Jiebing Li

KTH Royal Institute of Technology, Tukholma, Stockholm, Sweden

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Publications (30)84.22 Total impact

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    ABSTRACT: Xylan-lignin (XL), glucomannan-lignin (GML) and glucan-lignin (GL) complexes were isolated from spruce wood, hydrolyzed with xylanase or endoglucanase/β-glucosidase, and analyzed by analytical pyrolysis and 2D-NMR. The enzymatic hydrolysis removed most of the polysaccharide moieties in the complexes, and the lignin content and relative abundance of lignin-carbohydrate linkages increased. Analytical pyrolysis confirmed the action of the enzymatic hydrolysis, with strong decreases of levoglucosane and other carbohydrate-derived products. Unexpectedly it also revealed that the hydrolase treatment alters the pattern of lignin breakdown products, resulting in higher amounts of coniferyl alcohol. From the anomeric carbohydrate signals in the 2D-NMR spectra, phenyl glycoside linkages (undetectable in the original complexes) could be identified in the hydrolyzed GML complex. Lower amounts of glucuronosyl and benzyl ether linkages were also observed after the hydrolysis. From the 2D-NMR spectra of the hydrolyzed complexes, it was concluded that the lignin in GML is less condensed than in XL due to its higher content in β-O-4' ether substructures (62 % of side chains in GML vs 53 % in XL) accompanied by more coniferyl alcohol end units (16 vs 13 %). In contrast, the XL lignin has more pinoresinols (11 vs 6 %) and dibenzodioxocins (9 vs 2 %) than the GML (and both have ~13 % phenylcoumarans and 1 % spirodienones). Direct 2D-NMR analysis of the hydrolyzed GL complex was not possible due to its low solubility. However, after sample acetylation, an even less condensed lignin than in the GML complex was found (with up to 72 % β-O-4' substructures and only 1 % pinoresinols). The study provides evidence for the existence of structurally different lignins associated to hemicelluloses (xylan and glucomannan) and cellulose in spruce wood and, at the same time, offers information on some of the chemical linkages between the above polymers.
    Planta 02/2014; 239(5). DOI:10.1007/s00425-014-2037-y · 3.38 Impact Factor
  • Industrial Crops and Products 01/2014; 52:729-735. DOI:10.1016/j.indcrop.2013.11.035 · 3.21 Impact Factor
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    ABSTRACT: The effects and mechanism of pulp delignification by laccases in the presence of redox mediators have been investigated on unbleached eucalyptus kraft pulp treated with laccases from Pycnoporus cinnabarinus (PcL) and Myceliophthora thermophila (MtL) and 1-hydroxybenzotriazole (HBT) and methyl syringate (MeS) as mediators, respectively. Determination of corrected kappa number in eucalyptus pulps after the enzymatic treatments revealed that PcL-HBT exhibited more remarkable delignification effect than MtL-MeS. To obtain further insight, lignin-carbohydrate complexes (LCCs) were fractionated and subsequently characterized by NMR, thioacidolysis (followed by GC and SEC) and pyrolysis-GC/MS analyses before and after the enzymatic treatments and their controls. It can be concluded that the laccase-mediator treatments altered the lignin structures in such a way that more lignin was recovered in the xylan-lignin fractions, as shown by Klason lignin estimation, with lower amounts of both syringyl (S) and guaiacyl (G) uncondensed units, as shown by thioacidolysis -GC, especially after the PcL-HBT treatment. The laccase-mediator treatment produced oxidation at Cα and cleavage of Cα and Cβ bonds in pulp lignin, as shown by pyrolysis-GC/MS. The general mechanism of residual lignin degradation in the pulp by laccase-mediator treatments is discussed in the light of the results obtained.
    Biomacromolecules 07/2013; 14:3073-3080. DOI:10.1021/bm4006936 · 5.79 Impact Factor
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    ABSTRACT: It is of both theoretical and practical importance to develop a universally applicable approach for the fractionation and sensitive lignin characterisation of Lignin-Carbohydrate Complexes (LCCs) from all types of lignocellulosic biomass, both natively and after different types of processing. In the present study, the previously reported fractionation approach that is applicable for eucalyptus (hardwood) and flax (non-wood) was further improved by introducing an additional step of barium hydroxide precipitation to isolate the mannan-enriched LCC (glucomannan-lignin, GML) to suit softwood species as well. Spruce wood was used as the softwood sample. As revealed by the recovery yield and composition analysis, all of the lignin was recovered in three different LCC fractions: a glucan-enriched fraction (glucan-lignin, GL), a mannan-enriched fraction (glucomannan-lignin, GML) and a xylan-enriched fraction (xylan-lignin, XL). All of the LCCs had high molecular weights and were insoluble or barely soluble in a dioxane-water solution. Carbohydrate and lignin signals were observed in (1) H, (13) C CP-MAS and normal- or high-sensitivity 2D HSQC NMR analyses. The carbohydrate and lignin constituents in each LCC fraction are therefore believed to be chemically bonded instead of physically mixed with one another. The three LCCs fractions were found to be distinctly different from each other in their lignin structures, as further revealed by highly sensitive analyses using thioacidolysis-GC, thioacidolysis-SEC and pyrolysis-GC analyses. © 2013 The Authors. The Plant Journal © 2013 Blackwell Publishing Ltd.
    The Plant Journal 01/2013; DOI:10.1111/tpj.12124 · 6.82 Impact Factor
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    ABSTRACT: Unbleached Eucalyptus kraft pulps were treated by three methods and the bleaching effects have been evaluated. The treatments were performed by a laccase-mediator system (LMS), refining (R), and urea (U) alone and in combination of these methods. The bleached pulps were characterized in terms of κ number, hexenuronic acid content, brightness, and viscosity. In addition, the lignin-carbohydrate complexes (LCCs) were fractionated and characterized with regard to the fractionation yield, lignin content, and carbohydrate composition. Moreover, the 1H nuclear magnetic resonance spectra were recorded and the thioacidolysis-gas chromatography and thioacidolysis-size exclusion chromatography analyses were performed. The LMS treatment resulted mainly in a slightly better delignification as manifested by a κ number (K no.) reduction of 0.8 units. The effects of the U treatment included delignification (1.4 κ units), hexenuronic acid removal (3 μmol g-1), and improved pulp brightness (3.4 ISO units). The R treatment darkened the pulp (3 ISO units), whereas the bleaching of the R-pulp by subsequent LMS or U treatment enhanced the brightness (0.5 unit more) or delignification (0.3 unit more). The residual lignin in the pulp samples was present mainly as xylan-lignin. The Klason lignin content from the xylan-lignin fraction decreased as the degree of delignification increased. The pulp darkening followed by the R treatment was interpreted as the result of the formation of condensed lignin structures, but these condensed lignins were substantially removed by the subsequent LMS or U treatment.
    Holzforschung 01/2013; 67(6). DOI:10.1515/hf-2012-0140 · 2.34 Impact Factor
  • 11th International Symposium on Wood and Pulping Chemistry (ISWPC), Nice, France; 06/2011
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    ABSTRACT: Flax soda/AQ pulps were treated with different fungal laccase-mediator combinations followed by physical and chemical characterization of the pulps to obtain a thorough understanding of the laccase/mediator effects on hexenuronic acid (HexA) removal and the coupling of mediator onto pulps for fiber functionalization. Large differences were found and the presence of lauryl gallate (LG) during Trametes villosa laccase (TvL) treatment (TvL+LG) resulted in a much larger reduction of pulp-linked HexA than the combination of p-coumaric acid (PCA) and Pycnoporus cinnabarinus laccase (PcL). A major portion of LG became attached to the pulp as revealed by an increase in the kappa number and further confirmed by thioacidolysis and (1)H NMR analysis of solubilized pulp fractions. Additional experiments with other chemical pulps and isolated pulp xylan and lignin revealed that HexA seems to be the sole pulp component attacked by TvL+LG. As a substrate for TvL, the reaction preference order is PCA>HexA>LG.
    Bioresource Technology 02/2011; 102(4):3911-7. DOI:10.1016/j.biortech.2010.11.127 · 5.04 Impact Factor
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    ABSTRACT: The effect of milling time on the structure of lignin was investigated by analyzing the quantity and molecular size distribution of thioacidolysis products obtained from wood and pulp of eucalypt (Eucalyptus globulus). After milling, the ability of three solvent systems was determined to completely dissolve the wood or pulp meal. It was found that a mixture of DMSO and 50% aqueous tetrabutylammonium hydroxide was superior to either dimethylacetamide-LiCl or DMSO-tetrabutylammonium fluoride as solvent. By applying the minimum milling time required for complete dissolution, structurally unaltered wood or pulp could be further separated into lignin-carbohydrate fractions. These were analyzed by thioacidolysis. From eucalypt pulp, two different lignin-carbohydrate fractions were obtained, one glucan-and one xylan-enriched fraction, with the latter having more syringyl units in its lignin moieties. The developed solvent system seems to be universal because spruce and flax fibers and pulps could also be dissolved in it after milling.
    Holzforschung 01/2011; 65(1-1):43-50. DOI:10.1515/hf.2011.013 · 2.34 Impact Factor
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    ABSTRACT: Lignosulphonates are by-products from the sulphite pulping process, in which lignin is separated from cellulose by the addition of sulphonic acid groups to the α-position of lignin, thereby increasing the solubility of lignin in water. The predominant industrial utilisations of lignosulphonates are as dispersants, plasticisers and water-reducing agents in concrete preparation. The ability of lignosulphonates to function as a good plasticisers and water reducers is intimately linked with the purity of the lignosulphonate, its molecular weight and the number of charged groups present in the macromolecule. Currently, lignosulphonates are outrivaled by synthetic plasticisers termed superplasticisers due to their superior properties when used as additives to high-strength concrete. If lignosulphonates are to successfully compete with these superplasticisers, significant modifications are required. This paper describes a two-stage treatment of lignosulphonates in which the molecular weight is increased through laccase oxidation and carboxylic groups are introduced through ozonolysis. The technical significance of the results is also discussed.
    Industrial Crops and Products 11/2010; 32(3):458-466. DOI:10.1016/j.indcrop.2010.06.016 · 3.21 Impact Factor
  • Industrial Biotechnology 02/2010; 6(1):50-59. DOI:10.1089/ind.2010.6.050
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    ABSTRACT: The ability of laccases from Trametes villosa (TvL), Myceliophthora thermophila (MtL), Trametes hirsuta (ThL) and Bacillus subtilis (BsL) to improve the dispersion properties of calcium lignosulfonates 398 in the presence of HBT as a mediator was investigated. Size exclusion chromatography showed an extensive increase in molecular weight of the samples incubated with TvL and ThL by 107% and 572% from 28400 Da after 17h of incubation, respectively. Interestingly, FTIR spectroscopy, (13)C NMR and Py-GC/MS analysis of the treated samples suggested no substantial changes in the aromatic signal of the lignosulfonates, a good indication of the ability of TvL/ThL-HBT systems to limit their effect on functional groups without degrading the lignin backbone. Further, the enzymatic treatments led to a general increase in the dispersion properties, indeed a welcome development for its application in polymer blends.
    Bioresource Technology 02/2010; 101(14):5054-62. DOI:10.1016/j.biortech.2010.01.048 · 5.04 Impact Factor
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    ABSTRACT: Lignosulfonates are by-products from the sulfite pulping process. During this process, lignin is liberated from pulp fibers through sulfonation and washed away. As a consequence, the lignosulfonate molecules contain both hydrophobic and hydrophilic moieties. Lignosulfonates are low-value products with limited performance and are used as such as binders, surfactants, and plasticizers in concrete. Lignosulfonates face strong competition from synthetic petroleum-based plasticizers with superior quality. Therefore, increasing the performance of lignosulfonates is desirable not only from a sustainability point of view but also to expand their usage. One important aspect that describes how well lignosulfonates can act as plasticizers is the molecular weight. In this paper, the molecular weight of four commercial lignosulfonates is increased through oxidation by two laccases without utilization of mediators. Different parameters to obtain maximal molecular weight increase were identified and the technical significance of the experiments is discussed.
    Biomacromolecules 02/2010; 11(4):904-10. DOI:10.1021/bm901258v · 5.79 Impact Factor
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    ABSTRACT: The redox enzyme laccase can lead to cross-linking of lignin molecules by oxidising phenolic end groups to resonance-stabilised radicals that can undergo radical coupling to form covalent bonds. This property has potential for many technical applications. However, laccase treatment can also lead to degradation. Experiments were performed with two laccases of different oxidation potential and pH and temperature optima. The predominant reaction following laccase oxidation is the formation of 5-5' and 4-O-5' bonds. If the 5-position is blocked, other reactions occur, including coupling of the 1-position and oxidation of the a-position, which aggravates cross-linking of different lignin molecules. The product profile generated by the two laccases is somewhat different, mainly because of the different pH rather than differences in enzyme activity. Reaction mechanisms and the technical and biological significance of the results are discussed.
    Holzforschung 01/2010; 64(1):21-34. DOI:10.1515/HF.2010.001 · 2.34 Impact Factor
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    ABSTRACT: The structural characteristics of the lignin from jute (Corchorus capsularis ) fibers, which are used for high-quality paper pulp production, were studied. The lignin content (13.3% Klason lignin) was high compared to other nonwoody bast fibers used for pulp production. The lignin structure was characterized by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), 2D-NMR, and thioacidolysis. Upon Py-GC/MS, jute fibers released predominantly products from syringylpropanoid units with the S/G ratio being 2.1 and a H/G/S composition of 2:33:65. 2D-NMR of the milled wood lignin (MWL) isolated from jute fibers showed a predominance of beta-O-4' aryl ether linkages (72% of total side chains), followed by beta-beta' resinol-type linkages (16% of total side chains) and lower amounts of beta-5' phenylcoumaran (4%) and beta-1' spirodienone-type (4%) linkages and cinnamyl end groups (4%). The high predominance of the S-lignin units, together with the high proportion of beta-O-4' aryl ether linkages, which are easily cleaved during alkaline cooking, are advantageous for pulping. On the other hand, a small percentage (ca. 4%) of the lignin side chain was found to be acetylated at the gamma-carbon, predominantly over syringyl units. The analysis of desulphurated thioacidolysis dimers provided additional information on the relative abundances of the various carbon-carbon and diaryl ether bonds and the type of units (syringyl or guaiacyl) involved in each of the above linkage types. Interestingly, the major part of the beta-beta' dimers included two syringyl units, indicating that most of the beta-beta' substructures identified in the HSQC spectra were of the syringaresinol type (pinoresinol being absent), as already observed in the lignin of other angiosperms.
    Journal of Agricultural and Food Chemistry 10/2009; 57(21):10271-81. DOI:10.1021/jf900815x · 3.11 Impact Factor
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    ABSTRACT: In the present study, a steam explosion wood pre-treatment process, optimized earlier with respect to ethanol production, has been applied to both softwoods (Picea abies and Pinus sylvestris) and hardwoods (Betula verrucosa and Populus tremula). The alkaline extractable lignins have then been isolated to investigate lignin separation efficiency and lignin structure and to evaluate their potential for producing value-added products, such as biodiesel components or chemicals, in terms of the purity, molecular size, functional groups, beta-O-4' inter-unit linkage content, and degradability in a subsequent processing treatment. The mechanism of lignin modification and possible improvements to the steam explosion pre-treatment process are discussed.
    Bioresource Technology 02/2009; 100(9):2556-61. DOI:10.1016/j.biortech.2008.12.004 · 5.04 Impact Factor
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    ABSTRACT: Technical lignins from various sources can be converted into bio-oil with a low O/C ratio by pyrolysis in the presence of formic acid and an alcohol. By application of different analytical techniques, such as Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), electrospray ionization mass spectrometry (ESI−MS), and size-exclusion chromatography (SEC), it has been shown that a complete degradation of the lignin takes place irrespective of the origin. The resulting bio-oil has a low-molecular-mass distribution with a preponderance of aliphatic hydrocarbon structures. A substantial number of phenolic compounds are, however, also present, and some of these also contain carboxyl groups. The results clearly show that formic acid is a powerful supplier of atomic hydrogen. By further optimization of the pyrolysis reaction, it should be possible to further reduce the content of aromatic structures.
    Energy & Fuels 09/2008; 22(6). DOI:10.1021/ef800402f · 2.73 Impact Factor
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    ABSTRACT: The chemical structure of milled-wood lignins from Euca-lyptus globulus, E. nitens, E. maidenii, E. grandis, and E. dunnii was investigated. The lignins were characterized by analytical pyrolysis, thioacidolysis, and 2D-NMR that confirmed the predominance of syringyl over guaiacyl units and only showed traces of p-hydroxyphenyl units. E. globulus lignin had the highest syringyl content. The heteronuclear single quantum correlation (HSQC) NMR spectra yielded information about relative abundances of inter-unit linkages in the whole polymer. All the lignins showed a predominance of b-O-49 ether linkages (66–72% of total side-chains), followed by b-b9 resinol-type linkages (16–19%) and lower amounts of b-59 phe-nylcoumaran-type (3–7%) and b-19 spirodienone-type linkages (1–4%). The analysis of desulfurated thioaci-dolysis dimers provided additional information on the relative abundances of the various carbon-carbon and diaryl ether bonds, and the type of units (syringyl or guaiacyl) involved in each of the above linkage types. Interestingly, 93–94% of the total b-b9 dimers included two syringyl units indicating that most of the b-b9 sub-structures identified in the HSQC spectra were of the syringaresinol type. Moreover, three isomers of a major trimeric compound were found which were tentatively identified as arising from a b-b9 syringaresinol substruc-ture attached to a guaiacyl unit through a 4-O-59 linkage. Current address: Department of Fiber and Polymer Technology, a Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden. heteronuclear single quantum correlation (HSQC); milled-wood lignin (MWL); pyrolysis-GC/MS; thioacidolysis; trimers.
    Holzforschung 09/2008; 62(5):514-526. DOI:10.1515/HF.2008.096 · 2.34 Impact Factor
  • Jiebing Li, Göran Gellerstedt
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    ABSTRACT: Autohydrolysis of aspen wood breaks down lignin β-O-4 linkages via both acidolysis and homolytical cleavage. A simultaneous repolymerization by lignin–lignin condensation is the major reason for the low degree of delignification and the poor lignin reactivity. Modification of the autohydrolysis reaction by the addition of either NaOH or 2-naphthol changes the mechanism such that less acidolysis and fewer lignin–lignin condensation reactions take place, and an almost complete delignification can be achieved. The resulting isolated lignins have a low Mw, a light color and still contain some of the native β-O-4 linkages. Lignin from autohydrolysis in the presence of NaOH possesses more carboxylic acid groups, while the addition of 2-naphthol results in a lignin with a large amount of phenolic hydroxyl groups and incorporated naphthalene rings. These types of change are beneficial since the lignin structure becomes much more homogeneous with a greater potential for further upgrading and use.
    Industrial Crops and Products 03/2008; 27(2):175-181. DOI:10.1016/j.indcrop.2007.07.022 · 3.21 Impact Factor
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    ABSTRACT: Steam explosion is an important process for the fractionation of biomass components. In order to understand the behaviour of lignin under the conditions encountered in the steam explosion process, as well as in other types of steam treatment, aspen wood and isolated lignin from aspen were subjected to steam treatment under various conditions. The lignin portion was analyzed using NMR and size exclusion chromatography as major analytical techniques. Thereby, the competition between lignin depolymerization and repolymerization was revealed and the conditions required for these two types of reaction identified. Addition of a reactive phenol, 2-naphthol, was shown to inhibit the repolymerization reaction strongly, resulting in a highly improved delignification by subsequent solvent extraction and an extracted lignin of uniform structure.
    Bioresource Technology 12/2007; 98(16):3061-8. DOI:10.1016/j.biortech.2006.10.018 · 5.04 Impact Factor
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    ABSTRACT: Uronic acids can be quantified either by a colorimetric determination after treatment with concentrated sulfuric acid and carbazole or by gas chromatography after methanolysis and subsequent acetylation. Both methods suffer from incomplete hydrolysis, an unavoidable degradation of the products to be analysed, and an inability to separate and quantify different types of uronic acids. In the present work, the fundamental chemistry involved in the two methods has been evaluated, and some modifications to increase their accuracy are suggested. By combining the two methods, a complete quantification of all individual types of uronic acids present in a sample can be achieved.
    Carbohydrate Research 09/2007; 342(11):1442-9. DOI:10.1016/j.carres.2007.03.031 · 1.97 Impact Factor