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Special Issue "Lignin—Chemistry and Materials: Past, Present and Future"

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Natural Products Chemistry".

Deadline for manuscript submissions: closed (30 November 2019) | Viewed by 13621

Special Issue Editors

Prof. Dr. Claudia Crestini
E-Mail Website
Guest Editor
Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venice Via Torino 155, 30170 Venice Mestre, Italy
Interests: chemistry of renewable resources; green chemistry and biorefineries; natural polymers; lignin; tannin; nanocapsules; nanoparticles; nanofibers; targeted delivery; structure elucidation; flow chemistry
Dr. Heiko Lange
E-Mail Website
Guest Editor
Department of Pharmacy, University of Naples Federico II, Naples, Italy
Interests: biomaterials; natural polymers; polyphenols; lignin; tannin; micro- and nanovesicles; nanoparticles; nanofibers; targeted delivery; structure elucidation; synthetic chemistry; flow chemistry
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Many of the current environmental problems result from the exploitative use of fossil chemicals and materials. Plant-based, and thus renewable, natural polymers represent valuable alternatives for the production of energy, platform chemicals and materials. Lignin, as abundant part of lignocellulosic biomass, offers a broad variety of features that in principal makes it a very valueable starting material; its complex structure and infamous heterogeneity, however, often present major challenges.

Nevertheless, recent years have seen noteworthy improvements in all sectors of the value chain leading to economically viable lignin uses. The upgrading of lignins into new materials and also chemicals has recently gained momentum. Promising applications for novel materials such as nano- and microscaled lignins and specialty chemicals are emerging.

We invite everyone concerned with the isolation, characterisation and upgrading of lignin into chemcials and materials to share their latest developments. Rather than arriving at a Special Issue that reads like a mere continuation of mainstream works, we would like to use the opportunities offered by an open access journal to identify novel, highly synergistic routes, fundamentally new approaches and out-of-the-box applications to existing refining and chemical production processes and materials development. We also encourage studies related to the safety of lignin-based (nano)materials in situ, such as to also promote the use of lignins in biomedical fields.


Prof. Claudia Crestini
Dr. Heiko Lange
Guest Editors

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Keywords

  • biorefinery
  • lignin
  • structural characterisation
  • fractionation
  • valorisation
  • nanomaterials
  • performance polymers

Published Papers (9 papers)

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Research

Article
Lignosulfonate Microcapsules for Delivery and Controlled Release of Thymol and Derivatives
Molecules 2020, 25(4), 866; https://doi.org/10.3390/molecules25040866 - 16 Feb 2020
Cited by 16 | Viewed by 2308
Abstract
Thymol and the corresponding brominated derivatives constitute important biological active molecules as antibacterial, antioxidant, antifungal, and antiparasitic agents. However, their application is often limited, because their pronounced fragrance, their poor solubility in water, and their high volatility. The encapsulation of different thymol derivatives [...] Read more.
Thymol and the corresponding brominated derivatives constitute important biological active molecules as antibacterial, antioxidant, antifungal, and antiparasitic agents. However, their application is often limited, because their pronounced fragrance, their poor solubility in water, and their high volatility. The encapsulation of different thymol derivatives into biocompatible lignin-microcapsules is presented as a synergy-delivering remedy. The adoption of lignosulfonate as an encapsulating material possessing relevant antioxidant activity, as well as general biocompatibility allows for the development of new materials that are suitable for the application in various fields, especially cosmesis. To this purpose, lignin microcapsules containing thymol, 4-bromothymol, 2,4-dibromothymol, and the corresponding O-methylated derivatives have been efficiently prepared through a sustainable ultrasonication procedure. Actives could be efficiently encapsulated with efficiencies of up to 50%. To evaluate the applicability of such systems for topical purposes, controlled release experiments have been performed in acetate buffer at pH 5.4, to simulate skin pH: all of the capsules show a slow release of actives, which is strongly determined by their inherent lipophilicity. Full article
(This article belongs to the Special Issue Lignin—Chemistry and Materials: Past, Present and Future)
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Article
Characterization of Eucalyptus nitens Lignins Obtained by Biorefinery Methods Based on Ionic Liquids
Molecules 2020, 25(2), 425; https://doi.org/10.3390/molecules25020425 - 20 Jan 2020
Cited by 8 | Viewed by 1801
Abstract
Eucalyptus nitens wood samples were subjected to consecutive stages of hydrothermal processing for hemicellulose solubilization and delignification with an ionic liquid, i.e., either 1-butyl-3-methylimidazolium hydrogen sulfate or triethylammonium hydrogen sulfate. Delignification experiments were carried out a 170 °C for 10–50 min. The solid [...] Read more.
Eucalyptus nitens wood samples were subjected to consecutive stages of hydrothermal processing for hemicellulose solubilization and delignification with an ionic liquid, i.e., either 1-butyl-3-methylimidazolium hydrogen sulfate or triethylammonium hydrogen sulfate. Delignification experiments were carried out a 170 °C for 10–50 min. The solid phases from treatments, i.e., cellulose-enriched solids, were recovered by centrifugation, and lignin was separated from the ionic liquid by water precipitation. The best delignification conditions were identified on the basis of the results determined for delignification percentage, lignin recovery yield, and cellulose recovery in solid phase. The lignins obtained under selected conditions were characterized in deep by 31P-NMR, 13C-NMR, HSQC, and gel permeation chromatography. The major structural features of the lignins were discussed in comparison with the results determined for a model Ionosolv lignin. Full article
(This article belongs to the Special Issue Lignin—Chemistry and Materials: Past, Present and Future)
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Article
Valorization of Lignin as an Immobilizing Agent for Bioinoculant Production using Azospirillum brasilense as a Model Bacteria
Molecules 2019, 24(24), 4613; https://doi.org/10.3390/molecules24244613 - 17 Dec 2019
Cited by 2 | Viewed by 1048
Abstract
Plant growth-promoting bacteria (PGPB) have been largely considered as beneficial in harsh and limiting environments given their effects on alleviating plant stress. For practical applications, most of the PGPB are prepared in immobilization matrices to improve the stability and benefits of bacteria. Despite [...] Read more.
Plant growth-promoting bacteria (PGPB) have been largely considered as beneficial in harsh and limiting environments given their effects on alleviating plant stress. For practical applications, most of the PGPB are prepared in immobilization matrices to improve the stability and benefits of bacteria. Despite the long list of immobilizing agents/carriers tested to date, a long list of desired requirements is yet to be achieved. Here, lignin stands as a scarcely tested immobilizer for bioinoculants with great potential for this purpose. The aim of this work was to demonstrate the feasibility of lignin as a carrier of the nitrogen-fixing Azospirillum brasilense. These bacteria were cultured in liquid media with recovered organosolv lignin added for bacterial immobilization. Then, lignin was recovered and the immobilized biomass was quantified gravimetrically by DNA extraction and serial dilution plating. Fluorescent microscopy as well as Congo red agar plating showed the immobilization of the bacterial cells in the lignin matrix and crystal violet dyeing showed the biofilms formation in lignin particles. A high number of cells were counted per gram of dried lignin. Lignin can be readily used as low-cost, health-safe bioinoculant carrier to be used in soil and agricultural applications. Full article
(This article belongs to the Special Issue Lignin—Chemistry and Materials: Past, Present and Future)
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Article
Lignin-Only Polymeric Materials Based on Unmethylated Unfractionated Kraft and Ball-Milled Lignins Surpass Polyethylene and Polystyrene in Tensile Strength
Molecules 2019, 24(24), 4611; https://doi.org/10.3390/molecules24244611 - 17 Dec 2019
Cited by 2 | Viewed by 1169
Abstract
Functional polymeric materials composed solely of lignin preparations appeared only very recently. A gradual paradigm shift spanning 56 years has revealed how lignin–lignin blends can upgrade the performance of 100 wt% lignin-based plastics. The view, first espoused in 1960, that lignin macromolecules are [...] Read more.
Functional polymeric materials composed solely of lignin preparations appeared only very recently. A gradual paradigm shift spanning 56 years has revealed how lignin–lignin blends can upgrade the performance of 100 wt% lignin-based plastics. The view, first espoused in 1960, that lignin macromolecules are crosslinked reduces the plausibility of creating functional polymeric materials that are composed only of lignin preparations. Lignin-based materials would be much weaker mechanically if interstices remain in significant numbers between adjoining macromolecular structures that consist of rigid crosslinked chains. In 1982, random-coil features in the hydrodynamic character of kraft lignin (KL) components were evident from ultracentrifugal sedimentation equilibrium studies of their SEC behavior. In 1997, it was recognized that the macromolecular species in plastics with 85 wt% levels of KL are associated complexes rather than individual components. Finally, in 2016, the first polymeric material composed entirely of ball-milled softwood lignin (BML) was found to support a tensile strength above polyethylene. Except in its molecular weight, the BML was similar in structure to the native biopolymer. It was composed of associated lignin complexes, each with aromatic rings arranged in two domains. The inner domain maintains structural integrity largely through noncovalent interactions between cofacially-offset aromatic rings; the peripheral domain contains a higher proportion of edge-on aromatic-ring arrangements. Interdigitation between peripheral domains in adjoining complexes creates material continuity during casting. By interacting at low concentrations with the peripheral domains, non-lignin blend components can improve the tensile strengths of BML-based plastics to values well beyond those seen in polystyrene. The KL-based plastics are weaker because the peripheral domains of adjoining complexes are less capable of interdigitation than those of BML. Blending with 5 wt% 1,8-dinitroanthraquinone results in a tensile strength above that of polyethylene. Analogous effects can be achieved with 10 wt% maple γ-valerolactone (GVL) lignin which, with a structure close to the native biopolymer, imparts some native character to the peripheral domains of the KL complexes. Comparable enhancements in the behavior of BML complexes upon blending with 10 wt% ball-milled corn-stover lignin (BMCSL) result in lignin-only polymeric materials with tensile strengths well beyond polystyrene. Full article
(This article belongs to the Special Issue Lignin—Chemistry and Materials: Past, Present and Future)
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Article
PpNAC187 Enhances Lignin Synthesis in ‘Whangkeumbae’ Pear (Pyrus pyrifolia) ‘Hard-End’ Fruit
Molecules 2019, 24(23), 4338; https://doi.org/10.3390/molecules24234338 - 27 Nov 2019
Cited by 10 | Viewed by 1357
Abstract
A disorder in pears that is known as ‘hard-end’ fruit affects the appearance, edible quality, and market value of pear fruit. RNA-Seq was carried out on the calyx end of ‘Whangkeumbae’ pear fruit with and without the hard-end symptom to explore the mechanism [...] Read more.
A disorder in pears that is known as ‘hard-end’ fruit affects the appearance, edible quality, and market value of pear fruit. RNA-Seq was carried out on the calyx end of ‘Whangkeumbae’ pear fruit with and without the hard-end symptom to explore the mechanism underlying the formation of hard-end. The results indicated that the genes in the phenylpropanoid pathway affecting lignification were up-regulated in hard-end fruit. An analysis of differentially expressed genes (DEGs) identified three NAC transcription factors, and RT-qPCR analysis of PpNAC138, PpNAC186, and PpNAC187 confirmed that PpNAC187 gene expression was correlated with the hard-end disorder in pear fruit. A transient increase in PpNAC187 was observed in the calyx end of ‘Whangkeumbae’ fruit when they began to exhibit hard-end symptom. Concomitantly, the higher level of PpCCR and PpCOMT transcripts was observed, which are the key genes in lignin biosynthesis. Notably, lignin content in the stem and leaf tissues of transgenic tobacco overexpressing PpNAC187 was significantly higher than in the control plants that were transformed with an empty vector. Furthermore, transgenic tobacco overexpressing PpNAC187 had a larger number of xylem vessel elements. The results of this study confirmed that PpNAC187 functions in inducing lignification in pear fruit during the development of the hard-end disorder. Full article
(This article belongs to the Special Issue Lignin—Chemistry and Materials: Past, Present and Future)
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Article
The Application of Ferric Chloride-Lignin Sulfonate as Shale Inhibitor in Water-Based Drilling Fluid
Molecules 2019, 24(23), 4331; https://doi.org/10.3390/molecules24234331 - 27 Nov 2019
Cited by 13 | Viewed by 1188
Abstract
A series of ferric chloride-lignin sulfonate (FCLS) was prepared from ferric chloride and lignin sulfonate to be used as shale inhibitor. The swelling rate of clay with FCLS-2 (w/w = 0.3%) decreased to 41.9%. Compared with control, FCLS-2 displayed high inhibitive ability [...] Read more.
A series of ferric chloride-lignin sulfonate (FCLS) was prepared from ferric chloride and lignin sulfonate to be used as shale inhibitor. The swelling rate of clay with FCLS-2 (w/w = 0.3%) decreased to 41.9%. Compared with control, FCLS-2 displayed high inhibitive ability against the hydrating and swelling processes of clay. Thus, the swelling degree of samples with FCLS-2 was much lower than that of the control, as well as the mud ball was more stable in FCLS-2 solution. Essentially, these excellent performances in inhibitor were assigned to the hydrogen bonding, electrostatic interaction and anchoring between FCLS-2 and other components. In addition, FCLS-2 has good compatibility with other common drilling fluid additives, and it can reduce the viscosity of systems, regardless of the room temperature or high temperature. Full article
(This article belongs to the Special Issue Lignin—Chemistry and Materials: Past, Present and Future)
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Article
Rice Husk Hydrolytic Lignin Transformation in Carbonization Process
Molecules 2019, 24(17), 3075; https://doi.org/10.3390/molecules24173075 - 24 Aug 2019
Cited by 4 | Viewed by 1373
Abstract
Lignin processing products have an extensive using range. Because products properties depend on lignin precursor quality it was interesting to study lignin isolated from rice husk being a large tonnage waste of rice production and its structural transformations during carbonization. Lignin isolated by [...] Read more.
Lignin processing products have an extensive using range. Because products properties depend on lignin precursor quality it was interesting to study lignin isolated from rice husk being a large tonnage waste of rice production and its structural transformations during carbonization. Lignin isolated by the thermal hydrolysis method with H2SO4 1 wt % solution and its carbonized products prepared under different carbonization conditions were characterized using elemental analysis, IR, TPD-MS, XRD, TEM, and EPR. It was shown lignin degradation takes place over the wide (220–520 °C) temperature range. Silica presenting in lignin affects the thermal destruction of this polymer. Due to the strong chemical bond with phenolic hydroxylic group it decreases an evaporation of volatile compounds and as a result increases the temperature range of the lignin degradation. Rice husk hydrolytic lignin transformations during carbonization occur with generation of free radicals. Their concentration is decreased after condensation of aromatic rings with carbon polycycles formation, i.e., the graphite-like structure. Quantity and X-ray diffraction characteristics of the graphite-like phase depend on carbonization conditions. Morphology of the lignin-based carbonized products is represented by carbon fibers, carbon and silica nanoparticles, and together with another structure characteristics provides prospective performance properties of lignin-based end products. Full article
(This article belongs to the Special Issue Lignin—Chemistry and Materials: Past, Present and Future)
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Article
Rheology of Polyacrylonitrile/Lignin Blends in Ionic Liquids under Melt Spinning Conditions
Molecules 2019, 24(14), 2650; https://doi.org/10.3390/molecules24142650 - 22 Jul 2019
Cited by 3 | Viewed by 1383
Abstract
Lignin, while economically and environmentally beneficial, has had limited success in use in reinforcing carbon fibers due to harmful chemicals used in biomass pretreatment along with the limited physical interactions between lignin and polyacrylonitrile (PAN) during the spinning process. The focus of this [...] Read more.
Lignin, while economically and environmentally beneficial, has had limited success in use in reinforcing carbon fibers due to harmful chemicals used in biomass pretreatment along with the limited physical interactions between lignin and polyacrylonitrile (PAN) during the spinning process. The focus of this study is to use lignin obtained from chemical-free oxidative biomass pretreatment (WEx) for blending with PAN at melt spinning conditions to produce carbon fiber precursors. In this study, the dynamic rheology of blending PAN with biorefinery lignin obtained from the WEx process is investigated with the addition of 1-butyl-3-methylimidazolium chloride as a plasticizer to address the current barriers of developing PAN/lignin carbon fiber precursors in the melt-spinning process. Lignin was esterified using butyric anhydride to reduce its hydrophilicity and to enhance its interactions with PAN. The studies indicate that butyration of the lignin (BL) increased non-Newtonian behavior and decreased thermo-reversibility of blends. The slope of the Han plot was found to be around 1.47 for PAN at 150 °C and decreased with increasing lignin concentrations as well as temperature. However, these blends were found to have higher elasticity and solution yield stress (47.6 Pa at 20%wt BL and 190 °C) when compared to pure PAN (5.8 Pa at 190 °C). The results from this study are significant for understanding lignin–PAN interactions during melt spinning for lower-cost carbon fibers. Full article
(This article belongs to the Special Issue Lignin—Chemistry and Materials: Past, Present and Future)
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Article
Overexpression of Pear (Pyrus pyrifolia) CAD2 in Tomato Affects Lignin Content
Molecules 2019, 24(14), 2595; https://doi.org/10.3390/molecules24142595 - 17 Jul 2019
Cited by 12 | Viewed by 1556
Abstract
PpCAD2 was originally isolated from the ‘Wangkumbae’ pear (Pyrus pyrifolia Nakai), and it encodes for cinnamyl alcohol dehydrogenase (CAD), which is a key enzyme in the lignin biosynthesis pathway. In order to verify the function of PpCAD2, transgenic tomato (Solanum [...] Read more.
PpCAD2 was originally isolated from the ‘Wangkumbae’ pear (Pyrus pyrifolia Nakai), and it encodes for cinnamyl alcohol dehydrogenase (CAD), which is a key enzyme in the lignin biosynthesis pathway. In order to verify the function of PpCAD2, transgenic tomato (Solanum lycopersicum) ‘Micro-Tom’ plants were generated using over-expression constructs via the agrobacterium-mediated transformation method. The results showed that the PpCAD2 over-expression transgenic tomato plant had a strong growth vigor. Furthermore, these PpCAD2 over-expression transgenic tomato plants contained a higher lignin content and CAD enzymatic activity in the stem, leaf and fruit pericarp tissues, and formed a greater number of vessel elements in the stem and leaf vein, compared to wild type tomato plants. This study clearly indicated that overexpressing PpCAD2 increased the lignin deposition of transgenic tomato plants, and thus validated the function of PpCAD2 in lignin biosynthesis. Full article
(This article belongs to the Special Issue Lignin—Chemistry and Materials: Past, Present and Future)
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