Unmodified Kraft Lignin Research Articles

Tunable hydrophobicity and biodegradability of acetylated lignin/polyester fibrous mat for water/oil separation

ABSTRACT The development of eco-friendly and biodegradable biopolymer composites has become increasingly important. In this study, acetylated lignin (ACL) was synthesized, and its potential as an effective additive for biodegradable polymers was investigated. ACL was synthesized through a one-step acetylation process in which hydroxyl groups of lignin were substituted with acetyl groups. ACL exhibited enhanced molecular weight and thermal stability, along with improved solubility in organic solvents compared to unmodified kraft lignin (KL). Hydrophobic ACL was uniformly dispersed in a mixture of a polycaprolactone (PCL) polymer and organic solvent, leading to the successful fabrication of a fibrous mat using electrospinning. The ACL/PCL fibrous mat demonstrated enhanced mechanical strength and hydrophobicity, notably indicating a substantially high-water contact angle of 143.3 ± 1.4°. Subsequently, it was utilized as a water/oil separator, showing a separation efficiency exceeding 90% for oil within a short time, effectively addressing water/oil emulsions. Biodegradability results demonstrated enhanced hydrolysis degradation efficiency with the incorporation of ACL into PCL fibers. Consequently, this study proposes a feasible approach to enhance the efficacy of ACL as a biodegradable polymer additive, while presenting promising opportunities for membrane applications targeting water/oil separation.

Integration of unmodified kraft lignin powder in waterborne coatings and investigation of antifouling properties

AbstractAntifouling properties of unmodified kraft lignin for potential use in marine coatings were investigated. The study was based on preliminary findings that pointed toward lignin’s efficacy against seawater organisms during laboratory tests. Coatings were formulated that contained lignin as a filler and had a pigment volume concentration above the critical pigment volume concentration. This ensured direct interaction between lignin and seawater organisms, as the lignin particles remained incompletely wetted by the binder. Moreover, all formulations were waterborne to mitigate the release of volatile organic compounds. Despite the initial promise, the antifouling performance of the formulated lignin coatings during field experiments at the CoaST Maritime Test Center was limited, and the anticipated mechanism must be reconsidered. Additionally, it was found that high lignin concentrations, while facilitating organism interaction, compromised the coating's mechanical properties. Nevertheless, the waterborne coating formulation introduced here might provide a foundation for other researchers to further investigate lignin’s potential as a bio-based pigment or a filler in coatings.

Toughening brittle kraft lignin coating on mismatched substrate with spider Silk-Inspired protein as an interfacial modulator

Current production of functional coatings majorly relies on petrochemical formulations. While they have provided substantial benefits, their fabrication processes as well as their disposal created widespread ecological catastrophes. Thus, there is a pressing demand and calls for a radical transformation to develop sustainable solutions by using renewable building blocks. Herein, we report on a novel coating formulation by combining largely undervalued kraft lignin from the forest industry, with genetically engineered and recombinantly produced spider silk-inspired protein through the industrial biotechnology platform. Unmodified kraft lignin was used as the main bulk component in the coating given its abundance and low cost. The nanometer-thin spider silk-inspired protein (SSIP) was used as a primary layer exhibiting dual functionalities: (i) modulating the mechanical properties of inherently brittle kraft lignin, (ii) substantially increasing the interfacial binding of kraft lignin to the underlying rigid silica substrate with the mismatched physicochemical properties. Our findings demonstrate how synergistic interplay components could result in scalable and durable functional coatings which could potentially be used in various medical and industrial applications in the future.

Influence of structure and functional group of modified kraft lignin on adsorption behavior of dye

Utilization of kraft lignin to produce bio-based adsorptive material for effective dye adsorption from industrial wastewater is essential to fulfilling the significant environmental protection needs. Lignin is the most abundant byproduct material with a chemical structure containing various functional groups. However, the complicated chemical structure makes it somewhat hydrophobic and incompatible, which limits its direct application as an adsorption material. Chemical modification is a common way to enhance lignin properties. In this work, the kraft lignin was modified through direct amination using Mannich reaction and oxidization followed by amination as new route of lignin modification. The prepared lignins, including aminated lignin (AL), oxidized lignin (OL), and aminated-oxidized lignin (AOL), as well as unmodified kraft lignin, were analyzed by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), elemental analysis and 1H-nuclear magnetic resonance measurements (1HNMR). The adsorption behaviors of modified lignins for the malachite green in aqueous solution were investigated well and discussed, as well as the adsorption kinetics and thermodynamic equations. Compared with other aminated lignin (AL), the AOL displayed a high adsorption capacity of 99.1 % dye removal, due to its more effective functional groups. The change in structure and functional groups on the lignin molecules during oxidation and amination had no effect on its adsorption mechanisms. The adsorption process of malachite green on different kinds of lignin belongs to endothermic chemical adsorption, which mainly consists of monolayer adsorption. The modification of lignin through oxidation followed by amination process, afforded kraft lignin a broad potential application in the field of wastewater treatment.

Kraft lignin and its derivates – A study on the adsorption of mono and multielement metals, potential use for noble metal recycling and an alternative material for solid base catalyst

Lignin is a natural polymer containing diverse functional groups and displaying an affinity for metals. Kraft lignin can be used as a carbon source, as a cleaving lignin structure for aromatic macromers or in the addition and modification of functional groups by the development of new active chemical sites. In this context, the aim of the present study is to investigate the adsorption of mono and multi-element metals solutions on lignin derivatives (unmodified Kraft lignin, acetylated Kraft lignin, charcoal Kraft lignin and activated carbon Kraft lignin). Parameters that affect adsorption processes, such as pH, contact time and adsorbent dose, were optimized in each case. The best adsorption condition was obtained at pH 7.00, a contact time of 120 min and with adsorbent dose of 30 mg. Also, unmodified Kraft lignin shows high adsorption selectivity (99%) for gold and palladium in acidic solutions. Acetylated and charcoal Kraft lignin resulted in lower adsorption levels in comparison with unmodified Kraft lignin. Activated carbon, however, reached adsorptions of over 86% for all metals. Finally, unmodified Kraft lignin impregnated with palladium presents a promising heterogeneous support in the Suzuki-Miyaura reaction.

Oxidative coupling of Kraft lignin mediated with hypervalent iodine reagent (III) for enhanced removal of dye in water

One of the most attractive routes to valorize lignin is to prepare lignin-based materials which can be used as high-value products, such as dye absorbents. Various processes have been investigated to improve the properties of lignin. In this study, a hypervalent iodine reagent (III) was employed to achieve oxidative coupling of Kraft lignin (KL). The structural changes were investigated by FTIR, quantitative 31P NMR, 2D-HSQC, and GPC. Oxidative coupling between lignin aromatic C(sp2)H bonds and aromatic C(sp2)-H functionalization with aliphatic hydroxyl group occurred via inter- or intramolecular modes, with resultant decreases of the aromatic protons and hydroxyl groups. In addition, selective modification of aliphatic OH groups in β-O-4′ linkages occurred leading to the formation of aromatic carbonyl groups. Increases in molecular weights with the appearance of conjugated CO groups were also observed. The oxidative crosslinked lignin (KL-2.0) exhibited better adsorptive features for brilliant green (251.2 mg/g) than that of unmodified KL (59.4 mg/g). Their adsorption kinetics were investigated by pseudo-first-order, pseudo-second-order and mixed-order models. Furthermore, the Langmuir and Freundlich models were employed to study the adsorption isotherms.

Improving kraft pulp mill sustainability by lignosulfonates production from processes residues

Kraft lignin is considered residue of process, but the integration of the biorefinery concept is important to achieve a more sustainable development of kraft pulp mills. Biorefinery is a promising approach to promote a wider use of kraft lignin, which is currently incinerated in kraft recovery boilers for power and steam generation. The production of lignosulfonates is one of possible uses of technical lignin for the production of lignin derivative bioproduct. This study evaluates the production of lignosulfonates from eucalypt kraft lignin by two processes: sulfomethylation and acid sulfonation. For sulfomethylation process, three temperatures (100, 130 and 160 °C) and 3 M ratios of sodium hydroxymethylsulfonate/lignin (0.8; 1.2 and 1.6) were evaluated. For acid sulfonation process, the temperatures of 80, 100 and 120 °C and molar ratio H2SO4/lignin of 10, 20 and 30 were considered. The lignosulfonate produced by the sulfomethylation process (160 °C and molar ratio of 1.6) presented a sulfur content (5.23%) similar to that found for commercial lignosulfonate (5.28%). A reduction of acid-insoluble lignin content and increase of acid-soluble lignin content was also observed compared to unmodified kraft lignin. In addition, it was confirmed that the insertion of sulfonate groups verified through FTIR analysis. Some lignosulfonates produced by sulfomethylation obtained solubility values similar to the commercial lignosulfonate, showing that the chemical modification of kraft lignin was achieved. On the other hand, the acid sulfonation was not efficient for the production of lignosulfonates from kraft lignin. Based on the studied conditions, the best results were obtained with the molar ratio H2SO4/lignin of 20 at 80 °C. The lignosulfonate produced in this condition presented a sulfur content of 3.28%, solubility in water of 15.0% and FTIR analysis similar to those found in unmodified kraft lignin, showing the inefficiency of the process.

Microwave-assisted selective acetylation of Kraft lignin: Acetic acid as a sustainable reactant for lignin valorization

Lignin acetylation, one of the most widespread chemical modifications used for improve the solubility of this biopolymer in organic solvents and increase polymer-lignin compatibility, has been performed for decades using time-consuming methodologies and acetylating agents with serious drawbacks. Moreover, traditional acetylation reactions generally conduce to non-selective acetylation of both aliphatic and phenolic groups. In this work, we demonstrated that partial and selective acetylation of kraft lignin can be carried out through a greener, simple and fast microwave-assisted process using acetic acid as solvent and acetylating agent. Structural characterization via FTIR, 1H-13C HSQC and 31P NMR demonstrated that acetylation reaction occurs selectively only in aliphatic hydroxyls, preserving the phenolic hydroxyls. Optimal reaction conditions were obtained using 1% (v/v) of H2SO4 as catalyst and only 5 min as reaction time. The acetylated Kraft lignin (AKL) obtained, have enhanced solubility in organic solvents (ethyl acetate, chloroform and dichloromethane) compared to unmodified Kraft lignin (KL) and antioxidant capacity almost 8 times higher than a commercial antioxidant BHT. These characteristics make the partially and selectively acetylated Kraft lignin a potential green antioxidant additive to be used in polymers blends.

Using Lignin to Modify Starch-Based Adhesive Performance

Unmodified kraft lignin was used to create a starch-based adhesive via the Stein Hall process. Lignin up to 35 wt% was used in several formulations. Lignin was incorporated in both the carrier and slurry portions of the formulations and the effect on adhesive strength and water resistance was studied. The addition of lignin resulted in a significant increase in adhesive strength when the lignin was added solely to the slurry portion. When lignin was added solely to the carrier portion, the adhesive strength decreased. Other formulations, where lignin was present in both the carrier and slurry portions, showed moderate increases in adhesive strength. Finally, the addition of lignin increased the water-resistance of the adhesive bond in the paperboard.

Materials for the biorefinery: high bio-content, shape memory Kraft lignin-derived non-isocyanate polyurethane foams using a non-toxic protocol

Non-isocyanate polyurethane foams have been synthesized from unmodified Kraft lignin and a renewable diamine creating materials with 100% biobased carbon. The materials demonstrate impressive physical and mechaical properties competing with commercial polyurethanes.

Rigid polyurethane foams containing lignin oxyalkylated with ethylene carbonate and polyethylene glycol

A “green” oxyalkylation protocol employing ethylene carbonate (EC), polyethylene glycol 400 (PEG400), and water was developed to convert an industry byproduct, kraft lignin (KL), into biopolyols for the production of rigid polyurethane (RPU) foams. EC served as an oxyalkylation reagent for the derivatization of KL’s hydroxyl (OH) groups. PEG400 and water served as a co-solvent and a reactive additive, respectively, to tailor two properties of the KL-derived biopolyols, those being viscosity and OH number. For the oxyalkylated-KL (OKL), as characterized by 31P nuclear magnetic resonance (31P-NMR), more than 80% of OH content was aliphatic. The 14-fold increase in reactivity towards isocyanates for the OKL, over that for the unmodified KL, was attributed to the derivatization of lignin phenolic OHs to aliphatic OHs, the latter being more accessible and reactive during the RPU foam production. The preferred oxyalkylation conditions were 170 °C, 30 min, PEG400/EC ratios of 50/50 to 70/30 (wt/wt), and KL mass loadings of 20–50 wt%. Biopolyols synthesized under these conditions exhibited viscosities from 0.5 to 53 Pa·s, OH numbers from 459 to 659 mg KOH/g, and alkalinity numbers below 4 mg KOH/g. The biopolyols were directly used for RPU foam production. RPU foams produced under optimal conditions showed densities from 51 to 60 kg/m3 and compressive strengths from 139 to 204 kPa.

Lignin-Based Polyurethanes from Unmodified Kraft Lignin Fractionated by Sequential Precipitation

Lignin-based polyurethanes were synthesized from three unmodified softwood Kraft lignin fractions as the primary hydroxyl group providers which constituted >40% of the polymeric materials. High-, m...

Antioxidant activity of unmodified kraft and organosolv lignins to be used as sustainable components for polyurethane coatings

The antioxidative capacity of four different kraft lignins (KL) and one additional organosolv lignin (OSL) was studied using the Folin–Ciocalteu (FC) assay. To do so, the corresponding FC assay procedure was adapted and optimized to be appropriate for lignin analysis. Different solvents were tested, and DMSO and saturated sodium carbonate (Na2CO3) for pH adjustment showed the best results. The absorption wavelength of 740 nm was chosen due to highest determination coefficients. Continuous calibration is recommended on a daily basis to guarantee accuracy. The antioxidant capacity and related radical scavenging activity of various lignins were correlated with the biomass nature (soft wood vs grasses) and pulping methods (kraft vs organosolv). The results show higher antioxidant activity for kraft vs organosolv lignins. First lignin-derived polyurethane coatings were prepared using the unmodified kraft lignin. The films, prepared via spin coating, show a high flexibility and transparency.

Unmodified kraft lignin isolated at room temperature from aqueous solution for preparation of highly flexible transparent polyurethane coatings.

Polyurethane (PU) coatings were successfully produced using unmodified kraft lignin (KL) as an environmentally benign component in contents of up to 80 wt%. Lignin samples were precipitated from industrial black liquor in aqueous solution working at room temperature and different pH levels (pH 2 to pH 5). Lignins were characterized by UV-Vis, FTIR, pyrolysis-GC/MS, SEC and 31P-NMR. Results show a correlation between pH level, OH number and molecular weight Mw of isolated lignins. Lignin-based polyurethane coatings were prepared in an efficient one step synthesis dissolving lignin in THF and PEG425 in an ultrasonic bath followed by addition of 4,4-diphenylmethanediisocyanate (MDI) and triethylamine (TEA). Crosslinking was achieved under very mild conditions (1 hour at room temperature followed by 3 hours at 35 °C). The resulting coatings were characterized regarding their physical properties including ATR-IR, TGA, optical contact angle, light microscopy, REM-EDX and AFM data. Transparent homogeneous films of high flexibility resulted from lignins isolated at pH 4, possessing a temperature resistance up to 160 °C. Swelling tests revealed a resistance against water. Swelling in DMSO depends on index, pH of precipitation and catalyst utilization for PU preparation. According to AFM studies, surface roughness is between 10 and 28 nm.

Effect of unmodified kraft lignin concentration on the emulsion and miniemulsion copolymerization of styrene with n‐butyl acrylate and methacrylic acid to produce polymer hybrid latex

The introduction of non‐modified kraft LignoBoost® lignin (KL) to produce polymer hybrid latex has received much attention in recent years because it is derived from renewable resources. The focus of this work is to develop a polymer hybrid latex by emulsion and miniemulsion copolymerization of styrene with n‐butyl acrylate and methacrylic acid in the presence of different concentrations of KL furnished by the pulp and paper industry. The study intends to substitute a styrene in the system to understand the effect of non‐modified KL on the properties not only of the latexes, but also on the copolymers themselves. Each polymerization was carried out by shot‐process of tertbutyl hydroperoxide and sodium formaldehyde sulfoxylate as the redox system. The polymer latexes were characterized in relation to overall conversion, particle diameter, particle morphology, coagulum formation, surface tension, zeta potential, and atomic force microscopy. The polymers were evaluated through gel permeation chromatography, water absorption, and thermal properties. The results show that the addition of non‐modified KL results in inhibition of the polymerization and that KL acts as a colloid stabilizer. Small particles were generated in the initial stages of the polymerizations. The presence of the KL altered the color of the latexes; the increase in KL concentration resulted in increase in the absorption of water of the polymer films; the increase in KL concentration resulted in decrease of the molar mass of the copolymers.

Preparation of cationic softwood kraft lignin and its application in dye removal

The cationization of polymers was regarded as an effective method to improve their performance for various applications. In this work, the cationization of kraft lignin was investigated using glycidyl-trimethylammonium chloride (GTMAC) with kraft lignin in an aqueous solution under altered conditions. The conditions investigated were temperature, time, pH, GTMAC to lignin molar ratio, and lignin concentration. The optimized conditions based on charge density and solubility of cationic lignin were found to be 70°C, 1h, 12.5 pH, 2/1 GTMAC/lignin molar ratio, and 1.0wt.% lignin concentration. The solubility of the resulting cationic lignin reached 90% in 1wt.% lignin concentration and the charge density reached 1.10meq/g under the optimized conditions. The cationic lignin was characterized and compared with unmodified kraft lignin using elemental analysis, Fourier Transform Infrared (FTIR) spectrophotometer, proton nuclear magnetic resonance (1H NMR) and thermogravimetry (TGA) analysis in order to confirm the success of the grafting reaction. The cationic lignin was used as a flocculant for dye removal (Remazol Brilliant Violet, Reactive Black, and Direct Yellow) from model wastewater.

Kraft lignin as filler in PLA to improve ductility and thermal properties

Kraft lignin (KL) and acetylated Kraft lignin (AKL) were used as filler for the elaboration of composites with poly(lactic acid) (PLA) in different concentrations (0.5, 1, 5, 10 and 20%) by extrusion method at 200°C. Characterization of both lignins has been performed using HPLC, FT-IR, GPC, DSC and TGA. KL presented only 0.3% of ash content and molecular weight around 2000g/mol. The esterification increased the molecular weight and decreases the polydispersity of the lignin (AKL). Also, AKL had lower Tg and higher thermal stability than unmodified Kraft lignin. Lignin content increased the thermal stability of PLA, with the addition of both types of lignins. Contact angle was measured to assess the change in the hydrophobicity of PLA with the addition of lignins. Mechanical properties of different materials were also investigated in order to know the effect of lignin addition in PLA. Maximum strength was not severely affected at low concentrations of both lignins, but it decreased dramatically, especially in composites with 10 and 20% of KL. Elongation at break increased with the addition of low contents of AKL, at high content of both lignins the material becomes quite brittle.

Modified kraft lignin for bioremediation applications

Kraft lignin (KL) from industrial pulping of E. globulus wood was subjected to the oxidative modification with the aim to produce sorbent mimicking humic matter for the bioremediation purposes. Lignin was oxidized by polyoxometalate Na5[PMo10V2O40] (POM), solely or in the presence of laccase, under pre-selected aerobic conditions (50–60°C, 1–2h, oxygen pressure 5 bar). The most pronounced lignin oxidation without its depolymerisation was observed in the reaction system POM/O2. Modified lignins possessed increased amounts of COOH (up to 15 %) and CO (up to 500 %) groups, when compared to unmodified KL, and significantly higher molecular weights. Sorption capacity of KL before and after modification towards transition metals (cadmium (II) and mercury (II)) and triazine pesticide (atrazine) was assessed in batch experiments under equilibrium conditions. KL oxidation improved sorption capacity towards transition metals (up to 15 %) but not necessarily the uptake of atrazine that was higher for unmodified KL.

Lignin‐polypropylene composites. Part 1: Composites from unmodified lignin and polypropylene

AbstractLignin polypropylene composites were prepared in the range of 10–60% by weight lignin content. Blending of lignin with polypropylene resulted in materials with reduced tensile and flexural strength and a dramatic decrease in unnotched Izod impact strength compared to the properties of virgin polypropylene, although moduli (Young's and flexural) were improved. Traditional surface‐treated fillers such as mica and talc performed better than lignin, but when lignin and inorganic fillers were mixed, the strength properties were improved with respect to lignin alone, perhaps because of a better lignin‐filler‐particle interaction and distribution. This could be an alternate approach for obtaining improved strength composites containing large quantities of unmodified kraft lignin. Incorporation of maleic anhydride grafted polypropylene (MAPP) as a coupling agent also improved strength properties, although at high lignin contents (e.g. 60%) there was considerable variability in the tensile strength.

Gel formation of lignin and biodegradation of the lignin gels by microorganisms

The multifunctional, polyphenolic nature of isolated lignins invites practical applications in which lignin serves as the principal component of cross-linked network polymers. Unmodified kraft lignin was first condensated with phenols and then further condensated with resorcinol under alkaline conditions, to give lignin–phenol–resorcinol resin (LPR resin). Lignin gels were prepared from the methanol-diluted LPR resin with the use of organic cross-linking agent glutaraldehyde (GA) via reacting for 3 days at 25°C. The gel formation depended on the amounts of methanol, and not the amounts of GA. The lignin gel obtained exhibited a reversible expansion–contraction behavior when it was alternatively immersed in ethanol and in water. Degradation of cross-linked LPR–GA hydrogels by some microorganisms has been investigated. From the experimental results, the following findings were obtained. The lignin–GA gels are degraded by the four Basidiomycotia fungi examined. The most effective degradation of the lignin–GA gels was obtained with the fungus Flammulina velutipes. The present biodegradation results by wood-rotting fungi might give some clues as to future biotechnology of cross-linked lignin and lignin hydrogels.