose and cello-oligosaccharides (glucose, cellobiose, cellotetraose, and cellohexaose) was evaluated to test the resolution of the HPILC. In the resulting chromatograms, the corresponding peaks for each saccharide were found. Hydrolysed cellulose catalysed by a cellulase mixture in water was then prepared and dried. Then, this was dissolved in the polar IL to analyse its molecular weight distribution. The molecular weight distribution changed depending on the enzymatic reaction time. The peak for cellulose was found to decrease with the increase of the peak for cellobiose, and subsequently the peak for cellobiose decreased with the increase of that for glucose. In addition, cellulose oligomers except for cellobiose were scarcely observed, showing the catalytic feature of cellulase. Depolymerisation of cellulose in the polar IL was also carried out using ultrasonication. The peak for cellulose in the HPILC profiles shifted to a higher retention volume side and broadened with the sonication time, strongly suggesting random depolymerisation of cellulose. Thus, HPILC was confirmed to be effective for the dynamic analysis of cellulose depolymerisation.

Derivatization-free gel permeation chromatography elucidates enzymatic cellulose hydrolysis

BackgroundThe analysis of cellulose molecular weight distributions by gel permeation chromatography (GPC) is a powerful tool to obtain detailed information on enzymatic cellulose hydrolysis, supporting the development of economically viable biorefinery processes. Unfortunately, due to work and time consuming sample preparation, the measurement of cellulose molecular weight distributions has a limited applicability until now.ResultsIn this work we present a new method to analyze cellulose molecular weight distributions that does not require any prior cellulose swelling, activation, or derivatization. The cellulose samples were directly dissolved in dimethylformamide (DMF) containing 10-20% (v/v) 1-ethyl-3-methylimidazolium acetate (EMIM Ac) for 60 minutes, thereby reducing the sample preparation time from several days to a few hours. The samples were filtrated 0.2 μm to avoid column blocking, separated at 0.5 mL/min using hydrophilic separation media and were detected using differential refractive index/multi angle laser light scattering (dRI/MALLS). The applicability of this method was evaluated for the three cellulose types Avicel, α-cellulose and Sigmacell. Afterwards, this method was used to measure the changes in molecular weight distributions during the enzymatic hydrolysis of the different untreated and ionic liquid pretreated cellulose substrates. The molecular weight distributions showed a stronger shift to smaller molecular weights during enzymatic hydrolysis using a commercial cellulase preparation for cellulose with lower crystallinity. This was even more pronounced for ionic liquid-pretreated cellulose.ConclusionsIn conclusion, this strongly simplified GPC method for cellulose molecular weight distribution allowed for the first time to demonstrate the influence of cellulose properties and pretreatment on the mode of enzymatic hydrolysis.

Brightness reversion of eucalyptus kraft pulp: Effect of carbonyl groups generated by hypochlorous acid oxidation

Abstract The impact of hypochlorous acid (HOCl) treatment on a fully bleached eucalyptus kraft pulp was studied with respect to the final brightness as well as the brightness reversion under humid ageing conditions. The carbonyl contents in the pulps were determined by the CCOA method where carbazole-9-carboxylic acid [2-(2-aminooxethoxy)-ethoxy] amide (CCOA) was applied as the carbonyl-selective fluorescence label. The molecular weight distribution of cellulose and hemicelluloses was analyzed as well. The amount of carbonyl groups in pulp was observed to increase significantly after the HOCl treatment, and the carbonyl distribution in pulp to shift towards the low molecular weight fraction. Plotting the carbonyl content against the post color number (PCN) of the pulps revealed a linear correlation. Additionally, the effect of the hemicellulose content was investigated, and alkaline extraction was applied to partially remove the hemicelluloses in pulp. These hemicellulose-poor samples showed a lower reactivity with hypochlorous acid and less brightness reversion at equal carbonyl content.

Reactivity of Dissolving Pulp for Processing Viscose

AbstractSummary: Pulp reactivity is a kinetic term and is always connected with a certain derivatization process. The quality and hence the market value of the pulp is determined by such characteristics as α‐ cellulose content, solubility, brightness, ash content, as well as the amount of soluble material in dichloromethane. However, solubility data, especially S18 and S10 values do not characterise dissolving pulp reactivity. These are indicative of pulp solubility and provide some information regarding losses of material during pulp processing. One way by which the pulp reactivity for viscose making can be characterised is the investigation of the mercerisation step. Following the mercerisation kinetics by help of the molecular weight distribution of cellulose II the behaviour especially of the high molecular weight cellulose gives information regarding the accessibility and therefore, about the reactivity of the pulp aside from losses in low molecular weight cellulose. This behaviour will be shown on different pulps and the physicochemical background will be discussed in relation to results obtained from wide angle X‐ray scattering and Raman investigations. The influence of the behaviour of the pulp during mercerising on the viscose process, and the molecular weight distribution of the viscose including the distribution of the xanthogenate groups along the chain was investigated and will also be discussed.

Effect of cellulose concentration in NMMO·H2O solution on prediction of MW and MWD of cellulose using a rheology‐based method

AbstractPrediction of molecular weight (MW) and molecular weight distribution (MWD) of cellulose by means of a rheology‐based method is developed. In this method, the effect of cellulose concentration in N‐methlymorpholine‐N‐oxide monohydrate (NMMO·H2O) solution on predicting results is discussed. It is shown that there is no significant effect of cellulose concentration on predicting results when the cellulose concentration in NMMO·H2O solution is high enough. Meanwhile, the obtained results are compared with those of gel permeation chromatograghy (GPC) method. The comparison shows that the calculated peak MW, polydispersity index (PDI) and MWD curves have the same trends. Consequently, it may be feasible to compare the MW and MWD of cellulose by using the rheology‐based method. In addition, the rheology‐based method is simple and fast. Therefore it is a useful and easy way to analyze the MW and MWD of cellulose in the fiber industry. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

Dynamic rheology behavior of electron beam-irradiated cellulose pulp/NMMO solution

The rheological behavior of irradiated cellulose pulp solution by electron beam was investigated. Storage modulus G′, loss modulus G″, the dependence of complex viscosity η* and frequency ω of cellulose solutions were measured by DSR-200 Rheometer (Rheometrics co., USA). The molecular weight of irradiated cellulose was measured via the intrinsic viscosity measurement using an Ubbelohde capillary viscometer. The crystalline structure was studied by FTIR Spectroscopy. The results congruously showed that the molecular weight of pulp cellulose decrease and the molecular weight distribution of cellulose become narrow with increase in the irradiation dose. Moreover, the crystalline structure of the cellulose was destroyed, the force of the snarl between the cellulose molecules weakens and the accessibility of pulp spinning is improved. The study supplies some useful data for spinnability of irradiated cellulose and technical data to the filature industry.

Prediction of molecular weight scale and molecular weight distribution of cellulose using a rheology‐based method

AbstractPrediction of MW scale and MWD of cellulose by means of a rheology‐based method is developed. In this method, for the cellulose/NMMO·H2O solution, it is assumed that the cellulose MW values calculated by the Rouse terminal relaxation time can be regarded as the peak MW on the MWD curves of cellulose. Consequently, it is realized that the reciprocal of the frequency is converted to the MW scale, obtaining MWD scale curves of cellulose. Meanwhile, the obtained results are compared with those measured by the GPC method. The comparison shows that the calculated peak MW values are approximately equal, the calculated PDI values and MWD curves have the same trends. Consequently, it may be feasible to compare the MW scale and MWD of cellulose by using the rheology‐based method. In addition, the rheology‐based method is simple and fast. Therefore, it is a useful and easy way to analyze the MW scale and MWD of cellulose in the fiber industry. POLYM. ENG. SCI., 48:102–106, 2008. © 2007 Society of Plastics Engineers

Copper Corrosion: Comparison between Naturally Aged Papers and Artificially Aged Model Papers

AbstractSummary: Copper corrosion on paper works of art is commonly explained by copper ion‐catalysed cellulose oxidation, usually reflected by discoloration of pigment and surrounding paper as well as by loss of mechanical strength. In this study, model paper and historic paper samples, both containing copper pigments, were compared using fluorescence labelling of carbonyl groups and subsequent GPC analysis. The historic paper samples did not show any typical sign of copper pigment induced discoloration, but high brittleness. In artificially copper‐corroded paper samples the distribution of carbonyl groups in combination with the molecular weight distribution of cellulose clearly indicated the occurrence of oxidative processes. In contrast, only insignificant oxidative damage was detected in the case of the paper fragments from an original work of art, a codex from the 15th century. Here, mostly degradation by hydrolytic action was revealed. There was no introduction of carbonyl groups into the bulk section of the molecular weight distribution, and the gain in new carbonyl groups corresponded to the number of reducing end groups newly generated by hydrolysis.

Continuous modelling and kinetic parameter estimation for cellulose nitration

Cellulose nitration is useful in several industrial segments, especially in the production of gun powders and rocket or missile propellants. For these applications, a rigid control of the nitrocellulose produced is necessary, especially nitrogen content. Only off-line measurements of this particular parameter can be conducted and cellulose is a natural polymer which characteristics may vary. Because of that, the final product must have its non-uniformities compensated by blending of different batches. In this work, universal kinetic parameters, which depend only on structural descriptions of the cellulose, are fitted using typical nitration experiments and Maximum Likelihood procedures. The required mathematical modelling is carried on using a continuous mixtures approach, which lead to an integro-differential population balance equation, solved with an approximant built with block-pulse functions. Size-exclusion chromatography of the cellulose, with special solvents, can be used to elucidate the molecular weight distribution of cellulose, which, in conjunction with the kinetic framework, describes the reactional system.

Prediction of molecular weight distribution of cellulose by using the rheological method

AbstractIn this article, a rheological method that can predict the molecular weight distribution (MWD) of polymer was introduced. Using this method, the MWDs of four cellulose samples were compared from rheological data of the cellulose / N‐methyl morpholine N‐oxide (NMMO) / H2O solutions. The MWDs of cellulose also were determined by gel permeation chromatography (GPC) calibrated with narrow distribution polystyrene standards, using 0.5% lithium chloride (LiCl) in N,N‐dimethylacetamide (DMAc) as the eluent. Comparison of the results from rheology and GPC showed that the MW and MWD of cellulose could be roughly inferred from their rheological data. Although the differential MWD obtained from the rheological method was bell shaped and can not reflect the fine characteristics of cellulose as GPC, it may be feasible to compare the MWDs of cellulose by using the rheological method. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 598–603, 2004

Effect of Whole Cellulase on the Supramolecular Structure of Cotton Cellulose

Cotton fabrics are treated with cellulolytic enzyme preparations to alter the appearance of their surfaces. Desired objectives can be to effect a washed appearance in denims. to impart a smooth appearance by removing surface fuzz fibers, or to remove tangled bundles of surface fibers that do not pick up dyes and thus result in white specks. Such treatments are very mild and have been commercially successful. This study elucidates the effect such treatments have on the molecular, supramolecular, and morphological structures of cotton cellulose. Desized, scoured, and bleached cotton fabric is treated with a commercial textile cellulase preparation for 10, 60, and 180 minutes at 50°C in a 0.05 M (pH 4.8) acetate buffer in stainless steel canisters in the presence of stainless steel ball bearings. Changes are reported in fabric weight, fabric strength, fiber cell walls. moisture regain, cellulose molecular weight distribution, fiber pore size distribution, and cellulose micro structure as revealed by hydrogen bonding patterns.

Study on Molecular Weight Distribution of Cellulose by Using Rheological Methods.

The degree of polymerization (DP) and the molecular weight distribution (MWD) play a special role in producing cellulose fiber by using the N-methyl morpholine N-oxide (NMMO) process. In this paper, rheological methods have been used to determine the MWD of cellulose. It is shown that the limiting compliance J0e of cellulose samples increases strongly with the increasing broadness of MWD, and that the polydispersity index ‹τW›/‹τN› of the distribution of relaxation times can also well characterize the polydispersity of MWD of the cellulose samples. By using Tuminello's method, the cumulative weight distribution C(M) can be calculated from the terminal modulus and the plateau modulus of the cellulose/NMMO solution via 1-[G'(ω)/and G0N]0.5 (G'(ω) and G0N are the storage modulus and the plateau modulus respectively).

Molecular-weight distribution of cellulose after ripening

As a result of studying ripening of alkali cellulose by the Monte Carlo method, it was found that the following model most closely fits the experimental data on the MWD of alkali cellulose after ripening: alkali cellulose is ripened by the parallel occurrence of chance oxidative degradation (in amorphous regions) and depolymerization from the chain end with significant predominance of the number of depolymerization events; the shape of the MWD curve after ripening of alkali cellulose is determined by the parallel occurrence of depolymerization from the chain end and chance degradation; chance degradation in amorphous regions of the cellulose accelerates depolymerization from the chain end due to an increase in the number of chain ends.

The effect of Trichoderma cellulases on the fine structure of a bleached softwood kraft pulp

The mode of action of several Trichoderma reesei cellulase preparations was investigated in relation to their effect on the crystallinity and degree of polymerization of a fully bleached softwood kraft pulp. One complete (Celluclast 1.5L, Novo Industri) and six modified cellulases (Rohm Enzyme Finland Oy, former Primalco Ltd. Biotec) were used under a relatively low enzyme loading of 40 mg protein g −1 cellulose in a reaction mixture in which an excess of exogenous cellobiase activity was added (Novozym 188). This enzyme loading was used to assess the mode of action of the enzymes under both non-saturating and non-inhibitory conditions. The modified cellulase preparations were obtained from T. reesei by deleting the following components of the cellulase system: EG I and/or EG II or CBH I and/or CBH II. Characterization of hydrolysates by gel permeation chromatography (GPC) showed that short incubation times of 4 h with CBH I-deficient enzymes (CBH I− and CBH I/II−mutants) resulted in the highest shifts in the molecular weight distribution of cellulose. Compared to EG-deficient enzymes (EG I−, EG II− and EG I/II−mutants), the lack of CBH II resulted in equivalent changes in both polydispersities and average degrees of polymerisation of cellulose. This suggested that the role of CBH II in hydrolysis was similar to that of both endoglucanases I and II. The effectiveness of all mutant enzymes in hydrolysing cellulose was much lower than that obtained when a complete cellulase system such as Celluclast 1.5L was used. Our results also indicated that the lack of CBH I was very detrimental to hydrolysis and depolymerization of cellulose and that EG I has a greater effect on the substrate than EG II. However, there were no detectable changes in the degree of crystallinity of partially hydrolysed pulps, regardless of the enzyme system used.

Relationship Between Cotton Fiber Strength and Cellulose Molecular Weight Distribution: HVI Calibration Standards

High volume instrument (HVI) classing of the U.S. cotton crop has focused attention on fiber quality, particularly strength. Characteristic of polymers is the relationship between molecular weight and physical properties. Cotton fibers composed mostly of the polymer cellulose were dissolved in the solvent N,N-dimethylacetamide with lith ium chloride without cleanup or derivatization. Molecular weight distributions were determined by automated, nonaqueous gel permeation chromatography; HVI calibra tion standard cottons possessing a range of fiber lengths and strengths were sampled. Molecular compositional profiles indicate correlation of higher average molecular weight with greater strength of cotton fibers.

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

AbstractCellulose tricarbanilates (CTCs) were prepared from a range of cellulose samples (cotton linters, wood pulps, Avicel, amorphous cellulose, and cellulose II) for molecular weight distribution (MWD) studies by high performance size exclusion chromatography (HPSEC). The HPSEC columns were calibrated using CTC standards with the aid of a microcomputer. CTCs were prepared by reaction of cellulose samples with phenylisocyanate in pyridine at 80°C. For some samples, e.g., cellulose II, activation with liquid ammonia and pyridine was necessary prior to reaction in pyridine. All samples tested were also derivatised in dimethylsulfoxide at 70°C, although for high molecular weight (MW) cellulose samples some MW reduction occurred in this solvent. Conditions were determined for optimum precipitation of CTCs in aqueous methanol without coprecipitation of low MW impurities.