Hardwood Kraft Lignin Research Articles

Mechanistic insight into hydroxy-methylation of hardwood Kraft lignin

Mechanistic insight into hydroxy-methylation of hardwood Kraft lignin

Influence of Hardwood Lignin Blending on the Electrical and Mechanical Properties of Cellulose Based Carbon Fibers.

Carbon fibers (CFs) are fabricated by blending hardwood kraft lignin (HKL) and cellulose. Various compositions of HKL and cellulose in blended solutions are air-gap spun in 1-ethyl-3-methylimidazolium acetate (EMIM OAc), resulting in the production of virtually bead-free quality fibers. The synthesized HKL-cellulose fibers are thermostabilized and carbonized to achieve CFs, and consequently their electrical and mechanical properties are evaluated. Remarkably, fibers with the highest lignin content (65%) exhibited an electrical conductivity of approximately 42 S/cm, surpassing that of cellulose (approximately 15 S/cm). Moreover, the same fibers demonstrated significantly improved tensile strength (∼312 MPa), showcasing a 5-fold increase compared to pure cellulose while maintaining lower stiffness. Comprehensive analyses, including Auger electron spectroscopy and wide-angle X-ray scattering, show a heterogeneous skin-core morphology in the fibers revealing a higher degree of preferred orientation of carbon components in the skin compared to the core. The incorporation of lignin in CFs leads to increased graphitization, enhanced tensile strength, and a unique skin-core structure, where the skin's graphitized cellulose and lignin contribute stiffness, while the predominantly lignin-rich core enhances carbon content, electrical conductivity, and strength.

Phenolation to Improve Hardwood Kraft Lignin for Wood Adhesive Application.

Lignins, naturally occurring aromatic polymers with phenylpropane units, are promising bio-based alternatives for petroleum-based products. Resole-type phenol formaldehyde (PF) adhesive is commonly used in wood composites requiring durability and weather-proofness. However, PF adhesive is a petroleum-based product. The objective of this study is to transform the low-reactivity hardwood kraft lignin (KL) as the phenol substitute in the PF adhesive formulation by acidic phenolation. The variations in the molecular weights, chemical structures, and functional groups in lignins were investigated before and after the phenolation. The results indicate that the KL can be cleaved, and phenols are crosslinked onto KL to produce phenolated kraft lignin (PKL) under the suitable phenolation condition, heating 3/5 (w/w) of KL/phenol at 90 °C for 2 h with 5% H2SO4 as the catalyst. Resole-type PKL-PF adhesives can be directly synthesized after the phenolation in the same reactor. Plywood laminated with this adhesive obtains satisfactory strength and low formaldehyde emission. This not only reduces the usage of petroleum-based phenol but also increases the reactivity and applications for hardwood KL.

Self-supported lignin-based carbon fibrous aerogels with outstanding rate capability and high oil/seawater separation flux

The construction of hardwood kraft lignin (HKL)-based carbon fibrous aerogels (LCAs) for practical application still faces significant challenges. In this work, we proposed to enhance LCAs through the utilization of hydrogen-bonding interactions and π-π interactions. Self-supported LCA/graphene oxide (GO) composites were prepared based on the adhesion of HKL ultrafine fibers and GO, taking advantage of the strong interaction between HKL and GO. The morphology, thermal behavior, chemical structure and crystalline structure of LCA/GO composites were systemically investigated and discussed. Results suggested that HKL ultrafine fibers and GO formed a cohesive whole carbonization due to the influence of hydrogen-bonding and π-π interaction. The prepared LCA/GO composites exhibited outstanding rate capability and high oil/seawater separation flux with their three-dimensional hierarchical channel structures. The specific capacitance of the LCA/GO5.0 electrode was 152 F g−1 at 0.5 A g−1 and 94 F g−1 at 10 A g−1, respectively, while maintaining a retention rate of 113 % after 2000 cycles. The adsorption capacity of the LCA/GO7.5 composite reached up to 55.9 g g−1 and its oil/seawater separation flux was as high as 12,335 L m−2 h−1. The formation strategy, sustainable concept and excellent properties presented in this work will give some inspiration for the preparation of self-supported aerogels as well as their applications in compressible supercapacitors and oil/seawater separation.

Modulation of physicochemical and antioxidant properties of Pickering emulsions using colloidal lignin particles based on kraft softwood and hardwood acetone fractions

Colloidal lignin particles (CLPs) emerge as a sustainable alternative to traditional, fossil-based emulsion stabilizers. However, effectively outperforming the conventional ingredients requires addressing the challenges posed by lignin heterogeneity and structural complexity. In this study, one-step acetone fractionation was applied to softwood and hardwood kraft lignins to tackle the issue. The resulting soluble (AS) and insoluble (AI) fractions, along with the pristine lignins, underwent thorough characterization and were used to create CLPs through the hydrotropic precipitation. The acetone fraction-derived CLPs were tested for the first time as Pickering stabilizers. Notably, a strong correlation emerged between the structural traits of each lignin sample and the properties of the resulting Pickering emulsions. Such correlation allowed for a fine-tuning of their physicochemical and antioxidant features. The AS fractions, characterized by higher phenolic OH content and lower molecular weight, led to CLPs with larger sizes and reduced hydrophilic character compared to those derived from AI- and pristine lignins. The fraction-derived CLPs exhibited superior emulsifying capacity and imparted long-term stability to the formed emulsions. Moreover, the resulting Pickering emulsions showed high potential as antioxidant agents, proving their ability as multifunctional systems. Overall, this work demonstrates how the unique properties of lignin can be selectively enhanced through acetone fractionation method and seamlessly transferred to Pickering emulsions. This advancement promotes the use of lignin in high-value-added sectors such as cosmetics and personal care.

Aqueous ethanol fractionation of softwood and hardwood kraft lignins: Impact on purity and properties

Industrial kraft lignins are mixtures of macromolecular components variable in both structure and composition. To maximize their value in commercial applications, they often need to be homogenized and purified. Several fractionation methods have been reported to improve the properties of kraft lignins, but these reports have been mostly limited to kraft lignins of single origins. In this study, the physicochemical properties of fractions from four industrial kraft lignins were compared. Fractionation was performed on both softwood and hardwood lignins by partial dissolution in aqueous ethanol followed by precipitation with water. The yields of each fraction varied greatly between the lignins, with differences reaching up to 35% for a single fraction. All fractions were characterized which showed that fractions having remarkably similar properties and compositions can be obtained from different lignins. Organic and inorganic impurities were found to concentrate in specific fractions which allowed the isolation of highly purified fractions of kraft lignin. These results highlight the importance of matching individual kraft lignins with suitable applications.

Methylation of softwood and hardwood kraft lignins with chloromethane.

Methylation is a well-established means of enhancing the thermal stability, improving the compatibility in polymer blends, and lowering the glass-transition temperature of lignins. This process normally involves reagents that are costly, associated with poor atom economy and/or highly toxic. Herein, we report the methylation of softwood and hardwood kraft lignins using chloromethane in alkaline aqueous media. This reaction proceeds in high yields at 90-110 °C under moderate pressure (40 psi) while generating environmentally benign sodium chloride and water as by-products.

Comparison of the effects of three drying methods on lignin properties

In the last few years, a serious effort has been initiated to develop standard methods for lignin characterization at the national and international levels. Thus, several Canadian and ISO standards were recently developed. The current results were generated in an effort to assist the ISO/TC6 Committee come up with a reliable standard method for the measurement of the dry solids content of lignins. In particular, this work investigated the drying of lignin using three different drying methods: conduction oven drying (105 °C), vacuum oven drying at (60 °C), and freeze drying. Ten different lignins were used in this study including wet and air-dried softwood and hardwood kraft lignins in the acid and base forms from the industrial LignoForce™ process and hydrolysis lignin from the TMP-Bio™ process. The results showed that 7 h, 48 h and 24 h were sufficient to reach a constant solids content in the case of all lignins when oven drying, vacuum oven drying under negative pressure (150 mbar), and freeze drying (25 mT) were used, respectively.Kraft lignins in the base form showed higher sensitivity to degradation compared to lignins in the acid form. The total hydroxyl group content of air-dried and wet hardwood lignins in the base form decreased by more than 50 % after vacuum oven-drying for 71.5 h or oven-drying for 16 h compared to freeze-drying for 68 h. The decrease in the total hydroxyl groups was more pronounced (70 %) when the wet softwood lignin in the base form was dried in the oven compared to freeze drying for 68 h.

Using carboxyl groups to improve the compatibility of XNBR/lignin composites

AbstractThe paper and pulp industry produces lignin as a byproduct, which could be a bio‐based reinforcing filler for rubber. Carboxylated nitrile rubber (XNBR) contains carboxyl groups that form ionic bonds with zinc oxide, potentially increasing compatibility with lignin, compared to usual nonpolar rubbers. This study employed the traditional mixing method, two‐roll mill, to incorporate hardwood Kraft lignin without chemical or physical modification as a reinforcing filler in commercial XNBR. A mixture design of experiments was used to explore the effect on rubber/lignin interaction of the carboxyl group content (from 1% to 7% in blends of XNBR) and the amount of lignin (from 0 to 40 phr). Adding 40 phr of lignin increased stress at 100% in XNBR 7% from 1.7 to 6.3 MPa. In XNBR 1%, the increase was from 1.2 to 1.9 MPa. Lignin showed better interaction and dispersion with XNBR 7%, determined from response surface of G′ at high deformations and SEM, respectively. Loss of thermal transition in DMA indicates interaction through ionic groups. These results show that the presence of carboxyl groups enhances the rubber/lignin interaction. This research open possibilities of compatibilization of lignin, offering guidance for future studies and technologies involving lignin in technical applications.Highlights Lignin dispersion increased as the carboxyl group content increased to 7% (w/w). Stress at 100% elongation increased 370% with 40 phr of lignin and 7% carboxyl. Rubber/lignin interaction as per G′ increased with carboxyl groups. Loss of thermal transition suggests lignin/carboxy/zinc oxide interaction. Lignin can be used as a reinforcing filler in nitrile carboxylated rubber.

Potential of hardwood kraft lignin as a bio-based dye for cotton fabrics

The dyeing characteristics of hardwood kraft lignin (KL) were investigated on cotton fabrics, assessing its potential as a sustainable and environmentally friendly dye. Dyeability was evaluated by varying the KL concentrations, temperature, and time. An aqueous solution of Na2CO3 (1.0%) as the dye bath and a fabric-to-liquor ratio of 1:50 were used. Cationizing effects were studied using (3-chloro-2-hydroxypropyl) trimethylammonium chloride (CHPTAC), and the mordanting effects of various mordants were also evaluated. Post-mordanting was performed with FeSO4, FeCl2, Fe-lactate (Fe-lac), MgSO4, CuCl2, CuSO4, and Al2(SO4)3. A mordant concentration of 1 mM o.w.f. (0.5 mM for Al2(SO4)3), with a liquor ratio of 1:30, at 60 °C for 30 min were employed. Suitable dyeing conditions were 2.0% o.w.b., 90 °C, and 90 min, resulting in a brownish color of the cotton fabric. The fabrics exhibited a range of light brown to light grayish brown colors and showed lighter colors than the untreated fabrics when mordanted with MgSO4 and Al2(SO4)3. The color difference (ΔE) between cationized and uncationized cotton fabrics was 3.48. From the colorfastness assessment, KL-dyed cotton fabric showed good rubbing and washing fastness for staining, but poor light and washing fastness for fading.

Ether Bond Formation in Waste Biomass–Derived, Value-Added Technical Hardwood Kraft Lignin Using Glycolic Acid

Ether bond formation in technical hardwood kraft lignin (THKL) by crosslinking using glycolic acid was investigated for bio-adhesive applications. Industrial hardwood kraft black liquor was used to extract the THKL utilized by acidification. Chemical and thermal properties of the THKL with and without crosslinking were analyzed by Fourier transform infrared (FTIR) spectroscopy, solid-state 13C cross-polarization/magic angle spinning nuclear magnetic resonance (13C CP/MAS NMR) spectroscopy, X-ray photoelectron spectroscopy (XPS), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). FTIR results revealed a new peak corresponding to the ether bond and hemiacetal formation due to crosslinking at 1075 cm-1 and 1324 cm-1. 13C CP/MAS NMR spectra revealed the presence of a higher number of ether bonds due to the reduced aromatic and aliphatic hydroxyl groups in THKL and new bonds formed at 62-64 ppm and 168-191 ppm due to crosslinking. XPS results revealed that new bonds were formed between glycolic acid and THKL, leading to increased atomic oxygen percentage and carbon–oxygen bonds in crosslinked THKL detected by peak intensity changes at 287.7 and 288.8 related to O–C–O and O–C=O. Also, the oxygen content increased from 14.88% to 31.76% due to bond formation. GPC confirmed a higher molecular weight and broader molecular-weight distribution of THKL. DSC and TGA curves of crosslinked THKL revealed exothermic behavior, high thermal stability, and low thermal degradation rate. Owing to a significant amount of kraft black liquor being generated by wood pulp industries and attractive chemical properties of THKL, THKL demonstrates promise as a raw material to produce green, sustainable bio-adhesives via the crosslinking of its different hydroxyl groups using glycolic acid.

Self-crosslinking of acetone-fractionated and glyoxalated hardwood kraft lignin as bio-adhesives for wood bonding

The research on hardwood lignin is quite limited for lignin-based adhesives due to its heterogeneity and chemical complexity compared with those of softwood and non-wood lignin. Herein, a novel approach of producing entirely bio-based and nontoxic wood adhesives by self-crosslinking of industrial hardwood kraft lignin (HKL) is presented to replace formaldehyde-based resin adhesives. The key issues of converting HKL to bio-wood adhesive are their low reactivity for crosslinking capacity and high heterogeneity. For this, HKL extracted from industrial black liquor was acetone fractionated to reduce its heterogeneity, resulting in acetone-soluble HKL (AS-HKL) and acetone-insoluble HKL (AI-HKL), which were then glyoxylated to facilitate crosslinking and form a three-dimensional network structure. Lignin samples were analyzed by gel permeation chromatography (GPC), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), 31P nuclear magnetic resonance (31P NMR), solid state 13C cross-polarization/magic angle spinning (13C CP/MAS) NMR, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The adhesive strength of lignin-based adhesives was evaluated by determining the tensile shear strength of plywood. In this current research the chemical structure changes especially the crosslinked structure and adhesion performance were investigated. Results showed that the self-crosslinking was successfully formed by ether bonds formation between glyoxalated lignin. Also, the self-crosslinked acetone insoluble hardwood kraft lignin fractionation (AI-HKL) showed the best adhesion performance. FTIR, XPS and 13C CP/MAS NMR spectra revealed new peaks and ether bonds in the glyoxylated lignin. Therefore, these results indicate a successful self-crosslinking of the hardwood kraft lignin after acetone fractionation and glyoxalation for adhesives via network formation. The glyoxalated AI-HKL (AI-HKL–GLY) exhibited the highest viscosity and provided the best plywood adhesion strength (0.8 MPa) among the adhesives, and showed a good potential as wood adhesives. Thus, the results suggest that the self-crosslinking of hardwood kraft lignin after a proper fractionation and glyoxalation is a promising approach of developing lignin-based bio-adhesives for wood bonding.

Structure and property variations of mixed hardwood kraft lignins

Kraft lignin as an emerging renewable feedstock can be used to produce fuels, chemicals, and materials. Hardwood kraft lignin bears intrinsic variation due to wood species and the isolation process. The structure and property variation of hardwood kraft lignin could introduce new challenges and opportunities for its application. To better understand such variation, seven kraft lignin samples, originated from southern mixed hardwood (North America), northern mixed hardwood (North America), and Asian mixed hardwood, were isolated from commercial kraft pulping black liquor using both LignoBoost and LignoForce processes. Modern analytical techniques were used to elucidate the characteristics of mixed hardwood kraft lignins, including chemical composition, molecular weight, functional groups, and thermal properties. All lignin samples had a lignin content over 90% (92% to 96%) with one exception, which was northern mixed hardwood kraft lignin with 86% of lignin content and 6% polysaccharides. The elemental and methoxy analyses revealed the expected variation of hardwood kraft lignins with the methoxy content ranging from 0.85 to 1.20 per C9 unit. The weight average molecular weight exhibited a higher variation (from 4800 to 1895 Da) with a descending order of southern mixed hardwood kraft lignins, northern mixed hardwood lignins, and Asian mixed hardwood lignins. The aliphatic hydroxy groups ranged from 14 to 25 per 100 C9 units, and phenolic hydroxy groups ranged from 65 to 112 per 100 C9 units. The catecholic group content ranged from 12 to 34 per 100 C9 units, which is higher than softwood kraft lignin. The lignins isolated from the rapid displacement heating (RDH) pulping process were more condensed than from the regular kraft pulping process. 2D HSQC and quantitative 13C NMR revealed the drastic structure change upon kraft pulp with the low abundance of native lignin linkages and formation of new interunit linkages, such as stilbene, enol ethers, and 1-1’/5’. The S/G ratio was calculated using 2D HSQC spectra correcting for signal shift caused by the catecholic groups.

Synthesis of acetone-fractionated hardwood kraft lignin-based adhesive crosslinked with epichlorohydrin

Studies on lignin have garnered great interest for increasing the value of lignin-added products, especially lignin-based adhesives. However, even with the advantage of abundant aromatic materials in lignin, its aromaticity and heterogeneity require its fractionation with various solvents. This study used hardwood kraft lignin (HKL) extracted from black liquor and was acetone-fractionated to produce acetone-soluble HKL (AS-HKL) and acetone-insoluble HKL (AI-HKL). The lignins were crosslinked with different amounts of epichlorohydrin (ECH; 5%, 10%, and 15%) for the synthesis of lignin-based adhesives with a three-dimensional network. The crosslinked HKLs were characterized with gel permeation chromatography (GPC), Fourier transform infrared (FT-IR), nuclear magnetic resonance (13C-NMR), and differential scanning calorimetry (DSC) to investigate their molecular weight, chemical structure, and thermal curing behavior. AI-HKL exhibited higher molecular weight than that of AS-HKL. As expected, the FT-IR and 13C-NMR spectra showed successful crosslinking of HKL by ECH with the intensity reduction of − OH, increased C–O stretching, and new peak appearance. From the DSC results, the exothermic peak temperature for crosslinking was 100 °C–130 °C. HKL and AI-HKL plywoods showed good tensile shear strength with minimal variations when they were crosslinked with 10 and 15% ECH. These results suggest the potential of high molecular weight HKL as lignin-based adhesives for wood bonding.

Probing the relationship between chemical structure and thermal degradation behavior of acetone fractionated kraft lignin

This study reports the relationships between structure and thermal degradation behavior of industrial softwood and hardwood kraft lignin (KL) after acetone fractionation to obtain acetone soluble (AS) and acetone insoluble (AI) fractions with reduced structural polydispersity. The structure and thermal degradation behavior of AS-KL and AI-KL was examined by gel permeation chromatography, Fourier transform infrared, quantitative carbon-13 nuclear magnetic resonance spectroscopy, and thermogravimetric analysis. The results showed that the AS-KL fractions had reduced apparent molecular weight, lower polydispersity, less native wood lignin side chains, greater aromatic hydroxyl groups, and more condensed structures. In contrast, the AI-KL fractions showed substantially larger apparent molecular weight and polydispersity, as well as more aliphatic hydroxyl groups and native lignin side chains. Consequently, AI-KL samples exhibited greater thermal degradation activation energy than those of AS-KL samples because the former fractions had a larger apparent molecular weight as well as more aliphatic OH groups, which facilitated hydrogen bonding between lignin polymers, improving their thermal stability. This finding suggests that acetone fractionation of KL can be used to examine the relationship between structure and thermal degradation of industrial KL. These results also provide important information on the thermal degradation behavior of acetone fractionated products with relevant chemical and physical properties for a specific application, such as raw materials for lignin valorization.

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.

Chemical and Thermal Characteristics of Ion-Exchanged Lignosulfonate

Lignosulfonate features sulfonate groups, which makes it soluble in water and hence, suitable for a wide range of applications. However, its characterization is challenging because of its limited solubility in organic solvents. Thus, this study investigated the chemical and thermal characteristics of ion-exchanged sodium lignosulfonate (Na-LS) and compared it with those of industrial kraft lignin derived from softwood and hardwood. The results demonstrated that the ion exchange successfully converted Na-LS to lignosulfonic acid (H-LS), as proven by the Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and elemental analysis. H-LS has a greater apparent molecular weight than those of Na-LS and softwood and hardwood kraft lignin (SKL and HKL). According to 31P nuclear magnetic resonance (NMR) analysis, H-LS has less phenolic OH than SKL and HKL, indicating that it has more polymeric chains. Furthermore, H-LS has substantially more native side chains, such as β-O-4 units, than SKL and HKL. Thermal analysis revealed that H-LS has a greater glass temperature (Tg) than SKL and HKL, although Na-LS has a lower Tg than SKL and HKL. In addition, H-LS degraded faster than Na-LS did because the acid condition accelerated degradation reaction.

Effects of Precipitation pH of Black Liquor on Characteristics of Precipitated and Acetone-Fractionated Kraft Lignin

Two important steps in utilizing technical kraft lignin (KL) from black liquor to synthesize lignin-phenol-formaldehyde (LPF) resin are its extraction via precipitation and fractionation. However, the effects of precipitation pH and acetone fractionation on the characteristics of hardwood KL have not been studied for LPF resins. Therefore, this paper reports the effects of the precipitation pH of black liquor and acetone fractionation on the characteristics of KL from mixed hardwood species for LPF resins. The precipitation was conducted at various pH levels from 3 to 9 of black liquor to obtain crude KL (C-KL), which was used in acetone fractionation to produce acetone-soluble KL (AS-KL) and acetone-insoluble KL (AI-KL). Precipitation at pH 3 and 9 produced the highest and lowest yields of C-KL, respectively. As expected, the C-KL infrared spectra were similar regardless of the precipitation pH levels. As the pH increased, the molecular weight of C-KL increased. However, the molecular weight of AS-KL and AI-KL after acetone fractionation increased to a maximum of 4,170 and 47,190 g/mol at pH 7, then decreased to 3,210 and 19,970 g/mol at pH 9, respectively. The smallest molecular weights of AS-KL and AI-KL were 3,210 and 15,480 g/mol and were found at pH 9 and 3, respectively. These results suggest that both AS-KL at pH 9 and AI-KL at pH 3 have good potential as starting lignins for synthesizing LPF resins that require cross-linking for polymerization.

Assembly of electric double-layer capacitors with hardwood kraft lignin-based electrodes and separator together with ionic liquid electrolyte

Abstract This study aimed to assemble a high-performance electric double-layer capacitor (EDLC) using a hardwood kraft lignin (HKL)-based separator and HKL-based electrodes, which were fabricated from a nonwoven mat of electrospun HKL fibers. The separator was prepared by the thermostabilization of the mat derived from a mixed dope of HKL, hexamethylenetetramine, and polyethylene glycol (1.66/0.50/0.09, w/w) for electrospinning. Although a mat-type HKL-based electrode containing conductive carbon black (CB) has been reported to be suitable for a commercial cellulosic separator, this electrode was found to be unsuitable for the HKL-based separator because of its rough surface and poor contact with the separator interface. Hence, a powder-type electrode with a smooth surface was fabricated by grinding the mat, followed by casting with a carboxymethyl cellulose aqueous solution, and its EDLC possessed high energy (49 Wh kg−1) and power densities (151 kW kg−1). Moreover, to provide a simple process for electrode fabrication, another mat-type electrode was fabricated by adding CB to the mixed dope, followed by electrospinning, carbonization, and steam activation. The resultant EDLC exhibited excellent electrochemical performance with energy (58 Wh kg−1) and power densities (55 kW kg−1).

Surface chemistry and bioactivity of colloidal particles from industrial kraft lignins

The morphology control of lignin through particle size reduction to nanoscale seems to be a suitable conversion technology to overcome the intrinsic limitations of its native form to develop a wide range of biomaterials with high performance. Colloidal lignin particles (CLPs) in the range of 150–200 nm were synthesised from hardwood and softwood kraft lignins by the solvent shifting method. The initial molecular features of kraft lignins were evaluated in terms of purity, molecular weight distribution, and chemical functionalities. The impact of the lignin source and structure on the morphology, size distribution, and surface chemistry of CLPs was evaluated by particle size analyser, SEM, TEM and 1H NMR. The results evidenced the influence of the botanical origin on the morphology and surface chemistry of particles. Furthermore, the antioxidant properties and cytotoxicity of lignins and corresponding CLPs, towards lung fibroblast cells were compared. CLPs from hardwood kraft lignins exhibited higher antioxidant power against DPPH free radical and a higher cytotoxic effect (IC30 = 67–70 μg/mL) against lung fibroblast when compared to CLPs from softwood kraft lignin (IC30 = ~91 μg/mL). However, the cytotoxicity of these biomaterials was dose-dependent, suggesting their potential application as active ingredients in cosmetic and pharmaceutic products at low concentrations.