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A topical collection in Polymers (ISSN 2073-4360). This collection belongs to the section "Biobased and Biodegradable Polymers".

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Prof. Dr. Naozumi Teramoto

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Collection Editor

Department of Applied Chemistry, Faculty of Engineering, Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan
Interests: biomaterial; bio-based polymer; bioplastics; biodegradable polymer; biopolymer; composite material comprising a polymer matrix
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Prof. Dr. Ning Yan

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Department of Chemical Engineering and Applied Chemistry, Faculty of Applied Science & Engineering, University of Toronto, Toronto, ON, Canada
Interests: biomass; biopolymer and bio-based materials and chemicals; natural and fiber composites and nanocomposites; cellulose, lignin and extractives; polymer modification and functionalization; polymer adhesives; resins and coatings; smart and functional sensors and devices
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Topical Collection Information

Dear Colleagues,

Lignin is one of main components of ligneous biomass and is mainly obtained from forestry resources. Lignin is biologically produced, mainly from three monomers, p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol; however, their polymerized structure is very complicated. The content of aliphatic hydroxyl groups, phenolic hydroxy groups, methoxy groups, and carbonyl groups depends on the source plant. The whole molecular structure of lignin in its original state has not been fully determined yet, since lignin is covalently bound to cell wall polysaccharides and is insoluble in solvents because of its network structure. Therefore, the structural model of lignin has been proposed via integration of partial structures determined from chemically degraded lignin.

More practically, industrial lignin (partially degraded lignin) is obtained from the pulping process in the pulp and paper industry as low utilization value ligneous waste, and is mainly used for recovering energy by burning. Therefore, high-value utilization of industrial lignin has become a very important issue; it is not only required by the paper industry but also required to develop applications of cellulose nanofibers. Recent progress in polymer sciences and technologies has prompted several newly proposed methods of lignin utilization in material applications: (1) lignin-based thermosets, (2) lignin-based thermoplastics, (3) lignin-based additives for plastics such as plasticizers and antioxidants, and (4) lignin-based functional materials such as foams, films, and composites. However, many issues must be resolved before industrial output is possible; for example, we sometimes do not expect reproducibility of research results, because the chemical properties of lignin significantly vary, not only with the diversity of plant species but also according to the methods used to obtain it. Indeed, there are many methods to prepare lignin sources if minor modification is included. Generally, four methods are employed industrially: (1) sulfite pulping, (2) kraft pulping, (3) soda pulping and (4) organosolv pulping. The chemical properties of lignin obtained from each process varied with the quantity of functional groups such as phenolic hydroxy groups, sulfonate groups, and thiol groups. The solubility of lignin in water or organic solvents is also influenced by the extraction method. Though there exist a lot of obstacles to material applications, lignin is an attractive chemical due to its abundance and versatility. Therefore, we can expect steady development of lignin-based materials in future research.

In this collection, studies on the synthesis, physical and chemical properties, and novel functionality of lignin-based polymeric materials are welcome. Studies on the extraction, modification, and characterization of natural lignin and its applications are also welcome.

Dr. Naozumi Teramoto
Prof. Dr. Ning Yan
Collection Editors

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Keywords

lignin extraction and conversion
lignin-based chemicals and materials
biosynthesis of lignin
chemical structure and characterization of lignin
applications of lignin

Published Papers (6 papers)

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2024

12 pages, 3452 KiB

Open AccessArticle

Morphological, Thermal, and Mechanical Assessment of Polypropylene and Ammonium Phosphate Composites Enhanced with Lignosulfonate and Zirconium

by Keiti Gilioli Tosin, Cesar Aguzzoli and Matheus Poletto

Polymers 2024, 16(19), 2727; https://doi.org/10.3390/polym16192727 - 26 Sep 2024

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Abstract

Polypropylene and ammonium phosphate (AP) composites were synthesized at a 25 wt% concentration. The changes in the morphological, thermal, and physical behavior of the composites were analyzed with the addition of lignosulfonate (LG) and zirconium phosphate (ZrP). Additionally, metallic zirconium was deposited onto lignosulfonate using the magnetron sputtering technique to develop polypropylene and zirconium-modified lignosulfonate (LGMod) composites. Thus, composites of PP/25AP, PP/25AP/8LG/5ZrP, and PP/25AP/8LGMod were synthesized. The synthesis involved mixing the materials in a Hake mixer, followed by compression molding. The composites were characterized by field emission scanning electron microscopy (SEM–EDS), a thermogravimetric analysis (TGA) with combustion parameters, a vertical burn test (UL-94), a thermal camera, and mechanical properties. All composites achieved a V2 rating according to UL-94 standards. The PP/25AP extinguishes flames more quickly compared to other materials, approximately 99.2% faster than PP and showed the lowest temperature variation and mass loss after burning. The PP/25AP/8LG/5ZrP composite exhibited a 7% higher rigidity and 84.5% better flame retardancy compared to pure PP. Additionally, substituting ZrP with LGMod led to a lower environmental impact and improved thermal properties, despite some mechanical disadvantages. Full article

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20 pages, 4641 KiB

Open AccessArticle

Carboxyalkylated Lignin as a Sustainable Dispersant for Coal Water Slurry

by Hussein Ahmad Qulatein, Weijue Gao and Pedram Fatehi

Polymers 2024, 16(18), 2586; https://doi.org/10.3390/polym16182586 - 13 Sep 2024

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Abstract

Coal water slurry (CWS) has been considered a cleaner and sustainable alternative to coal. However, the challenging suspension of coal particles in CWS has created a major obstacle to its use in industry. This study presents a novel approach to enhance the stability and rheological properties of coal water slurry (CWS) through the utilization of carboxyalkylated lignin (CL) as a dispersant. The generated CL samples had high water solubility of around 9 g/L and a charge density of around 2 mmol/g. All CLs were able to stabilize the coal suspension, and their performance decreased due to the increase in the alkyl chain length of carboxyalkylated lignin. Carboxymethylated lignin (CL-1) improved the stability of the coal suspensions with the lowest instability index of less than 0.6. The addition of CLs reduced the contact angle of the coal surface from 45.3° to 34.6°, and the increase in the alkyl chain length hampered its effect on contact angle changes. The zeta potential measurements confirmed that the adsorption of CL enhanced the electrostatic repulsion between coal particles in suspensions, and the zeta potential decreased with the increased alkyl chain length of CLs due to increased steric hindrance. The rheology results indicated that CLs demonstrated shear thinning behavior. This innovative method showcases the affinity of carboxyalkylated lignin to improve the performance of CWS, offering an environmentally friendly alternative for producing a cleaner product, i.e., sustainable coal water slurry, with improved suspension stability. Full article

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32 pages, 9337 KiB

Open AccessEditor’s ChoiceReview

Benefits of Incorporating Lignin into Starch-Based Films: A Brief Review

by Lamia Zuniga Linan, Farayde Matta Fakhouri, Gislaine Ferreira Nogueira, Justin Zoppe and José Ignacio Velasco

Polymers 2024, 16(16), 2285; https://doi.org/10.3390/polym16162285 - 13 Aug 2024

Cited by 2 | Viewed by 1302

Abstract

Polysaccharides are an excellent renewable source for developing food-packing materials. It is expected that these packages can be an efficient barrier against oxygen; can reduce lipid peroxidation, and can retain the natural aroma of a food commodity. Starch has tremendous potential to be explored in the preparation of food packaging; however, due to their high hydrophilic nature, packaging films produced from starch possess poor protective moisture barriers and low mechanical properties. This scenario limits their applications, especially in humid conditions. In contrast, lignin’s highly complex aromatic hetero-polymer network of phenylpropane units is known to play a filler role in polysaccharide films. Moreover, lignin can limit the biodegradability of polysaccharides films by a physical barrier, mainly, and by non-productive bindings. The main interactions affecting lignin non-productive bindings are hydrophobic interactions, electrostatic interactions, and hydrogen-bonding interactions, which are dependent on the total phenolic –OH and –COOH content in its chemical structure. In this review, the use of lignin as a reinforcement to improve the biodegradability of starch-based films in wet environments is presented. Moreover, the characteristics of the used lignins, the mechanisms of molecular interaction among these materials, and the sensitive physicochemical parameters for biodegradability detection are related. Full article

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13 pages, 2268 KiB

Open AccessReview

Recent Progress on Conversion of Lignocellulosic Biomass by MOF-Immobilized Enzyme

by Juan Tao, Shengjie Song and Chen Qu

Polymers 2024, 16(7), 1010; https://doi.org/10.3390/polym16071010 - 8 Apr 2024

Cited by 1 | Viewed by 1564

Abstract

The enzyme catalysis conversion of lignocellulosic biomass into valuable chemicals and fuels showed a bright outlook for replacing fossil resources. However, the high cost and easy deactivation of free enzymes restrict the conversion process. Immobilization of enzymes in metal–organic frameworks (MOFs) is one of the most promising strategies due to MOF materials’ tunable building units, multiple pore structures, and excellent biocompatibility. Also, MOFs are ideal support materials and could enhance the stability and reusability of enzymes. In this paper, recent progress on the conversion of cellulose, hemicellulose, and lignin by MOF-immobilized enzymes is extensively reviewed. This paper focuses on the immobilized enzyme performances and enzymatic mechanism. Finally, the challenges of the conversion of lignocellulosic biomass by MOF-immobilized enzyme are discussed. Full article

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12 pages, 24391 KiB

Open AccessArticle

Effect of Iron Chloride Addition on Softwood Lignin Nano-Fiber Stabilization and Carbonization

by Maxime Parot, Denis Rodrigue and Tatjana Stevanovic

Polymers 2024, 16(6), 814; https://doi.org/10.3390/polym16060814 - 14 Mar 2024

Cited by 1 | Viewed by 1767

Abstract

This study presents the effect of iron chloride addition on the production of nanocarbon fibers from softwood Organosolv lignin. It was shown that adding 2% FeCl₃ to the lignin solution before electrospinning to produce lignin nanofibers increased the thermal resistance of lignin fibers during stabilization. FTIR and XPS analyses of the lignin fibers stabilized with and without FeCl₃ revealed that the temperature rate could be increased in the presence of FeCl₃ from 1 to 3 °C/min. The optimal temperature to stabilize the lignin fibers was found to be 250 °C, as higher temperatures led to thermal degradation. Also, carbon fibers were successfully produced from pure softwood Organosolv lignin fibers. Carbonization tests were conducted under nitrogen and the best parameters were determined to be a ramp of 10 °C/min until 600 °C with a holding time of 2 h. Furthermore, the effect of 2% FeCl₃ addition in the lignin solution was investigated during these processes. XPS analysis showed a 93% carbon content for fibers carbonized with and without FeCl₃ addition, while SEM images revealed some surface roughness in fibers with FeCl₃ after carbonization. These results confirm that FeCl₃ addition influences the carbon nanofiber production. Full article

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34 pages, 11139 KiB

Open AccessArticle

Kraft (Nano)Lignin as Reactive Additive in Epoxy Polymer Bio-Composites

by Christina P. Pappa, Simone Cailotto, Matteo Gigli, Claudia Crestini and Konstantinos S. Triantafyllidis

Polymers 2024, 16(4), 553; https://doi.org/10.3390/polym16040553 - 18 Feb 2024

Cited by 1 | Viewed by 2690

Abstract

The demand for high-performance bio-based materials towards achieving more sustainable manufacturing and circular economy models is growing significantly. Kraft lignin (KL) is an abundant and highly functional aromatic/phenolic biopolymer, being the main side product of the pulp and paper industry, as well as of the more recent 2nd generation biorefineries. In this study, KL was incorporated into a glassy epoxy system based on the diglycidyl ether of bisphenol A (DGEBA) and an amine curing agent (Jeffamine D-230), being utilized as partial replacement of the curing agent and the DGEBA prepolymer or as a reactive additive. A D-230 replacement by pristine (unmodified) KL of up to 14 wt.% was achieved while KL–epoxy composites with up to 30 wt.% KL exhibited similar thermo-mechanical properties and substantially enhanced antioxidant properties compared to the neat epoxy polymer. Additionally, the effect of the KL particle size was investigated. Ball-milled kraft lignin (BMKL, 10 μm) and nano-lignin (NLH, 220 nm) were, respectively, obtained after ball milling and ultrasonication and were studied as additives in the same epoxy system. Significantly improved dispersion and thermo-mechanical properties were obtained, mainly with nano-lignin, which exhibited fully transparent lignin–epoxy composites with higher tensile strength, storage modulus and glass transition temperature, even at 30 wt.% loadings. Lastly, KL lignin was glycidylized (GKL) and utilized as a bio-based epoxy prepolymer, achieving up to 38 wt.% replacement of fossil-based DGEBA. The GKL composites exhibited improved thermo-mechanical properties and transparency. All lignins were extensively characterized using NMR, TGA, GPC, and DLS techniques to correlate and justify the epoxy polymer characterization results. Full article

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2024

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