Lignin Particles Research Articles

Novel flexible, strong, thermal-stable, and high-barrier switchgrass-based lignin-containing cellulose nanofibrils/chitosan biocomposites for food packaging

Chitosan/lignin-containing cellulose nanofibrils (CS/LCNF) biocomposites were prepared by a facile and green method that combined hydrothermal pretreatment, mechanical fibrillation, and dry casting. LCNFs were isolated from switchgrass with various lignin contents, and their effects on the transparency, micromorphology, mechanical properties, interfacial compatibility, thermal stability, surface wettability, and barrier properties of the CS/LCNF biocomposites were comprehensively investigated. Their transparency was affected by changing the lignin and cellulose contents, as well as the order degree of cellulose. The hydrophobic micro/nano- lignin particles with the optimum contents (33.8%) coated on CNFs or embedded their networks prompt the dispersion of LCNF in CS matrices and enhance interfacial interaction of CS and LCNF. This synergistically improved the mechanical properties and thermal stability of CS/LCNF biocomposites. CS/LCNF8 maintained a ductility of 503% and showed a tensile strength that was 46.7% higher than that of CS/CNF, as well as a Tmax and WCA that were 2.6 °C and 11.06° higher, respectively. Furthermore, CS/LCNF8 displayed a more competitive OTR (0.20 cc/(m2 day)) than those of pure chitosan, mechanically-fibrillated CNFs, carboxymethylated CNFs, and TEMPO-oxidized CNF/CS films at the same ratio. This study provides promising environmentally-friendly biocomposite films with outstanding comprehensive performance for green food packaging.

Investigating the Effects of Tobacco Lignin on Polypropylene.

The utilization of eco-friendly materials, such as lignin, for higher value product applications became increasingly important as environmental concerns due to global warming increased. Melt blending is one of the easy ways to increase the usage of lignin in commercial applications. However, the degradation of the final product performance and increase in the production time and costs are of major concern. In the current work, the effects of blending lignin, extracted from tobacco plants, with polypropylene (PP) on the injection molding parameters, physical, thermal and mechanical properties are investigated. Blends of lignin (5, 15 and 30% by wt.) with PP were prepared using a Filabot single screw extruder. Results show that tensile strength decreases by 3.2%, 9.9% and 5.4% at 5 wt. %, 15 wt. %, and 30 wt. % of lignin addition, respectively. The tensile stiffness was almost unaffected by the addition of up to 15% lignin, but a 23% increase was observed at 30 wt. % loading. When compared to lignin processed via expensive processes, such as acetylation, tobacco lignin showed superior performance. The DSC results show unaffected crystallization and melting temperatures but a decrease in enthalpies and percentage of crystallinity. The SEM and optical micrographs of the coupon cross-sections show that the extrusion process has achieved a uniform distribution of lignin particles in the PP. Thermogravimetric analysis results show that tobacco lignin accelerates the onset decomposition temperature but does not influence the decomposition peak temperature. The increase in lignin content did not have a significant influence on the injection molding parameters, implying no additional processing costs for adding lignin to the PP. Overall, the performance of the tobacco lignin is comparable, if not better, than that of processed lignin reported in the literature.

Empowering alkali lignin with high performance in pickering emulsion by selective phenolation for the protection and controlled-release of agrochemical

Lignin is a versatile bioaromatic polymer, with great potentials in the preparation of advanced materials due to its anti-UV and anti-oxidant properties. However, the high heterogeneity of lignin seriously hinders its practical applications. In this study, alkali lignin with limited content of hydroxyl groups and a wide distribution of molecular weight was modified by selective phenolation, which not only resulted in a dramatical increase in the content of phenolic hydroxyl groups but also led to a more uniform structure of lignin. Catechol, as compared with phenol and pyrogallol, was the most suitable phenolation reagent to reacted with lignin, and the phenolic hydroxyl content of the catechol modified lignin increased by 318.89%. Besides, the molecular weight and polydispersity index of lignin after the modification decreased, which led to a small and regular size of lignin particles prepared by acid precipitation. Subseqently, lignin particles were used to prepare Pickering emulsions for avermectin (AVM) encapsulation, and the stability as well as the anti-UV and anti-oxidant capacities of Pickering emulsions prepared by using phenolated lignins as solid surfactants were obviously enhanced. The encapsulation efficiency of AVM in Pickering emulsions was also improved, which could reach high above 90%. Moreover, AVM protected by lignin-based Pickering emulsion could be controllably released in line with actual application demands, and the relatively high viscosity of emulsion could effectively avoid the loss of pesticide during spraying to the target.

Superhydrophobic aerogel membrane with integrated functions of biopolymers for efficient oil/water separation

A novel type of superhydrophobic biopolymer aerogel membrane (T-SA/lignin x /rGO-MTMS) is prepared for purifying oily wastewater. • A novel type of superhydrophobic biopolymer aerogel membrane between lignin and sodium alginate (T-SA/lignin x /rGO-MTMS) was prepared. • Confirmation of cooperative interaction between lignin and sodium alginate. • Demonstration of high-efficiency cyclicity for oil/water separation. • Degradable oil/water separation membranes. Superhydrophobic membranes have been playing crucial role in efficient remediation of organic pollutants contaminated water, especially for oily discharged wastewater. Taking advantages of the inherent features of graphene oxide (GO), sodium alginate (SA) and lignin, a novel type of superhydrophobic biopolymer aerogel membrane (T-SA/lignin x /rGO-MTMS) was prepared by freeze-casting technique and subsequent chemical vapor deposition, during which trimethoxymethylsilane (MTMS) silylation growth was achieved for the supreme protuberance, leading to the formation of rough and hydrophobic surface that favorably looks like a hedgehog carrying apples. Due to the air cushion induced by cooperative interaction between rough lignin particles and SA of 3D porous network with gas as a dispersion medium, and crumpled GO nanosheets, as-fabricated membrane with integrated functions of biopolymers possessed superhydrophobic surface characteristics (WCA = 161°). More favorably, utilizing the inherent molecular features, lignin has been successfully employed to de-oxidize GO during this preparative concept. By virtue of the low-surface-energy reduced GO (rGO) and abundant protuberance, T-SA/lignin x /rGO-MTMS exhibited potential cycling performance even with 10 cycles of oil/water separation and oil sorption. This study might shed light on the value-added utilization of integrated functions of biopolymers for designing task-specific functional materials for various applications.

Influence of Temperature and Lignin Concentration on Formation of Colloidal Lignin Particles in Solvent-Shifting Precipitation

Colloidal lignin particles offer a promising route towards material applications of lignin. While many parameters influencing the formation of these particles in solvent-shifting precipitation have been studied, only a small amount of research on the influence of temperature has been conducted so far, despite it being a major influence parameter in the precipitation of colloidal lignin particles. Temperature influences various other relevant properties, such as viscosity, density, and lignin solubility. This makes investigation of both temperature and lignin concentration in combination interesting. The present work investigates the precipitation at different temperatures and initial lignin concentrations, revealing that an increased mixing temperature results in smaller particle sizes, while the yield is slightly lowered. This effect was strongest at the highest lignin concentration, lowering the hydrodynamic diameter of the particles from 205 to 168 nm. Decreasing the lignin concentration resulted in significantly smaller particles (from 205 to 121 nm at 20 °C mixing temperature) but almost no change in particle yield (between 81.2 and 84.6% at 20 °C mixing temperature). This opens up possibilities for the process control and optimization of lignin precipitation.

Surface energy properties of lignin particles studied by inverse gas chromatography and interfacial adhesion in polyester composites with electromagnetic transparency

Surface energy properties of lignin particles studied by inverse gas chromatography and interfacial adhesion in polyester composites with electromagnetic transparency

Hydrophobic lignin/polyurethane composite foam: An eco-friendly and easily reusable oil sorbent

Global oil spill and water contamination issues are urgently requiring the development of next-generation oil sorbent materials that may desirably have the functionalities of reusability and biodegradability without generating secondary pollutions. Herein, a novel oil sorbent is introduced that could be practically useful in the cleanup for oils from contaminated water with low-cost and sustainability. The oil sorbent is composed of a polyurethane (PU) foam incorporated with hydrophobized lignin particles up to 40 wt%, in which the lignin is acetylated to increase the compatibility with the matrix and sorption capacity; for crude oil, the composite foam with an acetylated lignin content of 20 wt% shows increased absorption capacity of 8.06 g/g compared to the neat PU foam capacity of 4.51 g/g. The absorbed oil can be easily reclaimed simply by squeezing the foam with a good recyclability, which is maintained 97.9% and 92.3% of the mass-based sorption capacity even after 50 cycles for olive oil and crude oil, respectively. The developed composite foams and the methodology have enormous potential as a promising solution for the cleanup of organic contaminants.

Interfacial catalysis and lignin nanoparticles for strong fire- and water-resistant composite adhesives

Lignin was epoxidized using interfacial catalysis, which improved the reaction speed and solubility immensely. Epoxidized lignin was cured with lignin particles into thermosets that could be used as a strong adhesive or fire-resistant coating.

Production of lignin-containing nanocellulose from poplar using ternary deep eutectic solvents pretreatment

Developing green and sustainable reagents and materials is of great significance for the lignin-containing nanocellulose (LNC) production. In this study, new green ternary deep eutectic solvents (DESs) pretreatment followed by microfluidization were used to prepare LNC from poplar. Under optimal pretreatment conditions (choline chloride: lactic acid: p-toluenesulfonic acid molar ratio of 2:10:1, 100 °C), ultrafine ribbon-like LNCs about 23.29 nm wide and 1.16 nm thick with uniformly distributed spherical lignin particles were obtained. The yield of the LNC reached 64.65%. The LNC exhibited cellulose I crystal structure, good dispersion stability in water and high lignin content of 27.65%. The LNC also possessed high thermal stability (Tmax = 370 °C). Additionally, the LNC suspensions showed high viscosity and strong gel-like behavior. The novel ternary DESs pretreatment combined with microfluidization process offers a promising route in converting hardwood biomass into value-added LNC.

An efficient solution to determine surface energy of powders and porous media: Application to untreated and treated lignin

The estimation of solid surface energy is generally obtained through the determination of liquid/solid contact angles. Many questions arise in the literature about the appropriate contact angle to use (dynamic, quasi-static or static, measured at a macro or a micro-scale). Theoretically, equilibrium contact angles should be inserted into equations to determine surface energy components. However, for powders or porous materials more issues arise, notably due to the imbibition of the liquid into the medium. An apparent contact angle can be obtained using wicking tests and the modified Washburn equation. Nonetheless, Washburn hypotheses are not always respected or no longer valid during wicking meaning that this procedure could not allow to determine contact angles. This study has the aim to propose a new simple method to determine the surface energy components of powders and porous media. An experimental protocol coupled to a modified Jurin law is proposed. This protocol was applied to lignin particles used as reinforcement in polylactic acid (PLA). Some treatments were performed on lignin to improve the adhesion with PLA and the modifications due to the treatments were characterized. Reliable surface energy and components of untreated and treated lignin were obtained revealing the efficiency of the proposed method.

Rheological Properties of Lignocellulosic Nanomaterial Aqueous Suspensions as Influenced by Water-Soluble Biopolymer Additives

Rheological properties including gel strength, steady-state viscosity, and oscillatory rheology of four types of cellulose nanomaterials (CNMs) under the influence of two different biopolymers were studied. The processed CNMs had distinct fiber morphology (individual fibril vs bundles with/without lignin particles), composition (lignin content varying from 52.88% to 6.86%), and surface chemical properties (zeta potential values from −28.62 mV to −13.4 mV). The presence of lignin in lignin-containing nanofibrillated cellulose (LNFC) decreased a suspension’s gel strength, viscosity, and dynamic modulus. The chosen bleached NFC contained large fibril bundles, and the processed material with more individualized fibril and enhanced fluid rheology was demonstrated after regrinding the original NFC. Biopolymer xanthan gum (XG) showed a much larger effect in modifying gel strength, viscosity, and dynamic moduli compared with polyanionic cellulose (PAC). Among the three chosen rheological models, the Nasiri–Ashrafizadeh model fitted the measured shear stress and shear rate data the best for each fluid system with correlation coefficients larger than 0.99. The use of biopolymers (e.g., XG and PAC) helped reduce negative effect of lignin on gel strength and other rheological properties for LNFC. The much-improved rheological performance for biopolymer-modified LNFC suspensions open new opportunities for CNMs to be used as more environmentally friendly fluids for the energy industry.

Organosolv lignin aggregation behaviour of soluble lignin extract from Miscanthus x giganteus at different ethanol concentrations and its influence on the lignin esterification

BackgroundLignin is the second most abundant naturally occurring biopolymer from lignocellulosic biomass. While there are several lignin applications, attempts to add value to lignin are hampered by its inherent complex and heterogenous chemical structure. This work assesses the organosolv lignin aggregates behaviour of soluble lignin extract derived from Miscanthus × giganteus using different ethanol concentrations (50%, 40%, 30%, 20%, 10% and 1%). The effect of two different lignin concentrations using similar ethanol concentration on the efficacy of esterification was studied.ResultsOverall, particle size of lignin analysis showed that the particle size of lignin aggregates decreased with lower ethanol concentrations. 50% ethanol concentration of soluble lignin extract showed the highest particle size of lignin (3001.8 nm), while 331.7 nm of lignin particle size was recorded at 1% ethanol concentration. Such findings of particle size correlated well with the morphology of the lignin macromolecules. The lignin aggregates appeared to be disaggregated from population of large aggregates to sub-population of small aggregates when the ethanol concentration was reduced. Light microscopy images analysis by ImageJ shows that the average diameter and circularity of the corresponding lignin macromolecules differs according to different ethanol concentrations. The dispersion of lignin aggregates at low ethanol concentration resulted in high availability of hydroxyl group in the soluble lignin extract. The efficacy of the lignin modification via esterification was evidenced directly via FTIR using the similar ethanol concentration of soluble lignin extract at different lignin concentrations.ConclusionThis study provided the understanding of detail analysis on particle size determination, microscopic properties and structural insights of lignin aggregates at wider ethanol concentrations. The esterified lignin derived at 5 mg/mL is suggested to expand greater lignin functionality in the preparation of lignin bio-based materials.

Structure-controlled lignin complex for PLA composites with outstanding antibacterial, fluorescent and photothermal conversion properties

Polylactic acid (PLA) is increasingly being considered as an ideal biodegradable candidate to replace petroleum-based polymers. However, its practical applications are often hampered by the poor mechanical robustness and solo functionality. Herein, based on the mechanical property improvement of PLA we proposed a simple process of assembling lignin-hybridized modifier and PLA matrix, as opposed to the traditional trade-off between mechanical strength and functionality, while anchoring a biofluorescent moiety onto lignin surfaces. Specifically, the fluorophore group could act as interfacial compatibilizer of complex and facilitate the shape-tailored hybrids for promoting functionality flexibility. With the bimetallic hetero-particles, the preferable lignin-assembled complex could be controllably configured as an antibacterial, fluorophore and photothermal agent. Thus, mechanical enhancement, fluorescence introduction and favorable photothermal ability of the resulting PLA composites were successfully achieved for integrated unification of structural robustness, geometric integrity and functional multiplicity, which was never seen in the other reports. The results showed that PLA composites containing 5 wt% modified lignin, 10 wt% zinc oxide, and 5 wt% silver presented excellent mechanical, fluorescent, photothermal conversion properties. By controlling the ZnO content and morphology, strong inhibition of Escherichia coli (Gram-negative) than that of Staphylococcus Aureus (Gram-positive) was also observed. The flake-shaped ZnO /Ag hybrids contributed to better overall performance of PLA composites than the rod-shaped ZnO/Ag. In this work we developed a facile strategy to assemble a bioderived fluorophore with lignin particles for constructing a structure-controlled complex as a multitasking modifier, featuring mechanical unity and functional adaptability. Specifically, the lignin reinforcement and bimetallic hybrids with different morphologies were explored as an effective fluorophore, antibacterial and photothermal agent. Through multiple dehydration reactions, a conjugating fluorophore was successfully grafted on lignin surfaces to serve as an interface modifier without physical changing its structural robustness. And morphology-tailored hybrid was advantageously immobilized on predefined hetero-particle carrier of fluorescent lignin and endowed composites with desirable antimicrobial properties. The developed strategy would expand the functional applications of PLA materials in food packaging, biopharmaceuticals and simple fluorescent anti-counterfeiting.

Characteristics of calcium lignin from pulping waste liquor and application for the treatment middle-stage wastewater of paper making

ABSTRACT In order to obtain a lignin-based adsorbent with low cost, simple operation and no further modification, a calcium lignin adsorbent was prepared from chemical mechanical pulping (CMP) waste liquor by directly calcification from lime. The calcium lignin was characterized by BET, SEM, TEM, FT-IR and solid-state NMR analyses. The results showed that the molecular structure of the calcium lignin particles did not change when compared to sodium lignin, the formation mechanism of calcium lignin was revealed. The initial COD and lignin contents of CMP waste liquid were 54858 mg/L and 24.39 g/L, the conversion rate of lignin can reach 71.36% when was deal with lime. Thus, most of the lignin resources in the waste liquid were recovered. The middle-stage wastewater (MSWW) of pulping and papermaking was dealt with calcium lignin, the COD removal rate was up to 85.83%. The adsorption isotherms and kinetics were well fitted by the Langmuir model and pseudo-second-order kinetic model, respectively. Lime was regenerated from the used calcium lignin with high-temperature calcination, the conversion rate of calcium ions can reach 83.56%. Overall, the calcium lignin prepared by the one-step method exhibited great potential for effectively removing COD from middle-stage wastewater.

Tunable and functional deep eutectic solvents for lignocellulose valorization

Stabilization of reactive intermediates is an enabling concept in biomass fractionation and depolymerization. Deep eutectic solvents (DES) are intriguing green reaction media for biomass processing; however undesired lignin condensation is a typical drawback for most acid-based DES fractionation processes. Here we describe ternary DES systems composed of choline chloride and oxalic acid, additionally incorporating ethylene glycol (or other diols) that provide the desired ‘stabilization’ function for efficient lignocellulose fractionation, preserving the quality of all lignocellulose constituents. The obtained ethylene-glycol protected lignin displays high β-O-4 content (up to 53 per 100 aromatic units) and can be readily depolymerized to distinct monophenolic products. The cellulose residues, free from condensed lignin particles, deliver up to 95.9 ± 2.12% glucose yield upon enzymatic digestion. The DES can be recovered with high yield and purity and re-used with good efficiency. Notably, we have shown that the reactivity of the β-O-4 linkage in model compounds can be steered towards either cleavage or stabilization, depending on DES composition, demonstrating the advantage of the modular DES composition.

Assessing the effect of protic ionic liquid pretreatment of Pinus radiata from different perspectives including solvent-water ratio

In this study, pine (Pinus radiata) pretreated with PIL, triethylammonium hydrogen sulfate (TEAHSO4) at different water-PIL ratios (1:9, 1:4 and 3:7), biomass loadings (10–60%) and biomass particle sizes (<1.18 mm, 1.18–1.76 mm and 1.76–2.40 mm) was enzymatically transformed into fermentable sugars. TEAHSO4 removed 52% lignin with pretreatment at 170 °C, 20% loading and 1:4 water-PIL ratio for 3 h, from biomass with the largest particle size. Reducing the water content of PIL solution enhanced delignification performance of PIL under the same conditions; cellulose content of the biomass increased 2-fold by extracting 59% lignin from pine. Compositional changes were supported with saccharification and characterization analyses. Utilizing 1:4 water-PIL ratio introduced more constructive pretreatment conditions with respect to the changes in lignin particle size distribution. Attaining favorable compositional changes for pine as a recalcitrant softwood motivated the contribution of PILs to IL based biorefineries.

Fast Pyrolysis of Hydrolysis Lignin in Fluidized Bed Reactors

Fast pyrolysis of hydrolysis lignin was studied in fluidized bed units. Hydrolysis lignin, a bioproduct from the lignocellulosic ethanol production process (St1 Cellunolix), was processed in bench scale bubbling fluidized bed (BFB) and pilot scale circulating fluidized bed (CFB) units. Utilization of steam and ethanol as hydrogen sources was tested in a BFB unit. Major technical challenges identified were related to slow reaction rates of lignin degradation and the rapid secondary reactions in the vapor phase resulting in deposit formation and pressure buildup in product gas lines. The carbohydrate content of hydrolysis lignin had a clear correlation to its processability. More challenges with clogging and bed agglomeration were observed with lignin feedstock having lower carbohydrate content. The challenges with the bed agglomeration in the BFB unit were overcome by adding a rapidly rotating mixer in the reactor to break the agglomerates. With the CFB unit, bed agglomeration was not a problem, due to high gas velocities and forces applied to sand and lignin particles. In the BFB unit, the screw feeder was cooled and no significant melting problems were observed. In the CFB unit, melting problems were avoided by feeding the raw material in the cold section of reactor. However, severe increases in the pressure buildup and deposit formation rates were observed in both units. Steam and ethanol was tested, separately, in the BFB unit, to provide excess hydrogen in the system. Based on the product analyses both added hydrogen into the system, but hydrogen ended up mostly in the gas phase. To enhance the hydrogen transfer to the organic liquid, a catalyst active in hydrogen transfer is probably needed.

Biopolymeric Anticorrosion Coatings from Cellulose Nanofibrils and Colloidal Lignin Particles.

This study presents a process for preparation of cellulose–lignin barrier coatings for hot-dip galvanized (HDG) steel by aqueous electrophoretic deposition. Initially, a solution of softwood kraft lignin and diethylene glycol monobutyl ether was used to prepare an aqueous dispersion of colloidal lignin particles (CLPs) via solvent exchange. Analysis of the dispersion showed that it comprised submicron particles (D = 146 nm) with spherical morphologies and colloidal stability (ζ-potential = −40 mV). Following successful formation, the CLP dispersion was mixed with a suspension of TEMPO-oxidized cellulose nanofibers (TOCN, 1 and 2 g·L–1) at a fixed volumetric ratio (1:1, TOCN–CLPs), and biopolymers were deposited onto HDG steel surfaces at different potentials (0.5 and 3 V). The effects of these variables on coating formation, dry adhesion, and electrochemical properties (3.5% NaCl) were investigated. The scanning electron microscopy results showed that coalescence of CLPs occurs during the drying of composite coatings, resulting in formation of a barrier layer on HDG steel. The scanning vibrating electrode technique results demonstrated that the TOCN–CLP layers reduced the penetration of the electrolyte (3.5% NaCl) to the metal–coating interface for at least 48 h of immersion, with a more prolonged barrier performance for 3 V-deposited coatings. Additional electrochemical impedance spectroscopy studies showed that all four coatings provided increased levels of charge transfer resistance (Rct)—compared to bare HDG steel—although coatings deposited at a higher potential (3 V) and a higher TOCN concentration provided the maximum charge transfer resistance after 15 days of immersion (13.7 cf. 0.2 kΩ·cm2 for HDG steel). Overall, these results highlight the potential of TOCN–CLP biopolymeric composites as a basis for sustainable corrosion protection coatings.

Construction and foamability of lignin-reinforced low-density polyethylene biocomposites

Lignin was chemically modified with poly(ethylene-co-glycidyl methacrylate) copolymer (PEGMA) to form PEGMA-grafted lignin (PEGMA-g-lignin). The pristine lignin and PEGMA-g-lignin were successfully incorporated into a low-density polyethylene (LDPE) matrix. In the PEGMA-g-lignin/LDPE biocomposites, interfacial adhesion between the lignin particles and the LDPE matrix was better and stronger than that between the lignin particles and the LDPE matrix in pristine lignin/LDPE biocomposites. Analyses of the thermal behaviors and mechanical properties of the resultant biocomposites revealed that enhanced mechanical properties could be achieved without affecting the thermal characteristics of the LDPE matrix. Moreover, foamability of the biocomposites was studied in the presence of azodicarbonamide (chemical blowing agent) and dicumyl peroxide (crosslinking agent). The introduction of 20 wt.-% PEGMA-g-lignin led to good quality lignin-reinforced LDPE biocomposite foams, where the cell size frequency distribution of the resultant foams was uniform and the cell density and foam expansion were similar to those of neat LDPE foam.

Production of UV-shielded spherical lignin particles as multifunctional bio-additives for polyvinyl alcohol composite films

Production of UV-shielded spherical lignin particles as multifunctional bio-additives for polyvinyl alcohol composite films