Special Issue "Properties, Applications and Perspectives of Lignin"

A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Biobased and Biodegradable Polymers".

Deadline for manuscript submissions: closed (15 November 2019).

Special Issue Editors

Dr. Enrico Sanjust
Website
Guest Editor
Dipartimento di Scienze Biomediche, Università di Cagliari, Cagliari, Italy
Interests: biomimetic catalysis; applied enzymology; fungal phenol oxidases
Dr. Paolo Zucca

Guest Editor
Dipartimento di Scienze Biomediche, Università di Cagliari, Cagliari, Italy
Interests: catalytic degradation of organic pollutants; biochemical characterization of plant extracts

Special Issue Information

Dear Colleagues,

Lignin is among the most abundant organic substances, and is produced by vascular plants. It is an irregular aliphatic–aromatic heteropolymer based on C6C3 monomeric units. Arising from radical chain reactions, its hydrolysis to afford such monomeric units is quite a difficult task, whereas its highly cross-linked nature makes it almost insoluble in the common solvents, unless it is more or less deeply altered in its native structure.

Therefore, lignin biosynthesis deserves attention in order to elucidate the exact mechanism(s) by which plants build this robust structural polymer, and to intervene by means of genetic engineering tools to modulate its physico-chemical and mechanical properties. This could open the way towards tailor-made lignins (and consequently, woods) whose features could be pre-determined to optimize the required performances once the timber has to be utilized.

For the pulp and paper industry, lignin should be removed to leave cellulose fibers. However, the various processes that are currently available are still awaiting a full optimization, in terms of both efficiency and environmental impact: huge amounts of aggressive reagents are required, together with harsh and energy-consuming treatments, and produce enormous quantities of high-impact wastes.

Biological (mainly enzymatic) and biomimetic treatments are promising but far from showing a reasonable efficiency, so they require further deep studies to substantially move ahead.

This Special Issue welcomes experimental studies and reviews describing new insights and/or encompassing the state-of-the-art in the fields of lignin biosynthesis and its regulation/modulation, improvements of delignification treatments (both chemical and biological/biomimetic), and new frontiers in lignin utilization—possibly after suitable modification—as a biomaterial and/or as a promising source of derived chemicals.

Dr. Enrico Sanjust
Dr. Paolo Zucca
Guest Editors

Manuscript Submission Information

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Keywords

  • lignin biosynthesis
  • chemicals from lignin
  • heteropolymer
  • lignin-based materials

Published Papers (12 papers)

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Research

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Open AccessArticle
High Purity and Low Molecular Weight Lignin Nano-Particles Extracted from Acid-Assisted MIBK Pretreatment
Polymers 2020, 12(2), 378; https://doi.org/10.3390/polym12020378 - 08 Feb 2020
Cited by 1
Abstract
A simple and economical biorefinery method, organosolv methyl isobutyl ketone (MIBK) pretreatment assisted by Lewis acid ferric trichloride hydrolysis, was proposed for fractionating the lignin from extractive-free Eucalyptus powder at the nanoscale, accompanied by another product furfural, derived from hemicellulose. Under the conditions [...] Read more.
A simple and economical biorefinery method, organosolv methyl isobutyl ketone (MIBK) pretreatment assisted by Lewis acid ferric trichloride hydrolysis, was proposed for fractionating the lignin from extractive-free Eucalyptus powder at the nanoscale, accompanied by another product furfural, derived from hemicellulose. Under the conditions (180 °C, 1 h) optimized based on the best yield of furfural, 40.13% of the acid-insoluble lignin (AIL) could be obtained with a high purity of 100%, a low molecular weight of 767 (Mn) and improved thermostability. The extracted lignin was characterized by its chemical structure, thermostability, homogeneity, molecular weight, and morphology as compared with milled wood lignin (MWL). The results showed significant variations in chemical structures of the extracted lignin during the pretreatment. Specifically, the aryl ether linkage and phenylcoumarans were broken severely while the resinols were more resistant. The G-type lignin was more sensitive to degradation than the S-type, and after the pretreatment, H-type lignin was formed, indicating the occurrence of a demethoxylation reaction at high temperature. Moreover, the lignin nano-particles were identified visually by AFM and TEM images. The dynamic light scattering (DLS) showed that the average diameter of the measured samples was 131.8 nm, with the polydispersity index (PDI) of 0.149. The MIBK-lignin nano-particles prepared in our laboratory exhibit high potentials in producing high functional and valuable materials for the application in wide fields. Full article
(This article belongs to the Special Issue Properties, Applications and Perspectives of Lignin)
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Open AccessArticle
Revealing Structural Modifications of Lignin in Acidic γ-Valerolactone-H2O Pretreatment
Polymers 2020, 12(1), 116; https://doi.org/10.3390/polym12010116 - 05 Jan 2020
Abstract
γ-valerolactone (GVL)/H2O/acid solvent mixtures has been used in chemical pretreatment of lignocellulosic biomass, it was claimed that GVL lignins were structurally close to proto (native) lignins, or having low molecular weight with narrow polydispersity, however, the structural changes of GVL lignins [...] Read more.
γ-valerolactone (GVL)/H2O/acid solvent mixtures has been used in chemical pretreatment of lignocellulosic biomass, it was claimed that GVL lignins were structurally close to proto (native) lignins, or having low molecular weight with narrow polydispersity, however, the structural changes of GVL lignins have not been investigated. In this study, β-O-4 (β-aryl ether, GG), β-5 (phenylcoumaran), and β-β (resinol) lignin model compounds were treated by an acidic GVL-H2O solvent system, a promising pretreatment of lignocellulose for biomass utilization, to investigate the structural changes possibly related to the lignin involved. NMR characterization of the products isolated from the treated GG indicated that a phenyl dihydrobenzofuran, having typical C-H correlations at δCH 50.74/4.50 and 93.49/4.60 ppm in its HSQC spectrum, was produced from GG. In the pretreatment, the released formaldehyde from GG reacted fast with GG to form a novel 1,3-dioxane intermediate whose characteristic HSQC signals were: δCH 94.15–94.48/4.81–5.18 ppm and 80.82–83.34/4.50–4.94 ppm. The β-5 model, dihydrodehydrodiconiferyl alcohol, was converted into phenylcoumarone and stilbene having benzaldehyde that resulted from the allyl alcohol side chain. The β-β model, syringaresinol, was isomerized to form a mixture of syringaresinol, epi-, and dia-syringaresinol although being degraded slightly. Full article
(This article belongs to the Special Issue Properties, Applications and Perspectives of Lignin)
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Open AccessArticle
Structural Characterization and Antioxidant Activity of Milled Wood Lignin from Xylose Residue and Corncob
Polymers 2019, 11(12), 2092; https://doi.org/10.3390/polym11122092 - 13 Dec 2019
Cited by 2
Abstract
Xylose residue (XR), after diluted acid treatment of corncob, consists of cellulose and lignin. However, structural changes of XR lignin have not been investigated comprehensively, and this has seriously hindered the efficient utilization of lignin. In this study, corncob milled wood lignin (CC [...] Read more.
Xylose residue (XR), after diluted acid treatment of corncob, consists of cellulose and lignin. However, structural changes of XR lignin have not been investigated comprehensively, and this has seriously hindered the efficient utilization of lignin. In this study, corncob milled wood lignin (CC MWL), and xylose residue milled wood lignin (XR MWL) were isolated according to the modified milled wood lignin (MWL) method. The structural features of two lignin fractions were thoroughly investigated via fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), thermogravimetric analysis (TGA) and two dimensional nuclear magnetic resonance (2D NMR) spectroscopy techniques. XR MWL with higher yield and lower bound carbohydrate contents presented more phenolic OH contents than CC MWL due to partial cleavage of β-O-4. Furthermore, the molecular weights of XR MWL were increased, possibly because of condensation of the lignin during the xylose production. A study on antioxidant activity showed that XR lignin had better radical scavenging ability than that of 2,6-Di-tert-butyl-4-methyl-phenol (BHT) and CC MWL. The results suggested that the lignin in xylose residue, showing great antioxidant properties, has potential applications in food additives. Full article
(This article belongs to the Special Issue Properties, Applications and Perspectives of Lignin)
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Open AccessArticle
Effect of Lignin Plasticization on Physico-Mechanical Properties of Lignin/Poly(Lactic Acid) Composites
Polymers 2019, 11(12), 2089; https://doi.org/10.3390/polym11122089 - 13 Dec 2019
Cited by 2
Abstract
Kraft lignin (KL) or plasticized KL (PKL)/poly(lactic acid) (PLA) composites, containing different lignin contents and with and without the coupling agent, were prepared in this study using twin-screw extrusion at 180 °C. Furthermore, ε-caprolactone and polymeric diphenylmethane diisocyanate (pMDI) were used as a [...] Read more.
Kraft lignin (KL) or plasticized KL (PKL)/poly(lactic acid) (PLA) composites, containing different lignin contents and with and without the coupling agent, were prepared in this study using twin-screw extrusion at 180 °C. Furthermore, ε-caprolactone and polymeric diphenylmethane diisocyanate (pMDI) were used as a plasticizer of KL and a coupling agent to improve interfacial adhesion, respectively. It was found that lignin plasticization improved lignin dispersibility in the PLA matrix and increased the melt flow index due to decrease in melt viscosity. The tensile strength of KL or PKL/PLA composites was found to decrease as the content of KL and PKL increased in the absence of pMDI, and increased due to pMDI addition. The existence of KL and PKL in the composites decreased the thermal degradation rate against the temperature and increased char residue. Furthermore, the diffusion coefficient of water in the composites was also found to decrease due to KL or PKL addition. Full article
(This article belongs to the Special Issue Properties, Applications and Perspectives of Lignin)
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Open AccessArticle
The Use of Lignin as a Microbial Carrier in the Co-Digestion of Cheese and Wafer Waste
Polymers 2019, 11(12), 2073; https://doi.org/10.3390/polym11122073 - 12 Dec 2019
Cited by 3
Abstract
The aim of the article was to present the effects of lignin grafted with polyvinylpyrrolidone (PVP) as a microbial carrier in anaerobic co-digestion (AcoD) of cheese (CE) and wafer waste (WF). Individual samples of waste cheese and wafers were also tested. The PVP [...] Read more.
The aim of the article was to present the effects of lignin grafted with polyvinylpyrrolidone (PVP) as a microbial carrier in anaerobic co-digestion (AcoD) of cheese (CE) and wafer waste (WF). Individual samples of waste cheese and wafers were also tested. The PVP modifier was used to improve the adhesive properties of the carrier surface. Lignin is a natural biopolymer which exhibits all the properties of a good carrier, including nontoxicity, biocompatibility, porosity, and thermal stability. Moreover, the analysis of the zeta potential of lignin and lignin combined with PVP showed their high electrokinetic stability within a wide pH range, that is, 4–11. The AcoD process was conducted under mesophilic conditions in a laboratory by means of anaerobic batch reactors. Monitoring with two standard parameters: pH and the VFA/TA ratio (volatile fatty acids-to-total alkalinity ratio) proved that the process was stable in all the samples tested. The high share of N–NH4+ in TKN (total Kjeldahl nitrogen), which exceeded 90% for WF+CE and CE at the last phases of the process, proved the effective conversion of nitrogen forms. The microbiological analyses showed that eubacteria proliferated intensively and the dehydrogenase activity increased in the samples containing the carrier, especially in the system with two co-substrates (WF+CE/lignin) and in the waste cheese sample (CE/lignin). The biogas production increased from 1102.00 m3 Mg−1 VS (volatile solids) to 1257.38 m3 Mg−1 VS in the WF+CE/lignin sample, and from 881.26 m3 Mg−1 VS to 989.65 m3 Mg−1 VS in the CE/lignin sample. The research results showed that the cell immobilization on lignin had very positive effect on the anaerobic digestion process. Full article
(This article belongs to the Special Issue Properties, Applications and Perspectives of Lignin)
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Open AccessArticle
Efficient Mild Organosolv Lignin Extraction in a Flow-Through Setup Yielding Lignin with High β-O-4 Content
Polymers 2019, 11(12), 1913; https://doi.org/10.3390/polym11121913 - 20 Nov 2019
Cited by 3
Abstract
Current lignin fractionation methods use harsh conditions that alter the native lignin structure, resulting in a recalcitrant material which is undesired for downstream processing. Milder fractionation processes allow for the isolation of lignins that are high in β-aryl ether (β-O-4) content, however, at [...] Read more.
Current lignin fractionation methods use harsh conditions that alter the native lignin structure, resulting in a recalcitrant material which is undesired for downstream processing. Milder fractionation processes allow for the isolation of lignins that are high in β-aryl ether (β-O-4) content, however, at reduced extraction efficiency. The development of improved lignin extraction methods using mild conditions is therefore desired. For this reason, a flow-through setup for mild ethanosolv extraction (120 °C) was developed. The influence of acid concentration, ethanol/water ratio, and the use of other linear alcohol co-solvents on the delignification efficiency and the β-O-4 content were evaluated. With walnut shells as model feedstock, extraction efficiencies of over 55% were achieved, yielding lignin with a good structural quality in terms of β-O-4 linking motifs (typically over 60 per 100 aromatic units). For example, lignin containing 66 β-O-4 linking motifs was obtained with an 80:20 n-propanol/water ratio, 0.18 M H2SO4 with overall a good extraction efficiency of 57% after 5 h. The majority of the lignin was extracted in the first 2 hours and this lignin showed the best structural quality. Compared to batch extractions, both higher lignin extraction efficiency and higher β-O-4 content were obtained using the flow setup. Full article
(This article belongs to the Special Issue Properties, Applications and Perspectives of Lignin)
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Open AccessArticle
Laboratory Investigation of Lignocellulosic Biomass as Performance Improver for Bituminous Materials
Polymers 2019, 11(8), 1253; https://doi.org/10.3390/polym11081253 - 29 Jul 2019
Cited by 1
Abstract
Lignocellulosic biomass has gained increasing attention as a performance modifier for bituminous material due to the vast amount available, its low cost and its potential to improve the durability of pavement. However, a comprehensive study concerning both the binder and mixture performance of [...] Read more.
Lignocellulosic biomass has gained increasing attention as a performance modifier for bituminous material due to the vast amount available, its low cost and its potential to improve the durability of pavement. However, a comprehensive study concerning both the binder and mixture performance of modified bituminous material with lignocellulose is still limited. This research aims to evaluate the feasibility of applying lignocellulose as bitumen modifier by rheological, chemical and mechanical tests. To this end, two lignocellulosic biomass modified bituminous binders and corresponding mixtures were prepared and tested. The chemical characterization revealed the interaction between lignocellulosic biomass and bitumen fractions. Rheological test results have shown that lignocellulosic modifiers improve the overall performance of bituminous binder at high, intermediate and low temperatures. The findings obtained by mixture mechanical tests were identical to the binder test results, proving the positive effect of lignocellulosic biomass on overall paving performance of bituminous materials. Although lignocellulosic modifier slightly deteriorates the bitumen workability, the modified bitumen still meets the viscosity requirements mentioned in Superpave specification. This paper suggests that lignocellulosic biomass is a promising modifier for bituminous materials with both engineering and economic merits. Future study will focus on field validation and life cycle assessment of bituminous pavement with lignocellulosic biomass. Full article
(This article belongs to the Special Issue Properties, Applications and Perspectives of Lignin)
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Open AccessArticle
Efficient Conversion of Lignin Waste to High Value Bio-Graphene Oxide Nanomaterials
Polymers 2019, 11(4), 623; https://doi.org/10.3390/polym11040623 - 04 Apr 2019
Cited by 2
Abstract
Lignin graphene oxide was oxidized after Kraft lignin was graphitized by thermal catalytic conversion. The reduced lignin graphene oxide was derived from lignin graphene oxide through thermal reduction treatment. These Kraft lignin, lignin graphite, lignin graphene oxide, and reduced lignin graphene oxide were [...] Read more.
Lignin graphene oxide was oxidized after Kraft lignin was graphitized by thermal catalytic conversion. The reduced lignin graphene oxide was derived from lignin graphene oxide through thermal reduction treatment. These Kraft lignin, lignin graphite, lignin graphene oxide, and reduced lignin graphene oxide were characterized by scanning electron microscopy, raman microscopy, high-resolution transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, atomic force microscopy and thermogravimetric analysis. The results showed lignin graphite converted from Kraft lignin had fewer layers with smaller lateral size than natural graphite. Moreover, lignin graphene oxide was successfully produced from lignin graphite by an oxidation reaction with an hour-long reaction time, which has remarkably shorter reaction time than that of graphene oxide made from natural graphite. Meanwhile, this lignin-derived graphene oxide had the same XRD, FTIR and Raman peaks as graphene oxide oxidized from natural graphite. The SEM, TEM, and AFM images showed that this lignin graphene oxide with 1–3 average layers has a smaller lateral size than that of graphene oxide made from natural graphite. Moreover, the lignin graphene oxide can be reduced to reduced lignin graphene oxide to fabricate graphene-based aerogel, wire, and film for some potential applications. Full article
(This article belongs to the Special Issue Properties, Applications and Perspectives of Lignin)
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Open AccessArticle
Oxidative Depolymerization of Cellulolytic Enzyme Lignin over Silicotungvanadium Polyoxometalates
Polymers 2019, 11(3), 564; https://doi.org/10.3390/polym11030564 - 26 Mar 2019
Cited by 2
Abstract
The aim of this study was to explore the catalytic performance of the oxidative depolymerization of enzymatic hydrolysis lignin from cellulosic ethanol fermentation residue by different vanadium substituted Keggin-type polyoxometalates (K5[SiVW11O40], K6[SiV2W10 [...] Read more.
The aim of this study was to explore the catalytic performance of the oxidative depolymerization of enzymatic hydrolysis lignin from cellulosic ethanol fermentation residue by different vanadium substituted Keggin-type polyoxometalates (K5[SiVW11O40], K6[SiV2W10O40], and K6H[SiV3W9O40]). Depolymerized products were analyzed by gel permeation chromatography (GPC), gas chromatography–mass spectrometer (GC/MS), and two-dimensional heteronuclear single quantum coherence nuclear magnetic resonance (2D HSQC NMR) analysis. All catalysts showed an effective catalytic activity. The best result, concerning the lignin conversion and lignin oil production, was obtained by K6[SiV2W10O40], and the highest yield of oxidative depolymerization products of 53 wt % was achieved and the main products were monomer aromatic compounds. The HSQC demonstrated that the catalysts were very effective in breaking the β-O-4 structure, the dominant linkage in lignin, and the GPC analysis demonstrated that the molecular of lignin was declined significantly. These results demonstrate the vanadium substituted silicotungstic polyoxometalates were of highly active and stable catalysts for lignin conversion, and this strategy has the potential to be applicable for production of value-added chemicals from biorefinery lignin. Full article
(This article belongs to the Special Issue Properties, Applications and Perspectives of Lignin)
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Open AccessArticle
The Impact of Lignin Structural Diversity on Performance of Cellulose Nanofiber (CNF)-Starch Composite Films
Polymers 2019, 11(3), 538; https://doi.org/10.3390/polym11030538 - 21 Mar 2019
Cited by 5
Abstract
Lignin fractions having different molecular weights and varied chemical structures isolated from kraft lignins of both softwood and hardwood via a sequential solvent fractionation technique were incorporated into a tunicate cellulose nanofibers (CNF)—starch mixture to prepare 100% bio-based composite films. The aim was [...] Read more.
Lignin fractions having different molecular weights and varied chemical structures isolated from kraft lignins of both softwood and hardwood via a sequential solvent fractionation technique were incorporated into a tunicate cellulose nanofibers (CNF)—starch mixture to prepare 100% bio-based composite films. The aim was to investigate the impact of lignin structural diversity on film performance. It was confirmed that lignin’s distribution in the films was dependent on the polarity of solvents used for fractionation (acetone > methanol > ethanol > ethyl acetate) and influenced the optical properties of the films. The –OH group content and molecular weight of lignin were positively related to film density. In general, the addition of lignin fractions led to decrease in thermal stability and increase in Young’s modulus of the composite films. The modulus of the films was found to decrease as the molecular weight of lignin increased, and a higher amount of carboxyl and phenolic –OH groups in the lignin fraction resulted in films with higher stiffness. The thermal analysis showed higher char content formation for lignin-containing films in a nitrogen atmosphere with increased molecular weight. In an oxygen atmosphere, the phenol content, saturated side chains and short chain structures of lignin had impacts on the maximum decomposition temperature of the films, confirming the relationship between the chemical structure of lignin and thermo-oxidative stability of the corresponding film. This study addresses the importance of lignin diversities on composite film performance, which could be helpful for tailoring lignin’s applications in bio-based materials based on their specific characteristics. Full article
(This article belongs to the Special Issue Properties, Applications and Perspectives of Lignin)
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Review

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Open AccessReview
Lignin-Based Hydrogels: Synthesis and Applications
Polymers 2020, 12(1), 81; https://doi.org/10.3390/polym12010081 - 03 Jan 2020
Cited by 4
Abstract
Polymers obtained from biomass are an interesting alternative to petro-based polymers due to their low cost of production, biocompatibility, and biodegradability. This is the case of lignin, which is the second most abundant biopolymer in plants. As a consequence, the exploitation of lignin [...] Read more.
Polymers obtained from biomass are an interesting alternative to petro-based polymers due to their low cost of production, biocompatibility, and biodegradability. This is the case of lignin, which is the second most abundant biopolymer in plants. As a consequence, the exploitation of lignin for the production of new materials with improved properties is currently considered as one of the main challenging issues, especially for the paper industry. Regarding its chemical structure, lignin is a crosslinked polymer that contains many functional hydrophilic and active groups, such as hydroxyls, carbonyls and methoxyls, which provides a great potential to be employed in the synthesis of biodegradable hydrogels, materials that are recognized for their interesting applicability in biomedicine, soil and water treatment, and agriculture, among others. This work describes the main methods for the preparation of lignin-based hydrogels reported in the last years, based on the chemical and/or physical interaction with polymers widely used in hydrogels formulations. Furthermore, herein are also reviewed the current applications of lignin hydrogels as stimuli-responsive materials, flexible supercapacitors, and wearable electronics for biomedical and water remediation applications. Full article
(This article belongs to the Special Issue Properties, Applications and Perspectives of Lignin)
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Open AccessEditor’s ChoiceReview
Lignin-Based Polyurethanes: Opportunities for Bio-Based Foams, Elastomers, Coatings and Adhesives
Polymers 2019, 11(7), 1202; https://doi.org/10.3390/polym11071202 - 18 Jul 2019
Cited by 11
Abstract
Polyurethane chemistry can yield diverse sets of polymeric materials exhibiting a wide range of properties for various applications and market segments. Utilizing lignin as a polyol presents an opportunity to incorporate a currently underutilized renewable aromatic polymer into these products. In this work, [...] Read more.
Polyurethane chemistry can yield diverse sets of polymeric materials exhibiting a wide range of properties for various applications and market segments. Utilizing lignin as a polyol presents an opportunity to incorporate a currently underutilized renewable aromatic polymer into these products. In this work, we will review the current state of technology for utilizing lignin as a polyol replacement in different polyurethane products. This will include a discussion of lignin structure, diversity, and modification during chemical pulping and cellulosic biofuels processes, approaches for lignin extraction, recovery, fractionation, and modification/functionalization. We will discuss the potential of incorporation of lignins into polyurethane products that include rigid and flexible foams, adhesives, coatings, and elastomers. Finally, we will discuss challenges in incorporating lignin in polyurethane formulations, potential solutions and approaches that have been taken to resolve those issues. Full article
(This article belongs to the Special Issue Properties, Applications and Perspectives of Lignin)
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