Preparation and Characterization of Various Kraft Lignins and Impact on Their Pyrolysis Behaviors

Molybdenum oxide loaded ceria catalysts for the selective production of monomeric alkyl phenols from the hydrogenolysis of Kraft lignin

Lignin, an aromatic biopolymer produced in large quantities as a byproduct of biorefineries, has garnered significant attention for its potential to be valorized into valuable compounds. This demands for the development of an efficient catalyst. This study is the first evaluate the catalytic efficiency of a synthesized Mo-loaded CeO2 (5Mo/CeO2-syn) catalyst for an in-situ upgradation of lignin oil. The 5Mo/CeO2-syn catalyst demonstrated exceptional performance, achieving a high lignin liquefaction yield of 66.7 wt%, compared to 48.1 wt% for 5Mo/CeO2-com and 35.5 wt% for the non-catalytic (N-cat) reaction. The effects of varying metal loadings and different alcoholic solvents were systematically investigated for kraft lignin (KL) depolymerization. The results of GC-MS and elemental analysis for the bio-oils revealed a significant increase in calorific value (36 MJ/kg, 5Mo/CeO2-syn), attributed to the efficient removal of oxygenates. The N-cat bio-oil contained a high proportion of guaiacyl (G-type) phenols (73.4 %), which were significantly reduced during catalytic reactions as they were transformed into alkyl (H-type) phenols. The GPC analysis also evaluated for the lignin and optimum bio-oils, to confirm the breakage of the macro-polymeric structure of lignin into respective monomeric compounds. Moreover, the 5Mo/CeO2-syn catalyst was further evaluated across four catalytic cycles, demonstrating its stability and reusability.

Lignosulfonate as a versatile regulator for the mediated synthesis of Ag@AgCl nanocubes

The remarkable catalytic activity, optical properties, and electrochemical behavior of nanomaterials based on noble metals (NM) are profoundly influenced by their physical characteristics, including particle size, morphology, and crystal structure. Effective regulation of these parameters necessitates a refined methodology. Lignin, a natural aromatic compound abundant in hydroxyl, carbonyl, carboxyl, and sulfonic acid groups, has emerged as an eco-friendly surfactant, reducing agent, and dispersant, offering the potential to precisely control the particle size and morphology of NM-based nanomaterials. In this study, lignosulfonate (LS) was utilized as a versatile regulator efficient in the capacities of reduction, capping, and dispersal for the synthesis of Ag@AgCl nanocubes. LS concentration and reaction time were identified as crucial factors impacting the ultimate particle size and morphology of Ag@AgCl nanocubes. The Ag@AgCl nanocubes, with a particle size of 30 ± 10 nm, were successfully synthesized under the optimized conditions of a 1.0 mM LS concentration and a 1-hour reaction period. As a reducing agent, LS facilitates the conversion of silver ions originating from AgCl to silver nanoparticles, following an etching-like mechanism that yields AgCl seeds with a uniform cubic particle size. The obtained Ag@AgCl nanocubes exhibit a stable morphology and excellent dispersion characteristics.

Is Kraft Pulping the Future of Biorefineries? A Perspective on the Sustainability of Lignocellulosic Product Development

By reflecting on the history and environmental impact of conventional biorefining, such as kraft pulping, we aim to explore important questions about how natural polymers can be more sustainably sourced to develop bio-products and reduce reliance on plastics. Since the Industrial Revolution, chemical pulping processes have enabled the mass production of cellulosic products from woody biomass. Kraft pulping, which dominates within modern pulp and paper mills, has significantly contributed to environmental pollution and carbon emissions due to sulfurous byproducts and its high water and energy consumption. While chemical pulping technologies have advanced over time, with improvements aimed at enhancing sustainability and economic feasibility, conventional biorefineries still face challenges related to biomass conversion efficiency and environmental impact. For example, efforts to fully utilize wood resources, such as isolating lignin from black liquor, have made limited progress. This perspective provides a thoughtful examination of the growth of chemical pulping, particularly the kraft process, in the production of consumer goods and its environmental consequences. It also presents key insights into the bottlenecks in developing truly sustainable biomass conversion technologies and explores potential alternatives to traditional chemical pulping.

Dye-Decolorizing Peroxidases Maintain High Stability and Turnover on Kraft Lignin and Lignocellulose Substrates

Fungal enzyme systems for the degradation of plant cell wall lignin, consisting of, among others, laccases and lignin-active peroxidases, are well characterized. Additionally, fungi and bacteria contain dye-decolorizing peroxidases (DyP), which are also capable of oxidizing and modifying lignin constituents. Studying DyP activity on lignocellulose poses challenges due to the heterogeneity of the substrate and the lack of continuous kinetic methods. In this study, we report the kinetic parameters of bacterial DyP from Amycolatopsis 75iv2 and fungal DyP from Auricularia auricula-judae on insoluble plant materials and kraft lignin by monitoring the depletion of the cosubstrate of the peroxidases with a H2O2 sensor. In the reactions with spruce, both enzymes showed similar kinetics. On kraft lignin, the catalytic rate of bacterial DyP reached 30 ± 2 s-1, whereas fungal DyP was nearly 3 times more active (81 ± 7 s-1). Importantly, the real-time measurement of H2O2 allowed the assessment of continuous activity for both enzymes, revealing a previously unreported exceptionally high stability under turnover conditions. Bacterial DyP performed 24,000 turnovers of H2O2, whereas the fungal DyP achieved 94,000 H2O2 turnovers in 1 h with a remaining activity of 40 and 80%, respectively. Using mass spectrometry, the depletion of the cosubstrate H2O2 was shown to correlate with product formation, validating the amperometric method.

Flexible high electrochemical collagen/lignin composite hydrogel for sensing and supercapacitor applications

Synthesis of polymer-based highly conductive hydrogels from natural and renewable sources with robust mechanical performances in flexible electronics remains a great challenge. In this research, a dynamic redox system is designed by using collagen (CL), sulfonate lignin (SL), acrylic acid (AA), and Al3+ to synthesize CL/PAA/SL/Al hydrogels. The formation of effective complexes of Al3+ with the abundant functional groups of CL, SL and PAA, the prepared hydrogel delivers various specific properties, for example, excellent ionic conductivity (4.61 S·m-1), stretchability and antimicrobial performance. The CL/PAA/SL/Al hydrogel demonstrates good mechanical strength, while the maximum tensile strength of the hydrogels is ∼604 kPa at a stretching of 1254 %, and the maximum compressive strength is ∼0.45 MPa, with the maximum stretching of 59.6 %. The CL/PAA/SL/Al hydrogel acts as a flexible strain sensor with high sensitivity. Enough hydroxyl and carboxyl groups in the hydrogels are essential for delivering the maximum 191 mV of open circuit voltage (Voc) rendered during moisture spraying. The supercapacitor assembled from CL/PAA/SL/Al hydrogel manifests specific capacitance (Cs), maximum energy density (Ed) and power density (Pd) of 268.75 F·g-1, 23.89 Wh·kg-1 and 2.4 kW·kg-1, respectively. The supercapacitor can retain its capacitance of 95.8 % after 5000 consecutive charge-discharge cycles.

Preparation of lignin-based hydrogels, their properties and applications

Polymers obtained from biomass are a concerning alternative to petro-based polymers because of their low cost of manufacturing, biocompatibility, ecofriendly and biodegradability. Lignin as the second richest and the only polyaromatics bio-polymer in plant which has been most studied for the numerous applications in different fields. But, in the past decade, the exploitation of lignin for the preparation of new smart materials with improved properties has been broadly sought, because lignin valorization plays one of the primary challenging issues of the pulp and paper industry and lignocellulosic biorefinery. Although, well suited chemical structure of lignin comprises of many functional hydrophilic and active groups, such as phenolic hydroxyls, carboxyls and methoxyls, which provides a great potential to be applied in the preparation of biodegradable hydrogels. In this review, lignin hydrogel is covered with preparation strategies, properties and applications. This review reports some important properties, such as mechanical, adhesive, self-healing, conductive, antibacterial and antifreezing properties were then discussed. Furthermore, herein also reviewed the current applications of lignin hydrogel, including dye adsorption, smart materials for stimuli sensitive, wearable electronics for biomedical applications and flexible supercapacitors. Overall, this review covers recent progresses regarding lignin-based hydrogel and constitutes a timely review of this promising material.

Amphiphilic Lignin Nanoparticles Made from Lignin-Acrylic Acid-Methyl Methacrylate Copolymers

In this study, a novel amphiphilic KL-AA-MMA nanoparticle was prepared through the graft copolymerization of kraft lignin (KL) with acrylic acid (AA) and methyl methacrylate (MMA), using potassium persulfate as an initiator in a water/dimethyl sulfoxide solvent medium, which was followed by the nanoprecipitation technique using dimethylformamide as a solvent and deionized water as an antisolvent. The successful graft polymerization was verified by ¹H-nuclear magnetic resonance (NMR), ³¹P-NMR, and Fourier transform infrared (FTIR) analyses; and the grafting yield of the generated KL-AA-MMA copolymer ranged from 68.2% to 96.5%. Transmission electron microscopy (TEM) observation revealed the formation of amorphous KL-AA-MMA nanoparticles. Additionally, KL-AA-MMA9 nanoparticles with the highest yield exhibited the minimum hydrodynamic diameter and polydispersity of 261 nm and 0.153, respectively. Moreover, the amphiphilicity of KL-AA-MMA nanoparticles was significantly improved by the grafting of MMA monomers. Finally, the adsorption performance of KL-AA-MMA nanoparticles at the xylene interface was evaluated by a quartz crystal microbalance with dissipation (QCM-D). The results demonstrated that the most amphiphilic sample, KL-AA-MMA9 nanoparticles, with the smallest hydrodynamic size displayed the highest adsorption on the oil/water interface. This product provides a wide range of applications in oil/water emulsions.

Lignin-containing hydrogels with anti-freezing, excellent water retention and super-flexibility for sensor and supercapacitor applications

We developed a highly conductive and flexible, anti-freezing sulfonated lignin (SL)-containing polyacrylic acid (PAA) (SL-g-PAA-Ni) hydrogel, with a high concentration of NiCl₂. Ni²⁺ contributes multi-functions to the preparation of the hydrogel and its final properties, such as fast polymerization reaction as a result of the presence of redox pairs of Ni³⁺/Ni²⁺ and hydroquinone/quinone, and anti-freezing properties of the hydrogel due to the salt effects of NiCl₂ so that at -20 °C the hydrogel shows similar properties to those at the room temperature. Thanks to the effective coordinations of Ni²⁺ with catecholic groups and carboxylic groups, as well as the rich hydrogen bonding capacity, the resultant hydrogel possesses excellent mechanical properties. High ionic conductivity (6.85 S·m^-1) of the hydrogel is obtained due to the supply of high concentration of Ni²⁺. Moreover, the ionic solvation effect of NiCl₂ in the hydrogel imparts excellent water retention ability, with water retention of ~93 % after 21-day storage. The SL-g-PAA-Ni hydrogel can accurately detect various human motions at -20 °C. The supercapacitor assembled from SL-g-PAA-Al hydrogel at -20 °C manifests a high specific capacitance of 252 F·g^-1, with maximum energy density of 26.97 Wh·kg^-1, power density of 2667 W·kg^-1, and capacitance retention of 96.7 % after 3000 consecutive charge-discharge cycles.

Recent advances in lignosulfonate filled hydrogel for flexible wearable electronics: A mini review

With the rapid development of flexible wearable devices, various polymer hydrogels have gained immense progress due to their adjustable mechanical properties, high conductivity, super sensitivity, good biocompatibility and adaptable wearability. Lignosulfonate (LS), generating from the sulfite pulping industry, was emerged as a promising filler in polymer hydrogels with great potential for multifunctional wearable electronics. Herein, we comprehensively review the latest research progress associated with LS-based hydrogels. Firstly, the function mechanism of lignosulfonate in diverse polymer hydrogels was introduced in detail. Then, the rational design strategies of LS filled multifunctional hydrogels was summarized as toughening filler, adhesive agent, conductive filler dispersant, UV protectant and catalysts. Finally, the future development of LS filled hydrogel for flexible wearable electronics was proposed.

High lignin containing hydrogels with excellent conducting, self-healing, antibacterial, dye adsorbing, sensing, moist-induced power generating and supercapacitance properties

Herein, we design a dynamic redox system of using high contents of lignosulfonate (LS) and Al³⁺ to prepare poly acrylic acid (PAA) (LS-g-PAA-Al) hydrogels. The presence of high LS and Al³⁺ contents, in combination with the effective Al³⁺ complexes formed, renders the resultant hydrogel with some unique attributes, including excellent ionic conductivity (as high as 7.38 S·m^-1) and antibacterial activity; furthermore, a very fast gelation (in 1 min) was obtained. As a flexible strain sensor, the LS-g-PAA-Al hydrogel with high conductivity demonstrates superior sensitivity in human movement detection. In addition, the rich anionic hydrophilic groups, such as sulfonic groups, phenolic hydroxyl groups, in the hydrogels impart the resultant hydrogels with excellent adsorption capacity for cationic dyes: when using Rhodamine B (RB) as a model cationic dye, the adsorption capacity of the resultant hydrogel reaches 334.64 mg·g^-1; as a moist-induced power generator, it generates maximum 150.5 mV open circuit voltage with moist air flow. When the hydrogel electrolyte is assembled into a supercapacitor assembly, it shows high specific capacitance of 245.4 F·g^-1, with the maximum energy density of 21.8 Wh·kg^-1, power density of 2.37 kW·kg^-1, and capacitance retention of 95.1% after 5000 consecutive charge-discharge cycles.

Design of Fe3+-Rich, High-Conductivity Lignin Hydrogels for Supercapacitor and Sensor Applications

Preparation of natural polymer-based highly conductive hydrogels with tunable mechanical properties for applications in flexible electronics is still challenging. Herein, we report a facile method to prepare lignin-based Fe³⁺-rich, high-conductivity hydrogels via the following two-step process: (1) lignin hydrogels are prepared by cross-linking sulfonated lignin with poly(ethylene glycol) diglycidyl ether (PEGDGE) and (2) Fe³⁺ ions are impregnated into the lignin hydrogel by simply soaking in FeCl₃. Benefiting from Fe³⁺ ion complexation with catechol groups and other functional groups in lignin, the resultant hydrogels exhibit unique properties, such as high conductivity (as high as 6.69 S·m^-1) and excellent mechanical and hydrophobic properties. As a strain sensor, the as-prepared lignin hydrogel shows high sensitivity when detecting various human motions. With the flow of moist air, the Fe³⁺-rich lignin hydrogel generates an output voltage of 162.8 mV. The assembled supercapacitor of the hydrogel electrolyte demonstrates a high specific capacitance of 301.8 F·g^-1, with a maximum energy density of 26.73 Wh·kg^-1, a power density of 2.38 kW·kg^-1, and a capacitance retention of 94.1% after 10 000 consecutive charge-discharge cycles. These results support the conclusion that lignin-based Fe³⁺-rich, high-conductivity hydrogels have promising applications in different fields, including sensors and supercapacitors, rendering a new platform for the value-added utilization of lignin.

Preparation of lignosulfonate ionic hydrogels for supercapacitors, sensors and dye adsorbent applications

Lignin, an abundant natural polymer but presently under-utilized, has received much attention for its green/sustainable advantages. Herein, we report a facile method to fabricate lignosulfonate (LS) ionic hydrogels by simple crosslinking with poly (ethylene glycol) diglycidyl ether (PEGDGE). The as-obtained LS-PEGDGE hydrogels were comprehensively characterized by mechanical measurements, FT-IR, and SEM. The rich sulfonic and phenolic hydroxyl groups in LS hydrogels play key roles in imparting multifunctional smart properties, such as adhesiveness, conducting, sensing and dye adsorption, as well as superconductive behavior when increasing the moisture content. The hydrogels have a high adsorption capacity for cationic dyes, using methylene blue as a model, reaching 211 mg·g^-1. As a moist-induced power generator, the maximum output voltage is 181 mV. The LS-PEGDGE hydrogel-based flexible strain sensors exhibit high sensitivity when detecting human movements. As the hydrogel electrolyte, the assembled supercapacitor shows high specific capacitance of 236.9 F·g^-1, with the maximum energy density of 20.61 Wh·kg^-1, power density of 2306.4 W·kg^-1, and capacitance retention of 92.9% after 10,000 consecutive charge-discharge cycles. Therefore, this multifunctional LS hydrogels may have promising applications in various fields, providing a new platform for the value-added utilization of lignin from industrial waste.