Kraft Lignin Fractions Research Articles

Dielectric characterisation of chitosan-based composite membranes containing fractionated kraft and organosolv lignin

Chitosan-based composite membranes with fractionated kraft and organosolv lignin were prepared by solvent casting. A small lignin fraction (1%) was added to the neat chitosan to obtain a good distribution. The influence of lignin extraction with ethyl acetate and consequently ethanol on the dielectric and conductive properties of the composites was investigated by dielectric thermal analysis (DETA). Overall, the chitosan-lignin composites exhibit three relaxation mechanisms (β, βwet, and α) and two conductivity phenomena (σ and MWS). FTIR analysis showed that the composites with organosolv lignin fractions have fewer hydroxyl groups than those with kraft lignin, which decreases slightly further for both after ethanol extraction. The lignin fractions with lower molecular weight and higher OH content show stronger interactions with chitosan, due to hydrogen bonding. These interactions affect the thermal activation and cooperativity of the β-, βwet, and α-relaxation. Furthermore, the kraft lignin fractions with many polar groups are very compatible with the chitosan matrix, resulting in a more compact structure and higher fragility. The membranes CS OLEA and CS KLE have a lower electron conductivity and a higher proton conductivity. Thus, they have promising conductivity properties for fuel cell applications.

Selected Kraft lignin fractions as precursor for carbon foam: Structure-performance correlation and electrochemical applications

The rapid exhaustion of fossil fuels brings to the fore the need to search for energy efficient strategies. The conversion of lignin into advanced functional carbon-based materials is considered one of the most promising solutions for environmental protection and the use of renewable resources. This study analyzed the structure-performance correlation of carbon foams (CF) when lignin-phenol-formaldehyde (LPF) resins produced with different fractions of kraft lignin (KL) were employed as carbon source, and polyurethane foam (PU) as sacrificial mold. The lignin fractions employed were KL, fraction of KL insoluble in ethyl acetate (LFIns) and fraction of KL soluble in ethyl acetate (LFSol). The produced CFs were characterized by thermogravimetric analysis (TGA), X-ray diffractometry (XRD), Raman spectroscopy, 2D HSQC Nuclear magnetic resonance (NMR) analysis, scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), and electrochemical measurements. The results showed that when LFSol was employed as a partial substitute for phenol in LPF resin synthesis, the final performance of the produced CF was infinitely higher. The improved solubility parameters of LFSol along with the higher S/G ratio and β-O-4/α-OH content after fractionation were the key to produce CF with better carbon yields (54 %). The electrochemical measurements showed that LFSol presented the highest current density (2.11 × 10−4 mA.cm−2) and the lowest value of resistance to charge transfer (0.26 KΩ) in relation to the other samples, indicating that the process of electron transfer was faster in the sensor produced with LFSol. LFSol's potential for application as an electrochemical sensor was tested as a proof of concept and demonstrated excellent selectivity for the detection of hydroquinone in water.

Selection of kraft lignin fractions as a partial substitute for phenol in synthesis of phenolic resins: Structure-property correlation

In this work, a strategy was proposed aiming to describe an efficient kraft lignin (KL) fractionation method to extract large amounts of low molar mass lignin to partially replace non-renewable phenol with the KL fractions in the synthesis of phenolic resins. KL from Eucalyptus urograndis wood was refined by a fractionation process in ethyl acetate (EtAc). The lignin-phenol-formaldehyde (LPF) resins were formulated by replacing 25% and 50% of phenol with the fractionated lignin. The lignin employed were KL, fraction of KL insoluble in EtAc (LFIns) and fraction of KL soluble in EtAc (LFSol). The LFSol and LFIns fractions were analyzed for composition, functional group content, and thermal properties. Gel Permeation Chromatography (GPC) results indicated that the lower molar mass lignin fractions (LFSol) showed higher solubility in EtAc. The total hydroxyl groups content (by 31 P NMR) of the soluble EtAc fraction increased to 4.73 mmol.g −1 after fractionation. The phenolic resin based on monomers derived from LFSol showed adhesion strength, glass transition temperature and thermal stability with values close to commercial phenolic resins. The better homogeneity of the LPF resin produced from LFSol at 25% phenol substitution resulted in adhesion properties similar to the control resin. On the other hand, LFSol could successfully directly replace 15% of the commercial PF resin (corresponding to > 30% phenol replacement) showing the performance similar to the commercial PF control and significantly higher than the LFIns and non-fractionated KL. • Extraction method of low molar mass kraft lignin. • Structure-performance correlation of selection of kraft lignin fractions. • Partial replacement of non-renewable phenol by lignin fractions. • Improved performance of the soluble lignin fraction as an adhesive.

Fractionation of Lignin with Decreased Heterogeneity: Based on a Detailed Characteristics Study of Sequentially Extracted Softwood Kraft Lignin

Industrial lignin fractionation is attracting increasing interest due to its enormous potential in the development of high value-added materials. However, the widely reported fractionation approaches are primarily focused on the separation of fractions with a low polydispersity index (PDI). In this study, based on the detailed characteristic examination of carefully sequential-extracted softwood Kraft lignin fractions, a novel method to isolate lignin fraction with decreased heterogeneity (LGF-dh), was established in consideration of impurities, elemental composition, molar mass distribution, carbohydrate content, functional hydroxyl content, and the content of lignin-relevant aromatic units. To characterize the mentioned properties, an elemental analyzer, SEC-MALS, GC–MS, GC-FID, Py/GC–MS, 31P-NMR, and HSQC-NMR were used to compare the differences of the sequential lignin fractions that were obtained by methyl tert-butyl ether (MTBE), ethyl acetate (EtOAc), ethanol (EtOH), methanol (MeOH), acetone, and dioxane. Moreover, a practical and feasible three-step extraction process was proposed to separate the low heterogeneity lignin fraction from industrial lignin according to the different solubilities of each fraction in the green cosolvent system of EtOH/water, MeOH/water, and acetone/water. Overall, this work presented a comprehensive study on the properties of softwood lignin as well as proposed a feasible and convenient method to reduce the heterogeneity of lignin, which would promote its valorization.

Probing the molecular weights of sweetgum and pine kraft lignin fractions

The present investigation undertook a systematic investigation of the molecular weight (MW) of kraft lignins throughout the pulping process to establish a correlation between MW and lignin recovery at different extents of the kraft pulping process. The evaluation of MW is crucial for lignin characterization and utilization, since it is known to influence the kinetics of lignin reactivity and its resultant physicochemical properties. Sweetgum and pine lignins precipitated from black liquor at different pHs (9.5 and 2.5) and different extents of kraft pulping (30–150 min) were the subject of this effort. Gel permeation chromatography (GPC) was used to deter- mine the number average molecular weight (Mn), mass average molecular weight (Mw), and polydispersity of the lignin samples. It was shown that the MW of lignins from both feedstocks follow gel degradation theory; that is, at the onset of the kraft pulping process low molecular weightlignins were obtained, and as pulping progressed, the molecular weight peaked and subsequently decreased. An important finding was that acetobromination was shown to be a more effective derivatization technique for carbohydrates containing lignins than acetylation, the technique typically used for derivatization of lignin.

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

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

Enhancement of charge transport in interconnected lignin-derived carbon fibrous network for flexible battery-supercapacitor hybrid device

Self-supporting and flexible carbon fibrous mats are promising electrode materials for wearable devices. The contact resistance between adjacent fibers is still a limit for further improvement of energy storage performance. Herein, an activated interconnected lignin-derived carbon fibrous network (AILCFN) is fabricated by electrospinning followed by heat treatment. The unique interconnected structure between fibers in AILCFN is designed by controlling the ratio of soft Kraft lignin fractions with different thermal mobility. While the interconnected fibers are benefited for the electron transport and conductive property of the carbon networks, the high specific surface area is synergistically conduced to the direct channels for the fast ion transfer. The as-prepared AILCFN-3 exhibits an excellent specific capacitance and a high rate capability (69% from the current density from 1 to 20 mA cm−2). Further, AILCFN-3 can act as the scaffold to support the electrodeposited Ni-Co-S nanosheets. The AILCFN/Ni-Co-S composite electrode displays a high specific capacity of 1140.0 C g−1 at a current density of 10 A g−1. The assembled AILCFN/Ni-Co-S//AILCFN-3 BSH exhibits a high energy density of 30.8 Wh kg−1 with a power density of 0.8 kW kg−1 and demonstrates both excellent cyclability and flexibility, attributed to the high effective specific surface area and advantageous interconnected structure. The self-powered system assembled onto a lab coat can continuously power for the electronic watch under sunlight illumination and dark environment, demonstrating the promising potential of AILCFN in future wearable electronics. This work represents a “waste into wealth” direction of conversion strategy from biomass waste lignin to value-added energy storage materials, which conversely turns different thermal property of lignin fractions to good account, and breaks through the application limits caused by the heterogeneity.

Evaluation of lignin-enriched side-streams from different biomass conversion processes as thickeners in bio-lubricant formulations

This study explores the suitability of residual lignin-containing fractions generated as side-streams in different conversion processes of eucalypt and pine woods as thickening agents in bio-lubricant formulations. These conversion processes included fermentable sugars extraction by autohydrolysis or steam explosion and kraft pulping. Structural properties of lignin fractions were characterized by FTIR, 1H and 13C NMR, two-dimensional NMR, TGA and SEC, whereas their compositions were analysed by standard analytical methods. On the other hand, chemical oleogels were prepared with NCO-functionalized residual lignin fractions, and characterized by means of rheological, tribological and AFM techniques. Hydrolysis lignin fractions exhibited a great content of carbohydrates, especially glucose (46.0–48.5%), xylose (4.3–15.6%) and lignin (32.5–39.9%) with a well-maintained structure, displaying the main inter-unit linkages and low phenolic content. By contrast, kraft lignin fractions presented a lower carbohydrate content, mainly xylose (3.4–4.3%), and higher content (44.9–67%) of severely degraded lignin, showing a dramatic reduction of inter-unit linkages, and thereby high phenolic content. The rheological response of NCO-functionalized lignin fractions-based oleogels is highly influenced by the composition and chemical structure of residual lignin fractions. Moreover, these oleogels presented suitable tribological properties with values of the friction coefficient lower than those typically exhibited by standard lubricating greases.

Kraft lignin fractionation by organic solvents: Correlation between molar mass and higher heating value

The new concept of integrated biorefineries has significantly changed pulp and paper industries. Lignin, which until then was only burned to generate energy, is now an important raw material for new products production. Kraft lignin (KL) fractions obtained by sequential fractionation with five organic solvents. This sequence allows to extract fractions from lower molar mass to higher molar one, resulting in more homogeneous samples. Lignin’s fractions were characterized by FTIR, GPC, TGA and Higher Heating Value (HHV). HHV for KL was 24966, the lowest being 17,891 (F5) and the highest being 27051 J/g (F1), inversely proportional to the molar masses of fractions. This is a very important result indicating that the lower HHV fractions can be used for certain applications, such as antioxidants, additives, polymers, among others, adding value to kraft lignin. Fractions with higher HHV could be used for energy generation in the cellulose paper industry.

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...

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.

Tunable Thermosetting Epoxies Based on Fractionated and Well-Characterized Lignins.

Here we report the synthesis of thermosetting resins from low molar mass Kraft lignin fractions of high functionality, refined by solvent extraction. Such fractions were fully characterized by 31P NMR, 2D-HSQC NMR, SEC, and DSC in order to obtain a detailed description of the structures. Reactive oxirane moieties were introduced on the lignin backbone under mild reaction conditions and quantified by simple 1H NMR analysis. The modified fractions were chemically cross-linked with a flexible polyether diamine ( Mn ≈ 2000), in order to obtain epoxy thermosets. Epoxies from different lignin fractions, studied by DSC, DMA, tensile tests, and SEM, demonstrated substantial differences in terms of thermo-mechanical properties. For the first time, strong relationships between lignin structures and epoxy properties could be demonstrated. The suggested approach provides unprecedented possibilities to tune network structure and properties of thermosets based on real lignin fractions, rather than model compounds.

Carbohydrate-free and highly soluble softwood kraft lignin fractions by aqueous acetone evaporation fractionation

Carbohydrate-free and highly soluble softwood kraft lignin fractions by aqueous acetone evaporation fractionation

Carbohydrate-free and highly soluble softwood kraft lignin fractions by aqueous acetone evaporation fractionation - OPEN ACCESS

Carbohydrate-free and highly soluble softwood kraft lignin fractions by aqueous acetone evaporation fractionation - OPEN ACCESS

Characterization of Kraft Lignin Fractions Obtained by Sequential Ultrafiltration and Their Potential Application as a Biobased Component in Blends with Polyethylene

Fractionation of Kraft lignin from black liquor is necessary to reduce its heterogeneity, which exerts negative effects upon lignin-commercial polymer composite materials. In this work, Kraft lignin was dissolved in acetic acid to get low viscosity lignin solution and fractionated into specific molecular weight fractions by sequential ultrafiltration with different molecular weight cut-offs. The fractionated lignins were characterized, and their suitability in polyethylene–lignin composites was evaluated. After ultrafiltration with 5k and 3k Da cutoff, fractionation resulted in three fractions of differing molecular weights and lower polydispersity than the original Kraft lignin (F1 (7010 g/mol), F2 (3540 g/mol), and F3 (1890 g/mol)). The results from spectroscopic characterization of lignin (31P, 13C, and 2D-HSQC NMR) and thermal stability analysis (TGA and DSC) indicated that the contents of various linkages and functional groups and the thermal properties of each fraction varied as a function of its mo...

Macroscopic Behavior of Kraft Lignin Fractions: Melt Stability Considerations for Lignin–Polyethylene Blends

Questions that pertain to the behavior of softwood kraft lignin fractions as opposed to the whole lignin still prevail. In an effort to further understand such effects at a macroscopic level, we have examined the issue of melt stability of polyethylene (PE) in blends with fractionated and unfractionated softwood kraft lignin. While methylation of the phenolic OH groups significantly stabilizes any lignin/PE melt, more in depth data demonstrate that when separate, acetone soluble (ASKL) and acetone insoluble (AIKL) kraft lignin fractions behave completely differently than the original unfractionated material. The low molecular weight methylated ASKL offers unexpected plasticizing action to PE melts, possibly as a consequence of its low molecular weight and spherical configuration. The higher molecular weight AIKL offers relatively stable PE melts, possibly manifesting its rigid nature and higher glass transition temperature likely occurring due to π stacking operating among its aromatic rings. Mixing these...

Preparation of Nanocapsules via the Self-Assembly of Kraft Lignin: A Totally Green Process with Renewable Resources

Kraft lignin (KL), the byproduct from the alkali pulping process in the paper industry, is an abundant renewable resource. It was found that KL could be used to form nanocapsules via self-assembly induced by adding water to an ethanol solution of KL. From the results of various imaging techniques and laser light scattering techniques, the hollow sphere feature of this product was confirmed. It was found that there is a higher percentage of ethanol enriched in the interior of the nanocapsules and that the different KL fractions can be spontaneously distributed in the shells according to their hydrophilic–lipophilic sequence. The π–π interactions between the aromatic rings are considered to be an important driving force in the assembly process of the KL nanocapsules. Moreover, the sizes of these KL nanocapsules can vary in the range of tens to hundreds of nanometers, depending on the preparation conditions, which enhance their flexibility to adapt to the potential applications in various fields. Preparation...

Correlations of the Antioxidant Properties of Softwood Kraft Lignin Fractions with the Thermal Stability of Its Blends with Polyethylene

Since technical lignins are increasingly considered as additives to polyolefins, an effort is made here to understand the fundamental antioxidant properties of softwood kraft lignin and its fractions on the thermal stability of its blends with polyethylene. Lower molecular weight acetone soluble kraft lignin (ASKL) fractions showed better antioxidant properties than unfractionated and acetone insoluble kraft lignin (AIKL). By selectively methylating the phenolic hydroxyl groups of the lignin and its fractions, it was shown that the lignin had no antioxidant ability. The phenolic OH groups in lignin, therefore, play a vital role toward imparting antioxidant characteristics in it. To further understand the role of lignin during the thermal processing of polyethylene, we measured the oxidation induction temperature (OITtemp) of its blends with softwood kraft lignin and its fractions. Once again, the role of the phenolic OH was found to be extremely important toward the thermal oxidative characteristics of kraft lignin and its fractions. Since acetone soluble softwood kraft lignin contains 54% more phenolic units than its acetone insoluble counterpart, its blends (5 wt %) with polyethylene improved its OITtemp by about 50 °C with no additional increases at higher lignin contents. At elevated processing temperatures, when polyethylene blends of lignin start to degrade, the aromatic nature of the created char reduces its rate of degradation, concomitantly increasing the thermal degradation temperature of polyethylene. This effect was further investigated and details of the relative contributions of the phenolic OH stabilization mechanism to the charring mechanism are discussed.

Preparation and Characterization of Interconnected, Kraft Lignin‐Based Carbon Fibrous Materials by Electrospinning

Inter‐connected carbon sub‐µm fibrous materials are prepared by electrospinning of Kraft lignin solutions in DMF followed by thermal treatment consisting of oxidative thermostabilization at 250 °C and carbonization in the temperature range 600–1000 °C. Inter‐fiber bonding is achieved by taking advantages of the intrinsic differences in thermal mobility between different Kraft lignin fractions. Inter‐fiber bonding is observed to enhance the mechanical properties of both the thermostabilized and carbonized materials and enhances the electrical conductivity of the carbonized materials. The surface area, morphological, and structural characteristics are also characterized by the BET method, scanning electron microscopy, and Raman spectroscopy, respectively.

Preparation and Characterization of Kraft Lignin-Based Moisture-Responsive Films with Reversible Shape-Change Capability

Preparation of moisture-responsive Kraft lignin-based materials by electrospinning blends of Kraft lignin fractions with different physical properties is presented. The differences in thermal mobility between lignin fractions are shown to influence the degree of interfiber fusion occurring during oxidative thermostabilization of electrospun nonwoven fabrics, resulting in different material morphologies including submicrometer fibers, bonded nonwovens, porous films, and smooth films. The relative amount of different lignin fractions and degree of fiber flow and fiber fusion is shown to influence the tendency for the electrospun materials to be transformed into moisture-responsive materials capable of reversible changes in shape. Material characterization by scanning electron microscopy and atomic force microscopy as well characterization of the chemical and physical properties of Kraft lignin fractions by dynamic rheology, 1H and 13C NMR, and gel permeation chromatography combined with multiangle laser light scattering are presented. A proposed mechanism underlying moisture-responsiveness, shape change, and shape recovery is discussed based on the differences in chemical structure and physical properties of Kraft lignin fractions.