Lignin for polymer and nanoparticle production: Current status and challenges

Lignin and functional polymer-based materials: Synthesis, characterization and application for Cr (VI) and As (V) removal from aqueous media

In this study, lignin derived from corncobs was chemically modified by substituting the hydroxyl groups present in its structure with methacrylate groups through a catalytic reaction using methacrylic anhydride, resulting in methacrylated lignin (ML). These MLs were incorporated in polymerization reaction of the monomer 2-[(acryloyloxy)ethyl trimethylammonium] chloride (Cl-AETA) and Cl-AETA, Cl-AETA/ML polymers were obtained, characterized (spectroscopic, thermal and microscopic analysis), and evaluated for removing Cr (VI) and As (V) from aqueous media in function of pH, contact time, initial metal concentrations and adsorbent amount. The Cl-AETA/ML polymers followed the Langmuir adsorption model for the evaluated metal anions and were able to remove up to 91 % of Cr (VI) with a qmax (maximum adsorption capacity) of 201 mg/g, while for As (V), up to 60 % could be removed with a qmax of 58 mg/g. The results demonstrate that simple modifications in lignin enhance its functionalization and properties, making it suitable for removing contaminants from aqueous media, showing promising results for potential future applications.

Undergoing lignin-coated seeds to cold plasma to enhance the growth of wheat seedlings and obtain future outcome under stressed ecosystems

Climate changes threat global food security and food production. Soil salinization is one of the major issues of changing climate, causing adverse impacts on agricultural crops. Germination and seedlings establishment are damaged under these conditions, so seeds must be safeguard before planting. Here, we use recycled organic tree waste combined with cold (low-pressure) plasma treatment as grain coating to improve the ability of wheat seed cultivars (Misr-1 and Gemmeza-11) to survive, germinate and produce healthy seedlings. The seeds were coated with biofilms of lignin and hash carbon to form a protective extracellular polymeric matrix and then exposed them to low-pressure plasma for different periods of time. The effectiveness of the coating and plasma was evaluated by characterizing the physical and surface properties of coated seeds using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), nuclear magnetic resonance (NMR) spectroscopy, and wettability testing. We also evaluated biological and physiological properties of coated seeds and plants they produced by studying germination and seedling vigor, as well as by characterizing fitness parameters of the plants derived from the seeds. The analysis revealed the optimal plasma exposure time to enhance germination and seedling growth. Taken together, our study suggests that combining the use of recycled organic tree waste and cold plasma may represent a viable strategy for improving crop seedlings performance, hence encouraging plants cultivation in stressed ecosystems.

Lignin Nanoparticles: Transforming Environmental Remediation

In the face of escalating environmental challenges driven by human activities, the quest for innovative solutions to counter pollution, contamination, and ecological degradation has gained paramount importance. Traditional approaches to environmental remediation often fall short in addressing the complexity and scale of modern-day environmental problems. As industries transition towards sustainable paradigms, the exploration of novel materials and technologies becomes crucial. Lignin nanoparticles have emerged as a promising avenue of exploration in this context. Once considered a mere byproduct, lignin's unique properties and versatile functional groups have propelled it to the forefront of environmental remediation research. This review paper delves into the resurgence of lignin from an environmental perspective, examining its pivotal role in carbon cycling and its potential to address various environmental challenges. The paper extensively discusses the synthesis, properties, and applications of lignin nanoparticles in diverse fields such as water purification and soil remediation. Moreover, it highlights the challenges associated with nanoparticle deployment, ranging from Eco toxicological assessments to scalability issues. Multidisciplinary collaboration and integration of research findings with real-world applications are emphasized as critical factors for unlocking the transformative potential of lignin nanoparticles. Ultimately, this review underscores lignin nanoparticles as beacons of hope in the pursuit of cleaner, healthier, and more harmonious coexistence between humanity and nature through innovative environmental remediation strategies.

Highly Specific Polyphenolic Colloids as Alternatives to Antimicrobials in Livestock Production

The dispersion of antibiotics in livestock farming represents a health concern worldwide, contributing to the spread of antimicrobial-resistant bacteria through animals, the environment, and humans. Phenolic compounds could be alternatives to antibiotics, once drawbacks such as their low water solubility, bioavailability, and reduced stability are overcome. Although nano- or micro-sized formulations could counter these shortcomings, they do not represent cost-effective options. In this study, three phenolic compounds, obtained from wood-processing manufacturers, were characterized, revealing suitable features such as their antioxidant activity, size, and chemical and colloidal stability for in-field applications. The minimum inhibitory concentration (MIC) of these colloidal suspensions was measured against six bacterial strains isolated from livestock. These particles showed different inhibition behaviors: Colloidal chestnut was effective against one of the most threatening antibiotic-resistant pathogens, i.e., S. aureus, but ineffective toward E. coli. Instead, colloidal pine showed a weak effect on S. aureus but specificity toward E. coli. The present proof-of-concept points at colloidal polyphenols as valuable alternatives for antimicrobial substitutes in the livestock context.

Eco-friendly lignin nanoparticles as antioxidant and antimicrobial material for enhanced textile production

Natural polymers are bioactive compounds that are used in the treatment of several disorders. Natural lignin, an amorphous polymer, offers significant potential for use as a building block in the production of bio-renovation materials. This study used an alkaline solvent technique to extract lignin from two Egyptian cotton cultivar byproducts, Giza 86 and 90. We then created nano-lignin to recycle cotton stalks into an environmentally beneficial product. The characterization of L86, L90, LNP86, and LNP90 was carried out using particle size, zeta potential, FT-IR, and TEM. Antioxidant activity using the DPPH assay and antimicrobial activity were determined for lignin and nano-lignin. Seven pathogenic bacteria (Bacillus cereus, Staphylococcus aureus, Staphylococcus sciuri, Salmonella typhi, Salmonella enterica, Escherichia coli, and Pseudomonas aeruginosa) and five mycotoxigenic fungi (Aspergillus flavus, Aspergillus ochraceus, Aspergillus niger, Fusarium proliferatum and Penicillium verrucosum) were used for antimicrobial activity. The results showed high antioxidant efficiency for LNP90, with an IC50 of 10.38 µg/mL. The antimicrobial activity showed positive growth inhibition for all studied microorganisms, with significant differences in nano-lignin compared to ordinary lignin. lignin and nano-lignin were effectively applied to treated textiles for medical purposes. The study concluded that single-use medical textiles with anti-microbial and anti-oxidant properties, made from lignin and nano-lignin, could benefit patients intolerant to antibiotics.

Self-Formation of Lignin Particles Through Melt-Extrusion for Active Biodegradable Food Packaging

This study presents a method for the self-formation of lignin particles within a polylactic acid (PLA) matrix during melt-extrusion, eliminating the need for separation and drying steps typically associated with submicro-size lignin particles. This method effectively mitigates the problem of agglomeration often associated with the drying step. Softwood kraft lignin, guaiacyl lignin (GL-lignin), was dissolved in low-molecular-weight poly(ethylene glycol) (PEG) and was introduced into a twin-screw extruder using a liquid feeder. Lignin particles within a particle size range of 200-500 nm were observed in the extrudate of the PLA/PEG/GL-lignin composites. PLA/PEG/GL-lignin composite films were produced through blown film extrusion. These composite films demonstrated superior ultraviolet (UV)-barrier and antioxidant properties compared to neat PLA films, with optical and mechanical characteristics comparable to those of neat PLA. Moreover, migration values of the composite films in various food simulants were below regulatory limits, suggesting their potential for food packaging applications. This self-formation process offers a promising approach for utilizing lignin for PLA applications.

Biodegradable poly(ethylene glycol-glycerol-itaconate-sebacate) copolyester elastomer with significantly reinforced mechanical properties by in-situ construction of bacterial cellulose interpenetrating network

To address the concern that biodegradable elastomers are environmental-friendly but usually associated with poor properties for practical utilization, we report a star-crosslinked poly(ethylene glycol-glycerol-itaconate-sebacate) (PEGIS) elastomer synthesized by esterification, polycondensation and UV curing, and reinforced by bacterial cellulose (BC). The interpenetrating network of primary BC backbone and vulcanized elastomer is achieved by the "in-situ secondary network construction" strategy. With the well dispersion of BC without agglomeration, the mechanical properties of PEGIS are significantly enhanced in tensile strength, Young's modulus and elongation at break. The reinforcement strategy is demonstrated to be efficient and offers a route to the development of biodegradable elastomers for a variety of applications in the future.

Sustainable Materials from Organosolv Fibers and Lignin, Kraft Fibers, and Their Blends

The aim of this study was to investigate new materials from organosolv fibers, organosolv lignin, kraft fibers, and their blends. The organosolv fibers showed reprecipitated lignin on the surface, a comparably low fiber length of 0.565 mm on average, and a high fines content of 82.3%. Handsheets were formed and thermopressed at 175 °C and 50 MPa, yielding dense materials (1050-1100 kg/m3) with properties different to that of regular paper products. The thermopressing of organosolv fibers alone produced materials with similar or better tensile strength (σb = 18.6 MPa) and stiffness (E* = 2.8 GPa) to the softwood Kraft reference pulp (σb = 14.8 MPa, E* = 1.8 GPa). The surface morphology was also smoother with fewer cavities. As a result, the thermopressed organosolv fibers exhibited higher hydrophobicity (contact angle > 95°) and had the lowest overall water uptake. Combinations of Kraft fibers with organosolv fibers or organosolv lignin showed reduced wetting and a higher density than the Kraft fibers alone. Furthermore, the addition of organosolv lignin to Kraft fibers greatly improved tensile stiffness and strength (σb = 23.8 MPa, E* = 10.5 GPa), likely due to the lignin acting as a binder to the fiber network. In conclusion, new thermopressed materials were developed and tested, which show promising potential for sustainable fiber materials with improved water resistance.

Enhancement of elongation at break and UV-protective properties of poly(lactic acid) film with cationic ring opening polymerized (CROP)-lignin

In this study, the intrinsic brittleness of poly(lactic acid) (PLA) was overcome by chemical modification using ethyl acetate-extracted lignin (EL) via cationic ring-opening polymerization (CROP). The CROP was conducted to promote homopolymerization under starvation of the initiator (oxyrane). This method resulted in the formation of lignin-based polyether (LPE). LPE exhibited enhanced interfacial compatibility with nonpolar and hydrophobic PLA owing to the fewer hydrophilic hydroxyl groups and a long polyether chain. In addition, because of the UV-protecting and radical-scavenging abilities of lignin, LPE/PLA exhibited multifunctional properties, resulting in improved chemical properties compared with the neat PLA film. Notably, one of the LPE/PLA films (EL_MCF) exhibited excellent elongation at break of 297.7 % and toughness of 39.92 MJ/m3. Furthermore, the EL_MCF film showed superior UV-protective properties of 99.52 % in UVA and 88.95 % in UVB ranges, both significantly higher than those of the PLA film, without sacrificing significant transparency in 515 nm. In addition, the radical scavenging activity improved after adding LPE to the PLA film. These results suggest that LPEs can be used as plasticizing additives in LPE/PLA composite films, offering improved physicochemical properties.

Recent Advances of Lignin Functionalization for High-Performance and Advanced Functional Rubber Composites

The biomass lignin is the only large-volume renewable feedstock that is composed of aromatics but has been largely underutilized and is sought for valorization as a value-added material. Recent research has highlighted lignin as a promising alternative to traditional petrol-based reinforcements and functional additives for rubber composites. This review summarized the recent advances in the functionalization of lignin for a variety of rubber composites, as well as the compounding techniques for effectively dispersing lignin within the rubber matrix. Significant progress has been achieved in the development of high-performance and advanced functional rubber/lignin composites through carefully designing the structure of lignin-based additives and the optimization of interfacial morphologies. This Review discussed the effect of lignin on composite properties, including mechanical reinforcement, dynamic properties, antiaging performance, and oil resistance, and also the advanced stimuli-responsive performance in detail. A critical analysis for the future development of rubber/lignin composites is presented as concluding remarks.

Lignocellulosic Bionanomaterials for Biosensor Applications

The rapid population growth, increasing global energy demand, climate change, and excessive use of fossil fuels have adversely affected environmental management and sustainability. Furthermore, the requirements for a safer ecology and environment have necessitated the use of renewable materials, thereby solving the problem of sustainability of resources. In this perspective, lignocellulosic biomass is an attractive natural resource because of its abundance, renewability, recyclability, and low cost. The ever-increasing developments in nanotechnology have opened up new vistas in sensor fabrication such as biosensor design for electronics, communication, automobile, optical products, packaging, textile, biomedical, and tissue engineering. Due to their outstanding properties such as biodegradability, biocompatibility, non-toxicity, improved electrical and thermal conductivity, high physical and mechanical properties, high surface area and catalytic activity, lignocellulosic bionanomaterials including nanocellulose and nanolignin emerge as very promising raw materials to be used in the development of high-impact biosensors. In this article, the use of lignocellulosic bionanomaterials in biosensor applications is reviewed and major challenges and opportunities are identified.

Physicochemical properties of lignin nanoparticles from softwood and their potential application in sustainable pre-harvest bagging as transparent UV-shielding films

Technical lignin can be mainly obtained as a waste by-product from pulp industry, and it exhibits unique properties including ultraviolet adsorption, biodegradable, antibacterial, and antioxidant which can be utilized for bioplastic applications. However, common limitations of technical lignin for plastic applications are compatibility mainly due to poor interfacial adhesion, relatively large particle size and impurity. In this study lignin nanoparticles from softwood (S-LNPs) were successfully produced through a continuous-green-scalable antisolvent precipitation and the suitability of S-LNPs for fabrication of bio-composite polybutylene succinate (PBS) films using conventional blown film extrusion was examined. The attained S-LNPs showed lower ash content, higher phenolic content and higher lignin content compared to pristine softwood kraft lignin (S-lignin). Rheological property including shear viscosity and melt-flow index was determined. The obtained PBS/S-LNP composite films showed improved tensile modulus, higher water vapor transmission rate and excellent UV-shielding ability compared to neat PBS and PBS/S-lignin films. Accelerated weathering testing was conducted to replicate outdoor conditions. Degradation indices including carbonyl, vinyl and hydroxyl of the weathered PBS/lignin composites were evaluated for photo-oxidative stability. The S-LNPs as multifunctional bio-additives in biodegradable composite film exhibited superior performances of transparency, UV-absorption and stiffness with high photo-oxidative stability suitable for outdoor applications.

Enhanced Performance of Lignin Recovery with a Carbon Dioxide Acidification Method

Lignin particles were recovered from the bagasse soda pulping black liquor by acidification with carbon dioxide continuously fed in a semibatch reactor. An experimental model based on the response surface methodology was selected to investigate the effect of parameters and optimize the process for maximizing the lignin yield, and the physicochemical properties of the obtained lignin under the optimum conditions were investigated for further potential applications. A total of 15 experimental runs of three controlled parameters including temperature, pressure, and residence time were carried out based on the Box-Behnken design (BBD). The mathematic model for lignin yield prediction was successfully estimated at 99.7% accuracy. Temperature played a more significant role in lignin yield than pressure and residence time. Higher temperature could faciltate a higher lignin yield. Approximately 85 wt % lignin yield was obtained under the optimum conditions with a purity higher than 90%, high thermal stability, and slightly broad molecular weight distribution. The p-hydroxyphenyl-guaiacyl-syringyl (HGS)-type lignin structure and spherical shape were confirmed by Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FE-SEM). These characteristics confirmed that the obtained lignin could be used in high-value products. Moreover, this work indicated that the CO₂ acidification unit for lignin recovery could be efficiently improved for achieving high yield and purity from black liquor by adjustment of the process.

Challenges and perspectives of green-like lignocellulose pretreatments selectable for low-cost biofuels and high-value bioproduction

Lignocellulose represents the most abundant carbon-capturing substance that is convertible for biofuels and bioproduction. Although biomass pretreatments have been broadly applied to reduce lignocellulose recalcitrance for enhanced enzymatic saccharification, they mostly require strong conditions with potential secondary waste release. By classifying all major types of pretreatments that have been recently conducted with different sources of lignocellulose substrates, this study sorted out their distinct roles for wall polymer extraction and destruction, leading to the optimal pretreatments evaluated for cost-effective biomass enzymatic saccharification to maximize biofuel production. Notably, all undigestible lignocellulose residues are also aimed for effective conversion into value-added bioproduction. Meanwhile, desired pretreatments were proposed for the generation of highly-valuable nanomaterials such as cellulose nanocrystals, lignin nanoparticles, functional wood, carbon dots, porous and graphitic nanocarbons. Therefore, this article has proposed a novel strategy that integrates cost-effective and green-like pretreatments with desirable lignocellulose substrates for a full lignocellulose utilization with zero-biomass-waste liberation.

Organosolv Lignin as a Green Sizing Agent for Thermoformed Pulp Products

The purpose of this study was to investigate the use of organosolv lignin as a sizing agent for thermoformed pulp products as a sustainable material with improved water resistance. For this purpose, an in-house-produced organosolv lignin from softwood (Norway Spruce) was mixed with bleached and unbleached chemi-thermomechanical pulp fibers. In addition, the isolated organosolv lignin was characterized by ATR-FTIR spectroscopy, size-exclusion chromatography, and thermogravimetric analysis. The analysis showed that organosolv lignin was of a high purity and practically ash-free, exhibiting low molecular weight, a glass transition temperature below the thermoforming temperature, and a high content of phenolic OH groups. The mechanical properties and water resistance of the organosolv lignin-sized thermoformed pulp materials were measured. A small decrease in strength and an increase in stiffness and density were observed for the lignin-sized thermoformed materials compared to the reference, that is, unsized materials. The addition of organosolv lignin decreased the wettability and swelling of the thermoformed product. These results are due to the distribution of organosolv lignin on the surface, filling in the pores and cavities, and providing a tighter fit within the thermoformed materials. In conclusion, the results from our study encourage the use of organosolv lignin as a sizing additive to thermoformed products, which can improve the water resistance to use it in sustainable packaging applications.

Role of lignin-based nanoparticles in anticancer drug delivery and bioimaging: An up-to-date review

Lignin, an aromatic biopolymer, is the second most abundant naturally occurring one after cellulose that has drawn a great deal of interest over the years for its potential uses owing to the presence of high content of phenolic compounds, ecofriendly feature and cost-efficiency in comparison to the synthetic polymers. Nevertheless, with the intention of advancing its development, several efforts have been performed in the direction of utilizing lignin on the nanoscale due to its inimitable properties. The notable absorption capacity, fluorescence emission, biodegradability and non-toxicity of lignin nanoparticles permit its appropriateness as a vehicle for drugs and as a bioimaging material. Moreover, lignin nanoparticles have shown plausible therapeutic effects, such as anticancer, antimicrobial, and antioxidant. The current review sheds light on the recent development in the formulation and anticancer applications of lignin nanoparticles as a drug carrier and as a diagnostic tool. The surface properties of the nanomaterial affect the end product characteristics, hence, factors namely; lignin source, isolation technique, purification and quantitation methods, are discussed in this review. This study represents original work that has not been published elsewhere and that has not been submitted simultaneously for publication elsewhere. The manuscript has been read, revised, and approved by the authors.

Green synthesis of sodium lignosulfonate nanoparticles using chitosan for significantly enhanced multifunctional characteristics

Nanoparticles of green materials have gained enormous interest due to their broad range of applications in several disciplines since they have significantly improved multifunctional activities. This article attempts a sustainable green approach to synthesize sodium lignosulfonate nanoparticles (SLS NPs) using another biomolecule, i.e., chitosan. The synthesized SLS NPs (with an average diameter of ~125 nm to 129 nm) have demonstrated synergetic efficacy by exhibiting outstanding multifunctional properties due to the presence of two types of biomolecules (i.e., lignosulfonate as well as chitosan) in their structure. The synthesized SLS NPs have bestowed excellent antibacterial activity against both the Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria. Moreover, SLS NPs have displayed ~92% antioxidant property. Having polyphenolic entities in the structure of SLS NPs, they have shown UV-visible absorption peak at 224 nm, which directly indicates that they can act as an outstanding UV protective agent which has also been proven experimentally.

High-Molecular-Weight Fractions of Spruce and Eucalyptus Lignin as a Perspective Nanoparticle-Based Platform for a Therapy Delivery in Liver Cancer

The natural polymer, lignin, possesses unique biodegradable and biocompatible properties, making it highly attractive for the generation of nanoparticles for targeted cancer therapy. In this study, we investigated spruce and eucalyptus lignin nanoparticles (designated as S-and E-LNPs, respectively). Both LNP types were generated from high-molecular-weight (M_w) kraft lignin obtained as insoluble residues after a five-step solvent fractionation approach, which included ethyl acetate, ethanol, methanol, and acetone. The resulting S-and E-LNPs ranged in size from 16 to 60 nm with uniform spherical shape regardless of the type of lignin. The preparation of LNPs from an acetone-insoluble lignin fraction is attractive because of the use of high-M_w lignin that is otherwise not suitable for most polymeric applications, its potential scalability, and the consistent size of the LNPs, which was independent of increased lignin concentrations. Due to the potential of LNPs to serve as delivery platforms in liver cancer treatment, we tested, for the first time, the efficacy of newly generated E-LNPs and S-LNPs in two types of primary liver cancer, hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA), in vitro. Both S-LNPs and E-LNPs inhibited the proliferation of HCC cells in a dose-dependent manner and did not affect CCA cell line growth. The inhibitory effect toward HCC was more pronounced in the E-LNP-treated group and was comparable to the standard therapy, sorafenib. Also, E-LNPs induced late apoptosis and necroptosis while inhibiting the HCC cell line. This study demonstrated that an elevated number of carbohydrates on the surface of the LNPs, as shown by NMR, seem to play an important role in mediating the interaction between LNPs and eukaryotic cells. The latter effect was most pronounced in E-LNPs. The novel S- and E-LNPs generated in this work are promising materials for biomedicine with advantageous properties such as small particle size and tailored surface functionality, making them an attractive and potentially biodegradable delivery tool for combination therapy in liver cancer, which still has to be verified in vivo using HCC and CCA models.

Lignin-Mediated Silver Nanoparticle Synthesis for Photocatalytic Degradation of Reactive Yellow 4G and In Vitro Assessment of Antioxidant, Antidiabetic, and Antibacterial Activities

This study explored the potential of abundantly available sodium lignosulfonate (LS) as a reducer and fabricating agent in preparing silver nanoparticles (LS–Ag NPs). The operational conditions were optimized to make the synthesis process simpler, rapid, and eco-friendly. The prepared LS–Ag NPs were analyzed via UV–Vis spectroscopy, X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, and high-resolution transmission electron microscopy. Results demonstrated that LS–Ag NPs were of crystalline structure, capped with LS constituents, and spherical in shape with a size of approximately 20 nm. Under optimized conditions, LS–Ag NPs exhibited significant photocatalytic activity in Reactive Yellow 4G degradation. The effects of photocatalyst (LS–Ag NPs) dosage, dye concentration, and its reusability for dye degradation were studied to make the process practically applicable in textile wastewater treatment. Additionally, the synthesized LS–Ag NPs displayed significant free radical scavenging against 2-diphenyl-1-picrylhydrazyl (DPPH) with an IC₅₀ value of (50.2 ± 0.70 µg/mL) and also exhibited antidiabetic activity in terms of inhibition in the activity of carbohydrate-degrading marker enzyme α-glucosidase with an IC₅₀ value of (58.1 ± 0.65 µg/mL). LS–Ag NPs showed substantial antibacterial potential against pathogenic strains, namely E. coli and S. aureus. In conclusion, LS–Ag NPs can be a reliable and eco-friendly material for their possible application in the treatment of dye-containing wastewater and have a great perspective in the biomedical and pharmaceutical sectors.

Efficient and selective removal of Pb(ii) from aqueous solution by a thioether-functionalized lignin-based magnetic adsorbent

The effective and selective removal of heavy metal ions from sewage is a major challenge and is of great significance to the treatment and recovery of metal waste. Herein, a novel magnetic lignin-based adsorbent L@MNP was synthesized by a thiol-ene click reaction under ultraviolet (UV) light irradiation. Multiple characterization techniques, including Fourier transform infrared (FT-IR) spectrometry, X-ray diffraction (XRD), elemental analysis, vibrating sample magnetometry (VSM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), confirmed the formed nano-morphology and structure of L@MNP. The effects of pH, contact time, initial metal concentration and temperature on the batch adsorption of Pb(ii) by L@MNP were investigated. Due to the existence of sulfur and oxygen-containing sites, the maximum adsorption capacity of L@MNP for Pb(ii) could reach 97.38 mg g^-1, while the adsorption equilibrium was achieved within 30 min. The adsorption kinetics and isotherms were well described by the pseudo-second-order model and Langmuir model, respectively, suggesting a chemical and monolayer adsorption process. In addition, L@MNP showed a high adsorption selectivity (k _Pb = 0.903) toward Pb(ii) in the presence of other co-existing metal ions. The experimental results also revealed that L@MNP displayed structural stability, ease of recovery under an external magnetic field, and acceptable recyclability after the fifth cycle. Considering its facile preparation, low cost and high adsorption efficiency, the developed L@MNP adsorbent demonstrated great potential in removing heavy metal ions from wastewater.

Antisolvent versus ultrasonication: Bottom-up and top-down approaches to produce lignin nanoparticles (LNPs) with tailored properties

In spite of the increasing amount of literature on the production and application of lignin nanoparticles (LNPs), little or no attention has been paid so far to the influence of different production methods on the properties of these nanostructures. Herein, we propose a comprehensive study to assess the impact of several factors on the color, morphology, colloidal stability, antioxidant capacity, and UV-shielding performance of LNPs. LNPs were obtained by two different routes: a bottom-up approach based on the self-assembly in a solvent-antisolvent system with acetone/lignin/water; or a top-down approach based on the ultrasonication of never-dried lignin aqueous suspensions. The starting lignin was extracted from elephant grass leaves or stems, so that the influence of anatomical origin and molecular weight could also be investigated. Moreover, lignin was oxidized prior to being converted into LNPs, allowing for comparisons between different oxidation degrees. This study showed that interesting properties of LNPs can be easily tailored and combined focusing on the various applications of these versatile nanostructures. In a model application, different types of LNPs were incorporated into poly(vinyl alcohol)-based nanocomposites, modulating the UV-protection capability of the polymer matrix.

Recent Developments in the Formulation and Use of Polymers and Particles of Plant-based Origin for Emulsion Stabilizations

The main scope of this Review was the recent progress in the use of plant-based polymers and particles for the stabilization of Pickering and non-Pickering emulsion systems. Due to their availability and promising performance, it was discussed how the source, modification, and formulation of cellulose, starch, protein, and lignin-based polymers and particles would impact their emulsion stabilization. Special attention was given toward the material synthesis in two forms of polymeric surfactants and particles and the corresponding formulated emulsions. Also, the effects of particle size, degree of aggregation, wettability, degree of substitution, and electrical charge in stabilizing oil/water systems and micro- and macro-structures of oil droplets were discussed. The wide range of applications using such plant-based stabilizers in different technologies as well as their challenge and future perspectives were described.

Multifunctional lignin-based nanocomposites and nanohybrids

Significant progress in lignins valorization and development of high-performance sustainable materials have been achieved in recent years. Reports related to lignin utilization indicate excellent prospects considering green chemistry, chemical engineering, energy, materials and polymer science, physical chemistry, biochemistry, among others. To fully realize such potential, one of the most promising routes involves lignin uses in nanocomposites and nanohybrid assemblies, where synergistic interactions are highly beneficial. This review first discusses the interfacial assembly of lignins with polysaccharides, proteins and other biopolymers, for instance, in the synthesis of nanocomposites. To give a wide perspective, we consider the subject of hybridization with metal and metal oxide nanoparticles, as well as uses as precursor of carbon materials and the assembly with other biobased nanoparticles, for instance to form nanohybrids. We provide cues to understand the fundamental aspects related to lignins, their self-assembly and supramolecular organization, all of which are critical in nanocomposites and nanohybrids. We highlight the possibilities of lignin in the fields of flame retardancy, food packaging, plant protection, electroactive materials, energy storage and health sciences. The most recent outcomes are evaluated given the importance of lignin extraction, within established and emerging biorefineries. We consider the benefit of lignin compared to synthetic counterparts. Bridging the gap between fundamental and application-driven research, this account offers critical insights as far as the potential of lignin as one of the frontrunners in the uptake of bioeconomy concepts and its application in value-added products.

Functional Lignin Nanoparticles with Tunable Size and Surface Properties: Fabrication, Characterization, and Use in Layer-by-Layer Assembly

Lignin is the richest source of renewable aromatics and has immense potential for replacing synthetic chemicals. The limited functionality of lignin is, however, challenging for its potential use, which motivates research for creating advanced functional lignin-derived materials. Here, we present an aqueous-based acid precipitation method for preparing functional lignin nanoparticles (LNPs) from carboxymethylated or carboxypentylated lignin. We observe that the longer grafted side chains of carboxypentylated lignin allow for the formation of larger LNPs. The functional nanoparticles have high tolerance against salt and aging time and well-controlled size distribution with R_h ≤ 60 nm over a pH range of 5-11. We further investigate the layer-by-layer (LbL) assembly of the LNPs and poly(allylamine hydrochloride) (PAH) using a stagnation point adsorption reflectometry (SPAR) and quartz crystal microbalance with dissipation (QCM-D). Results demonstrate that LNPs made of carboxypentylated lignin (i.e., PLNPs with the adsorbed mass of 3.02 mg/m²) form a more packed and thicker adlayer onto the PAH surface compared to those made of carboxymethylated lignin (i.e., CLNPs with the adsorbed mass of 2.51 mg/m²). The theoretical flux, J, and initial rate of adsorption, (dΓ/dt)₀, analyses confirm that 22% of PLNPs and 20% of CLNPs arriving at the PAH surface are adsorbed. The present study provides a feasible platform for engineering LNPs with a tunable size and adsorption behavior, which can be adapted in bionanomaterial production.

Characterization of Organosolv Birch Lignins: Toward Application-Specific Lignin Production

Organosolv pretreatment represents one of the most promising biomass valorization strategies for renewable carbon-based products; meanwhile, there is an overall lack of holistic approach to how extraction conditions affect the suitable end-usages. In this context, lignin extracted from silver birch (Betula pendula L.) by a novel hybrid organosolv/steam-explosion treatment at varying process conditions (EtOH %; time; catalyst %) was analyzed by quantitative NMR (¹H-¹³C HSQC; ¹³C NMR; ³¹P NMR), gel permeation chromatography, Fourier transform infrared (FT-IR), Pyr-gas chromatography-mass spectroscopy (GC/MS), and thermogravimetric analysis, and the physicochemical characteristics of the lignins were discussed regarding their potential usages. Characteristic lignin interunit bonding motifs, such as β-O-4', β-β', and β-5', were found to dominate in the extracted lignins, with their abundance varying with treatment conditions. Low-molecular-weight lignins with fairly unaltered characteristics were generated via extraction with the highest ethanol content potentially suitable for subsequent production of free phenolics. Furthermore, β-β' and β-5' structures were predominant at higher acid catalyst contents and prolonged treatment times. Higher acid catalyst content led to oxidation and ethoxylation of side-chains, with the concomitant gradual disappearance of p-hydroxycinnamyl alcohol and cinnamaldehyde. This said, the increasing application of acid generated a broad set of lignin characteristics with potential applications such as antioxidants, carbon fiber, nanoparticles, and water remediation purposes.

Lignin-Based Nanoparticles: A Review on Their Preparations and Applications

Lignin is the most abundant by-product from the pulp and paper industry as well as the second most abundant natural renewable biopolymer after cellulose on earth. In recent years, transforming unordered and complicated lignin into ordered and uniform nanoparticles has attracted wide attention due to their excellent properties such as controlled structures and sizes, better miscibility with polymers, and improved antioxidant activity. In this review, we first introduce five important technical lignin from different sources and then provide a comprehensive overview of the recent progress of preparation techniques which are involved in the fabrication of various lignin-based nanoparticles and their industrial applications in different fields such as drug delivery carriers, UV absorbents, hybrid nanocomposites, antioxidant agents, antibacterial agents, adsorbents for heavy metal ions and dyes, and anticorrosion nanofillers.

Technological advancement in the synthesis and applications of lignin-based nanoparticles derived from agro-industrial waste residues: A review

Over the years, lignin has drawn a great deal of interest for their potential use as bio-polymers due to the presence of high amount of phenolic compounds, non-polluting feature and cost-competitiveness as compared to synthetic polymers. However, in order to fast-track their development, different attempts are made towards the usage of lignin in nano form since it exhibits some unique properties in nanoscale range. The present review article provides a detail analysis on the recent advancement in the synthesis and applications of lignin nanoparticles (LNPs) derived from agro-industrial waste residues. In view of that, an in-depth morphological analysis was reviewed to assess the structural influence on the characteristics of LNPs. Further, application of LNPs is explored in different fields including bio-medical engineering, pharmaceuticals, skin-care products and food industries. Finally, the paper is concluded discussing various challenges associated with the synthesis, modification and development with an aspiration of futuristic developments. The readers of this review article will be highly benefitted after acquiring a comprehensive knowledge on LNPs and its different synthesis processes along with various applications.

Sustainable Strategies in the Synthesis of Lignin Nanoparticles for the Release of Active Compounds: A Comparison

The preparation of nanoparticles represents a powerful tool for lignin valorization, as it combines easy methodologies with high application potential. Different synthetic strategies and various lignin sources have been employed in the process. However, the great variability in the lignin structure prevents a direct comparison of the so far reported lignin nanoparticles (LNPs), especially as regards their physicochemical and functional properties. To this purpose, two green protocols, that is, solvent-antisolvent and hydrotropic, were optimized and used to generate LNPs from the same softwood kraft lignin. The nanomaterials were fully characterized to extrapolate structure/property relationships and reveal any differences in the mechanism of self-assembly. Furthermore, tests on methylene blue entrapment capacity and release behavior at two different pH values (2.0 and 7.4) evidenced a clear dependence on the LNPs characteristics and thus on the strategy adopted for their production.

Direct Precipitation of Lignin Nanoparticles from Wheat Straw Organosolv Liquors Using a Static Mixer

Micro- and nanosize lignin shows improved properties compared to standard lignin available today and has been gaining interest in recent years. Lignin is the largest renewable resource with an aromatic skeleton on earth but it is used for relatively low-value applications. Lignin in micro- to nanoscale; however, could facilitate rather valuable applications. Current production methods consume high amounts of solvents for purification and precipitation. The process investigated in this work uses the direct precipitation of lignin nanoparticles from organosolv pretreatment extract in a static mixer and can reduce solvent consumption drastically. The pH value, ratio of antisolvent to organosolv extract and flowrate in the mixer were investigated as precipitation parameters in terms of the resulting particle properties. Particles with dimensions ranging from 97.3 to 219.3 nm could be produced, and at certain precipitation parameters, carbohydrate impurities reach values as low as in purified lignin particles. Yields were found independent of the precipitation parameters with 48.2 ± 4.99%. Results presented in this work can be used to optimize precipitation parameters with emphasis on particle size, carbohydrate impurities or the solvent consumption.