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Special Issue "The Lignin Challenge: Exploring Innovative Applications"

A special issue of International Journal of Molecular Sciences (ISSN 1422-0067). This special issue belongs to the section "Biochemistry".

Deadline for manuscript submissions: closed (15 October 2017) | Viewed by 74276

Special Issue Editors

Dr. Araceli García
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Guest Editor
Organic Chemistry Department, University of Córdoba, Campus de Rabanales, Edificio Marie Curie (C-3), Crta Nnal IV, km 396 E-14014 Córdoba, Spain
Interests: cellulose and chitin nanofibers and nanocrystals; natural antioxidants; green chemistry processes; lignocellulosic residues; biomass-based materials and chemicals; agricultural and food wastes
Special Issues, Collections and Topics in MDPI journals
Dr. Luis Serrano
E-Mail
Guest Editor
CNRS-Centre National de la Recherche Scientifique, Laboratoire de Génie des Procédés Papetiers (LGP2), Grenoble-INP Pagora, 461 rue de la Papeterie, 38402 Saint-Martin-d'Hères Cedex, France
Interests: lignin; cellulose; oligosaccharides; biorefinery; wood chemistry; lignocellulosic biomass; pulp and paper; biobased materials
Prof. Dr. Vladimír Křen
E-Mail Website
Guest Editor
Institute of Microbiology, Academy of Sciences of the Czech Republic, Laboratory of Biotransformation, National Centre of Biocatalysis and Biotransformation, Videnska 1083, CZ 142 20 Praha 4, Czech Republic
Interests: biocatalysis and biotransformation; immobilized microbial cells, their use in production and biotransformation of natural products; biotransformation of natural products by enzymes and microorganisms; preparation of glycosidases of microbial origin and their use for glycosylation of natural compounds: glycoconjugates, multivalent compounds, ergot alkaloids, flavonoids, antioxidants and chemoprotectants
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The emerging new technologies in second generation biorefineries has led to an exponential increase of lignin supply as by-product. This situation, and the urgency in traditional pulp and paper mills to diversify their market opportunities, encourages transforming lignin into more diverse and valuable products. The amazing structure of lignin, a highly aromatic and functionalized 3D macromolecule, provides protection against insects and pathogens, waterproofing, toughness, and other key properties to the native vegetal wall in biomass. Moreover, recent advances in biomass pre-treatment processes has facilitated high purity lignin production, which could be directed to new uses for this biopolymer: Engineered plastics and thermoplastic elastomers, polymeric foams, active molecules, and commodity chemicals. This new generation of products invites a move away from the primitive uses of lignin (energy production, dispersant, painting additive) to move towards an innovative future based on renewable materials, and opens a niche market as a thrilling challenge for the scientific community.
We have the pleasure of inviting research scientists to submit original research, mini and full reviews for this Special Issue of the International Journal of Molecular Sciences, entitled “The Lignin Challenge: Exploring Innovative Applications”, dedicated to the lignin macromolecule, covering new advances in elucidation of its chemical structure, the discovery of new properties, or research on innovative applications.

Dr. Araceli García
Dr. Luis Serrano
Prof. Dr. Vladimír Křen
Guest Editors

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Keywords

  • lignin functionality
  • aromatic structure
  • biopolymer
  • active molecule
  • building-blocks from biorefinery
  • antioxidant/biocide agent
  • renewable materials
  • smart materials
  • biobased materials

Published Papers (20 papers)

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Research

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Article
Bio-Based Cellulose Acetate Films Reinforced with Lignin and Glycerol
Int. J. Mol. Sci. 2018, 19(4), 1143; https://doi.org/10.3390/ijms19041143 - 10 Apr 2018
Cited by 5 | Viewed by 3195
Abstract
Two sets of four cellulose acetate (degree of substitution = 2.2) were incorporated with lignin extracted from the macaúba endocarp, before and after being chemically modified to sodium carboxymethyl-lignin and aluminum carboxymethyl-lignin, respectively. The eight membranes were prepared by the casting method after [...] Read more.
Two sets of four cellulose acetate (degree of substitution = 2.2) were incorporated with lignin extracted from the macaúba endocarp, before and after being chemically modified to sodium carboxymethyl-lignin and aluminum carboxymethyl-lignin, respectively. The eight membranes were prepared by the casting method after dissolution in acetone and embedded with lignins (0.1% w/w), one without modification (CAc-Lig) and two chemically modified (CAc-CMLNa) and (CAc-CMLAl), compared to membranes of pure acetate (CAc). In group II, in the four membranes prepared, glycerol was added (10% w/w) as a plasticizer. The membranes were characterized by a number of techniques: thermal (differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA)), morphological (scanning electron microscope (SEM) and atomic force microscopy (AFM)), structural (X-ray powder diffraction (XRD)), hydrophobic (contact angle and water vapor permeability), and thermomechanical (dynamic thermal mechanical analysis and tensile tests). The results show that despite some incompatibility with the cellulose acetate, the incorporation of the lignin in a concentration of 0.1% w/w acts as a reinforcement in the membrane, greatly increasing the tension rupture of the material. The presence of glycerol in a concentration of 10% w/w also acts as a reinforcement in all membranes, in addition to increasing the tension rupture. In this study, glycerol and acetate both increased the compatibility of the membranes. Full article
(This article belongs to the Special Issue The Lignin Challenge: Exploring Innovative Applications)
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Article
Protic Ionic Liquids for Lignin Extraction—A Lignin Characterization Study
Int. J. Mol. Sci. 2018, 19(2), 428; https://doi.org/10.3390/ijms19020428 - 31 Jan 2018
Cited by 40 | Viewed by 3574
Abstract
Protic ionic liquids (PILs) have been established as effective solvents for the selective extraction and recovery of lignin from lignocellulosic biomass. In this study, we utilize extensive analytical techniques to characterize the PIL-extracted lignins to (1) expand on the physical/chemical structure, and to [...] Read more.
Protic ionic liquids (PILs) have been established as effective solvents for the selective extraction and recovery of lignin from lignocellulosic biomass. In this study, we utilize extensive analytical techniques to characterize the PIL-extracted lignins to (1) expand on the physical/chemical structure, and to (2) develop a better understanding of the mechanism behind the lignin dissolution process. The PIL-lignins were characterized using elemental and FT-IR analyses, alongside molecular weight distribution and chemical modeling via MM2. For the more ionic pyrrolidinium acetate ([Pyrr][Ac]), there is an increase in the fragmentation of lignin, resulting in lignin with a smaller average molecular weight and a more uniform dispersity. This lends better understanding to previous findings indicating that higher ionicity in a PIL leads to increased lignin extraction. Full article
(This article belongs to the Special Issue The Lignin Challenge: Exploring Innovative Applications)
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Article
Modulation of Innate Immunity by lignin-Carbohydrate, a Novel TLR4 Ligand, Results in Augmentation of Mucosal IgA and Systemic IgG Production
Int. J. Mol. Sci. 2018, 19(1), 64; https://doi.org/10.3390/ijms19010064 - 26 Dec 2017
Cited by 4 | Viewed by 2175
Abstract
Previous study revealed that a specific lignin-carbohydrate preparation, named as lignin-rich enzyme lignin (LREL) derived from plant husk, is a novel toll-like receptor 4 ligand and shows a potent immune-stimulatory activity against dendritic cells (DCs) in vitro. In this report, we investigated immune-stimulatory [...] Read more.
Previous study revealed that a specific lignin-carbohydrate preparation, named as lignin-rich enzyme lignin (LREL) derived from plant husk, is a novel toll-like receptor 4 ligand and shows a potent immune-stimulatory activity against dendritic cells (DCs) in vitro. In this report, we investigated immune-stimulatory activity of LREL in vivo. Single intraperitoneal (i.p.) or oral treatment of LREL elicited activation of systemic and mucosal DCs, which were accompanied by significant elevation of cell surface activation markers and ratio of IL-12p40 producing cells. In addition, LREL-fed mice showed not only mucosal DCs activation but also significant increase of IFN-γ+ CD4+ T cells in mesenteric lymph node (MLN), respectively. We further examined the effect of LREL oral immunization in combination with ovalbumin (OVA) on the activation of acquired immune system. In LREL administered group, total mucosal IgA concentration was significantly increased, while antigen-specific immunoglobulin A (IgA) concentration was not changed between groups. On the other hand, both total and antigen-specific IgG concentrations in plasma were significantly increased in the LREL administered group. Taken together, oral treatment of LREL is able to affect mucosal and systemic antibodies induction and might be useful for effective immune-stimulatory functional foods and mucosal vaccine adjuvant. Full article
(This article belongs to the Special Issue The Lignin Challenge: Exploring Innovative Applications)
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Article
Structural Differences between the Lignin-Carbohydrate Complexes (LCCs) from 2- and 24-Month-Old Bamboo (Neosinocalamus affinis)
Int. J. Mol. Sci. 2018, 19(1), 1; https://doi.org/10.3390/ijms19010001 - 21 Dec 2017
Cited by 25 | Viewed by 3094
Abstract
The lignin-carbohydrate complex (LCC) was isolated from milled wood lignin of 2- and 24-month-old crude bamboo (Neosinocalamus affinis) culms using acetic acid (AcOH) and then characterized. The results have shown that the LCC preparation from 2-month-old bamboo (L2) exhibited [...] Read more.
The lignin-carbohydrate complex (LCC) was isolated from milled wood lignin of 2- and 24-month-old crude bamboo (Neosinocalamus affinis) culms using acetic acid (AcOH) and then characterized. The results have shown that the LCC preparation from 2-month-old bamboo (L2) exhibited a slightly lower molecular weight than the LCC preparation from the 24-month-old bamboo (L24). Further studies using Fourier transform infrared spectroscopy (FT-IR) and heteronuclear single quantum coherence (2D-HSQC) NMR spectra analyses indicate that the LCC preparations included glucuronoarabinoxylan and G-S-H lignin-type with G>S>>H. The content of the S lignin units of LCC in the mature bamboo was always higher than in the young bamboo. Combined with sugar composition analysis, the contents of phenyl glycoside and ether linkages in the L24 preparation were higher than in the L2 preparation; however, there was a reverse relationship of ester LCC bonds in L2 and L24. Lignin–xylan was the main type of LCC linkage in bamboo LCCs. Lignin–lignin linkages in the LCC preparations included β-β, β-5 and β-1 carbon-to-carbon, as well as β-O-4 ether linkages, but β-1 linkages were not present in L2. Full article
(This article belongs to the Special Issue The Lignin Challenge: Exploring Innovative Applications)
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Article
Controlling the Molecular Weight of Lignosulfonates by an Alkaline Oxidative Treatment at Moderate Temperatures and Atmospheric Pressure: A Size-Exclusion and Reverse-Phase Chromatography Study
Int. J. Mol. Sci. 2017, 18(12), 2520; https://doi.org/10.3390/ijms18122520 - 24 Nov 2017
Cited by 8 | Viewed by 2754
Abstract
The molecular weights of lignosulfonates (LSs) are modified by a rather simple process involving an alkaline oxidative treatment at moderate temperatures (70–90 °C) and atmospheric pressure. Starting from LSs with an average molecular weight of 90,000 Da, and using such a treatment, one [...] Read more.
The molecular weights of lignosulfonates (LSs) are modified by a rather simple process involving an alkaline oxidative treatment at moderate temperatures (70–90 °C) and atmospheric pressure. Starting from LSs with an average molecular weight of 90,000 Da, and using such a treatment, one can prepare controlled molecular weight LSs in the range of 30,000 to 3500 Da based on the average mass molecular weight. The LS depolymerisation was monitored via reverse-phase and size-exclusion chromatography. It has been shown that the combination of O2, H2O2 and Cu as a catalyst in alkaline conditions at 80 °C induces a high LS depolymerisation. The depolymerisation was systemically accompanied by a vanillin production, the yields of which reached 1.4 wt % (weight percentage on LS raw basis) in such conditions. Also, the average molecular weight and vanillin concentration were correlated and depended linearly on the temperature and reaction duration. Full article
(This article belongs to the Special Issue The Lignin Challenge: Exploring Innovative Applications)
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Article
A Comprehensive Study on Pyrolysis Mechanism of Substituted β-O-4 Type Lignin Dimers
Int. J. Mol. Sci. 2017, 18(11), 2364; https://doi.org/10.3390/ijms18112364 - 09 Nov 2017
Cited by 27 | Viewed by 2980
Abstract
In order to understand the pyrolysis mechanism of β-O-4 type lignin dimers, a pyrolysis model is proposed which considers the effects of functional groups (hydroxyl, hydroxymethyl and methoxyl) on the alkyl side chain and aromatic ring. Furthermore, five specific β-O [...] Read more.
In order to understand the pyrolysis mechanism of β-O-4 type lignin dimers, a pyrolysis model is proposed which considers the effects of functional groups (hydroxyl, hydroxymethyl and methoxyl) on the alkyl side chain and aromatic ring. Furthermore, five specific β-O-4 type lignin dimer model compounds are selected to investigate their integrated pyrolysis mechanism by density functional theory (DFT) methods, to further understand and verify the proposed pyrolysis model. The results indicate that a total of 11 pyrolysis mechanisms, including both concerted mechanisms and homolytic mechanisms, might occur for the initial pyrolysis of the β-O-4 type lignin dimers. Concerted mechanisms are predominant as compared with homolytic mechanisms throughout unimolecular decomposition pathways. The competitiveness of the eleven pyrolysis mechanisms are revealed via different model compounds, and the proposed pyrolysis model is ranked in full consideration of functional groups effects. The proposed pyrolysis model can provide a theoretical basis to predict the reaction pathways and products during the pyrolysis process of β-O-4 type lignin dimers. Full article
(This article belongs to the Special Issue The Lignin Challenge: Exploring Innovative Applications)
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Article
Lignin-Modified Carbon Nanotube/Graphene Hybrid Coating as Efficient Flame Retardant
Int. J. Mol. Sci. 2017, 18(11), 2368; https://doi.org/10.3390/ijms18112368 - 08 Nov 2017
Cited by 19 | Viewed by 4094
Abstract
To reduce fire hazards and expand high-value applications of lignocellulosic materials, thin films comprising graphene nanoplatelets (GnPs) and multi-wall carbon nanotubes (CNTs) pre-adsorbed with alkali lignin were deposited by a Meyer rod process. Lightweight and highly flexible papers with increased gas impermeability were [...] Read more.
To reduce fire hazards and expand high-value applications of lignocellulosic materials, thin films comprising graphene nanoplatelets (GnPs) and multi-wall carbon nanotubes (CNTs) pre-adsorbed with alkali lignin were deposited by a Meyer rod process. Lightweight and highly flexible papers with increased gas impermeability were obtained by coating a protective layer of carbon nanomaterials in a randomly oriented and overlapped network structure. Assessment of the thermal and flammability properties of papers containing as low as 4 wt % carbon nanomaterials exhibited self-extinguishing behavior and yielded up to 83.5% and 87.7% reduction in weight loss and burning area, respectively, compared to the blank papers. The maximum burning temperature as measured by infrared pyrometry also decreased from 834 °C to 705 °C with the presence of flame retardants. Furthermore, papers coated with composites of GnPs and CNTs pre-adsorbed with lignin showed enhanced thermal stability and superior fire resistance than samples treated with either component alone. These outstanding flame-retardant properties can be attributed to the synergistic effects between GnPs, CNTs and lignin, enhancing physical barrier characteristics, formation of char and thermal management of the material. These results provide great opportunities for the development of efficient, cost-effective and environmentally sustainable flame retardants. Full article
(This article belongs to the Special Issue The Lignin Challenge: Exploring Innovative Applications)
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Article
Deep Eutectic Solvents (DESs) for the Isolation of Willow Lignin (Salix matsudana cv. Zhuliu)
Int. J. Mol. Sci. 2017, 18(11), 2266; https://doi.org/10.3390/ijms18112266 - 28 Oct 2017
Cited by 74 | Viewed by 4066
Abstract
Deep eutectic solvents (DESs) are a potentially high-value lignin extraction methodology. DESs prepared from choline chloride (ChCl) and three hydrogen-bond donors (HBD)—lactic acid (Lac), glycerol, and urea—were evaluated for isolation of willow (Salix matsudana cv. Zhuliu) lignin. DESs types, mole ratio [...] Read more.
Deep eutectic solvents (DESs) are a potentially high-value lignin extraction methodology. DESs prepared from choline chloride (ChCl) and three hydrogen-bond donors (HBD)—lactic acid (Lac), glycerol, and urea—were evaluated for isolation of willow (Salix matsudana cv. Zhuliu) lignin. DESs types, mole ratio of ChCl to HBD, extraction temperature, and time on the fractionated DES-lignin yield demonstrated that the optimal DES-lignin yield (91.8 wt % based on the initial lignin in willow) with high purity of 94.5% can be reached at a ChCl-to-Lac molar ratio of 1:10, extraction temperature of 120 °C, and time of 12 h. Fourier transform infrared spectroscopy (FT-IR) , 13C-NMR, and 31P-NMR showed that willow lignin extracted by ChCl-Lac was mainly composed of syringyl and guaiacyl units. Serendipitously, a majority of the glucan in willow was preserved after ChCl-Lac treatment. Full article
(This article belongs to the Special Issue The Lignin Challenge: Exploring Innovative Applications)
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Article
Experimental and Kinetic Study on Lignin Depolymerization in Water/Formic Acid System
Int. J. Mol. Sci. 2017, 18(10), 2082; https://doi.org/10.3390/ijms18102082 - 01 Oct 2017
Cited by 13 | Viewed by 3532
Abstract
Microwave-assisted depolymerization of black-liquor lignin in formic acid was studied, concentrating on the yield of liquid fractions as bio-oil 1 (mainly aromatic monomers) and bio-oil 2 (mainly aromatic oligomers) and the distribution of the specific compositions. Bio-oil 1 (9.69%) and bio-oil 2 (54.39%) [...] Read more.
Microwave-assisted depolymerization of black-liquor lignin in formic acid was studied, concentrating on the yield of liquid fractions as bio-oil 1 (mainly aromatic monomers) and bio-oil 2 (mainly aromatic oligomers) and the distribution of the specific compositions. Bio-oil 1 (9.69%) and bio-oil 2 (54.39%) achieved their maximum yields under 160 °C with the reaction time of 30 min. The chemical compositions of bio-oil 1 and bio-oil 2 were respectively identified by means of Gas Chromatography-Mass Spectrometer (GC-MS) and Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Ethanone, 1-(4-hydroxy-3-methoxyphenyl) and Ethanone, 1-(4-hydrox-3,5-dimethoxyphenyl) were evidenced to be the two prominent compounds in bio-oil 1. Production of aromatic oligomers with the molecular weight of 328, 342, 358, 378, 394, 424 and 454 identified by MALDI-TOF MS was substantially tuned with the reaction temperature. A two-separate-stage kinetic model was proposed to describe the acidic solvolysis of lignin assisted by microwave heating, where the first stage is dominated by the depolyerization of lignin to monomers and oligomers with the activation energy of 40.27 kJ·mol−1, and the second stage with the activation energy of 49.18 kJ·mol−1 is mainly ascribed to the repolymerization of first-stage produced compounds. Full article
(This article belongs to the Special Issue The Lignin Challenge: Exploring Innovative Applications)
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Communication
High-Throughput Screening Assay for Laccase Engineering toward Lignosulfonate Valorization
Int. J. Mol. Sci. 2017, 18(8), 1793; https://doi.org/10.3390/ijms18081793 - 18 Aug 2017
Cited by 12 | Viewed by 4690
Abstract
Lignin valorization is a pending issue for the integrated conversion of lignocellulose in consumer goods. Lignosulfonates (LS) are the main technical lignins commercialized today. However, their molecular weight should be enlarged to meet application requirements as additives or dispersing agents. Oxidation of lignosulfonates [...] Read more.
Lignin valorization is a pending issue for the integrated conversion of lignocellulose in consumer goods. Lignosulfonates (LS) are the main technical lignins commercialized today. However, their molecular weight should be enlarged to meet application requirements as additives or dispersing agents. Oxidation of lignosulfonates with fungal oxidoreductases, such as laccases, can increase the molecular weight of lignosulfonates by the cross-linking of lignin phenols. To advance in this direction, we describe here the development of a high-throughput screening (HTS) assay for the directed evolution of laccases, with lignosulfonate as substrate and the Folin–Ciocalteau reagent (FCR), to detect the decrease in phenolic content produced upon polymerization of lignosulfonate by the enzyme. Once the reaction conditions were adjusted to the 96-well-plate format, the enzyme for validating the assay was selected from a battery of high-redox-potential laccase variants functionally expressed in S. cerevisiae (the preferred host for the directed evolution of fungal oxidoreductases). The colorimetric response (absorbance at 760 nm) correlated with laccase activity secreted by the yeast. The HTS assay was reproducible (coefficient of variation (CV) = 15%) and sensitive enough to detect subtle differences in activity among yeast clones expressing a laccase mutant library obtained by error-prone PCR (epPCR). The method is therefore feasible for screening thousands of clones during the precise engineering of laccases toward valorization of lignosulfonates. Full article
(This article belongs to the Special Issue The Lignin Challenge: Exploring Innovative Applications)
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Article
Functional Hybrid Materials Based on Manganese Dioxide and Lignin Activated by Ionic Liquids and Their Application in the Production of Lithium Ion Batteries
Int. J. Mol. Sci. 2017, 18(7), 1509; https://doi.org/10.3390/ijms18071509 - 12 Jul 2017
Cited by 18 | Viewed by 2880
Abstract
Kraft lignin (KL) was activated using selected ionic liquids (ILs). The activated form of the biopolymer, due to the presence of carbonyl groups, can be used in electrochemical tests. To increase the application potential of the system in electrochemistry, activated lignin forms were [...] Read more.
Kraft lignin (KL) was activated using selected ionic liquids (ILs). The activated form of the biopolymer, due to the presence of carbonyl groups, can be used in electrochemical tests. To increase the application potential of the system in electrochemistry, activated lignin forms were combined with manganese dioxide, and the most important physicochemical and morphological-microstructural properties of the novel, functional hybrid systems were determined using Fourier transform infrared spectroscopy (FTIR), elemental analysis (EA), scanning electron microscopy (SEM), zeta potential analysis, thermal stability (TGA/DTG) and porous structure analysis. An investigation was also made of the practical application of the hybrid materials in the production of lithium ion batteries. The capacity of the anode (MnO2/activated lignin), working at a low current regime of 50 mA·g−1, was ca. 610 mAh·g−1, while a current of 1000 mA·g−1 resulted in a capacity of 570 mAh·g−1. Superior cyclic stability and rate capability indicate that this may be a promising electrode material for use in high-performance lithium ion batteries. Full article
(This article belongs to the Special Issue The Lignin Challenge: Exploring Innovative Applications)
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Article
Improving Processing and Performance of Pure Lignin Carbon Fibers through Hardwood and Herbaceous Lignin Blends
Int. J. Mol. Sci. 2017, 18(7), 1410; https://doi.org/10.3390/ijms18071410 - 01 Jul 2017
Cited by 49 | Viewed by 3674
Abstract
Lignin/lignin blends were used to improve fiber spinning, stabilization rates, and properties of lignin-based carbon fibers. Organosolv lignin from Alamo switchgrass (Panicum virgatum) and yellow poplar (Liriodendron tulipifera) were used as blends for making lignin-based carbon fibers. Different ratios [...] Read more.
Lignin/lignin blends were used to improve fiber spinning, stabilization rates, and properties of lignin-based carbon fibers. Organosolv lignin from Alamo switchgrass (Panicum virgatum) and yellow poplar (Liriodendron tulipifera) were used as blends for making lignin-based carbon fibers. Different ratios of yellow poplar:switchgrass lignin blends were prepared (50:50, 75:25, and 85:15 w/w). Chemical composition and thermal properties of lignin samples were determined. Thermal properties of lignins were analyzed using thermogravimetric analysis and differential scanning calorimetry. Thermal analysis confirmed switchgrass and yellow poplar lignin form miscible blends, as a single glass transition was observed. Lignin fibers were produced via melt-spinning by twin-screw extrusion. Lignin fibers were thermostabilized at different rates and subsequently carbonized. Spinnability of switchgrass lignin markedly improved by blending with yellow poplar lignin. On the other hand, switchgrass lignin significantly improved thermostabilization performance of yellow poplar fibers, preventing fusion of fibers during fast stabilization and improving mechanical properties of fibers. These results suggest a route towards a 100% renewable carbon fiber with significant decrease in production time and improved mechanical performance. Full article
(This article belongs to the Special Issue The Lignin Challenge: Exploring Innovative Applications)
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Article
Activation of Magnesium Lignosulfonate and Kraft Lignin: Influence on the Properties of Phenolic Resin-Based Composites for Potential Applications in Abrasive Materials
Int. J. Mol. Sci. 2017, 18(6), 1224; https://doi.org/10.3390/ijms18061224 - 08 Jun 2017
Cited by 39 | Viewed by 3593
Abstract
Magnesium lignosulfonate and kraft lignin were activated by different oxidizing agents for use in phenolic resin composites used for the production of abrasive components. The physicochemical properties of the oxidized materials were analyzed by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), [...] Read more.
Magnesium lignosulfonate and kraft lignin were activated by different oxidizing agents for use in phenolic resin composites used for the production of abrasive components. The physicochemical properties of the oxidized materials were analyzed by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), dynamic mechanical-thermal analysis (DMTA) and inverse gas chromatography (IGC). The homogeneity of the model abrasive composites containing the studied products was assessed based on observations obtained using a scanning electron microscope (SEM). FTIR and XPS analysis of the oxidized products indicated that the activation process leads mainly to the formation of carbonyl groups. The IGC technique was used to assess changes in the surface energy and the acid–base properties of the studied biopolymers. The changes in the acid–base properties suggest that more groups acting as electron donors appear on the oxidized surface of the materials. DMTA studies showed that the model composites with 5% magnesium lignosulfonate oxidized by H2O2 had the best thermomechanical properties. Based on the results it was possible to propose a hypothetical mechanism of the oxidation of the natural polymers. The use of such oxidized products may improve the thermomechanical properties of abrasive articles. Full article
(This article belongs to the Special Issue The Lignin Challenge: Exploring Innovative Applications)
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Article
Large-Scale Membrane- and Lignin-Modified Adsorbent-Assisted Extraction and Preconcentration of Triazine Analogs and Aflatoxins
Int. J. Mol. Sci. 2017, 18(4), 801; https://doi.org/10.3390/ijms18040801 - 11 Apr 2017
Cited by 4 | Viewed by 2185
Abstract
The large-scale simultaneous extraction and concentration of aqueous solutions of triazine analogs, and aflatoxins, through a hydrocarbon-based membrane (e.g., polyethylene, polyethylene/polypropylene copolymer) under ambient temperature and atmospheric pressure is reported. The subsequent adsorption of analyte in the extraction chamber over the lignin-modified silica [...] Read more.
The large-scale simultaneous extraction and concentration of aqueous solutions of triazine analogs, and aflatoxins, through a hydrocarbon-based membrane (e.g., polyethylene, polyethylene/polypropylene copolymer) under ambient temperature and atmospheric pressure is reported. The subsequent adsorption of analyte in the extraction chamber over the lignin-modified silica gel facilitates the process by reducing the operating time. The maximum adsorption capacity values for triazine analogs and aflatoxins are mainly adsorption mechanism-dependent and were calculated to be 0.432 and 0.297 mg/10 mg, respectively. The permeation, and therefore the percentage of analyte extracted, ranges from 1% to almost 100%, and varies among the solvents examined. It is considered to be vapor pressure- and chemical polarity-dependent, and is thus highly affected by the nature and thickness of the membrane, the discrepancy in the solubility values of the analyte between the two liquid phases, and the amount of adsorbent used in the process. A dependence on the size of the analyte was observed in the adsorption capacity measurement, but not in the extraction process. The theoretical interaction simulation and FTIR data show that the planar aflatoxin molecule releases much more energy when facing toward the membrane molecule when approaching it, and the mechanism leading to the adsorption. Full article
(This article belongs to the Special Issue The Lignin Challenge: Exploring Innovative Applications)
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Article
Isolation and Characterization of Gramineae and Fabaceae Soda Lignins
Int. J. Mol. Sci. 2017, 18(2), 327; https://doi.org/10.3390/ijms18020327 - 04 Feb 2017
Cited by 39 | Viewed by 3765
Abstract
Some agricultural residues such as wheat or barley straw, as well as certain fast-growing plants like Leucaena leucocephala and Chamaecytisus proliferus, could be used as raw materials for the paper industry as an alternative to traditional plants (eucalyptus, pine, etc.). In the [...] Read more.
Some agricultural residues such as wheat or barley straw, as well as certain fast-growing plants like Leucaena leucocephala and Chamaecytisus proliferus, could be used as raw materials for the paper industry as an alternative to traditional plants (eucalyptus, pine, etc.). In the present study, four types of lignin obtained from the spent liquors produced by the pulping processes using the abovementioned feedstocks were isolated and characterized. Lignin samples were acquired through an acid precipitation from these spent liquors. The characterization of the precipitated lignin samples were performed using a Fourier transform infrared spectroscopy (FT-IR) and both liquid- and solid-state nuclear magnetic resonance spectroscopy (NMR) to analyse the chemical structure, and thermogravimetric analysis (TGA) for determining the thermal properties. Additionally, chemical composition of lignin fractions was also measured. Even though they were of different botanical origin, all the studied samples except for wheat straw lignin had a similar chemical composition and thermal behaviour, and identical chemical structure. Wheat straw lignin showed a greater amount of Klason lignin and lower carbohydrate content. Furthermore, this lignin sample showed a higher thermal stability and significantly different cross-peak patterns in the 2D-NMR experiments. The molecular structures corresponding to p-coumarate (PCA), ferulate (FA) and cinnamyl aldehyde end-groups (J) were only detected in wheat isolated lignin. Full article
(This article belongs to the Special Issue The Lignin Challenge: Exploring Innovative Applications)
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Article
Composition of Lignin-to-Liquid Solvolysis Oils from Lignin Extracted in a Semi-Continuous Organosolv Process
Int. J. Mol. Sci. 2017, 18(1), 225; https://doi.org/10.3390/ijms18010225 - 23 Jan 2017
Cited by 14 | Viewed by 3674
Abstract
The interest and on-going research on utilisation of lignin as feedstock for production of renewable and sustainable aromatics is expanding and shows great potential. This study investigates the applicability of semi-continuously organosolv extracted lignin in Lignin-to-Liquid (LtL) solvolysis, using formic acid as hydrogen [...] Read more.
The interest and on-going research on utilisation of lignin as feedstock for production of renewable and sustainable aromatics is expanding and shows great potential. This study investigates the applicability of semi-continuously organosolv extracted lignin in Lignin-to-Liquid (LtL) solvolysis, using formic acid as hydrogen donor and water as solvent under high temperature–high pressure (HTHP) conditions. The high purity of the organosolv lignin provides high conversion yields at up to 94% based on lignin mass input. The formic acid input is a dominating parameter in lignin conversion. Carbon balance calculations of LtL-solvolysis experiments also indicate that formic acid can give a net carbon contribution to the bio-oils, in addition to its property as hydrogenation agent. Compound specific quantification of the ten most abundant components in the LtL-oils describe up to 10% of the bio-oil composition, and reaction temperature is shown to be the dominating parameter for the structures present. The structural and quantitative results from this study identify components of considerable value in the LtL-oil, and support the position of this oil as a potentially important source of building blocks for the chemical and pharmaceutical industry. Full article
(This article belongs to the Special Issue The Lignin Challenge: Exploring Innovative Applications)
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Review

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Review
Catalytic Oxidation of Lignins into the Aromatic Aldehydes: General Process Trends and Development Prospects
Int. J. Mol. Sci. 2017, 18(11), 2421; https://doi.org/10.3390/ijms18112421 - 15 Nov 2017
Cited by 79 | Viewed by 3700
Abstract
This review discusses principal patterns that govern the processes of lignins’ catalytic oxidation into vanillin (3-methoxy-4-hydroxybenzaldehyde) and syringaldehyde (3,5-dimethoxy-4-hydroxybenzaldehyde). It examines the influence of lignin and oxidant nature, temperature, mass transfer, and of other factors on the yield of the aldehydes and the [...] Read more.
This review discusses principal patterns that govern the processes of lignins’ catalytic oxidation into vanillin (3-methoxy-4-hydroxybenzaldehyde) and syringaldehyde (3,5-dimethoxy-4-hydroxybenzaldehyde). It examines the influence of lignin and oxidant nature, temperature, mass transfer, and of other factors on the yield of the aldehydes and the process selectivity. The review reveals that properly organized processes of catalytic oxidation of various lignins are only insignificantly (10–15%) inferior to oxidation by nitrobenzene in terms of yield and selectivity in vanillin and syringaldehyde. Very high consumption of oxygen (and consequentially, of alkali) in the process—over 10 mol per mol of obtained vanillin—is highlighted as an unresolved and unexplored problem: scientific literature reveals almost no studies devoted to the possibilities of decreasing the consumption of oxygen and alkali. Different hypotheses about the mechanism of lignin oxidation into the aromatic aldehydes are discussed, and the mechanism comprising the steps of single-electron oxidation of phenolate anions, and ending with retroaldol reaction of a substituted coniferyl aldehyde was pointed out as the most convincing one. The possibility and development prospects of single-stage oxidative processing of wood into the aromatic aldehydes and cellulose are analyzed. Full article
(This article belongs to the Special Issue The Lignin Challenge: Exploring Innovative Applications)
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Review
Lignin from Micro- to Nanosize: Applications
Int. J. Mol. Sci. 2017, 18(11), 2367; https://doi.org/10.3390/ijms18112367 - 08 Nov 2017
Cited by 98 | Viewed by 5440
Abstract
Micro- and nanosize lignin has recently gained interest due to improved properties compared to standard lignin available today. As the second most abundant biopolymer after cellulose, lignin is readily available but used for rather low-value applications. This review focuses on the application of [...] Read more.
Micro- and nanosize lignin has recently gained interest due to improved properties compared to standard lignin available today. As the second most abundant biopolymer after cellulose, lignin is readily available but used for rather low-value applications. This review focuses on the application of micro- and nanostructured lignin in final products or processes that all show potential for high added value. The fields of application are ranging from improvement of mechanical properties of polymer nanocomposites, bactericidal and antioxidant properties and impregnations to hollow lignin drug carriers for hydrophobic and hydrophilic substances. Also, a carbonization of lignin nanostructures can lead to high-value applications such as use in supercapacitors for energy storage. The properties of the final product depend on the surface properties of the nanomaterial and, therefore, on factors like the lignin source, extraction method, and production/precipitation methods, as discussed in this review. Full article
(This article belongs to the Special Issue The Lignin Challenge: Exploring Innovative Applications)
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Review
Lignin from Micro- to Nanosize: Production Methods
Int. J. Mol. Sci. 2017, 18(6), 1244; https://doi.org/10.3390/ijms18061244 - 10 Jun 2017
Cited by 118 | Viewed by 6177
Abstract
Lignin is the second most abundant biopolymer after cellulose. It has long been obtained as a by-product of cellulose production in pulp and paper production, but had rather low added-value applications. A changing paper market and the emergence of biorefinery projects should generate [...] Read more.
Lignin is the second most abundant biopolymer after cellulose. It has long been obtained as a by-product of cellulose production in pulp and paper production, but had rather low added-value applications. A changing paper market and the emergence of biorefinery projects should generate vast amounts of lignin with the potential of value addition. Nanomaterials offer unique properties and the preparation of lignin nanoparticles and other nanostructures has therefore gained interest as a promising technique to obtain value-added lignin products. Due to lignin’s high structural and chemical heterogeneity, methods must be adapted to these different types. This review focuses on the ability of different formation methods to cope with the huge variety of lignin types and points out which particle characteristics can be achieved by which method. The current research’s main focus is on pH and solvent-shifting methods where the latter can yield solid and hollow particles. Solvent shifting also showed the capability to cope with different lignin types and solvents and antisolvents, respectively. However, process conditions have to be adapted to every type of lignin and reduction of solvent demand or the integration in a biorefinery process chain must be focused. Full article
(This article belongs to the Special Issue The Lignin Challenge: Exploring Innovative Applications)
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Review
Lignins and Their Derivatives with Beneficial Effects on Human Health
Int. J. Mol. Sci. 2017, 18(6), 1219; https://doi.org/10.3390/ijms18061219 - 07 Jun 2017
Cited by 120 | Viewed by 4358
Abstract
A review of the pharmacological applications of lignins provides evidence of their protective role against the development of different diseases. In many cases, the effects of lignins could be explained by their antioxidant capacity. Here, we present a systematic review of the literature [...] Read more.
A review of the pharmacological applications of lignins provides evidence of their protective role against the development of different diseases. In many cases, the effects of lignins could be explained by their antioxidant capacity. Here, we present a systematic review of the literature from the period 2010–2016 which provides information concerning new applications of lignins derived from recent research. The most promising findings are reported, including the methodologies employed and results obtained with lignins or their derivatives which may improve human health. We highlight potential applications in the treatment of obesity, diabetes, thrombosis, viral infections and cancer. Moreover, we report both that lignins can be used in the preparation of nanoparticles to deliver different drugs and also their use in photoprotection. Full article
(This article belongs to the Special Issue The Lignin Challenge: Exploring Innovative Applications)
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