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J M Fang - One of the best experts on this subject based on the ideXlab platform.

  • fractional isolation physico chemical characterization and homogeneous esterification of Hemicelluloses from fast growing poplar wood
    Carbohydrate Polymers, 2001
    Co-Authors: J M Fang, J Tomkinson, Z C Geng
    Abstract:

    Abstract Extraction of the dewaxed and partially delignified fast-growing poplar wood with 1.5, 3.0, 5.0, 7.5 and 8.5% NaOH at 20°C for 16 h solubilized 65.6, 71.6, 73.8, 85.6 and 89.3% of the original Hemicelluloses, respectively. Xylans were found to be the predominant hemicellulosic components in the cell walls of fast-growing poplar wood. The isolated five hemicellulosic preparations were further characterized by Fourier transform infrared (FT-IR), and carbon-13 magnetic resonance spectroscopy (13C NMR) as well as gel permeation chromatography (GPC). The results showed that the Hemicelluloses contain a main chain formed by d -xylopyranose residues linked by β-1,4 linkages. The hemicellulosic preparation, isolated with 8.5% NaOH at 20°C for 16 h, was esterified with propionyl, hexanoyl, lauroyl, and palmitoyl chlorides, respectively, in homogeneous N,N-dimethylformamide/lithium chloride system using 4-dimethylaminopyridine as a catalyst and triethylamine as a neutralizer. The effects of molar ratio of acyl chloride/anhydroxylose unit, triethylamine concentration, and reaction time and temperature on the yield and degree of substitution of the hemicellulose derivatives have been primarily examined. The degree of substitution was controlled between 0.34 and 1.44 under the reaction conditions given. Under an optimum condition (sample 8, molar ratio 3:1), over 70% of the total hydroxyl groups in native Hemicelluloses were palmitoylated at 75°C for 40 min. The results obtained from the molecular weight measurements (48 000–127 200 g mol−1) revealed only a minimal degradation of the macromolecular Hemicelluloses during the rapid reactions at 60–75°C for 25–40 min.

  • Stearoylation of Hemicelluloses from wheat straw
    Polymer Degradation and Stability, 2000
    Co-Authors: J M Fang, J Tomkinson
    Abstract:

    Abstract Stearoylated Hemicelluloses with degrees of substitution 0.20–1.71 were prepared by a rapid reaction of wheat straw Hemicelluloses with stearoyl chloride using 4-dimethylaminopyridine as catalyst and triethylamine as acid acceptor in a homogeneous N,N-dimethylformamide and lithium chloride system. Under optimum conditions approximately 92% of the free hydroxyl groups in native Hemicelluloses were stearoylated in 30 min at 75°C. Molecular weight measurements showed only minimal degradation (⩽8%) of hemicellulosic chains during the rapid reactions at 75°C for 10–35 min, while a noticeable degradation (∼20%) of the stearoylated Hemicelluloses was observed during the reaction at 85°C. Differential thermal analysis studies revealed an increase of the thermal stability of the stearoylated Hemicelluloses.

  • comparative study of Hemicelluloses from wheat straw by alkali and hydrogen peroxide extractions
    Polymer Degradation and Stability, 1999
    Co-Authors: J M Fang, D Salisbury, Paul Fowler, J Tomkinson
    Abstract:

    Abstract As compared to traditional alkaline extractions, alkaline peroxide was used to isolate Hemicelluloses from wheat straw. Yields of the solubilized Hemicelluloses ranged from 18.9% (2% H2O2 extraction at 90°C for 2 h at pH 11.5) to 26.6% (2% H2O2 extraction at 50°C for 16 h at pH 12.5). The optimum hemicellulose yield (92% of the original Hemicelluloses in water treated wheat straw) was obtained when the treatment was performed at 50°C for 16 h at pH 12.5 by use of 2% H2O2. All the hemicellulosic preparations were much lighter in color than those obtained using traditional alkaline extractions in the absence of bleaching. The results, obtained by the destructive method such as acid hydrolysis, showed that extraction of wheat straw with aqueous 10% KOH following alkaline bleaching released the hemicellulosic fractions, which were enriched in xylose, whereas extraction of the straw with aqueous 2% H2O2 under alkaline conditions (pH 11.5–12.5) solubilized the hemicellulosic fractions, which were relatively higher in arabinose and glucose. The nine isolated hemicellulosic samples were further characterized by non-destructive methods such as Fourier transform infrared (FT–IR), and carbon-13 magnetic resonance spectroscopy (13C-NMR) as well as gel permeation chromatography (GPC). It has been demonstrated that the alkaline peroxide treatments under the conditions used do not affect the overall structure of Hemicelluloses. The only one major change of the Hemicelluloses was found to be degradation during the beaching of alkali-soluble Hemicelluloses with 2% H2O2 at 60°C for a period of 16 h at pH 11.5 or bleaching using a relatively higher concentration (5%) of hydrogen peroxide at 60°C for 8 h at pH 11.5.

  • fractionation and characterization of ball milled and enzyme lignins from abaca fibre
    Journal of the Science of Food and Agriculture, 1999
    Co-Authors: J M Fang, A Goodwin, J M Lawther, A J Bolton
    Abstract:

    An Erratum has been published for this article in Journal of the Science of Food and Agriculture 79(15) 1999, 2122. Ball-milled and enzyme lignins were produced from abaca fibre via ball milling for 6 days followed by cellulase treatment for 3 days. The crude lignin preparations were fractionated into milled lignin (ML), enzyme lignin (EL), hemicellulose-rich milled lignin (HRML), and lignin-rich enzyme lignin (LREL) fractions using a two-step precipitation method instead of a traditional ether precipitation procedure. The yield and chemical composition of the resulting lignin samples are reported. The ML and EL fractions contained low amounts of associated neutral sugars (2.0–3.3%) and uronic acids (1.4–1.5%), and showed relatively low average molecular weights (2500–2660), while the LREL and HRML fractions contained large amounts of bound polysaccharides (35.6–38.3%), and showed high molecular weights (8800–25000). The four lignin fractions are composed of a large proportion of syringyl units with fewer guaiacyl and p-hydroxyphenyl units. The ML is mainly composed of β–O–4 ether bonds between the lignin structural units. The less common β–β, β–5 and 5–5′ carbon–carbon linkages are also present in the lignin molecules. It was found that uronic acids and 41–63% of p-coumaric acids are esterified to lignin in the three lignin-rich fractions of ML, EL and LREL. This level increased to over 90% in the hemicellulose-rich fraction of HRML. For ferulic acids, 92–97% were found to be etherified to lignin in the three lignin-rich fractions of ML, EL and LREL, while in the hemicellulose-rich fraction of HRML this reduced to only 13%, suggesting that a majority of the ferulic acids are esterified to Hemicelluloses or lignin in this fraction. © 1999 Society of Chemical Industry

  • fractionation and characterization of polysaccharides from abaca fibre
    Carbohydrate Polymers, 1998
    Co-Authors: J M Fang, A Goodwin, J M Lawther, A J Bolton
    Abstract:

    Abaca fibre polysaccharides were fractionated into water soluble, pectic, 1% NaOH soluble, hemicellulosic and cellulose fractions by extraction with hot water, dilute hydrochloric acid (pH 1.6), aqueous 1% NaOH and 17.5% NaOH, respectively. Cellulose (60.4–63.6%) and Hemicelluloses (20.8%) were the major polysaccharides in abaca fibres. The hot water soluble polysaccharides contained noticeable amounts of pectic substances and a large proportion of neutral polysaccharides. The pectic polysaccharide preparation was enriched in both galacturonic acid and neutral sugars, including xylose, glucose, galactose, arabinose, and rhamnose. Extraction of the fibre with aqueous 1% NaOH produced the hemicellulose–lignin complex, which was enriched in xylose and, to a lesser extent, glucose-, arabinose- and galactose-containing polysaccharides, together with 7.6% associated lignin. Further extraction of the delignified fibre residue with aqueous 17.5%. NaOH removed the hemicellulose fractions, which were strongly enriched in xylose-containing polysaccharides. Besides ferulic and p-coumaric acids, six other phenolic monomers were also detected in the mixtures of alkaline nitrobenzene oxidation of associated lignin in all the polysaccharide fractions. The content of bound lignin in water soluble, pectic, and 1% NaOH soluble polysaccharides (Fractions 1, 2, and 3), isolated directly from the lignified fibres, was 12 times that of the hemicellulosic preparations (Fractions 4 and 5) isolated from the delignified fibre residues.

Annsofi Jonsson - One of the best experts on this subject based on the ideXlab platform.

  • combined membrane filtration and enzymatic treatment for recovery of high molecular mass Hemicelluloses from chemithermomechanical pulp process water
    Chemical Engineering Journal, 2013
    Co-Authors: Holger Krawczyk, Petri Oinonen, Annsofi Jonsson
    Abstract:

    Hemicelluloses with high molecular mass are needed for the manufacture of value added products such as food packaging barrier films. In this work such molecules were recovered from chemithermomechanical pulp (CTMP) process water using an innovative three-stage process comprising membrane separation and enzymatic treatment with laccase. Microfiltration followed by ultrafiltration was found to be a suitable combination in the first stage, providing a concentrated and purified hemicellulose fraction suitable for enzymatic treatment. In both membrane processes a high average flux (260 and 115 l/m2 h) and a low fouling tendency were observed. A marked increase in the average molecular mass of Hemicelluloses with bound lignin moieties was achieved by laccase treatment in the second stage. The enzymatically crosslinked Hemicelluloses were finally recovered in the third stage using ultrafiltration. In the final high molecular mass solution the hemicellulose concentration was 54 g/l, the contribution of Hemicelluloses to the total solids content 43%, and the viscosity of the solution 27 mPa s. The results demonstrate that a hemicellulose fraction of high quality can be produced from CTMP process water, and that this could constitute a suitable feedstock for the production of, for example, barrier films for renewable packaging.

  • membrane performance during ultrafiltration of a high viscosity solution containing Hemicelluloses from wheat bran
    Separation and Purification Technology, 2011
    Co-Authors: Holger Krawczyk, Anders Arkell, Annsofi Jonsson
    Abstract:

    Hemicelluloses isolated from agricultural residues have the potential to replace fossil-based materials in high-value-added applications, provided that cost-efficient isolation processes are developed. In this study, a feed solution containing Hemicelluloses extracted from wheat bran with a particular high viscosity was used to study the performance of ultrafiltration for hemicellulose isolation at various operating conditions. The operating parameters affected the flux significantly, but had no influence on the retention of the membrane. The flux was doubled by: (i) increasing the cross-flow velocity from 2 to 5 m/s, (ii) increasing the feed temperature from 60 to 80 degrees C and (iii) decreasing the concentration of the solution by half. The flux increase could mainly be attributed to a decrease in the apparent viscosity of the feed solution. This indicates that low feed viscosity is the key to good membrane performance. The limiting flux during ultrafiltration was reached at the low transmembrane pressure of 0.8 bar, even when the cross-flow velocity and feed temperature were as high as 5 m/s and 80 degrees C, respectively. Low transmembrane pressure is thus preferable during ultrafiltration of solutions similar to that used in the present investigation. The results of this study suggest that ultrafiltration could be a suitable method for the isolation of Hemicelluloses from high-viscosity solutions. However, as the operating parameters affect the membrane performance significantly, they must be chosen with care to make the process cost-efficient. (C) 2011 Elsevier B.V. All rights reserved. (Less)

  • isolation of Hemicelluloses by ultrafiltration of thermomechanical pulp mill process water influence of operating conditions
    Chemical Engineering Research & Design, 2010
    Co-Authors: Tobias Persson, Annsofi Jonsson
    Abstract:

    Hemicelluloses could be used to replace fossil-based materials in several high-value-added products. Today, vast amounts of Hemicelluloses are discharged from pulp mills all over the world as waste, but these could be isolated by membrane filtration, and utilized in various applications. In this study, the hemicellulose galactoglucomannan was isolated from process water from a thermomechanical pulp mill using ultrafiltration. The retention of Hemicelluloses and lignin, and the flux and fouling of three ultrafiltration membranes (ETNA01, ETNA10 and UFX5) were studied at various operating conditions. One of the membranes (UFX5) was found to have a high hemicellulose retention (above 90%) independent of flux and pressure. With the ETNA01 membrane it was impossible to combine a high flux with high hemicellulose retention, while with the ETNA10 membrane the hemicellulose retention could be increased above 90% by running at transmembrane pressures above the critical flux. The UFX5 membrane could be used at the temperature of the process water in the pulp mill (75-85 degrees C), while the ETNA10 membrane could only withstand temperatures below 60 degrees C, increasing the cost due to the need to cool the process water. However, the susceptibility of UFX5 to fouling was much greater than for ETNA10, which would increase the cleaning cost of the UFX5 membrane. (C) 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. (Less)

  • economic evaluation of isolation of Hemicelluloses from process streams from thermomechanical pulping of spruce
    Applied Biochemistry and Biotechnology, 2007
    Co-Authors: Tobias Persson, Guido Zacchi, Annakarin Nordin, Annsofi Jonsson
    Abstract:

    Hemicelluloses, which are abundant in nature and have potential use in a wide variety of applications, may make an important contribution in helping relieve society of its dependence on petrochemicals. However, cost-efficient methods for the isolation of Hemicelluloses are required. This article presents an economic evaluation of a full-scale process to isolate Hemicelluloses from process water from a thermomechanical pulp mill. Experimental data obtained in laboratory scale were used for the scale up of the process by computer simulation. The isolation method consisted of two process steps. The suspended matter in the process water was removed by microfiltration and thereafter the Hemicelluloses were concentrated by ultrafiltration, and at the same time, separated from smaller molecules and ions in the process water. The isolated Hemicelluloses were intended for the production of oxygen barriers for food packaging, an application for which they have been shown to have suitable properties. The solution produced contained 30 g Hemicelluloses/L with a purity (defined as the ratio between the Hemicelluloses and the total solids) of approx 80%. The evaluation was performed for a plant with a daily production of 4 metric tonnes (0 of Hemicelluloses, which is the estimated future need of barrier films at Tetra Pak (Lund, Sweden.). The production cost was calculated to be EURO 670/t of Hemicelluloses. This is approx 9 times lower than the price of ethylene vinyl alcohol, which is produced by petrochemicals and is currently used as an oxygen barrier in fiber-based packaging materials. This indicates that it is possible to produce oxygen barriers made of Hemicelluloses at a price that is competitive with the materials used today. (Less)

  • Fractionation of Hemicelluloses by membrane filtration
    2005
    Co-Authors: Tobias Persson, Annsofi Jonsson, Guido Zacchi
    Abstract:

    Hemicellulosic materials are among the most abundant renewable resources on earth, but have not yet found any broad application. However, if a cost effective extraction method is developed, Hemicelluloses have the potential to be utilized to a much larger extent in the future. Ultrafiltration (UF) is a low energy demanding separation process that can be used to concentrate and purify Hemicelluloses from industrial process water. In this investigation the performance of six UF membranes was studied, when treating process water from thermo-mechanical pulping (TMP) of spruce. Four membranes were hydrophobic and two hydrophilic and the cut-off was 1-5 kDa. The hydrophobic membranes were subject to severe fouling problems and had a much lower flux than the hydrophilic membranes. The hydrophilic membrane C005F, from Microdyn Nadir GmbH with cut-off 5 kDa, had the highest flux and showed the best separation capability with respect to Hemicelluloses and contaminants (salts and monosaccharides). The flux was 140 l/m2.h at 0.8 MPa and 40°C. The retention of Hemicelluloses was 90% and the retention of monosaccharides 3%. High flux and efficient separation of product and contaminants reduce the investment costs of a hemicellulose extraction plant.

Juan Carlos Parajó - One of the best experts on this subject based on the ideXlab platform.

  • Manufacture of fibrous reinforcements for biocomposites and hemicellulosic oligomers from bamboo
    Chemical Engineering Journal, 2011
    Co-Authors: Valentín Santos, Juan Carlos Parajó
    Abstract:

    Autohydrolysis of bamboo (treatments with hot, compressed water) resulted in liquors containing mainly hemicellulose-derived products (oligo- and mono-saccharides), and in spent solids (enriched in cellulose and lignin) with potential utility as a reinforcement for composites. Autohydrolysis of bamboo was carried out under a variety of operational conditions, and the resulting solid and liquid phases were assayed for composition. Kinetic models (based on pseudo-homogeneous, first-order, and irreversible reactions) were developed for data interpretation. Under selected conditions, 62.6% of the initial Hemicelluloses present in the raw material were converted into oligosaccharides. The solid phase from the treatment leading to the maximal concentration of oligomeric compounds derived from Hemicelluloses was employed as a fibrous reinforcement for polylactic acid (PLA)-based biocomposites. For comparative purposes, other three types of reinforcements from bamboo were also employed for making PLA-based composites: bamboo flour, short bamboo fibers, and large bamboo fibers. Compared to neat PLA, reinforcement with bamboo-derived materials resulted in increased stiffness and lower strain at break, whereas little effects were caused in tensile strength. Additional information on thermal analysis and surface morphological characteristics of biocomposites is also provided. © 2011 Elsevier B.V.

  • Manufacture of fibrous reinforcements for biodegradable biocomposites from Citysus scoparius
    Journal of Chemical Technology & Biotechnology, 2011
    Co-Authors: Ana Rita Campos, Valentín Santos, António M. Cunha, Juan Carlos Parajó
    Abstract:

    BACKGROUND: Cytisus scoparius samples were processed with hot, compressed water (autohydrolysis treatments) to obtain both fiber-containing solids (suitable as reinforcements for composites) and a liquid phase containing sugar oligomers derived from Hemicelluloses. The solid phase from autohydrolysis, mainly made up of cellulose and lignin, was employed for manufacturing polylactic acid (PLA)-based biodegradable composites. The mechanical properties, water uptake and thermal properties of composites were assessed. RESULTS: The hydrolysis of the major hemicellulose polysaccharide components of Cytisus scoparius was interpreted using kinetic models based on sequential pseudo-homogeneous first-order, irreversible reactions. Operating under non-isothermal conditions, the autohydrolysis experiment carried out at up to 215 degrees C led to the maximum concentration of sugar oligomers (accounting for about 71% of the initial xylan). These compounds can be employed for a variety of purposes, including applications as prebiotics. Composites containing autohydrolyzed fibers presented both improved impact strength and reduced water absorption ability. CONCLUSIONS: Autohydrolysis of Cytisus scoparius led to a liquid phase containing xylooligosacharides with commercial value, and to a solid phase suitable as a reinforcement for PLA-based composites with reduced water retention ability. (C) 2010 Society of Chemical Industry

  • study on the deacetylation of Hemicelluloses during the hydrothermal processing of eucalyptus wood
    European Journal of Wood and Wood Products, 2001
    Co-Authors: Gil Garrote, Herminia Dominguez, Juan Carlos Parajó
    Abstract:

    wood samples were subjected to hydrothermal treatments at a liquor to wood ratio in the range 6–10 g/g and temperatures from 145 up to 190 °C. The effects caused by hydrothermolysis included extractive removal, hemicellulose degradation and deacetylation of both Hemicelluloses and acetylated oligosaccharides. An analytical procedure based on the determination of the xylose and acetic acid contained in liquors before and after a quantitative posthydrolysis allowed the determination of acetyl groups bound to residual xylan and oligosaccharides. Since hydronium ions (the catalytic species involved in the degradation of the polymeric fractions of biomass) are mainly generated from acetic acid, special attention was paid to interpretate the time course of acetyl groups hydrolysis from both xylan and xylan-degradation products, and their interrelationship with the concentration of acetic acid is established.

A J Bolton - One of the best experts on this subject based on the ideXlab platform.

  • fractionation and characterization of ball milled and enzyme lignins from abaca fibre
    Journal of the Science of Food and Agriculture, 1999
    Co-Authors: J M Fang, A Goodwin, J M Lawther, A J Bolton
    Abstract:

    An Erratum has been published for this article in Journal of the Science of Food and Agriculture 79(15) 1999, 2122. Ball-milled and enzyme lignins were produced from abaca fibre via ball milling for 6 days followed by cellulase treatment for 3 days. The crude lignin preparations were fractionated into milled lignin (ML), enzyme lignin (EL), hemicellulose-rich milled lignin (HRML), and lignin-rich enzyme lignin (LREL) fractions using a two-step precipitation method instead of a traditional ether precipitation procedure. The yield and chemical composition of the resulting lignin samples are reported. The ML and EL fractions contained low amounts of associated neutral sugars (2.0–3.3%) and uronic acids (1.4–1.5%), and showed relatively low average molecular weights (2500–2660), while the LREL and HRML fractions contained large amounts of bound polysaccharides (35.6–38.3%), and showed high molecular weights (8800–25000). The four lignin fractions are composed of a large proportion of syringyl units with fewer guaiacyl and p-hydroxyphenyl units. The ML is mainly composed of β–O–4 ether bonds between the lignin structural units. The less common β–β, β–5 and 5–5′ carbon–carbon linkages are also present in the lignin molecules. It was found that uronic acids and 41–63% of p-coumaric acids are esterified to lignin in the three lignin-rich fractions of ML, EL and LREL. This level increased to over 90% in the hemicellulose-rich fraction of HRML. For ferulic acids, 92–97% were found to be etherified to lignin in the three lignin-rich fractions of ML, EL and LREL, while in the hemicellulose-rich fraction of HRML this reduced to only 13%, suggesting that a majority of the ferulic acids are esterified to Hemicelluloses or lignin in this fraction. © 1999 Society of Chemical Industry

  • fractionation and characterization of polysaccharides from abaca fibre
    Carbohydrate Polymers, 1998
    Co-Authors: J M Fang, A Goodwin, J M Lawther, A J Bolton
    Abstract:

    Abaca fibre polysaccharides were fractionated into water soluble, pectic, 1% NaOH soluble, hemicellulosic and cellulose fractions by extraction with hot water, dilute hydrochloric acid (pH 1.6), aqueous 1% NaOH and 17.5% NaOH, respectively. Cellulose (60.4–63.6%) and Hemicelluloses (20.8%) were the major polysaccharides in abaca fibres. The hot water soluble polysaccharides contained noticeable amounts of pectic substances and a large proportion of neutral polysaccharides. The pectic polysaccharide preparation was enriched in both galacturonic acid and neutral sugars, including xylose, glucose, galactose, arabinose, and rhamnose. Extraction of the fibre with aqueous 1% NaOH produced the hemicellulose–lignin complex, which was enriched in xylose and, to a lesser extent, glucose-, arabinose- and galactose-containing polysaccharides, together with 7.6% associated lignin. Further extraction of the delignified fibre residue with aqueous 17.5%. NaOH removed the hemicellulose fractions, which were strongly enriched in xylose-containing polysaccharides. Besides ferulic and p-coumaric acids, six other phenolic monomers were also detected in the mixtures of alkaline nitrobenzene oxidation of associated lignin in all the polysaccharide fractions. The content of bound lignin in water soluble, pectic, and 1% NaOH soluble polysaccharides (Fractions 1, 2, and 3), isolated directly from the lignified fibres, was 12 times that of the hemicellulosic preparations (Fractions 4 and 5) isolated from the delignified fibre residues.

  • isolation and characterization of polysaccharides from abaca fiber
    Journal of Agricultural and Food Chemistry, 1998
    Co-Authors: J M Fang, A Goodwin, J M Lawther, A J Bolton
    Abstract:

    Cellulose and xylan were found to be the major polysaccharide constituents in abaca fiber. Both Hemicelluloses I and II were enriched in xylose, together with arabinose and glucose as the other major sugar constituents. These data implied that Hemicelluloses I and II are probably composed of arabinoxylan, glucoxylan, and/or xylan, which corresponded with the studies by FT-IR spectroscopy. Arabinose and galactose were higher in all fractions of Hemicelluloses I than in those of Hemicelluloses II, whereas xylose and mannose were higher in all fractions of Hemicelluloses II than in those of Hemicelluloses I, suggesting that the dilute alkali pretreatments mainly solubilize the more branched Hemicelluloses. The results obtained also suggested that dilute alkali pretreatments favored removal of small molecular chains of Hemicelluloses I (M w = 75 000-130 000) as compared to the Hemicelluloses II, which had a higher degree of polymerization with molecular average weights between 123 000 and 227 000. Further studies showed that lignins, rich in syringyl units, are tightly associated with Hemicelluloses in abaca fiber cell walls.

J Tomkinson - One of the best experts on this subject based on the ideXlab platform.

  • fractional isolation physico chemical characterization and homogeneous esterification of Hemicelluloses from fast growing poplar wood
    Carbohydrate Polymers, 2001
    Co-Authors: J M Fang, J Tomkinson, Z C Geng
    Abstract:

    Abstract Extraction of the dewaxed and partially delignified fast-growing poplar wood with 1.5, 3.0, 5.0, 7.5 and 8.5% NaOH at 20°C for 16 h solubilized 65.6, 71.6, 73.8, 85.6 and 89.3% of the original Hemicelluloses, respectively. Xylans were found to be the predominant hemicellulosic components in the cell walls of fast-growing poplar wood. The isolated five hemicellulosic preparations were further characterized by Fourier transform infrared (FT-IR), and carbon-13 magnetic resonance spectroscopy (13C NMR) as well as gel permeation chromatography (GPC). The results showed that the Hemicelluloses contain a main chain formed by d -xylopyranose residues linked by β-1,4 linkages. The hemicellulosic preparation, isolated with 8.5% NaOH at 20°C for 16 h, was esterified with propionyl, hexanoyl, lauroyl, and palmitoyl chlorides, respectively, in homogeneous N,N-dimethylformamide/lithium chloride system using 4-dimethylaminopyridine as a catalyst and triethylamine as a neutralizer. The effects of molar ratio of acyl chloride/anhydroxylose unit, triethylamine concentration, and reaction time and temperature on the yield and degree of substitution of the hemicellulose derivatives have been primarily examined. The degree of substitution was controlled between 0.34 and 1.44 under the reaction conditions given. Under an optimum condition (sample 8, molar ratio 3:1), over 70% of the total hydroxyl groups in native Hemicelluloses were palmitoylated at 75°C for 40 min. The results obtained from the molecular weight measurements (48 000–127 200 g mol−1) revealed only a minimal degradation of the macromolecular Hemicelluloses during the rapid reactions at 60–75°C for 25–40 min.

  • Characterization and esterification of Hemicelluloses from rye straw.
    Journal of Agricultural and Food Chemistry, 2000
    Co-Authors: Sun R, Fang Jm, J Tomkinson
    Abstract:

    Hemicelluloses were extracted with 10% KOH/0.5% Na2B4O7·10H2O from delignified rye straw. Esterification of the Hemicelluloses with various acyl chlorides was performed in a homogeneous N,N-dimethylformamide and lithium chloride system using 4-(dimethylamino)pyridine catalyst and triethylamine as a neutralizer. The degree of substitution was controlled between 0.37 and 1.65. Under an optimum condition (sample 14, molar ratio 3:1), >90% of the free hydroxyl groups in native Hemicelluloses were stearoylated at 75 °C for 40 min. Meanwhile, the products were characterized by FT-IR and GPC techniques as well as their solubilities. The molecular mass measurements (31400−123300 g mol-1) showed only a minimal degradation of the macromolecular Hemicelluloses during rapid reactions at 48−75 °C for 20−40 min. Keywords: Rye straw; extraction; Hemicelluloses; esterification; homogeneous system

  • Stearoylation of Hemicelluloses from wheat straw
    Polymer Degradation and Stability, 2000
    Co-Authors: J M Fang, J Tomkinson
    Abstract:

    Abstract Stearoylated Hemicelluloses with degrees of substitution 0.20–1.71 were prepared by a rapid reaction of wheat straw Hemicelluloses with stearoyl chloride using 4-dimethylaminopyridine as catalyst and triethylamine as acid acceptor in a homogeneous N,N-dimethylformamide and lithium chloride system. Under optimum conditions approximately 92% of the free hydroxyl groups in native Hemicelluloses were stearoylated in 30 min at 75°C. Molecular weight measurements showed only minimal degradation (⩽8%) of hemicellulosic chains during the rapid reactions at 75°C for 10–35 min, while a noticeable degradation (∼20%) of the stearoylated Hemicelluloses was observed during the reaction at 85°C. Differential thermal analysis studies revealed an increase of the thermal stability of the stearoylated Hemicelluloses.

  • comparative study of Hemicelluloses from wheat straw by alkali and hydrogen peroxide extractions
    Polymer Degradation and Stability, 1999
    Co-Authors: J M Fang, D Salisbury, Paul Fowler, J Tomkinson
    Abstract:

    Abstract As compared to traditional alkaline extractions, alkaline peroxide was used to isolate Hemicelluloses from wheat straw. Yields of the solubilized Hemicelluloses ranged from 18.9% (2% H2O2 extraction at 90°C for 2 h at pH 11.5) to 26.6% (2% H2O2 extraction at 50°C for 16 h at pH 12.5). The optimum hemicellulose yield (92% of the original Hemicelluloses in water treated wheat straw) was obtained when the treatment was performed at 50°C for 16 h at pH 12.5 by use of 2% H2O2. All the hemicellulosic preparations were much lighter in color than those obtained using traditional alkaline extractions in the absence of bleaching. The results, obtained by the destructive method such as acid hydrolysis, showed that extraction of wheat straw with aqueous 10% KOH following alkaline bleaching released the hemicellulosic fractions, which were enriched in xylose, whereas extraction of the straw with aqueous 2% H2O2 under alkaline conditions (pH 11.5–12.5) solubilized the hemicellulosic fractions, which were relatively higher in arabinose and glucose. The nine isolated hemicellulosic samples were further characterized by non-destructive methods such as Fourier transform infrared (FT–IR), and carbon-13 magnetic resonance spectroscopy (13C-NMR) as well as gel permeation chromatography (GPC). It has been demonstrated that the alkaline peroxide treatments under the conditions used do not affect the overall structure of Hemicelluloses. The only one major change of the Hemicelluloses was found to be degradation during the beaching of alkali-soluble Hemicelluloses with 2% H2O2 at 60°C for a period of 16 h at pH 11.5 or bleaching using a relatively higher concentration (5%) of hydrogen peroxide at 60°C for 8 h at pH 11.5.