Modification of cobalt-loaded zeolite catalysts for the selective fractionation of kraft lignin into guaiacyl phenolic monomers: Effect of oxophilic metal ions

Background: Rhodopseudomonas palustris is a metabolically versatile bacterium with significant biotechnological potential, including the ability to catabolize lignin and its heterogeneous breakdown products. Understanding the molecular determinants of growth on lignin-derived compounds is essential for advancing lignin valorization strategies under both aerobic and anaerobic conditions. Methods: R. palustris was cultivated on multiple lignin breakdown products (LBPs), including p-coumaryl alcohol, coniferyl alcohol, sinapyl alcohol, p-coumarate, sodium ferulate, and kraft lignin. Condition-specific transcriptomics and proteomics datasets were generated and used as input features to train machine-learning models, with experimentally measured growth rates as the prediction target. Artificial Neural Networks (ANNs), Random Forest (RF), and Support Vector Machine (SVM) models were evaluated and compared. Permutation feature importance analysis was applied to identify genes and proteins most influential for growth. Results: Among the tested models, ANNs achieved the highest predictive performance, with accuracies of 94% for transcriptomics-based models and 96% for proteomics-based models. Feature importance analysis identified the top twenty growth-associated genes and proteins for each omics layer. Integrating transcriptomic and proteomic results revealed eight key transport proteins that consistently influenced growth across LBP conditions. Re-training ANN models using only these eight transport proteins maintained high predictive accuracy, achieving 86% for proteomics and 76% for transcriptomics. Conclusions: This study demonstrates the effectiveness of ANN-based models for predicting growth-associated genes and proteins in R. palustris. The identification of a small set of key transport proteins provides mechanistic insight into lignin catabolism and highlights promising targets for metabolic engineering aimed at improving lignin utilization.

This study examines the effects of kraft lignin, milled hemp stalks, and dicumyl peroxide (DCP) crosslinking on polybutylene succinate (PBS) composites, focusing on rheological, mechanical, and thermal properties as well as accelerated weathering and fungal performance. Two composite series were produced via twin-screw extrusion, (a) simple blends (B-series) and (b) DCP-crosslinked formulations (R-series), with emphasis on hybrid lignin–hemp composites (B-PLH and R-PLH). Rheological analysis showed that hemp fiber increased viscosity, while lignin reduced it, and DCP further enhanced shear-thinning behavior. Mechanical testing confirmed that R-PLH exhibited a 16% increase in flexural strength (42.6 MPa) and a 2.4-fold increase in flexural modulus (1785 MPa) over neat PBS, but tensile strength declined by 19%. Thermal analysis revealed a 14–26% reduction in mass loss rate and increased char formation (up to 16.3% in R-PLH), indicating improved thermal stability. Water absorption showed that hemp fibers increased hydrophilicity, further increased by DCP. Accelerated weathering led to significant color change and surface degradation, particularly in R-PLH. Despite lignocellulosic content, all composites exhibited ≤2% fungal degradation, indicating limited mass loss due to fungal exposure under conditions used in this study. Overall, B-PLH and R-PLH offer a balance of stiffness and thermal stability, though trade-offs in tensile strength and weathering resistance should be considered for sustainable applications.

Lignin is a promising biostimulant for enhancing plant growth and stress tolerance. In this study, bamboo kraft lignin (BKL) and its oxygen-alkali-modified derivative (OBKL) were applied to maize seedlings to elucidate the structure-function relationship. The increased hydrophilic groups of OBKL improved its capacity to enhance water and nutrient uptake, resulting in a 50% increase in root elongation, 65% enhancement in photosynthesis, and a 106% rise in transpiration. Low-molecular-weight OBKL promoted chlorophyll synthesis and stress resilience, whereas high-molecular-weight lignin suppressed growth. Transcriptomics analysis revealed that OBKL upregulated 1333 genes, including key transcription factors such as AP2/ERF, WRKY, MYB, and NAC, which are involved in regulating cell proliferation, tropisms, carbon metabolism, and stress responses. Genomes and Gene Ontology analysis further identified plant hormone signal transduction regulated by lignin as a major pathway. These findings reveal that OBKL is an effective biostimulant for improving crop productivity and environmental adaptability.

Kraft lignin (KL), a major byproduct of the pulp and paper industry, is still largely underutilized, limiting its value in advanced materials. This work investigates whether incorporating carbonized kraft lignin (CKL) into polyvinyl alcohol (PVA) films can enhance their structural and functional properties and enable their use as gas-sensor membranes. PVA films containing 0, 10, 30, and 50 weight percent (wt.%) CKL were prepared and characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), water-contact-angle (wettability) measurements, and tensile testing, followed by ammonia (NH3), ethanol (C2H5OH), and toluene (C7H8) sensing. CKL increased thermal stability (temperature at 5% mass loss, T5%, up to 135 °C vs. 80 °C for neat PVA), raised carbonaceous residue to 15%, and improved Young’s modulus while reducing elongation and water contact angle. Gas-sensing tests revealed a strong, reversible current response to NH3, with PVA/50 wt.% CKL exhibiting the highest current (ca. 23 µA), along with detectable responses to ethanol and toluene. These results demonstrate that CKL is an effective bio-derived additive that upgrades PVA films for sustainable, high-performance gas-sensing applications.

PC-SAFT modeling of the dual, liquid–liquid equilibrium phase behavior for the Kraft Lignin–Ethanol–Water system

The incorporation of natural polymers into the synthesis of functional materials such as polyurethanes provides an effective approach for value-added biomass utilization. In this study, Lignin-containing polyol (LP) was prepared by simply mixing Kraft lignin, polyethylene glycol, and glycerol at mass ratio of 3 : 3.5 : 0.5. Lignin-based polyurethane foam (LPUF) was then prepared by mixing LP and polymethylene diphenyl diisocyanate (PMDI) using water as a foaming agent. Cellulose fibers from wood at various loadings (0%, 0.2%, 0.5%, 0.7%, and 1.0%) were incorporated as reinforcing skeletons to investigate the effects on the mechanical properties of LPUF. The results showed that the compressive strength, the flexural strength, and the tensile strength of LPUF were significantly increased by 72.3%, 154.5%, and 244.1% by 0.5% cellulose fiber addition, and reached 647.6 kPa, 1.28 MPa, and 1.17 MPa, respectively. Furthermore, improvement of thermal insulation performance of LPUF was also observed by the decrease of thermal conductivity from 0.0413 W m−1 K−1 to 0.0378 W m−1 K−1 by 0.5% cellulose fiber addition. However, cellulose fiber addition over 0.5% resulted in irregular pore morphology, ultimately impairing the mechanical performance of the LPUF. Cellulose and lignin are the major constructional constituents of woody biomass. The application of these natural polymers in polyurethane materials contributes to sustainable development and carbon neutrality.

This study investigates the performance of phenol–formaldehyde adhesives containing Eucalyptus lignin as an extender in their formulation. A commercial phenol–formaldehyde resin was used, and five different types of lignin were tested: (1) kraft lignin precipitated with carbon dioxide, (2) kraft lignin precipitated with sulfuric acid, (3) soda lignin precipitated with hydrochloric acid, (4) soda lignin precipitated with sulfuric acid, and (5) a second soda lignin where the wood underwent a phosphoric acid extraction process prior to alkaline extraction. The lignins were used both unmodified and activated through three different processes: hydroxymethylation, phenolysis in an acidic medium, and alkaline phenolysis. Adhesives were formulated with substitution percentages of the base resin ranging from 10% to 60%, in addition to a reference adhesive that contained no lignin. Wooden test specimens were manufactured to determine the tensile shear strength. Results indicate that best performance is achieved when lignins are activated through hydroxymethylation and when soda lignin is used. Under optimal conditions, it is possible to replace at least 45% of the base resin with activated Eucalyptus soda lignin, which represents a reduction of at least 30% in the cost of the final adhesive. This substitution results in a 46% increase in adhesive strength compared to the base adhesive (without lignin). These findings suggest that the valorization Eucalyptus soda lignin could have significant economic and environmental benefits.

Kraft lignin is the largest-tonnage technical lignin formed during kraft pulp cooking. According to statistics, approximately 70 mln t of such waste are generated annually. Most of it is disposed of in the system of chemicals recovery and thermal energy generation. Approximately 10…20 % of kraft lignin can be used to obtain a variety of products, for example, in the production of polymers, low-molecular compounds, activated carbon production, rubber industry, etc. For this purpose, kraft lignin is subjected to various types of modifications, including chemical ones: periodate oxidation, halogenation, sulfonation, sulfomethylation, nitration, nitrosation, etc. This article presents a new method for modification of kraft lignin with nitrous acid in a water-dioxane medium using solid-phase catalysis. The cation-exchange resins in H-form containing sulfogroups (cationite KU-2-8 and wofatite) have been used as catalysts. The optimal reagent consumption has been determined to be 50 % sodium nitrite and 230 % cationite from kraft lignin. It has been shown that the developed method and the well-known one using sulfuric acid as a catalyst give similar results. The molecular and electronic spectra of modified kraft lignin have been studied. In the electronic spectra of modified kraft lignin, a new absorption band appears characteristic of the nitroso group in the region of 400…500 nm with a maximum at 451 nm. By deconvolution, the electronic spectrum of modified kraft lignin is approximated by 6 Gaussians with an error of 2.5 %, while for the initial kraft lignin the spectrum can be described by 4 Gaussians with an error of 3.4 %. In contrast to the IR spectrum of kraft lignin, new absorption bands appear in the spectra of modified lignin at 615, 760, 1,330 and 1,550 cm–1, which are due to vibrations of NO bonds.

The sluggish kinetics of the oxygen reduction reaction (ORR) remain a major bottleneck for energy conversion systems such as fuel cells and metal-air batteries. Here, the synthesis of molybdenum single-atom catalysts (Mo SACs) derived from abundant and low-cost Kraft lignin is reported. By tuning nitrogen incorporation during carbonization, agglomerated Mo carbide clusters are progressively converted into atomically dispersed Mo active centers anchored on N-doped carbon. Extensive spectroscopic analyses confirm this structural evolution, while density functional theory calculations reveal that the optimized Mo coordination environment downshifts the d-band center, enabling the balanced adsorption of oxygen intermediates and thereby improving the intrinsic ORR activity. Electrochemical measurements demonstrate enhanced half-wave potential, near-four-electron transfer pathway, superior selectivity, and excellent durability, with ≈85% current retention over 50 h. Beyond performance, the use of minimally processed Kraft lignin underscores both the economic and environmental advantages of this approach, offering a scalable and sustainable pathway to practical ORR electrocatalysts.

Structural characterization of kraft lignin fractions obtained via pH adjustment and polyvinyl alcohol compatibility evaluation.

High production costs and sustainability issues are the main factors limiting the widespread application of carbon fibers in various industrial sectors. Lignin, a by-product from the paper and pulping industry, due to its high carbon content of up to 60%, can be considered a potential replacement for polyacrylonitrile in carbon fiber production. The production of lignins with distinct molecular weight distributions as well as group functionalities is essential to enhance high-value applications of lignin. In this study, we present a simple, green solvent-based fractionation method for LignoBoost softwood kraft lignin to obtain a lignin fraction with tailored physicochemical properties for electrospun carbon fiber production without polymeric spinning additives. Sequential solvent extraction was used to produce two fractions with distinct molecular weights: low-molecular-weight softwood kraft lignin (LMW-SKL) and high-molecular-weight softwood kraft lignin (HMW-SKL). The lignin fractions were characterized using size exclusion chromatography (SEC) for the molar mass distribution. The thermal properties of lignins were studied using thermogravimetry (TGA) and differential scanning calorimetry (DSC). Hydroxyl group content was quantified using quantitative 31P NMR spectroscopy. We successfully demonstrated the electrospinning of a high-molecular-weight lignin fraction—obtained in high yield from the fractionation process—without the use of any additives, followed by thermal conversion to produce electrospun carbon fibers. The presented results contribute to the valorization of lignin as well as to the development of green and sustainable technologies.

Upcycling eucalyptus kraft lignin into fluorescent graphene quantum dots for reproductive cell imaging in aquaculture biotechnology.

This study investigates the feasibility of using Kraft lignin in Hot and Warm Mix Asphalt (HMA and WMA), with a particular focus on its integration alongside Sasobit®. The research aims to evaluate the impact of Kraft lignin and Sasobit, individually and in combination, on the construction temperatures, compactability, and physical properties of asphalt mixtures. The experimental program included a reference HMA and modified mixes with 20% Kraft lignin, 3% Sasobit, and their combinations. These mixes were designed and subjected to tests to assess their volumetric and mass properties and to determine the construction temperatures using the Superpave Gyratory Compactor (SGC). The results demonstrated that adding Kraft lignin increased construction temperatures, while Sasobit effectively reduced these temperatures by lowering binder viscosity. When used together, Sasobit offset the increase in construction temperatures caused by Kraft lignin, resulting in compaction temperatures similar to the reference HMA mix. Additionally, Kraft lignin increased air voids, leading to reduced compactability at higher gyration levels. It also exhibited indications of a dual role, functioning as both a binder replacement and a filler. In conclusion, the combination of 20% Kraft lignin with 3% Sasobit offers a promising solution for enhancing the sustainability of asphalt mixtures.

Kraft lignin/polyurethane composites with enhanced mechanical strength, bioactive functionality, and superior wet wood adhesion.

Plasma-treated bacterial nanocellulose-lignin composites for biomedical applications.

Phenolated lignin nanoparticles with improved stability and biofunctionality: A comparative study of nanoprecipitation and solvent exchange fabrication techniques.

Transforming kraft lignin into supercapacitor electrodes via graphene oxide assisted co-pyrolysis and activation

Lignin, a naturally abundant biopolymer, possesses intrinsic ultraviolet (UV) shielding capabilities, making it a promising candidate for sustainable functional materials. However, conventional lignin isolation methods often lead to dark‐colored products due to structural condensation and chromophore formation, limiting its applicability in optical and esthetic applications. In this study, we introduce a novel fractionation strategy utilizing a system composed of thiolactic acid and choline chloride to selectively extract lignin from wood biomass. This environmentally benign process yields a light‐colored lignin with exceptional whiteness (>90%) and high recovery efficiency (70%). The preservation of lignin's bright appearance is attributed to its submicron‐scale morphology and chemical stabilization via thiolactic acid modification, which suppresses chromophore formation. Remarkably, the resulting white lignin demonstrates high visible light reflectance and significantly reduced solar heat gain compared to conventional kraft lignin. Furthermore, its strong UV absorption and high emissivity in the atmospheric transparency window position it as a compelling bio‐derived material for passive radiative cooling applications. This work highlights a sustainable pathway for valorizing lignin into high‐performance, multifunctional materials aligned with green chemistry principles.

Si’s enormous volume change (> 300%) causes pulverization and rapid capacity deterioration in lithium-ion batteries with Si electrodes. One strategy that has been explored previously for improving capacity retention and cycling stability is embedding Si into carbon matrices with optimized porosity and conductivity. We present a viable two-step emulsion polymerization and carbonization technique for transforming biomass into porous amorphous carbon cloud with commercial Si nanoparticles embedded within it. Henceforth, we refer to it as Si@CC. We developed and synthesized two different types of Si@CC (both with similar Si content). While, Si@CC1 was synthesized using Kraft lignin as the carbon source, Si@CC2 used a mixture of Kraft lignin and pre-carbonized soyhulls as the carbon source. Through a careful electrochemical analysis of Si@CC2 we identified anomalous electrochemical behavior - a constantly decreasing internal resistance and a downward shift in the charging plateau with cycling. This led us to speculate about novel in situ disorder reduction in the amorphous carbon cloud, which was later confirmed via Raman spectroscopy and X-ray diffraction studies. A higher proportion of mesopores (2 nm < pore sizes < 50 nm) in Si@CC2 led to a greater disorder reduction. Notably, we also propose a mechanism for the in situ disorder reduction (first report for LIBs) based on the interplay of Si’s volume fluctuations, the low compressibility of the liquid electrolyte, and the load transfer between the liquid electrolyte, Si nanoparticles, and the carbon cloud. The in situ disorder reduction leads to superior capacity retention for Si@CC2 (81% after 500 cycles at 0.42 A g-1) compared to pristine Si and Si@CC1. Hence, encapsulating Si in carbon cloud and the in situ disorder reduction in amorphous carbon cloud during cycling holds promise for the development of long-lasting, and energy-dense Si-anode LIBs.Acknowledgements:This work was partially supported by the United Soybean Board (USB) to develop the synthesis process of Si@CC materials described in this study. The authors also acknowledge financial support through Clemson University's Virtual Prototyping of Autonomy Enabled Ground Systems (VIPR-GS), under Cooperative Agreement W56HZV-21-2-0001 with the US Army DEVCOM Ground Vehicle Systems Center (GVSC), to develop and test batteries described in this study. The battery data presented herein was obtained at the Clemson Nanomaterials Institute, which Clemson University operates. The authors would like to thank Dr. Yanying Lu, Clemson University, for performing particle size analysis and tap density measurements. The authors also acknowledge informative discussions with Dr. Shailendra Chiluwal, Clemson University, on material synthesis and battery testing procedures. DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. OPSEC9603. Figure 1