Pure Lignin Research Articles

Streamlined fractionation for recovery of high-yield xylo-oligosaccharides, pure lignin and ethanol from poplar using short-chain organic acid/pentanol biphasic system

Biphasic pretreatment offers a sustainable method by integrating the fractionation of hemicellulose, lignin, and cellulose into a single process, thereby enhancing biomass resource utilization while reducing environmental impact. However, this process faces the challenge of diverse hemicellulose products with low added value. This study employed organic acid-catalyzed water/pentanol biphasic pretreatment to selectively convert hemicellulose into xylooligosaccharides (XOS), while simultaneously separating lignin and cellulose. Both the organic acids and pentanol used are biodegradable and compatible. The lactic acid (LA)/pentanol biphasic system was particularly effective for XOS production and lignin removal, attributed to the high acidity of LA and its relatively low partition coefficients in the water/pentanol system, crucial factors influencing hemicellulose and lignin separation efficiency. The XOS yields reached 46.9 %, while the lignin removal rate was 74.6 %. Additionally, LA/pentanol pretreatment significantly enhanced cellulose digestibility, demonstrated by an ethanol production of 54.1 g/L during simultaneous saccharification fermentation at 15 % solids loading. The recovered lignin from the organic phase retained the structural characteristics of native lignin. It also had a low molecular weight and abundant phenolic hydroxyl groups, indicating its suitability for further valorization. Pentanol maintained its performance after four cycles of reuse, demonstrating the stability and reusability of the solvent system. This study highlighted the potential of the LA/pentanol biphasic system for simultaneous hemicellulose conversion and lignin isolation, offering a simplified and sustainable one-step valorization route for biomass.

Eco-friendly synthesis of pure lignin nanoparticle and silver-doped lignin nanoparticle using fig tree bark for photocatalytic degradation of Rhodamine B dye and assessment of their anticancer and antibacterial performance

Lignin nanoparticles (lignin-NPs) have been successfully prepared from the bark of a fig tree by a hydrothermal method for the first time, next, synthesized lignin-NPs were doped with silver (Ag) metal. The Ag-doped lignin-NPs and pure lignin-NPs have been identified through UV–Vis, XRD, FT-IR, and FESEM/EDX techniques. XRD patterns of pure lignin-NPs and Ag-doped lignin-NPs have shown amorphous and crystalline structures respectively. The UV–Vis spectra of NPs presented strong absorption bands in 450, 228, and 289 nm. FESEM images of Ag-doped lignin-NPs and pure lignin-NPs exhibited spherical shapes via sizes of about 18.55 nm and 31.93 nm respectively. Also, the FTIR spectra revealed the same functional groups. Moreover, the photocatalytic performance of NPs for the decolorization of Rhodamine B (RhB) dye has been investigated under UVA light. As a result, Ag-doped lignin-NPs demonstrated a higher degradation percentage than pure lignin-NPs. The results of the MTT assay after 48 h indicate that pure lignin-NPs had little toxicity compared with Ag doped lignin-NPs on normal (L929) and cancer (Huh-7) cells. Also, according to the results of the agar diffusion test, Ag doped lignin-NPs had better antibacterial performance in comparison with pure lignin-NPs on Pseudomonas aeruginosa (POA1 and S7), and Enterococcus faecalis (clinical).

Formaldehyde-free biomass adhesive based on industrial alkali lignin with high strength and toughness

The preparation of industrial lignin-based adhesives generally requires the use of large amounts of petrochemical products or toxic and hazardous reagents, which severely limits their widespread application in the wood-based panel industry. In this study, we present a novel approach for synthesizing an eco-friendly lignin-based wood adhesive using aminated alkali lignin (AAL) and epoxy-terminated hyperbranched polyester (EHBP). The AAL was prepared by aminating alkali lignin through a green and formaldehyde-free method. The EHBP was synthesized by grafting epichlorohydrin onto biomass-derived hyperbranched polyester. The resulting adhesive performed excellent bonding strength of 2.41 MPa and debonding work of 0.711 J, which were 3.63 and 15.2 times higher than those of the pure lignin adhesive, respectively. This exceptional bonding strength surpassed that of most previously reported biomass adhesives. The moisture uptake value of the adhesive decreased by 75.6 % and the residual rate increased by 239.2 %. In addition, the prepared adhesive exhibited enhanced mold resistance. Importantly, the adhesive was primarily composed of biomass materials and their derivatives and was less costly than most commercial formaldehyde-based and bio-based adhesives. This work presents new possibilities for the high-value utilization of industrial lignin and the development of formaldehyde-free and environmentally friendly adhesives.

The Role of Lignin Molecular Weight on Activated Carbon Pore Structure.

Over the past decade, the production of biofuels from lignocellulosic biomass has steadily increased to offset the use of fuels from petroleum. To make biofuels cost-competitive, however, it is necessary to add value to the "ligno-" components (up to 30% by mass) of the biomass. The properties of lignin, in terms of molecular weight (MW), chemical functionality, and mineral impurities often vary from biomass source and biorefinery process, resulting in a challenging precursor for product development. Activated carbon (AC) is a feasible target for the lignin-rich byproduct streams because it can be made from nearly any biomass, and it has a market capacity large enough to use much of the lignin generated from the biorefineries. However, it is not known how the variability in the lignin affects the key properties of AC, because, until now, they could not be well controlled. In this work, various fractions of ultraclean (<0.6% ash) lignin are created with refined MW distributions using Aqueous Lignin Purification using Hot Agents (ALPHA) and used as precursors for AC. AC is synthesized via zinc chloride activation and characterized for pore structure and adsorption capacity. We show that AC surface area and the adsorption capacity increase when using lignin with increasing MW, and, furthermore, that reducing the mineral content of lignin can significantly enhance the AC properties. The surface area of the AC from the highest MW lignin can reach ~1830 m2/g (absorption capacity). Furthermore, single step activation carbonization using zinc chloride allows for minimal carbon burn off (<30%), capturing most of the lignin carbon compared to traditional burn off methods in biorefineries for heat generation.

Ionic Lignin Polymers for Controlled CO2 Capture, Release, and Conversion into High-Value Chemicals.

In this study, an innovative and cost-effective ionic polymer for CO2 capture and utilization for the first time, using abundant and nonfood-based biomass lignin is reported. The modified ionic polymer synthesizes through the reaction of glycidyltrimethylammonium chloride with lignin under alkaline conditions to yield quaternary ammonium ionic functionality. Subsequently, the hydroxide-based pure ionic lignin polymer is employed for CO2 capture from both direct air and concentrated CO2 sources at room temperature and atmospheric pressure. Structural characterization of the polymers is accomplished through 1H, 13C, and 2D-heteronuclear single quantum coherence (HSQC)NMR, and FT-IR spectroscopy. The CO2 capture process is established through the formation of bicarbonate ions alongside the presence of CO2. The captured CO2 is precisely quantified by using inverse-gated proton decoupled 13C NMR with an internal standard (trioxane). Remarkably, the captured-CO2 amounts of ionic lignin polymer are 1.06mmol g-1 (47mg g-1) from concentrated-CO2 source and 0.60mmol g-1 (26mg g-1) from direct-air. The captured-CO2 in ionic lignin polymer is released in controlled manner and utilized in the synthesis of cyclic carbonate, showcasing the productive application of the captured carbon. Moreover, the fully controlled recovering of ionic lignin polymer achieves via repeated CO2 release ↔ CO2 capture.

The Impact of Lignin Biopolymer Sources, Isolation, and Size Reduction from the Macro- to Nanoscale on the Performances of Next-Generation Sunscreen.

In recent years, concerns about the harmful effects of synthetic UV filters on the environment have highlighted the need for natural sun blockers. Lignin, the most abundant aromatic renewable biopolymer on Earth, is a promising candidate for next-generation sunscreen due to its inherent UV absorbance and its green, biodegradable, and biocompatible properties. Lignin's limitations, such as its dark color and poor dispersity, can be overcome by reducing particle size to the nanoscale, enhancing UV protection and formulation. In this study, 100-200 nm lignin nanoparticles (LNPs) were prepared from various biomass by-products (hardwood, softwood, and herbaceous material) using an eco-friendly anti-solvent precipitation method. Pure lignin macroparticles (LMPs) were extracted from beech, spruce, and wheat straw using an ethanol-organosolv treatment and compared with sulfur-rich kraft lignin (KL). Sunscreen lotions made from these LMPs and LNPs at various concentrations demonstrated novel UV-shielding properties based on biomass source and particle size. The results showed that transitioning from the macro- to nanoscale increased the sun protection factor (SPF) by at least 2.5 times, with the best results improving the SPF from 7.5 to 42 for wheat straw LMPs and LNPs at 5 wt%. This study underscores lignin's potential in developing high-quality green sunscreens, aligning with green chemistry principles.

Co-pyrolysis of subbituminous coal and lignin at isothermal and non-isothermal conditions: A ReaxFF molecular dynamics simulation

Understanding the co-pyrolysis behavior of sub-bituminous coal and lignin not only contributes to the efficient and clean use of coal but also enables low carbon emissions. The behavior and product evolution of pure coal, pure lignin, and co-pyrolysis systems under isothermal and non-isothermal conditions were explored using reactive force field molecular dynamics (ReaxFF MD) simulation. Through multiple isothermal simulation processes, the co-pyrolysis system showed an inhibition effect, promoting the generation of heavy compounds and inhibiting the generation of tar and gas. The inhibition effect at 2400 K was the most significant in the pyrolysis period. A similar phenomenon was found in the non-isothermal pyrolysis process at 2 K/ps. In addition, the H2 yield under non-isothermal conditions was lower than the calculated value. By distinguishing the same element from different sources, there were three types of H2 (Hcoal2, HcoalHlignin, and Hlignin2). Subsequently, the H atoms in lignin prefer to produce H2 than that in coal during co-pyrolysis. Finally, we further explored the evolution behavior of the configurations during the pyrolysis of non-isothermal coal and lignin systems. These findings enrich the theoretical information on the interaction between coal and lignin, providing the behavior of Hcoal and Hlignin atoms in the co-pyrolysis system.

Ethyl acetate fractionation improved the homogeneity and purity of CAOSA-extracted lignin

Lignin separated from the pulping and bio-refining industry is a cross-linked organic phenolic polymer and the most abundant renewable aromatic resource. However, its wide molecular weight distribution, inhomogeneity and complex functional groups are the factors restricting the application of lignin. The preparation of lignin with simple structures and low dispersity by fractionation is one of the main methods to transform lignin into higher-value materials. In this study, lignin fragments with lower dispersibility (Đ) were separated from CAOSA-extracted bamboo lignin by continuous organic solvent fractionation involving ethyl acetate, ethanol, acetone and dioxane/water (95:5). The lignin fragments extracted by ethyl acetate possessed a lower molecular weight (821 g/mol), lower glass transition temperature (Tg), higher purity and phenolic hydroxyl content (0.370 mmol/g). This method unlocked the versatility of the lignin components and provided a reference for the application of lignin in resin, rubber, antioxidant, asphalt and adhesive.

Thermogravimetric analysis on two Bambusa texlitis wastes slow pyrolysis behaviors and kinetics using isoconversional and parallel-reactions models

In this work, the pyrolysis behaviors and kinetics of two bamboo (Bambusa texlitis) wastes were investigated via thermogravimetric analysis. The weight loss behaviors of pyrolysis were studied by curvature of the conversion (α) curves. The curvature of α can depict the characteristic temperatures of pseudo component (hemicellulose, cellulose and lignin) pyrolysis. Model-free model was applied to estimate the apparent activation energies of the pure components for comparison with other kinetic models. Three parallel reaction (TPR) and parallel finite number first-order reaction (FNFOR) models were used for kinetic studies. The first-order TPR model underestimates the apparent activation energies of pseudo components. The nth-order TPR model underestimates the apparent activation energy of lignin and obtains characteristic temperatures that are inconsistent with those of pure lignin. The parallel FNFOR model is more reliable for simulating the kinetics of lignocellulosic biomass pyrolysis. The apparent activation energies of pseudo components depend on the variety of lignocellulosic biomass.

Generation of a lignin-polyester coating for the corrosion protection of steel surfaces applied by atmospheric plasma spraying

The natural process of metal corrosion causes significant losses in a wide range of industries, requiring substantial efforts to contain its effects. An alternative approach to corrosion protection is the use of renewable organic coating materials. This research proposes the use of lignin-polyester blends as coating materials. Due to the abundance of functional groups in the lignin structure, it can act as corrosion inhibition centers in the coating. The coatings are deposited on stainless steel surfaces by a novel process route via atmospheric plasma powder spraying (APPS). To determine the effect of the lignin content on the corrosion performance, the specific amounts of lignin and polyester have been varied in 10 % increments from 0 % to 100 % with constant coating parameters. The as-produced coatings exhibited thicknesses that ranged from 11 μm to 30 μm, respectively for the pure lignin and polyester coatings. Additionally, scanning electron microscopy (SEM) analysis demonstrated the meltability of the lignin and polyester powder through the plasma process. Coatings containing a greater proportion of polyester exhibited superior meltability and better coverage. Furthermore, it was observed that the APPS promoted cross-linking of the lignin particles, as determined by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). This, in conjunction with well-balanced lignin-polyester ratios, was instrumental in achieving advanced corrosion resistance as evidenced by Potentiodynamic polarization measurement (PDP). The lignin proportion between 40 % and 60 % produced the highest corrosion inhibition efficiency, with a maximum inhibition of 96 %. Furthermore, pull-off adhesion tests suggest that lignin contributes to the overall cohesive strength of the blend.

Aminated alkali lignin nanoparticles enabled formaldehyde-free biomass wood adhesive with high strength, toughness, and mildew resistance

The conversion of industrial lignin into wood adhesives offers a solution to issues related to formaldehyde pollution and the reliance on petrochemical resources of traditional formaldehyde-based resins, while promoting environmental and energy sustainability. However, conventional methods for preparing lignin-based adhesives generally involve the use of materials like formaldehyde, organic solvents, and costly epoxy, hindering their industrial application. This study introduces a novel approach for producing eco-friendly lignin-based wood adhesives using aminated lignin-Cu nanoparticles. The lignin-Cu nanoparticles were synthesized in water as a single solvent through a sedimentation method. Amination modification was achieved by grafting amino-terminated hyperbranched polyamide onto the nanoparticles via a Schiff base reaction. The prepared adhesive demonstrated a remarkable bonding strength of 1.51 MPa and debonding work of 0.272 J, which were 2.75 and 6.33 times higher than those of the pure lignin adhesive, respectively. Moreover, the adhesive exhibited improved water resistance with a wet shear strength of 1.15 MPa and sustained mildew resistance for approximately 100 days. Notably, this adhesive was synthesized without the use of formaldehyde, phenol, acids, or organic solvents, minimizing reliance on fossil resources and lowering costs compared to many formaldehyde-based and biomass adhesives. This research opens up new avenues for the efficient utilization of industrial lignin and the production of formaldehyde-free, environmentally friendly adhesives, which holds significant promise for energy conservation, emission reduction, and sustainable development within the wood-based panel industry.

Preparation and Characterization of Lignin Nanoparticles from Different Plant Sources.

This article presents new research on producing lignin nanoparticles (LNPs) using the antisolvent nanoprecipitation method. Acetone (90%) served as the lignin solvent and water (100%) as the antisolvent, using five types of lignins from various sources. Comprehensive characterization techniques, including NMR, GPC, FTIR, TEM, and DLS, were employed to assess both lignin and LNP properties. The antioxidant activity of the LNPs was evaluated as well. The results demonstrated the successful formation of spherical nanoparticles below 100 nm with initial lignin concentrations of 1 and 2%w/v. The study highlighted the crucial role of lignin purity in LNP formation and colloidal stability, noting that residual carbohydrates adversely affect efficiency. This method offers a straightforward, environmentally friendly approach using cost-effective solvents, applicable to diverse lignin sources. The innovation of this study lies in its demonstration of a cost-effective and eco-friendly method to produce stable, nanometric-sized spherical LNPs. These LNPs have significant potential as reinforcement materials due to their reinforcing capability, hydrophilicity, and UV absorption. This work underscores the importance of starting material purity for optimizing the process and achieving the desired nanometric dimensions, marking a pioneering advancement in lignin-based nanomaterials.

INVESTIGATION OF VARIOUS METHODS OF EXTRACTING LIGNIN FROM TREE BARK

This study explores various methods for extracting lignin from tree bark, a significant byproduct of the forestry and paper industries. The research aims to identify efficient and sustainable techniques for lignin extraction, which has potential applications in biopolymers, energy production, and as a natural binder. We evaluated several extraction methods, including solvent extraction, steam explosion, and enzymatic hydrolysis, focusing on yield, purity, and environmental impact. The findings reveal substantial differences in efficacy and sustainability among the methods. Solvent extraction demonstrated high lignin purity but raised environmental concerns. Steam explosion offered a balance between yield and eco-friendliness, while enzymatic hydrolysis emerged as the most sustainable, albeit with lower yields. This study contributes to the growing body of knowledge on lignin extraction and its potential industrial applications, highlighting the need for further research in optimizing these methods for commercial use. Keywords: lignin, extraction, tree bark, Solvent, Steam explosion, biopolymers.

Optimization of lignin precipitation from black liquor using organic acids and its valorization by preparing lignin nanoparticles

This work focuses on the precipitation of lignin from kraft black liquor (BL) along with its valorization into lignin nanoparticles (LNP). Two organic acids namely, acetic acid, and lactic acid were used for the precipitation of lignin as an alternative to sulfuric acid. An optimization study was carried out to determine the effect of three key variables, namely acid type, temperature, and pH, on the isolation yield and purity of lignin. The study showed that all factors primarily influenced the lignin yield, while the purity of precipitated lignin varied only around 1 % between minimum to maximum purity. Further, the acid precipitation method was selected for the preparation of LNP. The study aimed to observe the effect of pH, lignin concentration, and surfactant concentration over the properties of the prepared nanoparticles. The results showed that a smaller nanoparticle size and maximization of phenolic content was achieved with a lignin concentration of 35 mg/mL, a surfactant concentration of 10 % (w/w lignin), and a pH of 5. Additionally, the antibacterial activity of LNPs against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa bacteria was evaluated. The results showed only minor activity against Staphylococcus aureus. Overall, the study demonstrates the potential method for precipitation and valorization of lignin through the production of LNP with desirable properties.

Purification of soda lignin

Purity of technical lignin is one of the main obstacles in the utilization of lignin to value-added chemicals, products, and materials. The objective of this study was to investigate and compare single and two stage purification methods for obtaining soda lignin with high purity. Extensive washing and extraction with water was found effective, increasing the abundance of acid insoluble lignin while reducing its ash content. Extraction with organic solvents was conducted with 2-propanol or blends of n-heptane/1-butanol or cyclohexane/acetone. These solvents were shown to have little effect on the total lignin content, as determined by wet-chemical methods. Two-stage treatments (washing with water followed by solvent extraction) were hence not better than single stage water extraction in terms of the lignin purity. Still, selective removal of low molecular weight components after solvent extraction was noted, reducing the overall polydispersity of the lignin. Evaporation at 40 °C also showed little effect, whereas calcination at 150 °C significantly increased the molecular weight of the soda lignin. The latter effect was explained by thermally induced cross-linking. In addition, the UV absorbance of the calcinated lignin increased, which is likely related to changes in the aromatic structure. Such effect also entailed that UV/vis spectrophotometry was found less reliable in determining the total lignin content. At last, a mathematical model was adapted to predict the total lignin content from FTIR spectrometry. In conclusion, the tested procedures can be used to purify soda lignin and adjust its molecular weight.

Effect of Treatment Time on Deep Eutectic Solvent Treatment of Scots Pine Wood

Aim of study: The influence of the treatment time (1 hour, 2 hours, and 3 hours) on the deep eutectic solvent (DES) treatment of Scots pine (Pinus sylvestris L.) wood is investigated in this study. &#x0D; Area of the study: Determination of DES performance on the Scots pine wood chemical structure.&#x0D; Material and methods: Choline chloride (ChCl) and lactic acid (LA) mixture with molar ratio of 1:10 (w:w) was used as a DES solvent. Treatments were carried out in an autoclave at 121 °C. The effects of DES treatment on the properties of wood and lignin samples of Scots pine were determined according to the relevant standards.&#x0D; Main results: The delignification ratio, lignin purity, and lignin yield in the 3h-treated sample were determined to be 79.78%, 86.43%, and 82.48%, respectively. The crystallinity index (CrI) was increased from 55.87% to 71.58% with 3 h DES treatment. Brunauer-Emmett-Teller (BET) analysis results showed that the surface area of the sample increased with 3-h DES treatment (from 3.095 m2/g to 3.621 m2/g). The 1-hour DES-treated sample yielded the lightest colored lignin (L*: 71.62). &#x0D; Research highlights: Treatment time of Scots pine wood during DES treatment has a significant effect on the wood and lignin properties

Pure lignin induces overexpression of cytochrome P450 (CYP) encoding genes and brings insights into the lignocellulose depolymerization by Trametes villosa

Trametes villosa is a remarkable white-rot fungus (WRF) with the potential to be applied in lignocellulose conversion to obtain chemical compounds and biofuels. Lignocellulose breakdown by WRF is carried out through the secretion of oxidative and hydrolytic enzymes. Despite the existing knowledge about this process, the complete molecular mechanisms involved in the regulation of this metabolic system have not yet been elucidated. Therefore, in order to understand the genes and metabolic pathways regulated during lignocellulose degradation, the strain T. villosa CCMB561 was cultured in media with different carbon sources (lignin, sugarcane bagasse, and malt extract). Subsequently, biochemical assays and differential gene expression analysis by qPCR and high-throughput RNA sequencing were carried out. Our results revealed the ability of T. villosa CCMB561 to grow on lignin (AL medium) as the unique carbon source. An overexpression of Cytochrome P450 was detected in this medium, which may be associated with the lignin O-demethylation pathway. Clusters of up-regulated CAZymes-encoding genes were identified in lignin and sugarcane bagasse, revealing that T. villosa CCMB561 acts simultaneously in the depolymerization of lignin, cellulose, hemicellulose, and pectin. Furthermore, genes encoding nitroreductases and homogentisate-1,2-dioxygenase that act in the degradation of organic pollutants were up-regulated in the lignin medium. Altogether, these findings provide new insights into the mechanisms of lignocellulose degradation by T. villosa and confirm the ability of this fungal species to be applied in biorefineries and in the bioremediation of organic pollutants.

Effect of Iron Chloride Addition on Softwood Lignin Nano-Fiber Stabilization and Carbonization.

This study presents the effect of iron chloride addition on the production of nanocarbon fibers from softwood Organosolv lignin. It was shown that adding 2% FeCl3 to the lignin solution before electrospinning to produce lignin nanofibers increased the thermal resistance of lignin fibers during stabilization. FTIR and XPS analyses of the lignin fibers stabilized with and without FeCl3 revealed that the temperature rate could be increased in the presence of FeCl3 from 1 to 3 °C/min. The optimal temperature to stabilize the lignin fibers was found to be 250 °C, as higher temperatures led to thermal degradation. Also, carbon fibers were successfully produced from pure softwood Organosolv lignin fibers. Carbonization tests were conducted under nitrogen and the best parameters were determined to be a ramp of 10 °C/min until 600 °C with a holding time of 2 h. Furthermore, the effect of 2% FeCl3 addition in the lignin solution was investigated during these processes. XPS analysis showed a 93% carbon content for fibers carbonized with and without FeCl3 addition, while SEM images revealed some surface roughness in fibers with FeCl3 after carbonization. These results confirm that FeCl3 addition influences the carbon nanofiber production.

Electrospun PCL Filtration Membranes Enhanced with an Electrosprayed Lignin Coating to Control Wettability and Anti-Bacterial Properties.

This study reports on the two-step manufacturing process of a filtration media obtained by first electrospinning a layer of polycaprolactone (PCL) non-woven fibers onto a paper filter backing and subsequently coating it by electrospraying with a second layer made of pure acidolysis lignin. The manufacturing of pure lignin coatings by solution electrospraying represents a novel development that requires fine control of the underlying electrodynamic processing. The effect of increasing deposition time on the lignin coating was investigated for electrospray time from 2.5 min to 120 min. Microstructural and physical characterization included SEM, surface roughness analysis, porosity tests, permeability tests by a Gurley densometer, ATR-FTIR analysis, and contact angle measurements vs. both water and oil. The results indicate that, from a functional viewpoint, such a natural coating endowed the membrane with an amphiphilic behavior that enabled modulating the nature of the bare PCL non-woven substrate. Accordingly, the intrinsic hydrophobic behavior of bare PCL electrospun fibers could be reduced, with a marked decrease already for a thin coating of less than 50 nm. Instead, the wettability of PCL vs. apolar liquids was altered in a less predictable manner, i.e., producing an initial increase of the oil contact angles (OCA) for thin lignin coating, followed by a steady decrease in OCA for higher densities of deposited lignin. To highlight the effect of the lignin type on the results, two grades of oak (AL-OA) of the Quercus cerris L. species and eucalyptus (AL-EU) of the Eucalyptus camaldulensis Dehnh species were compared throughout the investigation. All grades of lignin yielded coatings with measurable antibacterial properties, which were investigated against Staphylococcus aureus and Escherichia coli, yielding superior results for AL-EU. Remarkably, the lignin coatings did not change overall porosity but smoothed the surface roughness and allowed modulating air permeability, which is relevant for filtration applications. The findings are relevant for applications of this abundant biopolymer not only for filtration but also in biotechnology, health, packaging, and circular economy applications in general, where the reuse of such natural byproducts also brings a fundamental demanufacturing advantage.

Fractionation and purification of a high-impurity, alkaline-pretreated, corn stover lignin with simple renewable solvents

Corn stover has been identified as a key resource in the transition from petrochemicals to sustainably sourced energy and materials; however, the as-recovered lignin from alkaline pretreatment contains unusually high levels of residual impurities, which must be removed to maximize potential application. Thus, the Aqueous Lignin Purification using Hot Agents (ALPHA) process was applied to a corn stover lignin containing ∼10 % carbohydrates and ∼3 % ash. Lignin fractions ∼100 times cleaner than the feed lignin and of controlled molecular weight (i.e., as low as one-fifth and as high as triple the absolute molecular weight (Mw) of the feed) were obtained. The ALPHA solvent was a hot (60 or 75 °C) solution of 80 % ethanol combined with the feed lignin at an unusually low, 3:1 solvent-to-feed lignin ratio – conditions that create the liquid–liquid equilibrium (LLE) phase split needed to practice ALPHA. Lignin fractionation then commenced by adding water to the original solution, decreasing the ethanol content in increments of 3–4 wt%. Surprisingly, the highest Mw fractions did not precipitate until the solution contained just below 50 % ethanol, by which point almost half of the starting lignin of near-average Mw had already precipitated. Another unexpected result was that the lignin waste stream from the initial purification step could be increased from 40 to 98 % lignin in a single equilibrium stage simply by re-processing that waste with another 80 % ethanol solution at the conditions given above. In summary, the efficacy of ALPHA for purifying and fractionating an impurities-laden corn stover lignin to ultraclean levels in a scalable manner requiring only aqueous bioethanol solutions has been demonstrated.