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Lignin: The Hidden Forest Product
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Lignin: The Hidden Forest Product

A special issue of Forests (ISSN 1999-4907). This special issue belongs to the section "Wood Science and Forest Products".

Deadline for manuscript submissions: closed (1 August 2023) | Viewed by 7377

Special Issue Editors

Dr. Biljana Bujanovic

E-Mail Website1 Website2
Guest Editor
USDA-FS-Forest Products Laboratory, Madison, WI, USA
Interests: chemical composition of wood; lignin; delignification; biorefineries; lignin valorization
Special Issues, Collections and Topics in MDPI journals
Dr. Ericka Redmond

E-Mail Website
Guest Editor
SUNY College of Environmental Science and Forestry, Syracuse, NY, USA
Interests: paper packaging; fiber and paper properties; pulping; bleaching; management; biorefinery; lignin valorization

Special Issue Information

Dear Colleagues,

Lignin is the most abundant aromatic polymer on Earth, representing a significant carbon sink with reserves of ~300 billion tonnes, which is much greater than its annual global extraction from biomass, which is estimated at ~70 million tonnes. Additionally, due to its intrinsically complex structure, species- and process-dependent variability, and high energy of consumption, most extracted lignin has historically been used for heat and power—without recovery from pulping liquors. Hence, the world’s commercial production of technical lignin is only ~1.65 million tonnes annually. Due to the urgent need to move away from petroleum dependence towards renewable biomass-based resources, our interest in developing a forest-based circular bioeconomy has prioritized efforts in removing barriers to realize broader production and utilization of lignin.

This Special Issue aims to advance lignin’s potential for high-value applications. Studies of interest include recovery and fractionation, which provide a lignin feedstock more amenable for use and further conversion; chemical, catalytic, and biological conversion methods and modifications; and the use of lignin as an alternative to current fossil-based chemicals and materials. In addition, studies on the characterization of lignin in situ and throughout processing, specifically in regard to its chemical structure and inherent abilities, including UV absorptivity and radical quenching, as well as thermal, antimicrobial, and flame retardant properties, are critical for advancing the knowledge and use of lignin. We invite the submission of recent research findings and comprehensive reviews of previously published reports in these areas. We hope that this Special Issue will gain wide interest and promote lignin valorization with the aim of transitioning towards a more sustainable world.

Dr. Biljana Bujanovic
Dr. Ericka Redmond
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Forests is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • lignin
  • isolation/recovery
  • fractionation
  • structure
  • properties
  • valorization
  • nanoparticles
  • thermoplastics
  • resins
  • foams
  • hydrogels
  • activated carbon
  • carbon fibers
  • chemical/catalytic/biological conversion

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Published Papers (4 papers)

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Research

19 pages, 5110 KiB  
Article
Lignin Use in Enhancing the Properties of Willow Pellets
by Autumn Elniski, Prajakta Dongre and Biljana M. Bujanovic
Forests 2023, 14(10), 2041; https://doi.org/10.3390/f14102041 - 12 Oct 2023
Cited by 3 | Viewed by 1304
Abstract
Shrub willow (Salix spp.) is an emerging lignocellulosic biomass utilized in fuel pellets as an energy source. However, improvements are needed to increase the efficacy of pellets in areas such as the energy content, durability, and hazardous carbon monoxide emissions. This study [...] Read more.
Shrub willow (Salix spp.) is an emerging lignocellulosic biomass utilized in fuel pellets as an energy source. However, improvements are needed to increase the efficacy of pellets in areas such as the energy content, durability, and hazardous carbon monoxide emissions. This study examined the effect of utilizing lignin as an additive on willow pellet properties. Two types of lignin were used in individual treatments: lignin recovered from the hot water extraction of willow (RecL) and commercial softwood kraft lignin (ComL). A statistical analysis of the ash content, energy content, bulk density, durability, pellet length, moisture absorption, and carbon monoxide emissions for the pellets with and without the addition of RecL or ComL lignin was conducted. The observed significant reduction in carbon monoxide emissions from RecL pellets was an important effect of the lignin addition. There were also significant increases in the energy content, bulk density, and durability of lignin-added pellets. While the production of carbon monoxide via pellets continues to be explored, lignin can be utilized as an additive to reduce carbon monoxide emissions and simultaneously improve other pellet properties. Full article
(This article belongs to the Special Issue Lignin: The Hidden Forest Product)
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15 pages, 6164 KiB  
Article
Characterization and Comparison of Some Kraft Lignins Isolated from Different Sources
by Çağrı Olgun and Saim Ateş
Forests 2023, 14(5), 882; https://doi.org/10.3390/f14050882 - 25 Apr 2023
Cited by 7 | Viewed by 2074
Abstract
Lignin characteristics are significantly affected by kraft processing and isolation conditions. In the studies carried out in this context, commercial lignins or isolated lignins from industrial black solutions are generally preferred. In this study, in order to conduct more comprehensive research, three lignin [...] Read more.
Lignin characteristics are significantly affected by kraft processing and isolation conditions. In the studies carried out in this context, commercial lignins or isolated lignins from industrial black solutions are generally preferred. In this study, in order to conduct more comprehensive research, three lignin samples were isolated from kraft black liquor obtained from laboratory cooking trials of pine, poplar, and wheat straw chips, representing softwoods, hardwoods, and annual plants, respectively, according to efficient pulping studies. In addition, another lignin-containing industrial waste was provided from a pulp mill (OBL). The acidification method was applied for isolating lignin from black liquor samples. After isolating the lignin samples from different sources, they were characterized and compared with the commercially available kraft lignin sample (Indulin AT). Total phenolic groups, carboxyl groups, purity, functional groups, nitrobenzene oxidation products, molecular weight, thermal stability, and element contents were analyzed. The isolated lignin samples (except wheat straw) were as pure as commercial lignin. Since the wheat straw was agricultural waste and an annual plant, inorganic elements such as P, K, and Si were more abundant than in the other samples. However, the polydispersity and molecular weight of all of the isolated lignin samples were higher than those of commercial lignin. Because the ash contents of the lignin samples for pine, poplar, OBL, and indulin AT were between 1 and 3%, they can be used for high-value applications. In particular, despite some disadvantages, wheat straw lignin has greater potential for use in extruders than softwood lignins due to their syringyl content. Full article
(This article belongs to the Special Issue Lignin: The Hidden Forest Product)
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10 pages, 2588 KiB  
Article
Structural Characterization of Acid DES-Modified Alkaline Lignin and Evaluation of Antioxidant Properties
by Penghui Li, Yuan Lu, Guifang Long, Sixian Li, Kongyan Li, Bo Jiang and Wenjuan Wu
Forests 2023, 14(3), 550; https://doi.org/10.3390/f14030550 - 10 Mar 2023
Cited by 3 | Viewed by 2053
Abstract
Lignin is an abundant and environmentally friendly biopolymer that contains a large number of phenolic hydroxyl functional group. In this paper, alkaline lignin was modified using different acidic DES (choline chloride/p-toluenesulfonic acid and choline chloride/lactic acid) at 130 ℃ (TC-lignin and [...] Read more.
Lignin is an abundant and environmentally friendly biopolymer that contains a large number of phenolic hydroxyl functional group. In this paper, alkaline lignin was modified using different acidic DES (choline chloride/p-toluenesulfonic acid and choline chloride/lactic acid) at 130 ℃ (TC-lignin and LC-lignin) and the conformational relationship between the modified products and the antioxidant activity was investigated. Lignin was characterized by 31P NMR, gel permeation chromatography (GPC) and Fourier transform infrared spectroscopy (FT-IR), and its antioxidant activity was evaluated. The results showed that the alkaline lignin products modified by acidic DES formed relatively homogenous dispersions and were characterized by a relatively low molecular weight and a high content of phenolic hydroxyl groups (e.g., TC-lignin, aliphatic-OH: 3.52 mmol/g, G-OH: 4.18 mmol/g, Mw: 3726, Mn: 2053, PDI: 1.81). The antioxidant activity (free radical scavenging rate, 90.35%) of TC-lignin was somewhat higher than that of LC-lignin (free radical scavenging rate, 89.12%) and both were higher than that of the commercially available antioxidant BHT (free radical scavenging rate, 88.79%). More specifically, we discussed the possible mechanisms of antioxidant reactions of lignin model substances in DPPH solutions. In addition, LC-lignin has an excellent UV-blocking capacity due to the specific phenolic hydroxyl and phenyl propane structure. A simple method is proposed for the modification of industrial lignin to make it suitable for use as an antioxidant and UV-resistant product. Full article
(This article belongs to the Special Issue Lignin: The Hidden Forest Product)
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9 pages, 1858 KiB  
Article
Analytical Pyrolysis as a Tool to Assess Residual Lignin Content and Structure in Maritime Pine High-Yield Pulp
by Ana Alves, José Graça and José Rodrigues
Forests 2022, 13(12), 2169; https://doi.org/10.3390/f13122169 - 17 Dec 2022
Viewed by 1369
Abstract
The residual lignin content of unbleached maritime pine (Pinus pinaster Aiton) Kraft pulps was assessed by analytical pyrolysis (Py-lignin) and the results were compared to the Klason lignin content and kappa number. Thirty samples, each from an individual tree, were delignified under [...] Read more.
The residual lignin content of unbleached maritime pine (Pinus pinaster Aiton) Kraft pulps was assessed by analytical pyrolysis (Py-lignin) and the results were compared to the Klason lignin content and kappa number. Thirty samples, each from an individual tree, were delignified under identical conditions. The residual lignin content of the pulps varied widely as assessed by Py-lignin (5.9%–9.2%), Klason (8.2–15.1), and kappa number (59–112). Despite a systematic difference between Py-lignin and Klason, they were strongly correlated (R2 = 0.90). The H/G ratio of the residual pulp lignin ranged from 0.145 to 0.195, with a mean of 0.165, which is more than two times the average H/G ratio of Maritime pine wood lignin (0.064). The results show that Kraft pulping, which selectively degrades lignin with more labile inter-unit links, changed the pattern of pyrolysis products of pulp lignin considerably and, consequently, its structure. This pattern shows an enrichment in H-lignin-derived products, namely phenol, p-cresol, and m-cresol, and in some G-lignin-derived products such as guaiacol and 4-mthylguaiacol, and a decrease in coniferylaldehyde, homovanillin, and eugenol. Principal component analysis (PCA) of the G- and H-lignin-derived pyrolysis products shows that pulps are distributed along PC 1 based on their residual lignin content. The loadings plot shows that this separation is mainly due to a small number of G-lignin products, including 4-methyl guaiacol, 4-vinyl guaiacol, isoeugenol (trans), and guaiacol, which are more abundant in pulps with higher residual lignin content. The obtained results show that analytical pyrolysis is an appropriate method for quantifying the residual lignin content and H/G ratio of unbleached Kraft pulps and provide information regarding how lignin is degraded during the pulping process. Full article
(This article belongs to the Special Issue Lignin: The Hidden Forest Product)
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