Eucalyptus Kraft Lignin Research Articles

Electrospinnability of PCL-doped eucalyptus kraft lignin and its application for structuring vegetable oils

This study explores the utilization of eucalyptus kraft lignin (EKL), extracted from black liquor of the pulp and paper industry, doped with polycaprolactone (PCL) to produce nanofibers with potential applications as vegetable oil structuring agents. Solutions of EKL:PCL in different weight ratios were prepared in a N,N-dimethylformamide/chloroform binary solvent, at concentrations ranging from 10 to 40 wt%, and submitted to electrospinning. Electrospinnability essentially correlates with the shear and extensional rheological properties of the solutions. Resulting electrospun EKL/PCL nanofibers were subsequently dispersed in castor oil at different concentrations (15 and 30 wt%). Stable gel-like dispersions were obtained with electrospun nanostructures predominantly composed of nanofibers or beaded fibers. The rheological properties and microstructure of EKL/PCL nanofiber-based oleo-dispersions were significantly influenced by both the EKL:PCL weight ratio and electrospun nanofiber concentration, with increases in the linear viscoelasticity functions and viscosity correlating with higher nanofiber concentrations and PCL proportions. These findings point out the potential of EKL/PCL nanofibers as eco-friendly vegetable oil structuring agents, in line with the principles of circular economy through the reuse of renewable waste materials.

Depolymerisation of Kraft Lignin by Tailor-Made Alkaliphilic Fungal Laccases.

Lignins released in the black liquors of kraft pulp mills are an underutilised source of aromatics. Due to their phenol oxidase activity, laccases from ligninolytic fungi are suitable biocatalysts to depolymerise kraft lignins, which are characterised by their elevated phenolic content. However, the alkaline conditions necessary to solubilise kraft lignins make it difficult to use fungal laccases whose activity is inherently acidic. We recently developed through enzyme-directed evolution high-redox potential laccases active and stable at pH 10. Here, the ability of these tailor-made alkaliphilic fungal laccases to oxidise, demethylate, and depolymerise eucalyptus kraft lignin at pH 10 is evidenced by the increment in the content of phenolic hydroxyl and carbonyl groups, the methanol released, and the appearance of lower molecular weight moieties after laccase treatment. Nonetheless, in a second assay carried out with higher enzyme and lignin concentrations, these changes were accompanied by a strong increase in the molecular weight and content of β-O-4 and β-5 linkages of the main lignin fraction, indicating that repolymerisation of the oxidised products prevails in one-pot reactions. To prevent it, we finally conducted the enzymatic reaction in a bench-scale reactor coupled to a membrane separation system and were able to prove the depolymerisation of kraft lignin by high-redox alkaliphilic laccase.

Partial Replacement of Cationic Starch by Cationic Hardwood Kraft Lignin Does Not Compromise Key Paper Properties

Competition issues with food industry have recently boosted the exploration of alternative solutions capable of replacing starch in papermaking to a certain extent. Covalent grafting of quaternary ammonium groups onto LignoBoost® Eucalyptus kraft lignin has recently shown promise in this regard as the cationic products feature excellent water solubility across the entire pH scale. Considering these suitable properties, cationic kraft lignin was applied and evaluated, for the first time, in the perspective of partial substitution of cationic starch in papermaking, using bleached Eucalyptus kraft pulp. Based on an assessment of key paper properties, such as mechanical (tensile, bursting, and tearing indexes), structural (roughness, capillarity rise, air resistance, internal strength, and water contact angle), and optical ones (brightness, opacity, and relative color change), it is safe to conclude that the partial replacement of conventional cationic starch by cationic lignin does not compromise these features. The results also show that properties can be fine-tuned by varying the degree of lignin derivatization, providing paper-specific solutions for replacing starch by lignin potentially available at large-scale at the pulp and paper industry, closing the loop within the circular economy concept.

Polyurethane Adhesives Based on Oxyalkylated Kraft Lignin

Lignin-based polyol was obtained via oxyalkylation reaction with propylene carbonate using eucalyptus kraft lignin isolated from the industrial cooking liquor by the Lignoboost® procedure. This lignin-based polyol (LBP) was used without purification in the preparation of polyurethane (PU) adhesives combined with polymeric 4,4'-methylenediphenyl diisocyanate (pMDI). A series of adhesives were obtained by varying the NCO/OH ratio of PU counterparts (pMDI and LBPs) and their performance was evaluated by gluing wood pieces under predefined conditions. The adhesion properties of the novel PU adhesive were compared with those of a commercial PU adhesive (CPA). The occurrence and extent of curing reactions and changes in the polymeric network of PA were monitored by Fourier transform infrared spectroscopy (FTIR) and dynamic mechanical analysis. Although the lap shear strength and glass transition temperature of the lignin-based PU adhesives have increased steadily with the NCO/OH ratio ranging from 1.1-2.2, chemical aging resistance can be compromised when the NCO/OH is very low. It was found that the lignin-based PU adhesive with an NCO/OH ratio of 1.3 showed better chemical resistance and adhesion efficiency than CPA possibly because the NCO/OH in the latter is too high as revealed by FTIR spectroscopy. Despite some lower thermal stability and shorter gelation time of lignin-based PU than CPA, the former revealed great potential to reduce the use of petroleum-derived polyols and isocyanates with potential application in the furniture industry as wood bonding adhesive.

Production of lignin/cellulose acetate fiber-bead structures by electrospinning and exploration of their potential as green structuring agents for vegetable lubricating oils

In this work we developed electrospun lignin/cellulose acetate fiber-bead nanostructures and explored their potential as structuring agents for vegetable oils to be used as eco-friendly lubricating oleogels. A variety of nanostructures were obtained from solutions containing 20 or 30 wt. % eucalyptus Kraft lignin (EKL) and cellulose acetate (CA) in variable weight ratios from 100:0 to 60:40 in an N , N -dimethylformamide/acetone mixture. The EKL/CA solutions were characterized in physicochemical terms from viscosity, surface tension and electrical conductivity measurements. Also, the electrospun nanostructures were characterized morphologically by scanning electron microscopy. Their morphology was found to be strongly dependent on the rheological properties of the biopolymer solution. Electrospun EKL/CA beaded nanofibers and well-developed uniform nanofiber mats allowed oleogels to be easily obtained by simply dispersing them in castor oil whilst nanoparticle clusters gave rise to unstable dispersions. The rheological properties of these gel-like dispersions can be tailored through the membrane concentration and/or EKL/CA ratio and depend to a large extent on the morphology of the electrospun nanostructures. The rheological and tribological properties of the oleogels were comparable to those previously reported for conventional and other bio-based lubricating greases. Overall, electrospun EKL/CA nanofibers allow easy, efficient structuring of vegetable oils to obtain oleogels holding potential for use as lubricants. • Electrospinning of eucalyptus kraft lignin and cellulose acetate solutions. • Higher cellulose acetate content improves electrospinnability of the solutions. • Electrospun lignin/cellulose acetate nanocomposites can be used to structure castor oil. • Rheological and tribological properties of oleogels tunable by cellulose acetate/lignin ratio. • A new way of valorizing lignocellulosic waste as vegetable oil structuring agent.

Improvement of Thermal Behavior of Rattan by Lignosulphonate Impregnation Treatment

Lignin derived from black liquor has a lot of potentials, particularly in its thermal stability, for making value-added chemicals. The purpose of this study was to determine the effect of washing frequency during hydrochloric acid lignin isolation on the properties of eucalyptus kraft lignin. To improve its thermal characteristics and enable its usage as an additive flame retardant, the isolated lignin was synthesized into lignosulphonate. The lignin produced by 3× and 5× washing treatments had a purity of 85.88 and 92.85%, respectively. An FTIR analysis indicated that lignosulphonate was successfully synthesized from isolated lignin after 3× and 5× washing treatments, as the S=O bond was detected at around 627 cm−1. The lignosulphonate exhibited a purity of 71.89 and 67.21%, respectively. Thermal gravimetry and differential scanning calorimetry analysis revealed that the lignin and lignosulphonate after 3× and 5× washing treatments had a char residue of 44, 42, 32, and 48%, respectively. Glass transition temperatures (Tg) of 141, 147, 129, and 174 °C were observed. According to the findings, washing frequency increases lignin purity and Tg, thereby improving the thermal properties of lignosulphonate. Furthermore, the flammability of rattan impregnated with lignosulphonate was V-0 in the UL-94 vertical burning test.

In‐Depth Identification of Phenolics Fractionated from Eucalyptus Kraft Lignin (Adv. Sustainable Syst. 5/2022)

Lignin Kraft lignin, the most abundant technical lignin resource, is a renewable alternative to fossil sources yet highly underutilized. In article number 2100406, Chengke Zhao, Fengxia Yue and co-workers identify a total of 20 lignin-derived compounds, including novel catechol monomers, 1,2-diarylethane dimers, and terphenyl trimers, in the low-Mw fraction of Eucalyptus kraft lignin, which provides in-depth insights into structural features, selective fractionation, and valorization of technical lignins.

In‐Depth Identification of Phenolics Fractionated from Eucalyptus Kraft Lignin

AbstractKraft lignin, the principal by‐product of the pulping industry, is an abundant yet highly underutilized aromatic resource. It is useful due to the vast scales involved as a source of fuels, chemicals, and functional materials when suitable postprocessing is applied. It is deemed to be a renewable alternative to fossil sources. Because of the extreme complexity of kraft lignin, in‐depth composition analysis and chemical structural identification are crucial for the development of effective valorization strategies. This work embarks on the characterization and identification of lignin‐derived phenolic compounds in representative hardwood (Eucalyptus) kraft lignin after selective fractionation using a single solvent. Advanced 2D heteronuclear single quantum coherence (HSQC) nuclear magnetic resonance (NMR), 31P NMR, and mass spectrometry in combination with synthetic authentic compounds are used for the structural identification of the low‐molecular‐weight fraction of kraft lignin. A total of 20 phenolic compounds, including several novel monomers (catechols), dimers (diarylethanes, diarylethenes, etc.), and trimers with triphenyl structures are systematically identified in the Eucalyptus kraft lignin. In addition, polysulfide is detected in the low‐molecular‐weight fraction, indicating that the oxidative polymerization of S2−/HS− occurrs during the kraft pulping process. An improved understanding of kraft lignin, especially the low‐Mw fraction, is expected to provide essential information for the selective fractionation and valorization of lignin.

Effect of organosolv extraction on the structure and antioxidant activity of eucalyptus kraft lignin

In this study, three lignin fractions F1, F2, and F3 were obtained from eucalyptus kraft lignin (EKL) by solvent extraction with ethyl acetate, acetone, and acetone/water. The antioxidant activity of these lignin fractions were measured and evaluated by using the DPPH radical scavenging activity, ABTS radical cation scavenging activity and ferric reducing antioxidant power analysis. These lignin fractions were also characterized by applying Gel permeation chromatography, Fourier transform infrared, 31P NMR and 2D HSQC NMR techniques. The three different lignin fractions had rather different average molecular sizes, as well as different phenolic and methoxy functional contents. The ethyl acetate fraction (F1) with the lowest average molecular weight (2342 g/mol) and the highest phenolic hydroxyl content (4.2457 mmol/g) and methoxy groups (6.2714 mmol/g) showed high homogeneity and the highest antioxidant activity. Its DPPH scavenging activity, ABTS+ scavenging activity, and ferric reducing the antioxidant power were 68.67%, 75.57%, and 91.89 μmol/g, respectively. Moreover, the antioxidant activity of F1 and F2 was found to be higher than that of butylated hydroxytoluene. Therefore, solvent extraction was shown to be an effective way to separate lignin fractions with high homogeneity, high antioxidant activity, which could lead to application of lignin with higher value.

Electrohydrodynamic Processing of PVP-Doped Kraft Lignin Micro- and Nano-Structures and Application of Electrospun Nanofiber Templates to Produce Oleogels

The present work focuses on the development of lignin micro- and nano-structures obtained by means of electrohydrodynamic techniques aimed to be potentially applicable as thickening or structuring agents in vegetable oils. The micro- and nano-structures used were mainly composed of eucalyptus kraft lignin (EKL), which were doped to some extent with polyvinylpyrrolidone (PVP). EKL/PVP solutions were prepared at different concentrations (10–40 wt.%) and EKL:PVP ratios (95:5–100:0) in N, N-dimethylformamide (DMF) and further physico-chemically and rheologically characterized. Electrosprayed micro-sized particles were obtained from solutions with low EKL/PVP concentrations (10 and 20 wt.%) and/or high EKL:PVP ratios, whereas beaded nanofiber mats were produced by increasing the solution concentration and/or decreasing EKL:PVP ratio, as a consequence of improved extensional viscoelastic properties. EKL/PVP electrospun nanofibers were able to form oleogels by simply dispersing them into castor oil at nanofiber concentrations higher than 15 wt.%. The rheological properties of these oleogels were assessed by means of small-amplitude oscillatory shear (SAOS) and viscous flow tests. The values of SAOS functions and viscosity depended on both the nanofiber concentration and the morphology of nanofiber templates and resemble those exhibited by commercial lubricating greases made from traditional metallic soaps and mineral oils.

Lignin dissolution model in formic acid–acetic acid–water systems based on lignin chemical structure

The separation of lignin from woody biomass and subsequent conversion into useful products requires a solution to the problem of its solubility. The expanded C9 formula of lignin, along with its atomic and functional groups, was determined by elemental analysis and NMRs spectroscopy. Based on the thus-obtained expanded C9 formula, the cohesion parameters of lignin dispersion (10.8–11.1 cal1/2·cm−3/2), polarity (4.15–4.31 cal1/2·cm−3/2), hydrogen bonding (6.30–7.38 cal1/2·cm−3/2), and solubility (13.2–14.0 cal1/2·cm−3/2) were respectively calculated using atomic and functional group contributions method. We established the relationship between lignin structure and lignin solubility parameters. The dissolution characteristics of wheat straw organic acid lignin, industrial eucalyptus kraft lignin, bamboo kraft lignin, and softwood kraft lignin in formic acid–H2O, acetic acid–H2O, and formic acid–acetic acid–H2O solvent systems were analyzed. The results indicate that the dissolution behavior of lignins follows the solubility parameters theory. We have developed a lignin dissolution model according to the lignin structure. This model obeys the solubility parameter theory, overcomes the limitations of the “like dissolves like” principle in organic acid–water systems, and provides a concise method for the selection of lignin solvent systems and the quantitative determination of their solvent composition.

The Use of South African Spent Pulping Liquor to Synthesize Lignin Phenol-Formaldehyde Resins

Abstract This study aims to investigate the potential of using lignin sourced from South African black liquor as a total phenol substitute in phenol-formaldehyde resins (PFRs), with a particular focus on bonding strength and curing properties. Four South African pulping-based lignins were used to synthesize these lignin-phenol formaldehyde resins (LPF100 resins), namely Eucalyptus Kraft lignin, Pine Kraft lignin, Bagasse Soda lignin, and Bagasse Steam Exploded lignin. Fourier-transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry were used to determine structural and curing properties. These resins were then used directly (unmodified) as adhesives to test shear bonding strength (R0 LPF100 adhesives). To improve the bonding properties of the unmodified LPF100 adhesives, the LPF100 resins were modified via the addition of a crosslinker (hexamine) as well as a hardener (either glyoxal, R1, or epichlorohydrin, R2). All R0 LPF100 adhesives fell below the GB/T 17657-2013 plywood standard of ≥0.7 MPa, with the Bagasse Soda LPF100 adhesive recording the highest bonding performance of 0.5 MPa, and the lowest curing temperature of 68°C. From the modified adhesives, the best performing were the Pine Kraft (R1) and the Eucalyptus Kraft (R2) LPF100 adhesives, recording 1.4 and 1.3 MPa, respectively. The curing temperatures of both these resins were 71°C and 80°C, respectively. Ultimately, the results of this study indicated that favorable adhesive properties may be obtained with the use of South African pulping-based lignins as a 100 percent phenol substitute in PFRs.

Ultra-Fast Selective Fructose Dehydration Promoted by a Kraft Lignin Sulfonated Carbon Under Microwave Heating

In this work, a highly acidic sulfonated carbon was obtained from eucalyptus kraft lignin, a byproduct from paper industry, and then used as catalyst in fructose dehydration. Reactions were performed employing dimethylsulfoxide (DMSO) as low cost/toxicity solvent and under microwave heating. The main product obtained was 5-hydroxymethylfurfural (5-HMF), a versatile platform compound that can be converted to several products of industrial interest. The catalyst is highly active to fructose dehydration and is able to convert 93.3% of the fructose (in a 10% m/v DMSO solution) with 98% of selectivity for 5-HMF in just 10 s at 393 K. Investigations about the catalyst dosage, reaction temperature and substrate concentration were carried out. In addition, the low-cost catalyst produced outperformed expensive commercial catalysts under the same conditions. After a simple regeneration process, the catalyst produced also can be recycled without significant loss in its catalytic activity.

Preparation of hyperbranched polymers from oxidized lignin modified with triazine for removal of heavy metals

This work describes the development of hyperbranched polymer from eucalyptus Kraft lignin for the removal of heavy metals present in water. The lignin versatile structure and reactive functional groups, such as phenolic hydroxyl groups have been explored. The oxidation of Kraft lignin was prepared under acid conditions, triazine was added in order to incorporate nitrogen heteroatoms and modify the lignin structure generating a hyperbranched polymer. Infrared spectroscopy, gel permeation chromatography, SEM-EDS Microscopy and Physisorption of N2 at 77 K were employed fot the characterization of adsorbents. It was also made a comparison of the amount of heavy metal removal using Kraft lignin (KL), oxidized Kraft lignin (OKL) and oxidized Kraft lignin cross-linked with triazine (OKL-CC). These were used in the adsorption of nickel and cadmium at 20 ppm, a pH of 4 and at 25 °C, with an amount of adsorbent of 25 mg. By atomic absorption was determined the concentration of the metals. The removal of cadmium was 96.1% for OKL-CC, 92.48% for OKL, while for KL it was 24.4%. The nickel removal with OKL-CC was 80.4%, with OKL was 68.8% and for the KL was 20.99%.

Eucalyptus Kraft Lignin as an Additive Strongly Enhances the Mechanical Resistance of Tree-Leaf Pellets

Pelleted biomass has a low, uniform moisture content and can be handled and stored cheaply and safely. Pellets can be made of industrial waste, food waste, agricultural residues, energy crops, and virgin lumber. Despite their many desirable attributes, they cannot compete with fossil fuel sources because the process of densifying the biomass and the price of the raw materials make pellet production costly. Leaves collected from street sweeping are generally discarded in landfills, but they can potentially be valorized as a biofuel if they are pelleted. However, the lignin content in leaves is not high enough to ensure the physical stability of the pellets, so they break easily during storage and transportation. In this study, the use of eucalyptus kraft lignin as an additive in tree-leaf pellet production was studied. Results showed that when 2% lignin is added the abrasion resistance can be increased to an acceptable value. Pellets with added lignin fulfilled all requirements of European standards for certification except for ash content. However, as the raw material has no cost, this method can add value or contribute to financing continued sweeping and is an example of a circular economy scenario.

From Waste to Wealth: From Kraft Lignin to Free-standing Supercapacitors

Pure eucalyptus Kraft lignin derived carbon fiber mats were produced based on a model workflow. It covers the preparation and characterization of the lignin precursor and the carbon materials and its testing in the final application (supercapacitor). Sequential solvent extraction was employed to produce a eucalyptus Kraft lignin precursor which could be electrospun into lignin fibers without any additives. The fiber formation from low molecular weight lignin is assigned to strong intermolecular interactions via hydrogen bonding and π-π-stacking between individual lignin macromolecules which gives rise to association complexes in the electrospinning solution. By stabilization in air, carbonization in N2 and an activation step in CO2, free-standing microporous carbon fiber mats could be produced. These fiber mats possess mainly basic oxygen functional groups which proved to be beneficial when tested as free-standing electrodes in symmetric supercapacitors. Consequently, the CO2-activated fiber mats showed a high specific gravimetric capacitance of 155 F/g at 0.1 A/g, excellent rate capability with 113 F/g at 250 A/g and good capacitance retention of 94% after 6000 cycles when tested in 6 M KOH electrolyte. Therefore, we conclude that lignin itself is a promising precursor to produce microporous, oxygen functionalized carbon fibers serving as free-standing electrodes in aqueous supercapacitors.

Determination of the absolute molar mass of acetylated eucalyptus kraft lignin by two types of size-exclusion chromatography combined with multi-angle laser light-scattering detectors

Abstract The molar mass (MM) and polydispersity indices (PDI) of acetylated hardwood kraft lignin (Ac-HWKL) and Ac-HWKL fractions were measured by size-exclusion chromatography with multi-angle laser light scattering (SEC-MALLS). The detectors worked at LL658 nm and LL785 nm. The MM of Ac-HWKL measured at 785 nm was much smaller than that measured at 658 nm. The number-average (Mn) and weight-average (Mw) molar masses of Ac-HWKL determined at 785 nm were approximately 6.2 and 6.5 times larger, respectively, than the values estimated using a conventional calibration curve created with authentic polystyrene standards in tetrahydrofuran (THF). Based on the Mw of Ac-HWKL fractions, the Mark-Houwink-Sakurada equation for Ac-HWKL was established to be [η]/ml g−1=0.320 M0.24 in THF and [η]/ml g−1=0.142 M0.26 in dimethyl sulfoxide (DMSO). These results demonstrate that Ac-HWKL has a more compact structure in an organic solvent than polystyrene.

High-value utilization of eucalyptus kraft lignin: Preparation and characterization as efficient dye dispersant

The dark color of industrial lignin is the main obstacle for their high value-added use in areas such as dyestuff dispersants. A kind of light-colored lignosulfonate with favorable dispersibility and remarkable stain resistance is prepared using fractionated eucalyptus kraft lignin. The fractionated lignins named as D (insoluble part) and X (soluble part) and sulfonated lignin fractions named as SD and SX are characterized by FTIR spectroscopy, 1H NMR spectroscopy, GPC and brightness test. The results reveal that fraction X presents a lower molecular weight but a higher hydroxyl content than that of fraction D, which lead to the differences on the SO3H content, dispersibility and color performance of SD and SX. The sulfonated fractions perform a similar molecular weight to that of unsulfonated lignins and show light color due to the phenolic hydroxyl blocking of 1,4–BS (1,4–butane sultone) and the postprocessing of sodium borohydride. The SX that performs the best of all exhibits obvious decrease on phenolic hydroxyl groups and increase on brightness value which is improved by 85.8% compared with control sample. The SX reaches the highest level (grade 5) in the dispersibility test and presents remarkable stain resistance on different textiles, especially on the dacron and cotton.

Color reduction of sulfonated eucalyptus kraft lignin

Several eucalyptus lignins named as HSL, SML and BSL were prepared by high temperature sulfonation, sulfomethylation, butane sultone sulfonation respectively. The color properties of samples were investigated. Under optimized conditions the sulfonic group (SO3H) content of HSL, SML and BSL reached 1.52, 1.60 and 1.58mmol/g, respectively. Samples were characterized by UV–vis spectroscopy, FTIR spectroscopy, 1H NMR spectroscopy, GPC and brightness test, respectively. The results revealed that BSL performed a higher molecular weight and lighter color due to the phenolic hydroxyl blocking by 1,4-butane sultone (1,4-BS). The color reduction of sodium borohydride treated BSL (labeled as SBSL) was further enhanced and the brightness value was improved by 76.1% compared with the darkest HSL. SBSL process was much better than HSL and SML process. Hydroxyl blocking effect of 1,4-BS and reducibility of sodium borohydride played important roles in the color reduction of sulfonated eucalyptus kraft lignin.

Ionic Liquid-Based Molecular Oxygen Oxidation of Eucalyptus Kraft Lignin to Obtain a Suite of Monomeric Aromatic By-Products

The oxidative degradation of eucalyptus kraft lignin as a function of an oxygen-enriched ionic liquid (IL) medium was investigated as part of a fundamental study to examine its capacity to degrade lignin into a suite of potentially valuable by-products relative to a standard sodium hydroxide solution (control). The variables of temperature, oxygen pressure, reaction time, and catalyst on the aromatic monomer products were controlled, whereas it was found that the yields of various aromatic monomer products were significantly improved when ionic liquid was used as the solvent instead of sodium hydroxide solution. These yields increased more substantially when a mixture of ionic liquid and sodium hydroxide was exploited as the reaction solvent. A quantity of 105.3 mg/g aromatic monomer products can be obtained at a temperature of 150°C, reaction time of two hours, and oxygen pressure of 6 MPa using CuO as the catalyst. In addition to the formation of aromatic monomer products, there were a number of other fascinating functional group and chemical linkage changes observed in the lignin macromolecule within the IL-based reaction system.