Exploring the role of lignin structure in molecular dynamics of lignin/bio-derived thermoplastic elastomer polyurethane blends

Optimization of areca leaf sheath nanolignin synthesis by a mechanical method for in situ modification of ultra-low molar ratio urea-formaldehyde adhesives

This study addresses the optimization of the nanolignin preparation method from the areca leaf sheath (ALS) by a mechanical process using a high shear homogenizer at 13,000-16,000 rpm for 1-4 h and its application in enhancing the performance of ultralow molar ratio urea-formaldehyde (UF) adhesive. Response surface methodology (RSM) with a central composite design (CCD) model was used to determine the optimum nanolignin preparation method. The mathematical model obtained was quadratic for the particle size response and linear for the zeta potential response. Under the optimum conditions, a speed of 16,000 rpm for 4 h resulted in a particle size of 227.7 nm and a zeta potential of -18.57 mV with a high desirability value of 0.970. FE-SEM revealed that the characteristic changes of lignin to nanolignin occur from an irregular or nonuniform shape to an oval shape with uniform particles. Nanolignin was introduced during the addition reaction of UF resin synthesis. UF modified with nanolignin (UF-NL) was analyzed for its adhesive characteristics, functional groups, crystallinity, and thermomechanical properties. The UF-NL adhesive had a slightly greater solid content (73.23 %) than the UF adhesive, a gelation time of 4.10 min, and a viscosity of 1066 mPa.s. The UF-NL adhesive had similar functional groups as the UF adhesive, with a lower crystallinity of 59.73 %. Compared with the control plywood which has a tensile shear strength value of 0.79 MPa, the plywood bonded with UF-NL had a greater tensile shear strength of 1.07 MPa, with a lower formaldehyde emission of 0.065 mg/L.

Sustainable lignin nanoparticles from coconut fiber waste for enhancing multifunctional properties of macroalgae biofilms

Multifunctional and sustainable packaging biofilms felicitous to changeable conditions are in large demand as substitutes to petroleum-derived synthetic films. Macroalgae with noticeable film-formation, abundant, low-cost, and edible properties is a promising bioresource for sustainable and eco-friendly packaging materials. However, the poor hydrophobicity and mechanical properties of sustainable macroalgae biofilms seriously impede their practical applications. Herein, lignin nanoparticles (LNPs) produced by a sustainable approach from black liquor of coconut fiber waste were incorporated in the macroalgae matrix to improve the water tolerance and mechanical characteristics of the biofilms. The effect of different LNPs loadings on the performance of biofilms, such as physical, morphological, surface roughness, structural, water resistance, mechanical, and thermal behaviors, were systematically evaluated and found to be considerably improved. Biofilm with 6 % LNPs presented the optimum enhancement in most ultimate performances. The optimized biofilm exhibited great hydrophobic features with a water contact angle of over 100° and high enhancement in the tensile strength of >60 %. This study proposes a facile and sustainable approach for designing and developing LNPs-macroalgae biofilms with excellent and multifunctional properties for sustainable high-performance packaging materials.

The mechanism of self-assembly of lignin in deep eutectic solvent based on sulfamic acid and urea through molecular dynamics simulation

Due to the diversity of industrial lignin sources and the complexity of its structure, its application as a high-value material is limited. Lignin nanoparticles (LNPs) have emerged as a hotspot for research due to their advantages of high specific surface area and high dispersion and the solvent transfer method is commonly used for the preparation of LNPs. In this paper, LNPs were prepared by solvent transfer method using DES based on sulfamic acid and urea (S/U DES) as solvent and water as anti-solvent. To explore the internal mechanism of the self-assembly of nanoparticles, a theoretical model of the solvent system and model lignin compound was constructed with the assistance of quantum chemistry and molecular dynamics theories. Through classical molecular dynamics (MD) simulations, the interaction energy, radius of gyration (ROG), solvent accessible surface area (SASS), radial and spatial distribution function (RDFs/SDFs), hydrogen bonding, and the morphology changes were analyzed to reveal the internal mechanism of self-assembly of model lignin compounds in S/U DES. This study is useful in revealing the mechanism of interaction between lignin and DES, as well as providing a benchmark for the green and efficient preparation of lignin nanoparticles.

High performance plant-derived thermoplastic polyester elastomer foams achieved by manipulating charging order of mixed blowing agents

Plant-derived thermoplastic polyester elastomer (TPEE) is an environment friendly polymer known for its exceptional tear strength and mechanical properties, whose monomers are generated from crops. To prepare high-performance TPEE foams is still challenging due to the intrinsic shrinkage behavior. Herein, two microcellular foaming routes with different charging orders of mixed blowing agents, namely "CO2 firstly charging process (CO2-F-process)" and "N2 firstly charging process (N2-F-process)", were developed to elucidate the effects of mixed blowing agents on foaming behavior. Compared with the case in N2-F-process, more carbon dioxide and less nitrogen were adsorbed in CO2-F-process. Thus, TPEE foams prepared by N2-F-process show less shrinkage and higher creep recovery ratio than those prepared by CO2-F-process. Thanks to better structural stability and smaller shrinkage, TPEE foams prepared by N2-F-process exhibited enhanced strength and resilience. For the foams with similar density, compression strength can be increased by 52 %, and energy loss coefficient can be reduced to 50 %, by using N2-F-process. Thus, not only biomass TPEE foams with enhanced mechanical performance shows promising prospects in those areas that needs lightweight, insulation and high resilience, but also novel microcellular foaming technique with mixed blowing agents opens a new way for developing high-performance polymeric foams.

Three-Dimensional Printing of Shape Memory Liquid Crystalline Thermoplastic Elastomeric Composites Using Fused Filament Fabrication

Liquid crystalline elastomers (LCEs) are stimuli-responsive materials utilised in shape memory applications. The processability of these materials via advanced manufacturing is being paid increasing attention to advance their volume production on an industrial scale. Fused filament fabrication (FFF) is an extrusion-based additive manufacturing (AM) technique that offers the potential to address this. The critical challenge, however, is the rheological characteristics of LCEs that need to be tuned to achieve a facile processability through the extrusion-based method. In this work, new filaments of liquid crystalline thermoplastic elastomer (LCTPE) and its composites with lignin were made by the ternary system of LCE, thermoplastic polyurethane (TPU), and lignin. The results showed that TPU improves the melt flow index of the LCTPE system to approximately 10.01 g/10 min, while adding lignin further enhances the value of this index for the composites up to 21.82 g/10 min. The microstructural analysis indicated that the effective distribution of lignin and reduced domain size of the LCEs in the ternary blend contribute to the enhanced flowability of this filament through 3D printing. Samples of 3D-printed LCTPE and LCTPE/lignin composites maintained their shape memory characteristics via thermomechanical activation. Full shape recovery of the new LCTPE matrix and its composites with lignin was achieved in 39 s and 32 s at 130 °C, followed by 28 s and 24 s at 160 °C, respectively. The successful fabrication of LCTPE and LCTPE/lignin composite samples through 3D printing demonstrates a potential procedure for processing these shape memory materials using the FFF technique, and lignin offers a sustainable and cost-effective material solution that enhances the properties of this composite material.

Characterization and 3D printing of a biodegradable polylactic acid/thermoplastic polyurethane blend with laccase-modified lignin as a nucleating agent

Polylactic acid (PLA) has been used in fused deposition method (FDM) based 3D printing for many years. Alkali lignin is an undervalued industrial by-product that could upgrade PLA's poor mechanical properties. This work presents a biotechnological approach consisting of a partial degradation of alkali lignin using Bacillus ligniniphilus laccase (Lacc) L1 for its use as a nucleating agent in a polylactic acid/thermoplastic polyurethane (PLA/TPU) blend. Results showed that adding enzymatically modified lignin (EL) increased the elasticity modulus to a maximum of 2.5-fold than the control and conferred a maximum biodegradability rate of 15 % after 6 months under the soil burial method. Furthermore, the printing quality rendered satisfactory smooth surfaces, geometries and a tunable addition of a woody color. These findings open a new door for using laccase as a tool to upgrade lignin's properties and its use as a scaffold in manufacturing more environmentally sustainable filaments with improved mechanical properties for 3D printing.

Novel lignin-supported copper complex as a highly efficient and recyclable nanocatalyst for Ullmann reaction

In this work, we prepared polyhydroxylated lignin by demethylation and hydroxylation of lignin, and grafted phosphorus-containing groups by nucleophilic substitution reaction, the resulting material could be used as a carrier for the preparation of heterogeneous Cu-based catalysts (PHL-CuI-OPR₂). The optimal PHL-CuI-OP^tBu₂ catalyst was characterized by FT-IR, TGA, BET, XRD, SEM-EDS, ICP-OES, XPS. The catalytic performance of PHL-CuI-OP^tBu₂ in the Ullmann CN coupling reaction was evaluated using iodobenzene and nitroindole as model substrates under nitrogen atmosphere with DME and H₂O as cosolvent at 95 °C for 24 h. The applicability of modified lignin-supported copper catalyst was investigated of various aryl/heteroaryl halides with indoles under optimal conditions, the corresponding products were obtained with high yield. Additionally, it could be easily recovered from the reaction medium by an easy centrifugation and washing.

The role of acetone-fractionated Kraft lignin molecular structure on surface adhesion to formaldehyde-based resins

One of the key strategies for valorizing kraft lignin (KL) into value-added products such as bio-based adhesives is to perform solvent fractionation of KL to produce lignin with improved homogeneity. Understanding the structure and properties of fractionated KL will aid in the selection of the best samples for certain applications. In this study, acetone-fractionated KL from softwood and hardwood was characterized to understand its chemical structure, elemental composition, molecular weight, and thermal properties. The results revealed that acetone-insoluble KL (AIKL) fractions from softwood and hardwood have greater molecular weight, polydispersity, glass temperature, carbohydrate content, aliphatic hydroxyl groups, and a variety of native wood lignin side chains. In contrast, acetone-soluble KL (ASKL) fractions have a significantly lower molecular weight and polydispersity, a lower glass-transition temperature, a more condensed structure, more aromatic hydroxyl groups, and fewer native wood lignin side chains. In addition, the ASKL samples demonstrated stronger adhesive force and work of adhesion toward phenol-formaldehyde (PF) and urea-formaldehyde (UF) resins than the AIKL samples, regardless of the lignin source. These findings suggest that ASKL has great potential as a substitute for phenol in PF resins and as a green additive to reinforce UF resins.

Different Kraft lignin sources for electrospun nanostructures production: Influence of chemical structure and composition

This work focuses on the structural features and physicochemical properties of different Kraft lignins and how they can influence the electrospinning process to obtain nanostructures. Structural features of Kraft lignins were characterized by Nuclear Magnetic Resonance, Size Exclusion Chromatography, Fourier-transform Infrared Spectroscopy, and thermal analysis, whereas chemical composition was analyzed by standard method. The addition of cellulose acetate (CA) improves the electrospinning process of Kraft lignins (KL). Thus, solutions of KL/CA at 30 wt% with a KL:CA weight ratio of 70:30 were prepared and then physicochemical and rheologically characterized. The morphology of electrospun nanostructures depends on the intrinsic properties of the solutions and the chemical structure and composition of Kraft lignins. Then, surface tension, electrical conductivity and viscosity of eucalypt/CA and poplar/CA solutions were suitable to obtain electrospun nanostructures based on uniform cross-linked nanofibers with a few beaded fibers. It could be related with the higher purity and higher linear structure, phenolic content and S/G ratios of lignin samples. However, the higher values of electrical conductivity and viscosity of OTP/CA solutions resulted in electrospun nanostructure with micro-sized particles connected by thin fibers, due to a lower purity, S/G ratio and phenolic content and higher branched structure in OTP lignin.

Lignocellulosic Materials for the Production of Biofuels, Biochemicals and Biomaterials and Applications of Lignocellulose-Based Polyurethanes: A Review

The present review is devoted to the description of the state-of-the-art techniques and procedures concerning treatments and modifications of lignocellulosic materials in order to use them as precursors for biomaterials, biochemicals and biofuels, with particular focus on lignin and lignin-based products. Four different main pretreatment types are outlined, i.e., thermal, mechanical, chemical and biological, with special emphasis on the biological action of fungi and bacteria. Therefore, by selecting a determined type of fungi or bacteria, some of the fractions may remain unaltered, while others may be decomposed. In this sense, the possibilities to obtain different final products are massive, depending on the type of microorganism and the biomass selected. Biofuels, biochemicals and biomaterials derived from lignocellulose are extensively described, covering those obtained from the lignocellulose as a whole, but also from the main biopolymers that comprise its structure, i.e., cellulose, hemicellulose and lignin. In addition, special attention has been paid to the formulation of bio-polyurethanes from lignocellulosic materials, focusing more specifically on their applications in the lubricant, adhesive and cushioning material fields. High-performance alternatives to petroleum-derived products have been reported, such as adhesives that substantially exceed the adhesion performance of those commercially available in different surfaces, lubricating greases with tribological behaviour superior to those in lithium and calcium soap and elastomers with excellent static and dynamic performance.

Next generation applications of lignin derived commodity products and their life cycle, techno-economical and societal analysis

The pulp and biorefining industries produce their waste as lignin, which is one of the most abundant renewable resources. So far, lignin has been remained severely underutilized and generally burnt in a boiler as a low-value fuel. To demonstrate lignin's potential as a value-added product, we will review market opportunities for lignin related applications by utilizing the thermo-chemical/biological depolymerization strategies (with or without catalysts) and their comparative evaluation. The application of lignin and its derived aromatics in various sectors such as cement industry, bitumen modifier, energy materials, agriculture, nanocomposite, biomedical, H₂ source, biosensor and bioimaging have been summarized. This comprehensive review article also highlights the technical, economic, environmental, and socio-economic variable that affect the market value of lignin-derived by-products. The review shows the importance of lignin, and its derived products are a platform for future bioeconomy and sustainability.

Towards producing high-quality lignin-based carbon fibers: A review of crucial factors affecting lignin properties and conversion techniques

The production of low-cost and high-quality carbon fibers (CFs) from biorenewable lignin precursors has been of worldwide interest for decades. Although numerous works have been reported and the proposed "1.72 GPa/172 GPa" target set by the Department of Energy (DOE) has been closely met in a few studies, most lignin-based CFs (LCFs) have poor strength properties compared to industrial PAN (polyacrylonitrile)-based CFs. The production of LCFs involves several steps, and the final quality of LCFs is governed by both lignin's properties and the manufacturing processes. Therefore, understanding the key factors of producing high quality LCF is of high importance. In this review, we firstly outlined several lignin's properties (e.g., impurities, thermal properties, molecular structure) that may play important role in determining its processability and suitability as carbon fiber precursor. Secondly, conversion strategies include spinning, stabilization and carbonization, and corresponding parameters influencing the final quality of LCF are comprehensively analyzed. Last, additional characterization methods are proposed as a means to facilitate analyzing of lignin and LCF. This review attempts to provide insights towards high-quality LCF production from both material and manufacturing aspects.

The role of lignin and lignin-based materials in sustainable construction - A comprehensive review

The construction industry in the 21st century faces numerous global challenges associated with growing concerns for the environment. Therefore, this review focuses on the role of lignin and its derivatives in sustainable construction. Lignin's properties are defined in terms of their structure/property relationships and how structural differences arising from lignin extraction methods influence its application within the construction sector. Lignin and lignin composites allow the partial replacement of petroleum products, making the final materials and the entire construction sector more sustainable. The latest technological developments associated with cement composites, rigid polyurethane foams, paints and coatings, phenolic or epoxy resins, and bitumen replacements are discussed in terms of key engineering parameters. The application of life cycle assessment in construction, which is important from the point of view of estimating the environmental impact of various solutions and materials, is also discussed.

Reduction of lignin heterogeneity using aqueous two-phase system: A facile and universal "one-step-three-fractions" approach

As the most abundant aromatic biopolymer, lignin presents great potential to produce valuable materials and chemicals. However, its large-scale value-added application is still facing many practical challenges and one of them is the unstable properties caused by lignin heterogeneity. Herein, we developed a novel "one-step-three-fractions" fractionation strategy to reduce lignin heterogeneity using aqueous two-phase system (ATPS) composed of (NH₄)₂SO₄ and ethanol. In contrast to conventional step-wise fractionation processes, the proposed process subdivided heterogeneous lignin into three homogeneous fractions in only one step: the first fraction (F1) dissolved in the ethanol-rich top layer; the second fraction (F2) dissolved in the salt-rich bottom layer and the last fraction (F3) insoluble in both two layers. F2 presented the lowest molecular weight followed by F1 while F3 showed the highest molecular weight. With the increase of molecular weight, the contents of guaiacyl unit and β-O-4 linkage increased while the content of hydrophilic groups (carboxyl and aromatic hydroxyl) decreased significantly. Moreover, the ATPS exhibited satisfactory recyclability and the fractionation approach could be applied to different types/sources of lignin. Consequently, the work indicates that ATPS is a novel and effective way to fractionate lignin and reduce its molecular weight polydispersity and structural heterogeneity in one step.

Development of functional lignin-based spherical particles for the removal of vanadium(V) from an aqueous system

A new type of functional lignin-based spherical particles (L-CTAB) prepared with the use of hexadecyltrimethylammonium bromide (CTAB) was applied as an effective biosorbent for removing vanadium(V) ions. The porous structure, characteristic functional groups, electrokinetic stability, morphology and size of the L-CTAB particles were examined. The conditions of removal were also investigated, including pH (2-12), sorbent mass (0.1-0.5 g), concentration (10-100 mg/dm3), phase contact time (1-240 min) and temperature (293-333 K). At pH 5.0 the maximum sorption percentage (%S) of V(V) was 45%, while at pH 2.0 it was 32%. The maximum sorption capacity of V(V) for L-CTAB was found to be 10.79 mg/g. The kinetic data indicate that the sorption followed the pseudo-second-order and film diffusion models. Sorption equilibrium for V(V) ions removal by L-CTAB was reached after 60 min at the initial concentrations 10 and 50 mg/dm³. It has been shown that the adsorption of V(V) ions on the surface of L-CTAB is a heterogeneous, endothermic and spontaneous reaction, as evidenced by the calculated values of thermodynamic parameters - free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) - for the tested systems at different temperatures. HCl solutions, used as an L-CTAB regeneration agent, quantitatively eluted V(V) ions.

Lignin derived nano-biocarbon and its deposition on polyurethane foam for wastewater dye adsorption

Historically, lignin has been produced as a waste by-product in industrial processes. In this study, lignosulfonate nanoparticles were fabricated and freeze-dried for use as a precursor material for carbonization. The use of the carbonized lignins for the adsorption of textile effluent as a value-added application is demonstrated. Characterization of the as received lignin (LN) and the developed nano-based freeze-dried lignin (NFLN) were performed prior to and after carbonization at 600, 750, 900 and 1050 °C. Using probe sonication, lignosulfonates were broken down into nanoparticles with lower weight-average molecular weight as verified by dynamic and static light scattering techniques. The difference between the LN and the NFLN was determined to be primarily morphological as the sonication and freeze-drying process imparted a platelet-like shape to the NFLN biocarbons and an increased surface area, while the remaining functionality was similar. The adsorption behaviour of methylene blue (MB), a synthetic cationic dye, was investigated using adsorption isotherm and kinetic models, with the NFLN exhibiting a maximum adsorption capacity of 109.77 mg/g. Overall, electrostatic attraction and hydrogen bonding contribute significantly to the MB adsorption. Further preliminary work was also performed demonstrating the coating of polyurethane foam for the adsorption of MB. These renewable biocarbons show promising properties for use as additive in adsorbent, coating, pigment or as a filler in polymer composite applications.

Fine tuning of CdxZn1-xS for photo-depolymerization of alkaline lignin into vanillin

Lignin is abundant and contains a large number of aromatic groups. Herein, Cd_xZn_1-xS photocatalyst with tunable band gap energy was successfully synthesized by using 3-mercaptopropionic acid as a structure tuning additive. Cd_xZn_1-xS can depolymerize alkaline lignin to vanillin by the photocatalytic process. Each gram of alkaline lignin can produce 46.5 mg of vanillin. 2-Phenoxy-1-phenylethanol (PP-ol) and other model compounds were used to understand the depolymerizing process of lignin. Fine tuned Cd_xZn_1-xS can effectively cleave the C_β-O-4 bond existed in PP-ol under simulated sunlight. The highest conversion of PP-ol was 89.5% with phenol and acetophenone yields of 66.2% and 33.5%, respectively. The mechanism studies confirm that the C_α-H in PP-ol and lignin is firstly dehydrogenated to form C_α radical intermediates, and then the photogenerated electrons break the adjacent C_β-O bond. This research provides a new strategy to prepare valuable chemicals by virtue of renewable biomass and simulated sunlight.

Enhancement of the antioxidant abilities of lignin and lignin-carbohydrate complex from wheat straw by moderate depolymerization via LiCl/DMSO solvent catalysis

A facile and environmentally-friendly strategy for increasing antioxidant activity is a crucial issue for value-added lignin and lignin-carbohydrate complex (LCC) as alternative antioxidants. However, the antioxidant activities of lignin and LCC by the traditional solid-liquid extraction (SLE) methods were restricted by the relatively lower solubility induced from high molecular weight (Mw), and the less functional groups including, phenolic hydroxyl and carboxyl. To improve the antioxidantion of lignin and LCC, lithium chloride/dimethyl sulfoxide (LiCl/DMSO) solvent fractionation (LDSF) was conducted to increase the functional groups and reduce Mw, in which LiCl/DMSO acted triple roles as solvent, acid, and metal chloride catalyst for the depolymerization reaction synchronously. The β-O-4' linkages were cleaved to release the phenolic hydroxyl, resulting in decreasing Mw; the hydroxyl of the side-chain of lignin was oxidized into carboxyl. Thus, the lignin (LD-RL) and LCC (LD-LCC) samples from LDSF had a higher syringyl (S)/guaiacyl (G) ratio, phenolic hydroxyl, and carboxyl contents, but less Mw than control groups from SLE. Consequently, they presented more excellent scavenging rates toward DPPH and ABTS radicals, up to 90%. This work provided panoramic perspectives and basics of the green and convenient approach to isolate and modify lignin and LCC for great antioxidantion with LDSF.

Lignin-containing polyurethane elastomers with enhanced mechanical properties via hydrogen bond interactions

In this work, lignin-containing polyester polyol (LPES) was successfully synthesized by vacuum melting method with lignin instead of polyol, and then reacted with isocyanate and chain extender to obtain lignin-based polyurethane elastomer (LPUE). The effects of lignin as reactive raw material, chain extender, and filler on the structure, thermostability, mechanical performance, and self-healing properties of elastomers were systematically studied, respectively. The comprehensive mechanical properties of the obtained materials were significantly enhanced after the introduction of lignin, especially the maximum tensile strength increased to 26.6 MPa and elongation at break reached 408.6%, which were 1510.3% and 2130.5% higher than that of the original polyurethane elastomer (PUE). Results revealed that lignin in the hard segment had a significant effect on the thermal stability and mechanical properties of polyurethane elastomer, and lignin in the soft segment had an obvious impact on the healing properties. Due to the hydrogen bonding interaction of the polar groups in the molecular chain of lignin to form a microphase-ordered structure, LPUE with excellent mechanical properties can be obtained.

Nitrogen-doped lignin-derived biochar with enriched loading of CeO2 nanoparticles for highly efficient and rapid phosphate capture

Development of lignin-derived carbon adsorbents with ultrahigh phosphate adsorption activity and rapid adsorption kinetics is of great importance, yet limited success has been achieved. Herein, we develop a CeO₂ functionalized N-doped lignin-derived biochar (Ce@NLC) via a cooperative modification strategy for effective and fast phosphate capture. The novel modification strategy not only contributes greatly to the loading of well-dispersed CeO₂ nanoparticles with a smaller size, but also significantly increases the relative concentration of Ce(III) species on Ce@NLC. Consequently, an enhanced capture capacity for phosphate (196.85 mg g^-1) as well as extremely rapid adsorption kinetics were achieved in a wide operating pH range (2-10). Interestingly, Ce@NLC exhibited a strong phosphate adsorption activity at even low-concentration phosphorus-containing water. The removal efficiency and final P concentration reached 99.87% and 2.59 μg P L^-1 within 1 min at the phosphate concentration of 2 mg P L^-1. Experiments and characterization indicated that Ce(III) species plays a predominant role for the phosphate capture, and ligand exchange, together with electrostatic attraction, are the main adsorption mechanism. This work develops not only an efficient carbon-based adsorbent for phosphate capture, but also promotes the high-value application of industrial lignin.

Effects of sacrificial coordination bonds on the mechanical performance of lignin-based thermoplastic elastomer composites

In this work, the coordination-based energy sacrificial bonds have been constructed in the interphase between lignin and polyolefin elastomer to prepare high performance lignin-based thermoplastic elastomers (TPEs). The strength and toughness of lignin-based TPEs can be adjusted by choosing different nitrogen heterocyclic compounds as reactive assistants and Fe³⁺ or Zn²⁺ as metal coordination centers. It was demonstrated that 3-Amino-1,2,4-triazole with three nitrogen atoms in the heterocyclic ring and one nitrogen branch chain could form the most efficient coordination bond system and generate the best mechanical performance. The system with ferric iron as coordination center exhibited better enhancement effect than divalent zinc. By adjusting the nitrogen-containing reactive additives or metal salts as coordination centers, the mechanical performance of the lignin-based TPE can be regulated, which provides a method for making green bio-composites with good strength and toughness, and also promotes the high value utilization of lignin in polymer materials.

Systematic Review on Isolation Processes for Technical Lignin

Technologies for the isolation of lignin from pulping process streams are reviewed in this article. Based on published data, the WestVaco process, the LignoBoost process, the LigoForce SystemTM and the SLRP process are reviewed and discussed for the isolation of lignin from Kraft black liquor. The three new processes that have now joined the WestVaco process are compared from the perspective of product quality. Further, isolation processes of lignosulfonates from spent sulfite liquor are reviewed. The limitation for this review is that data are only available from lab scale and pilot scale experiments and not from industrial processes. Key output of this paper is a technology summary of the state of the art processes for technical lignins, showing the pros and cons of each process.

Safety aspects of kraft lignin fractions: Discussions on the in chemico antioxidant activity and the induction of oxidative stress on a cell-based in vitro model

Lignin is a complex phenolic biopolymer present in plant cell walls and a by-product of the cellulose pulping industry. Lignin has functional properties, such as antioxidant activity, that make it a potential natural active ingredient for health-care products. However, not all safety aspects of lignin fractions have been adequately investigated. Herein, we evaluated the antioxidant and genotoxic potential of two hardwood kraft lignins (F3 and F5). The chemical characterization of F3 and F5 demonstrated their thermal stability and the presence of different phenolic units, while the DPPH assay confirmed the antioxidant activity of these lignin fractions. Despite being antioxidants in the DPPH assay, F3 and F5 were capable of generating intracellular reactive oxygen species (ROS) and subsequently causing oxidative DNA damage (Comet assay) in HepG2 cells. The biological relevance of the DPPH assay might be uncertain in some cases; therefore, we suggest combining in chemico tests with biological system-based tests to determine efficacy and safety levels of lignins and define appropriate applications of lignins for consumer products. Moreover, kraft lignins obtained by acid precipitation may pose risks to human health; however, as genotoxicity is not the sole endpoint of toxicity required in hazard assessments, additional toxicological evaluations are needed.

Understanding the dissolution of softwood lignin in ionic liquid and water mixed solvents

Lignin is the most abundant heterogeneous aromatic polymer on earth to produce a large number of value-added chemicals. Besides, the separation of lignin from the lignocellulosic biomass is essential for cellulosic biofuel production. For the first time, we report a cosolvent-based approach to understand the dissolution of lignin with 61 guaiacyl subunits at the molecular level. Atomistic molecular dynamics simulations of the lignin were performed in 0%, 20%, 50%, 80%, and 100% 1-Ethyl-3-Methylimidazolium Acetate (EmimOAc) systems. The lignin structure was significantly destabilized in both 50%, and 80% EmimOAc cosolvents, and pure EmimOAc systems leading to the breakdown of intrachain hydrogen bonds. Lignin-OAc and lignin-water hydrogen bonds were formed with increasing EmimOAc concentration, signifying the dissolution process. The OAc anions mostly solvated the alkyl chains and hydroxy groups of lignin. Besides, the imidazolium head of Emim cations contributed to solvation of methoxy groups and hydroxy groups, whereas ethyl tail interacted with the benzene ring of guaiacyl subunits. Effective dissolution was obtained in both the 50% and 80% EmimOAc cosolvent systems. Overall, our study presents a molecular view of the lignin dissolution focusing on the role of both cation and anion, which will help to design efficient cosolvent-based methods for lignin dissolution.

2G waste lignin to fuel and high value-added chemicals: Approaches, challenges and future outlook for sustainable development

Lignin is produced as a byproduct in cellulosic biorefinery as well in pulp and paper industries and has the potential for the synthesis of a variety of phenolics chemicals, biodegradable polymers, and high value-added chemicals surrogate to conventional petro-based fuels. Therefore, in this critical review, we emphasize the possible scenario for lignin isolation, transformation into value addition chemicals/materials for the economic viability of current biorefineries. Additionally, this review covers the chemical structure of lignocellulosic biomass/lignin, worldwide availability of lignin and describe various thermochemical (homogeneous/heterogeneous base/acid-catalyzed depolymerization, oxidative, hydrogenolysis etc.) and biotechnological developments for the production of bio-based low molecular weight phenolics, i.e. polyhydroxyalkanoates, vanillin, adipic acid, lipids etc. Besides, some functional chemicals applications, lignin-formaldehyde ion exchange resin, electrochemical and production of few targeted chemicals are also elaborated. Finally, we examine the challenges, opportunities and prospects way forward related to lignin valorization.

Efficient isolation of organosolv lignin-carbohydrate complexes (LCC) with high antioxidative activity via introducing LiCl/DMSO dissolving

Lignin-carbohydrate complexes (LCC) have shown great potential as biocompatible antioxidants. But it is difficult to isolate LCC efficiently from lignocellulose by traditional Solid-Liquid Extraction method (SLE), which is blamed to the innate bioimpedance caused by the complex supramolecular structure of the lignocellulose, and a great mass transferring resistance between the extracting solution and solid lignocellulose. To release these restrictions above and improve the efficiency of LCC isolation, a modified isolating method named Liquid-Liquid Extraction (LLE) was proposed, in which ball-milled wheat stalk was dissolved in lithium chloride/dimethyl sulfoxide (LiCl/DMSO) solution, then regenerated by dioxane aqueous to extract LL-LCCs. The effect of the LLE on the LCC isolating was evaluated and results showed that both the total yield and antioxidant activity of LL-LCCs were higher than that of control group. It proved the dissolution of wheat stalk in LiCl/DMSO solution could reduce the mass transfer resistance during the extraction. Due to the catalyzation of LiCl as Lewis acid, LL-LCCs had lower molecular weight but more phenolic hydroxyl groups and higher S/G ratios. These factors of LL-LCCs resulted in greater free-radical scavenging ability than control sample. The modified isolation protocol could facilitate the isolation and utilization of LCCs as a free-radical scavenger.

Tailored organosolv banana peels lignins: Improved thermal, antioxidant and antimicrobial performances by controlling process parameters

There is a growing environmental concern in the world for replacing the traditional petroleum-based products. The aim of this work was to evaluate the structure - property relationship of banana peel lignins (BPLs) as antioxidant and antimicrobial agents by controlling the parameters of organosolv process. The milled banana peel was hydrolyzed using an aqueous acetic acid solution (70, 80 and 90% v/v) and 2.0% v/v HCl at 110 °C for 1, 2 and 3 h. BPLs were characterized by FTIR, ¹H NMR, ¹H¹³C HSQC, ³¹P NMR, GPC and TGA. The antioxidant capacity of BPLs was evaluated by DPPH, ABTS and H₂O₂ assays, comparing their performance with that of ascorbic and gallic acid. The antimicrobial activity of BPLs was evaluated against E. coli. The reaction time and acetic acid/water ratio had significant effects on the yield and purity of BPLs. The composition of organosolv solution also affected their total amount of hydroxyls (0.71-0.82 mmol g^-1), M_w (2759-3954 g mol^-1), T_onset (232-254 °C), antioxidant and antimicrobial activities. It can be concluded that the control of organosolv parameters can be a useful tool for tuning the structural features of lignins and to maximize their performance.

Tuning the functional properties of lignocellulosic films by controlling the molecular and supramolecular structure of lignin

This study investigated the relationships between lignin molecular and supramolecular structures and their functional properties within cellulose-based solid matrix, used as a model biodegradable polymer carrier. Two types of derivatives corresponding to distinct structuration levels were prepared from a single technical lignin sample (PB1000): phenol-enriched oligomer fractions and colloidal nanoparticles (CLP). The raw lignin and its derivatives were formulated with cellulose nanocrystals or nanofibrils to prepare films by chemical oxidation or pressure-assisted filtration. The films were tested for their water and lignin retention capacities, radical scavenging capacity (RSC) and antimicrobial properties. A structural investigation was performed by infrared, electron paramagnetic resonance spectroscopy and microscopy. The composite morphology and performance were controlled by both the composition and structuration level of lignin. Phenol-enriched oligomers were the compounds most likely to interact with cellulose, leading to the smoothest film surface. Their RSC in film was 4- to 6-fold higher than that of the other samples. The organization in CLP led to the lowest RSC but showed capacity to trap and stabilize phenoxy radicals. All films were effective against S. aureus (gram negative) whatever the lignin structure. The results show the possibility to tune the performances of these composites by exploiting lignin multi-scale structure.

Photocatalytic depolymerization of organosolv lignin into valuable chemicals

Catalytic conversion of lignin to certain aromatic compounds has been extensively studied but still has great challenges. Photocatalytic depolymerizing lignin is a very promising method to obtain valuable chemicals. Herein, Zn₄In₂S₇ (ZIS)-based photocatalyst was successfully synthesized by simply combining ZIS and graphene oxide (GO). Photocatalyst ZIS-100 can efficiently depolymerize organosolv lignin into phenols and ketones. The relative content of valuable compounds in the depolymerized product was increased by 2.5 times as compared that without photocatalyst. The photocatalyst can effectively break C_β-O bonds in 2-phenoxy-1-phenylethanol (PP-ol, a model compound) and the conversion of PP-ol is 93.27%. Mechanism studies show that the thiol groups on the surface of ZIS-100 play an important role in the formation of C_α radical intermediates. Photocatalytic cleavage of C_β-O bond mainly follows a one-step reaction mechanism through a self‑hydrogen transfer process. This study provides a new strategy for selectively breaking C_β-O bond in lignin to form valuable chemicals.

Potential applications of polycarbohydrates, lignin, proteins, polyacids, and other renewable materials for the formulation of green elastomers

Renewable resources including polycarbohydrates, lignin, proteins, and polyacids are the intrinsically valuable class of materials that are naturally available in great quantities. Their utilization as green additives and reinforcing bio-fillers, in substitution of environmentally perilous petroleum-based fillers, for developing high-performance green rubber blends and composites is presently a highly tempting option. Blending of these renewable materials with elastomers is not straight-forward and research needs to exploit the high functionality of carbohydrates and other natural materials as proper physicochemical interactions are essential. Correlating and understanding the structural properties of lignin, carbohydrates, polyacids, and other biopolymers, before their incorporation in elastomers, is a potential approach towards the development of green elastomers for value-added applications. Promising properties i.e., biodegradability, biocompatibility, morphological characteristics, high mechanical properties, thermal stability, sustainability, and various other characteristics along with recent advancements in the development of green elastomers are reviewed in this paper. Structures, viability, interactions, properties, and use of most common natural polycarbohydrates (chitosan and starch), lignin, and proteins (collagen and gelatin) for elastomer modification are extensively reviewed. Challenges in commercialization, applications, and future perspectives of green elastomers are also discussed. Sustainability analysis of green elastomers is accomplished to elaborate their cost-effectiveness and environmental friendliness.

Characterization of a lignin from Crataeva tapia leaves and potential applications in medicinal and cosmetic formulations

Lignins are phenolic macromolecules that have several applications. In this work, we examine some biological activities of a lignin-like macromolecule isolated from the Crataeva tapia leaves, not yet studied to evaluate its potential applications in medicinal and cosmetic formulations. Lignin was obtained by alkaline delignification and its physical-chemical characterization was made by means of FT-IR, UV-Vis, NMR spectroscopy, elementary analysis, molecular mass determination and thermal analysis. Lignin is of the GSH type, with levels of hydrogen (5.10%), oxygen (27.18%), carbon (67.60%), nitrogen (0.12%) and phenolic content of 189.6 ± 9.6 mg GAE/g. In addition, it is a thermally stable macromolecule with low antioxidant activity. Cytotoxicity and cytokine production were assessed by flow cytometry. The photoprotective activity was evaluated by adding different concentrations of lignin to a commercial cream. Lignin was not cytotoxic, it stimulated the production of TNF-α, IL-6 and IL-10 and did not promote a significant change in nitric oxide levels. In addition, this macromolecule was able to promote increased absorption of ultraviolet light from a commercial cream. These results reinforce the ethnopharmacological use of C. tapia leaves and suggest the need for further studies to determine the potential medicinal and cosmetic applications (sunscreen) of lignin from C. tapia leaves.

Effect of the incorporation of lignin microparticles on the properties of the thermoplastic starch/pectin blend obtained by extrusion

The present study aimed to produce thermoplastic starch films with different concentrations of thermoplastic pectin and the addition of 4% lignin microparticles as a reinforcing and active agent. The pectin improved the modulus of elasticity, and decreased the elongation at break. In addition, it improved the UV light protection to 100% at 320 nm and 95.9% at 400 nm. The incorporation of lignin microparticles improved the thermal stability of the blends made with 25% and 50% thermoplastic pectin when compared to the pectin-free blends. The blend with 25% thermoplastic pectin led to an increase of 75.8% and 34% in elongation at break and deformation of the films, respectively. This blend also improved the UV light protection to 100% due to its dark brown color. Regarding the permeability properties, the films with 25% and 50% thermoplastic pectin showed lower oxygen permeability (48% and 65%) and an increase in the antioxidant activities from 2.7% to 71.08% and 4.1% to 79.28%, respectively. Thus, the polymer blend with 25% thermoplastic pectin with the incorporation of lignin microparticles proved to be a good alternative for use in foods sensitive to the effects of oxygen and UV light.

Facile Tailoring of Structures for Controlled Release of Paracetamol from Sustainable Lignin Derived Platforms

Nowadays, sustainable materials are receiving significant attention due to the fact that they will be crucial for the development of the next generation of products and devices. In the present work, hydrogels have been successfully synthesized using lignin which is non-valorized biopolymer from the paper industry. Hydrogels were prepared via crosslinking with Poly(ethylene) glycol diglycidyl ether (PEGDGE). Different crosslinker ratios were used to determine their influence on the structural and chemical properties of the resulting hydrogels. It has been found that pore size was reduced by increasing crosslinker amount. The greater crosslinking density increased the swelling capacity of the hydrogels due to the presence of more hydrophilic groups in the hydrogel network. Paracetamol release test showed higher drug diffusion for hydrogels produced with a ratio lignin:PEGDGE 1:1. The obtained results demonstrate that the proposed approach is a promising route to utilize lignocellulose waste for producing porous materials for advanced biomedical applications in the pharmacy industry.

3-D hierarchical porous carbon from oxidized lignin by one-step activation for high-performance supercapacitor

To convert lignin into high-valued carbon materials and understand the lignin structure function, oxidized lignin, a by-product from lignocellulose PHP-pretreatment (phosphoric acid plus hydrogen peroxide), was carbonized by one-step KOH-activation; the physico-chemical characteristics and electrochemical performances of the harvested carbons were also investigated. Results indicated the resultant carbons displayed 3-dimensional hierarchical porous morphology with maximum specific surface area of 3094 m² g^-1 and pore volume of 1.72 cm³ g^-1 using 3:1 KOH/lignin ratio for carbonization. Three-electrode determination achieved a specific capacitance of 352.9 F g^-1 at a current of 0.5 A g^-1, suggesting a superior rate performance of this carbon. Two-electrode determination obtained an excellent energy density of 9.5 W h kg^-1 at power density of 25.0 W kg^-1. Moreover, 5000 cycles of charge/discharge reached 88.46% retention at 5 A g^-1, implying an outstanding cycle stability. Basically, low molecular weight and abundant oxygen-containing functional groups of employed lignin mainly related to the excellent porous morphology and the outstanding electrochemical performances, suggesting the oxidized lignin was an ideal precursor to facilely prepare activated carbon for high-performance supercapacitor. Overall, this work provides a new path to valorize lignin by-product derived from oxidative pretreatment techniques, which can further promote the integrality of lignocellulose biorefinery.

Revealing the structural characteristics of lignin macromolecules from perennial ryegrass during different integrated treatments

To reveal the structural characteristics and physicochemical properties of perennial ryegrass lignin, sequential alkali extractions or double ball-milling and enzymatic hydrolysis on the basis of ultrasonic and hydrothermal pretreatments were proposed in this study. Results revealed that sequential alkali extractions released 89.4% of original lignin from the ryegrass cell walls and 0.75-4.16% of associated carbohydrates as compared to the double ball-milling and enzymatic hydrolysis (96.0% and 18.39%). It was observed that the two types of lignin prepared were SGH-type and had different amounts of p-coumarates and ferulates, and primarily consisted of β-O-4' linkages combined with minor amounts of β-β' and β-5' linkages. Besides, alkali-soluble lignins exhibited relatively fewer β-O-4' linkages, higher S/G ratios and H-type units, and abundant phenolic OH groups as compared to the double enzymatic lignin. Overall, the deeper investigation of the lignin structure of ryegrass will provide useful information for the efficient utilization of lignin macromolecules in biorefineries.

Synthesis, characterization and aging tests of functional rigid polymeric biocomposites with kraft lignin

This study concerns the synthesis of biocomposites with kraft lignin, investigation of their physicochemical properties, and tests of their resistance to environmental factors such as UV irradiation and water. The biocomposites were synthesized using bisphenol A glycerolate (1 glycerol/phenol) diacrylate (BPA.DA) as a main monomer, ethylene glycol dimethacrylate (EGDMA) as a reactive diluent, and kraft lignin (L) as an environmentally friendly filler, in a UV curing process. Morphological analysis of the resulting materials was carried out using scanning electron microscopy and confocal microscopy. Thermal properties were investigated using thermogravimetric analysis. Tensile and flexural tests were performed for all obtained materials. Additionally, the wettability and swelling of the obtained composite samples were analyzed. The changes observed in the structure and properties of the polymers as a result of aging were investigated by means of ATR-FTIR analysis, optical profilometry and hardness tests. The results obtained regarding the effect of lignin addition on the properties of composite materials, with particular emphasis on their resistance to environmental factors, may be of crucial importance for their further applications, inter alia as UV-curable coating materials.

Wood-Derived Hydrogels as a Platform for Drug-Release Systems

Wood (cellulose and lignin)-based hydrogels were successfully produced as platforms for drug-release systems. Viscoelastic and cross-linking behaviors of precursor solutions were tuned to produce highly porous hydrogel architectures via freeze-drying. Pore sizes in the range of 100-160 μm were obtained. Varying lignin molecular structure played a key role in tailoring swelling and mechanical performance of these gels with organosolv-type lignin showing optimum properties due to its propensity for intermolecular cross-linking, achieving a compressive modulus around 11 kPa. Paracetamol was selected as a standard drug for release tests and its release rate was improved with the presence of lignin (50% more compared to pure cellulose hydrogels). This was attributed to a reduction in molecular interactions between paracetamol and cellulose. These results highlight the potential for the valorization of lignin as a platform for drug-release systems.

One-pot fabrication of lignin-based aromatic porous polymers for efficient removal of bisphenol AF from water

To remove the bisphenol AF (BPAF) from aqueous solution, two different types of lignin-based aromatic porous polymers (LAPP-1 and LAPP-2) were fabricated via one-pot crosslinking of lignin with 1,4-dichloroxylene and 4,4'-bis(chloromethyl)-1,1'-biphenyl, respectively. The successful synthesis of LAPPs was confirmed by FTIR and XPS, SEM, TEM and N₂ adsorption-desorption analysis. Then, batch adsorption experiments were conducted to investigate adsorption properties toward BPAF. Based on the results, the adsorption processes were in accordance with the pseudo-second-order kinetic model and the Freundlich isotherm model, and the thermodynamic studies showed that the adsorption was a spontaneous and exothermic process. It is remarkable that LAPPs exhibited good adsorption performance in wide ranges of pH and ionic strength as well as in recycling process. Notably, compared to LAPP-1, LAPP-2 exhibited higher adsorption capacity for BPAF, which can be ascribed to its higher porosity and content of aromatic ring. Moreover, the comprehensive analysis of experimental and theoretical results indicated that the π-π interactions and pore adsorption may jointly drive the uptake process of BPAF. Considering the simple fabrication method employed and excellent BPAF adsorption performance, LAPPs provided new insights into the development of advanced lignin-based adsorbents for removal of BPAF from water.

Lignocellulosic Fibers from Renewable Resources Using Green Chemistry for a Circular Economy

The sustainable development of lignocellulose fibers exhibits significant potential to supplant synthetic polymer feedstocks and offers a global platform for generating sustainable packaging, bioplastics, sanitary towels, wipes, and related products. The current research explores the dynamics of fiber production from wood, non-wood, and agro-residues using carbonate hydrolysis and a mild kraft process without bleaching agents. With respect to carbonate hydrolysis, high yield, and good coarseness fibers are attained using a simple, low-cost, and ecofriendly process. Fibers produced using a mild kraft process have lower Klason lignin, carboxyl content, surface charges, and higher fiber length, and crystallinity. Eucalyptus fibers show the highest crystallinity while softwood carbonate fibers show the lowest crystallinity. Hemp hurd fibers contain the highest concentration of hard-to-remove water, and thus, suffer maximum flattening visualized by the microscopic images. The relatively high yield sustainable fibers with versatile properties can provide a significant economic benefit since fiber is the dominant cost for producing various bioproducts to meet society's current and future needs.

Separation of biobutanol from ABE fermentation broth using lignin as adsorbent: A totally sustainable approach with effective utilization of lignocellulose

Adsorption is considered to be a promising butanol recovery method for solving the issue of inhibition in the ABE (acetone-butanol-ethanol) fermentation. As a byproduct in the second generation biobutanol industry, lignin was found to be a good adsorbent for the butanol enrichment. It is conducive to the full utilization of renewable lignocellulose biomass resource. Kinetic and equilibrium experiments indicated that lignin had a satisfactory adsorption rate and capacity that are comparable to those of many synthetic materials. Multicomponent adsorption experiments revealed that lignin had higher adsorption selectivity toward butanol than that of ethanol and acetone. The adsorption capacity of lignin for butanol first increased and then gradually decreased with increasing temperature. And maximum adsorption capacity reached 304.66 mg g^-1 at 313 K. The inflection point of temperature is close to the ABE fermentation temperature of 310 K. The condensed butanol by desorption was 145 g L^-1, with a satisfying regeneration performance. ¹H NMR and FT-IR spectra indicated that the aromatic units of lignin formed π-systems with A/B/E. The π-system is particularly significant for butanol due to its longer hydrocarbon chain. These results could contribute to the emerging lignin-based materials for butanol separation.

Selective hydrodeoxygenation of lignin model compound (3,4-dimethoxybenzyl alcohol) by Pd/CNX catalyst

Upgrading of lignin derived bio-oil is an essential step for producing sustainable bio-based chemicals and fuel. Taken into account that α hydroxyl is the abundant functional group in lignin, high effective and selective catalytic alcoholysis for cleaving the C_α-OH linkages would be desirable. However, an in-depth understanding of the reaction mechanisms involved in the cleavage of C_aromatic-C_α and C_α-O bonds over a novel catalyst is still needed. Herein, we report an efficient liquid-phase hydrogen transfer strategy for the selective hydrodeoxygenation of a non-phenolic lignin model compound, 3,4-dimethoxybenzyl (veratryl) alcohol, under mild conditions. By employing iso-propanol as solvent and H-donor, and palladium nanoparticles immobilized on nitrogen-doped carbon (Pd/CN_X) as efficient multifunctional catalyst, veratryl alcohol dehydroxylation exhibited almost 100% conversion along with very high selectivity for 1,2-dimethoxy-benzene (46%) and 3,4-dimethoxytoluene (54%). Compared with other Pd catalysis, the Pd/CN_X has excellent catalytic performances and exhibits higher selectivity for 3,4-dimethoxytoluene under incorporation with 1% HCOOH at 220 °C. The proportion of Pd (0) significantly increases in Pd/CN_X catalyst when introduced into N precursor because of its highly dispersed Pd NPs and preventing the reoxidation of Pd (0). The dehydrogenation reaction occurred through the hydrogen generation of a secondary alcohol. Then, the C_α-OH and C_aromatic-C_α bonds of veratryl alcohol were selectively cleaved by catalytic transfer hydrogenolysis. The alcoholysis mechanism is supported by dispersion-corrected density functional theory computations.

Fractionation of lignin using organic solvents: A combined experimental and theoretical study

Refining of industrial lignin to produce homogeneous fractions is essential for high-value applications. However, the understanding of key interactions between a variety of solvents with lignin polymer is still uncertain. In this work, single-step fractionation of industrial hardwood kraft lignin (HKL) using organic solvents of different polarities - ethanol, acetone, diethyl ether and hexane - was investigated by combining an experimental and theoretical approach. Experimental results revealed that higher polarity solvents (ethanol and acetone) exhibited higher solubility yield compared to moderate and low polarity solvents. The chemical differences between lignin fractions were proven by pyrolysis gas chromatography mass spectrometry and near infrared spectroscopy. Density functional theory (DFT) results indicated that ethanol presented higher interaction energy followed by acetone, diethyl ether and hexane, which was consistent with experimental findings. Hydrogen bond and non-covalent interaction results from DFT demonstrated that the predominant interaction was found for high polarity of ethanol over other solvents and γ-OH in the lignin model is the key site.

Analysis of the functional group composition of the spruce and birch phloem lignin

In this article, the functional group composition of the spruce (Pícea ábies) and birch (Bétula péndula) phloem lignin is described. The features of the chemical structure were studied by analyzing dioxane lignin using the elemental analysis, UV-Vis, FT-IR, and 1D NMR spectroscopy. For comparison, samples of xylem dioxane lignin isolated from the corresponding wood species were also analyzed. FT-IR spectroscopy data suggest that the lignins of birch phloem and xylem are similar in chemical structure. However, there are differences in absorption bands in the spectra of spruce dioxane lignin, which indicate the opposite. Quantitative analysis of the functional group composition was performed using ¹³C and ³¹P NMR data. It was found that free phenolic hydroxyl groups of catechol and p-hydroxyphenyl types are dominated in the composition of spruce phloem lignin. Birch phloem lignin has a qualitative and quantitative composition of functional groups characteristic of hardwood lignins. However, the content of G-units is greater than S-units, in contrast to the birch xylem lignin, where S-units predominate. The revealed differences are relevant from the point of view of plant physiology. The practical significance of the study is connected with understanding the reactivity of lignins when considering the chemical processing of tree bark.

Phosphorylated kraft lignin with improved thermal stability

The low cost, environmental friendliness, and reproducibility of kraft lignin (KL) make it a potential candidate for the development of new green material. The phosphorylation of KL can extend its application as a flame-retardant material. Herein, the phosphorylated kraft lignin (PKL) was systematically fabricated in a sustainable process by utilizing a green phosphating reagent, NH₄H₂PO₄, in the presence of urea. The influence of the reaction parameters, i.e., reaction time and temperature, and NH₄H₂PO₄/lignin ratio on the phosphorylation process were investigated. Advanced characterization techniques including ¹H NMR, ³¹P NMR, and XPS confirmed that the phosphorus groups were successfully introduced to lignin molecules. The active phenolic and aliphatic hydroxy groups of kraft lignin underwent a nucleophilic substitution reaction with the phosphate group to generate phosphorylated lignin. Compared with KL, PKL showed excellent thermal stability, and its maximum decomposition temperature was 620 °C compared with 541 °C for KL.