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Advanced Study on Lignin-Containing Composites

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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 June 2026) | Viewed by 9022

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Editors

Dr. Florian Zikeli

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Department of Civil and Environmental Engineering, University of Perugia, 05100 Terni, Italy
Interests: lignin; wood chemistry; lignocellulose; lignin nanoparticles; biocomposites; bio-based polymers
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Dr. Debora Puglia

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Guest Editor

Department of Civil and Environmental Engineering, University of Perugia, 05100 Terni, Italy
Interests: bionanocomposites; natural fibers composites; lignin nanoparticles; nanocellulose; active packaging; polymeric nanocomposites
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Special Issue Information

Dear Colleagues,

Aromatic lignin, along with structural polysaccharides such as cellulose and hemicellulose, contribute to the exceptional strength of plant cell walls on the nanoscale and wood on the macroscopic scale, providing humanity with a versatile building and crafting material for thousands of years.

The extensive processing of lignocellulosic biomass for various uses, including construction, pulp and paper, and food production, results in significant residual biomass and, in particular, lots of lignin in side and waste streams. This byproduct has recently been increasingly utilized as a foundational element for developing specialized materials tailored to address specific research applications.

The purpose of this Special Issue is to explore a wide range of lignin-based or lignin-containing polymer composites that have been applied to tackle contemporary, innovative research challenges within the context of a circular bioeconomy. Original research and review articles are welcome.

Dr. Florian Zikeli
Dr. Debora Puglia
Guest Editors

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Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

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-anonymized peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access semimonthly 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 2700 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
biobased polymers
biocomposites
lignocellulose
cross-linked polymers
phenolic compounds
resins

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Published Papers (9 papers)

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Research

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16 pages, 4066 KB

Open AccessArticle

Mechanical, Morphological, Corrosion, and Thermally Activated Dimensional Recovery Behavior of Epoxy Composites Reinforced with Kraft Lignin/Fe–Mn–Si Alloy Hybrid Fillers

by Semih Tanfer Ileri and Mert Yildirim

Polymers 2026, 18(13), 1622; https://doi.org/10.3390/polym18131622 - 30 Jun 2026

Viewed by 190

Abstract

In this study, epoxy composites reinforced with kraft lignin, a promising green biofiller, and Fe–Mn–Si alloy particles as metallic functional fillers were developed, and their morphological properties, elemental distribution, mechanical properties, corrosion behavior, and thermally activated dimensional recovery behavior were investigated. Epoxy resin was used as the matrix, while kraft lignin and Fe–Mn–Si particles were incorporated as hybrid fillers. The composites were fabricated by casting with kraft lignin loadings of 1, 3, and 5 wt.% and a fixed Fe–Mn–Si alloy content of 3 wt.%. Neat epoxy was also prepared as a control sample. The specimens were characterized using scanning electron microscopy, energy-dispersive spectroscopy with elemental mapping, tensile testing, Shore D hardness measurements, electrochemical corrosion testing, and dimensional recovery tests. SEM–EDS observations showed that the composite containing 1 wt.% lignin exhibited a relatively uniform fracture morphology and more locally dispersed filler-related elemental signals, whereas higher lignin contents promoted particle-rich regions, microvoid-like features, and increased microstructural heterogeneity. The composite containing 1 wt.% lignin exhibited the highest tensile strength and elongation at break, with values of 39.09 MPa and 2.11%, respectively, and also showed the highest dimensional recovery ratio of 2.5%. The composite containing 3 wt.% lignin exhibited the lowest measured corrosion rate of 0.08 µm/year, while the composite containing 5 wt.% lignin showed the highest elastic modulus and Shore D hardness, with values of 5.80 GPa and 79, respectively. Overall, low lignin loading provided the most balanced mechanical and recovery-related performance, whereas higher lignin contents increased stiffness and hardness but also promoted greater microstructural heterogeneity. Full article

(This article belongs to the Special Issue Advanced Study on Lignin-Containing Composites)

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25 pages, 4445 KB

Open AccessArticle

Sustainable Protective Composite Textiles: Valorizing Hemp Hurd and Corn Stover Lignin via Electrospinning

by Dorota B. Szlek, Nara Han, Chang Geun Yoo and Margaret W. Frey

Polymers 2026, 18(9), 1124; https://doi.org/10.3390/polym18091124 - 2 May 2026

Viewed by 1315

Abstract

Valorization of abundant agricultural residues, particularly lignin, provides the opportunity to divert waste streams while enabling materials to inherently exhibit durable functionalities, including UV-blocking, antioxidant properties and water repellency. This study reports the side-by-side valorization of hemp hurd (HL) and corn stover lignin (CL), extracted using the CELF process, into electrospun lignin/nylon 6 nanofiber membranes, establishing how lignin botanical origin, molecular weight (M_w), and blend ratio govern multifunctional performance relevant to protective membranes in textiles. Lignin–nylon 6 hydrogen bonding was regulated by the OH content and accessibility, M_w, and purity, and influenced the functional properties of the fibers. While stronger in low-M_w nanofibers, these interactions were weakest in low-M_w HL samples due to the lowest purity, despite the highest OH content. Fibers with low-M_w lignin yielded finer, brittle fibers with higher UV blocking, whereas high-M_w fractions showed higher antioxidant performance due to decreased interactions with nylon 6. Overall, lignin/nylon 6 nanofiber membranes delivered biobased UPF 50+ performance, 55–61% antioxidant activity at the optimal concentration, and exhibited tunable water repellency via fraction selection and the blend ratio. In combination with a nanofiber architecture, these membranes can impart durable inherent functionality onto textile substrates without affecting their existing properties, including water vapor permeability, without the use of chemical finishing, while utilizing renewable resources from agricultural residues. Full article

(This article belongs to the Special Issue Advanced Study on Lignin-Containing Composites)

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20 pages, 6526 KB

Open AccessArticle

Synthesis and Application of Kraft Lignin-Based Polyurethane Coatings for Functional Paper Packaging Materials

by Julia de Cristo Figueiredo, Fernando José Borges Gomes, Ericka Figueiredo Alves Redmond, Biljana Bujanovic, Roberto Carlos Costa Lelis, Mayara Felix Santana and Clayton Mickles

Polymers 2026, 18(7), 787; https://doi.org/10.3390/polym18070787 - 25 Mar 2026

Cited by 1 | Viewed by 736

Abstract

The packaging sector presents a significant sustainability challenge, particularly due to the prevalence of plastic packaging. There is a growing interest in sustainable packaging alternatives. The main challenge is to develop packaging with comparable and competitive characteristics. In this context, this manuscript aims to evaluate the performance of lignin-based polyurethane applied as a coating on recycled linerboard. Industrial softwood kraft lignin was fully characterized in terms of purity, functional groups (FTIR and ³¹P NMR) and molecular weight (GPC). Aiming at coating applications, the lignin sample was solubilized in dimethyl sulfoxide (DMSO) and used as a polyol substitute in the reaction, replacing polyethylene glycol (PEG) at levels of 70%, 80%, and 90%. Subsequently, hexamethylene diisocyanate (HDI) was added to initiate polyurethane formation. After polymerization, the coating was applied in multiple layers onto the linerboard paper. Regarding water resistance, all applications demonstrated effectiveness. The lignin-based polyurethane coating improved the Cobb1800 with reductions in the range of 1147.4 to 1155.8 g/m² compared to the uncoated paper. Water vapor permeability was reduced by more than 94%. In the evaluation of oil resistance, samples with three layers and 90% lignin replacement performed particularly well, achieving a high value in a kit test for oil and grease (kit test number 12). These results highlight a promising approach to paper-based packaging, with potential applications across a wide range of products. Full article

(This article belongs to the Special Issue Advanced Study on Lignin-Containing Composites)

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12 pages, 2320 KB

Open AccessArticle

Multifunctional Performance Lignin-Crosslinked-PVA Composite Film Based on a Dual Crosslinking Network

by Weipeng Yao, Shuzhen Ni, Yongchao Zhang and Yingjuan Fu

Polymers 2026, 18(5), 605; https://doi.org/10.3390/polym18050605 - 28 Feb 2026

Cited by 1 | Viewed by 875

Abstract

The development of high-performance biocomposites based on poly vinyl alcohol (PVA) and lignin is often hindered by the limited interfacial compatibility. Herein, we reporte a synchronized crosslinking strategy to seamlessly integrate lignin and PVA into a uniform and robust composite film. The vinyl groups were introduced into both lignin and PVA molecular chains, which enable the formation of dense covalent bonds through reactions between these unsaturated carbon–carbon double bonds. This dual network structure combining covalent crosslinking with hydrogen bonding effectively strengthened the interfacial compatibility between lignin and PVA, which substantially enhanced film toughness, exhibiting an elongation at break of up to 4300%. Furthermore, the prepared composite film also demonstrated outstanding UV-blocking efficiency (>90%), strong antioxidant activity (82% DPPH scavenging), enhanced hydrophobicity (water contact angle of 97.9°), and improved thermal stability. The dramatic enhancements were attributed to the homogeneous dispersion of modified lignin within the covalently bonded network, which ensured efficient stress transfer and reduced the availability of hydrophilic groups. This synchronized crosslinking approach presents a versatile and effective route for fabricating high-value lignin-based composite materials. Full article

(This article belongs to the Special Issue Advanced Study on Lignin-Containing Composites)

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21 pages, 4659 KB

Open AccessArticle

Effect of Different Aqueous Solvents with and Without Solubilized Lignin on the Swelling Behavior of Holocellulose Fibers

by Cornelia Hofbauer, Thomas Harter, Ulrich Hirn, Michael Harasek, Luis Zelaya-Lainez, Josef Füssl, Markus Lukacevic and Sebastian Serna-Loaiza

Polymers 2025, 17(23), 3103; https://doi.org/10.3390/polym17233103 - 22 Nov 2025

Cited by 2 | Viewed by 1324

Abstract

The modification of lignocellulosic fibers through controlled swelling and impregnation plays a decisive role in tailoring their structure and reactivity for use in sustainable composite materials. In this study, holocellulose fibers were swollen in various solvents (sodium hydroxide at 2 and 4 wt% and ethanol–water mixtures at 0, 50, 70, and 100 wt%) to evaluate their impact on swelling and fiber characteristics. The pulp was produced with peracetic acid at 90 °C for 120 min from spruce wood chips and used for the swelling treatment. The fibers underwent swelling for 4 h in the different solvents, both without and with solubilized lignin at concentrations of 10 and 30 g/L, to investigate the impregnation ability of the fibers for lignin as a natural binder. Fiber morphology, lignocellulosic composition, and liquid retention values were analyzed to assess the effects of solvent–binder interactions on fiber swelling and lignin uptake. The results revealed significant differences in fiber characteristics influenced by both solvent choice and lignin presence, demonstrating the feasibility and optimization potential of a single-step swelling-impregnation process. These findings highlight key factors that can improve the uptake of natural binders in wood fibers, offering insights for effective fiber preconditioning in composite production. Full article

(This article belongs to the Special Issue Advanced Study on Lignin-Containing Composites)

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23 pages, 3230 KB

Open AccessArticle

A Multi-Analytical Study of Nanolignin/Methylcellulose-Coated Groundwood and Cotton Linter Model Papers

by Mia Bloss, Marianne Odlyha and Charis Theodorakopoulos

Polymers 2025, 17(21), 2934; https://doi.org/10.3390/polym17212934 - 31 Oct 2025

Viewed by 1159

Abstract

This paper presents the synthesis of sustainable lignin nanoparticles (LNPs) and their application in methylcellulose (MC) as LNP/MC coatings for handmade papers. LNPs were produced from bulk kraft lignin via an acetone/water and sonication method, then incorporated into a 1 wt% methylcellulose (MC) matrix at concentrations of 0.4, 1, and 2 wt%. Groundwood and cotton linter papers were coated and exposed to 90 °C and 45% relative humidity (RH) for 16 days and the samples’ response to ageing at different concentrations of nanolignin was tested using a multi-analytical approach. The morphology of the LNPs was revealed with scanning electron microscopy, and most LNPs measured below a diameter of 30.8 nm. Colourimetry showed coated samples were inherently darker than uncoated samples but mostly stable in colour. pH remained near neutral for coated groundwood papers during ageing, but cotton papers were consistently acidic. Fourier transform infrared (FTIR) spectroscopy identified spectral similarities between uncoated and coated groundwood samples at approximately 1635 cm^–1 and 1725 cm^–1, attributed to carbonyl and carboxyl groups, suggesting that LNPs did not contribute to the formation of these groups during ageing. Controlled environment dynamic mechanical analysis (DMA-RH) found improved consolidation and lower elongation in most LNP/MC-treated samples. These results indicate that there may be potential for LNPs within paper conservation. Full article

(This article belongs to the Special Issue Advanced Study on Lignin-Containing Composites)

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17 pages, 15586 KB

Open AccessArticle

Wheat Straw Lignin Nanoparticles as Active Filler in Thermoplastic Starch Films

by Florian Zikeli, Franco Dominici, Marco Rallini, Sebastian Serna-Loaiza, Walter Wukovits, Anton Friedl, Michael Harasek, Luigi Torre and Debora Puglia

Polymers 2025, 17(17), 2308; https://doi.org/10.3390/polym17172308 - 26 Aug 2025

Cited by 1 | Viewed by 1434

Abstract

Starch and lignin are promising biopolymers for the production of biodegradable biocomposite materials. The possibility of processing starch into thermoplastic materials qualifies it as a starting material for the preparation of thermoplastic packaging films, and the combination with lignin can even out some inherent weak points of starch, such as moisture and water sensitivity, and can add additional features like antioxidant activity. Lignins from herbaceous biomass carry building blocks that are not found in wood lignins and are known for their bioactivity, such as p-coumaric acid or ferulic acid. In this work, a protocol was developed to initially prepare hybrids of wheat starch granules and lignin nanoparticles, which were then plasticized using glycerol in an extrusion process to produce thin films. The lignin-containing thermoplastic starch films showed higher Young’s moduli and less elongation at break compared to neat thermoplastic starch films, while tensile strength remained at the level of the neat films. Thermal stability was slightly increased by lignin addition, and oxygen transmission rates were low for lignin contents as low as 1 wt%. The hydrophobicity of the lignin-containing films increased strongly, and they showed an elevated antioxidant activity over several hours, which was also maintained after 24 h. The preparation of hybrid wheat starch lignin particles was successfully tested for the extrusion of thermoplastic starch films with improved thermomechanical properties, decreased water sensitivity, and prolonged antioxidant activity. Full article

(This article belongs to the Special Issue Advanced Study on Lignin-Containing Composites)

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Review

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27 pages, 5089 KB

Open AccessReview

Toward Predictive Design of Lignocellulosic Mycelium-Bound Composites: A Process–Structure–Property Framework, Quantitative Synthesis, and Standardization Roadmap

by Musiliu A. Liadi, Tawakalt O. Ayodele, Ibrahim A. Bello, C. Igathinathane and Hammed M. Ademola

Polymers 2026, 18(13), 1652; https://doi.org/10.3390/polym18131652 (registering DOI) - 2 Jul 2026

Viewed by 185

Abstract

Mycelium-bound composites (MBCs) have emerged as a promising class of biofabricated materials that integrate fungal hyphal networks with lignocellulosic substrates to form lightweight, biodegradable structures without synthetic adhesives. Despite rapid growth in the field, the current literature remains fragmented, with inconsistent methodologies and widely varying reported material properties. This review advances the field by moving beyond descriptive synthesis toward a quantitative and conceptual integration of existing studies. We systematically analyze how key fabrication variables—including fungal species, substrate composition, growth conditions, and post-processing parameters—govern density, porosity, and mechanical performance. A process–structure–property (PSP) framework is proposed to combine these relationships and explain discrepancies across studies. We highlight the dominant role of densification and moisture conditioning in determining compressive strength, often outweighing species-level effects. A comparative synthesis of reported data reveals significant variability in compressive strength (0.05–1.2 MPa) and elastic modulus, attributable to inconsistencies in sample preparation, testing protocols, and environmental conditioning. To address this, we identify critical gaps in standardization and propose actionable testing protocols and reporting guidelines for reproducibility. Furthermore, we assess the technology readiness level (TRL) of MBC systems and distinguish between laboratory-scale innovations and commercially viable processes. While hybridization strategies and biofunctional applications offer promising avenues, their maturity varies widely. This work provides a decision-oriented framework for MBC design and a roadmap for transitioning these materials from experimental systems to scalable, standardized, and application-ready biomaterials. Full article

(This article belongs to the Special Issue Advanced Study on Lignin-Containing Composites)

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29 pages, 17904 KB

Open AccessReview

Interphase Engineering in Lignin-Containing Nanocellulose Composites from Tropical Biomass: Evidence-Weighted Comparative Framework, Product Windows, and Biorefinery Constraints

by José Roberto Vega-Baudrit and Mary Lopretti

Polymers 2026, 18(10), 1238; https://doi.org/10.3390/polym18101238 - 19 May 2026

Viewed by 542

Abstract

Tropical lignocellulosic residues are increasingly relevant feedstocks for lignin-containing nanocellulose composites, but their performance cannot be predicted from botanical origin or bulk lignin percentage alone. This review defines the interface as the geometrical boundary between phases and the interphase as the finite, compositionally graded region in which lignin distribution, nanocellulose morphology, adsorbed water, and the surrounding matrix jointly govern stress transfer and mass transport. Using an evidence-weighted framework, the literature is organized into the following categories: residual-lignin nanofibrils, redeposited-lignin systems, lignin nanoparticle assemblies, compatibilized thermoplastic hybrids, and all-lignocellulosic sheets. Representative quantitative observations show that controlled residual lignin can the increase water contact angle from approximately 35 degrees to 78 degrees and reduce oxygen permeability by up to 200-fold in nanopapers, while selected PLA/LCNF systems show tensile-strength and modulus increases of 37% and 61%, respectively; however, high or poorly distributed lignin can suppress fibrillation, lower viscosity, weaken gel networks, and reduce reproducibility. The most defensible near-term product windows are packaging layers, grease/oil barrier papers, coatings, paper-like multilayers, and selected porous media. Thermoplastic matrices remain process-sensitive, and biomedical, additive-manufacturing, nano-reactor, and energy-material claims require stronger validation of the extractables, rheology, humidity history, TEA/LCA metrics, and end-of-life behavior. This review, therefore, provides a critical, application-backward roadmap for tropical biorefineries in which interfacial function, wet handling, drying energy, and process integration are assessed together rather than treated as independent variables. The abbreviations used in the abstract are defined as follows: CNFs, cellulose nanofibrils; CNC, cellulose nanocrystals; LCNF, lignin-containing cellulose nanofibrils; LCNCs, lignin-containing cellulose nanocrystals; PLA, poly(lactic acid); PHB, polyhydroxybutyrate; PHAs, polyhydroxyalkanoates; PVA, poly(vinyl alcohol); DESs, deep eutectic solvents; TEA, techno-economic analysis; LCA, life-cycle assessment; ML, machine learning. Full article

(This article belongs to the Special Issue Advanced Study on Lignin-Containing Composites)

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