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The demand for biodegradable materials across various industries has recently surged due to environmental concerns and the need for the adoption of renewable materials. In this context, lignin has emerged as a promising alternative, garnering significant attention as a biogenic resource that endows functional properties. This is primarily ascribed to its remarkable origin and structure that explains lignin's capacity to bind other molecules, reinforce composites, act as an antioxidant, and endow antimicrobial effects. This review summarizes recent advances in lignin-based composites, with particular emphasis on innovative methods for modifying lignin into micro and nanostructures and evaluating their functional contribution. Indeed, lignin-based composites can be tailored to have superior physicomechanical characteristics, biodegradability, and surface properties, thereby making them suitable for applications beyond the typical, for instance, in ecofriendly adhesives and advanced barrier technologies. Herein, we provide a comprehensive overview of the latest progress in the field of lignin utilization in emerging composite materials. [ABSTRACT FROM AUTHOR]

A renewable source of carbon black is introduced by the processing of lignin from agro‐forestry residues. Lignin side streams are converted into spherical particles by direct aerosolization followed by carbonization. The obtained submicron black carbon is combined with cellulose nanofibers, which act as a binder and rheology modifier, resulting in a new type of colloidal bioink. The bioinks are tested in handwriting and direct ink writing. After consolidation, the black bioinks display total light reflectance (%R) at least three times lower than commercial black inks (reduction from 12 to 4%R). A loading of up to 20% of nanofibers positively affects the cohesion of the dried bioink (1 to 16 MPa), with no significant reduction in light reflectance. This is a result of the superstructuring of the ink components, which disrupts particle packing, intensifies colloidal interactions, introduces light absorption, and non‐reflective multiple scattering. [ABSTRACT FROM AUTHOR]

Nanocellulose is very hydrophilic, preventing interactions with the oil phase in Pickering emulsions. This limitation is herein addressed by incorporating lignin nanoparticles (LNPs) as co-stabilizers of nanocellulose-based Pickering emulsions. LNP addition decreases the oil droplet size and slows creaming at pH 5 and 8 and with increasing LNP content. Emulsification at pH 3 and LNP cationization lead to droplet flocculation and rapid creaming. LNP application for emulsification, prior or simultaneously with nanocellulose, favors stability given the improved interactions with the oil phase. The Pickering emulsions can be freeze–dried, enabling the recovery of a solid macroporous foam that can act as adsorbent for pharmaceutical pollutants. Overall, the properties of nanocellulose-based Pickering emulsions and foams can be tailored by LNP addition. This strategy offers a unique, green approach to stabilize biphasic systems using bio-based nanomaterials without tedious and costly modification procedures. [ABSTRACT FROM AUTHOR]

This study aims to overcome the challenges of high-value utilization of technical lignins that encounters chemical complexity, heterogeneity and broad molecular mass distribution. Kraft lignin was fractionated through a practical strategy involving sequential dissolution in solvents of different polarities (water, tetrahydrofuran, and water/tetrahydrofuran v/v = 3/7). Lignin self-assembled drawing on the anti-solvent method, generating particles of controllable surface energy. Considering the governing factors in multiphase stabilization, the morphology, wetting characteristics and chemical composition of the kraft lignin particles (KLPs) were examined as a means to achieve controllable Pickering stabilization of oil-in-water (O/W) emulsions. The most anionic and hydrophilic KLPs formed aggregated networks (∼185 nm), which acted as a surfactant-type emulsifier following reversible adsorption at the O/W interfaces. Notably, the particles of the least hydrophilicity (∼146 nm) displayed a characteristic hollow structure. Such particles adsorbed slowly and weakly at the O/W interface, forming a viscoelastic layer around the oil droplets. The smallest lignin particles (∼39 nm) presented an intermediate hydrophilic character. They were uniform in size and formed rigid interfacial layers on the oil droplets. Accordingly, the devised relationship between particle morphogenesis and O/W stabilization capacity enabled the customization of lignin (size and wetting characteristics), allowing broader utilization in multiphase systems. [ABSTRACT FROM AUTHOR]

We introduce a simple spray drying method for the scaleup production of spherical organic (lignin) particles with sizes between 0.85 and 1.57 µm. We assess the surface energy of the lignin particles by inverse gas chromatography to reveal their role in composites synthesized with unsaturated polyester. Such nanocomposites are shown to be transparent to electromagnetic irradiation (millimeter wave bands). The permittivity and tanδ of the composite material reached values 3.01 and 0.01 at 28 GHz with 10% lignin content. Vinyl groups were introduced on the surface of the particles to achieve enhanced interfacial adhesion, and resulted in a reduced relative permittivity (2.75). Together with wave interactions, the mechanical and thermal properties of the composites are put in perspective, opening new opportunities in the development of bio-based devices for 5G high-speed communication. [ABSTRACT FROM AUTHOR]

Significant progress in lignins valorization and development of high-performance sustainable materials have been achieved in recent years. Reports related to lignin utilization indicate excellent prospects considering green chemistry, chemical engineering, energy, materials and polymer science, physical chemistry, biochemistry, among others. To fully realize such potential, one of the most promising routes involves lignin uses in nanocomposites and nanohybrid assemblies, where synergistic interactions are highly beneficial. This review first discusses the interfacial assembly of lignins with polysaccharides, proteins and other biopolymers, for instance, in the synthesis of nanocomposites. To give a wide perspective, we consider the subject of hybridization with metal and metal oxide nanoparticles, as well as uses as precursor of carbon materials and the assembly with other biobased nanoparticles, for instance to form nanohybrids. We provide cues to understand the fundamental aspects related to lignins, their self-assembly and supramolecular organization, all of which are critical in nanocomposites and nanohybrids. We highlight the possibilities of lignin in the fields of flame retardancy, food packaging, plant protection, electroactive materials, energy storage and health sciences. The most recent outcomes are evaluated given the importance of lignin extraction, within established and emerging biorefineries. We consider the benefit of lignin compared to synthetic counterparts. Bridging the gap between fundamental and application-driven research, this account offers critical insights as far as the potential of lignin as one of the frontrunners in the uptake of bioeconomy concepts and its application in value-added products. [ABSTRACT FROM AUTHOR]

Sugar‐based biorefineries have faced significant economic challenges. Biorefinery lignins are often classified as low‐value products (fuel or low‐cost chemical feedstock) mainly due to low lignin purities in the crude material. However, recent research has shown that biorefinery lignins have a great chance of being successfully used as high‐value products, which in turn should result in an economy renaissance of the whole biorefinery idea. This critical review summarizes recent developments from our groups, along with the state‐of‐the‐art in the valorization of technical lignins, with the focus on biorefinery lignins. A beneficial synergistic effect of lignin and cellulose mixtures used in different applications (wood adhesives, carbon fiber and nanofibers, thermoplastics) has been demonstrated. This phenomenon causes crude biorefinery lignins, which contain a significant amount of residual crystalline cellulose, to perform superior to high‐purity lignins in certain applications. Where previously specific applications required high‐purity and/or functionalized lignins with narrow molecular weight distributions, simple green processes for upgrading crude biorefinery lignin are suggested here as an alternative. These approaches can be easily combined with lignin micro‐/nanoparticles (LMNP) production. The processes should also be cost‐efficient compared to traditional lignin modifications. Biorefinery processes allow much greater flexibility in optimizing the lignin characteristics desirable for specific applications than traditional pulping processes. Such lignin engineering, at the same time, requires an efficient strategy capable of handling large datasets to find correlations between process variables, lignin structures and properties and finally their performance in different applications. [ABSTRACT FROM AUTHOR]

In recent years, there have been many advances toward developing sustainable, micro- and nanoscale materials from biobased resources such as lignin aimed at strengthening the bioeconomy. It is critical to study the factors affecting nucleation and growth mechanisms, as well as the stability of lignin micro-and nanoparticles (LPs), to further enhance the development of such materials. However, there remains a gap in the literature examining the many interactions present during and after LP formation. These interactions vary with the chemical composition and molecular weight distribution of different kraft lignin (KL) fractions. To examine the composition of different lignin fractions, KL can be fractionated using water-miscible organic solvents of different polarities such as tetrahydrofuran (THF), acetone, and ethanol. Herein, we show that the micro- and nanoparticles formed from each lignin fraction exhibit significant differences in their size (50–300 nm), particle aggregation and fusion propensity, and spherical morphology in aqueous suspensions. These differences are proposed to be a result of the solvent–lignin–water interactions related to molecular weight and functional groups of the lignin fractions and solvent/water polarity. Another factor affecting the nucleation and growth of LPs is the lignin concentration. The LPs formed at low lignin concentrations exhibit a larger average particle size compared to the LPs formed at higher lignin concentrations due to the aggregation and fusion of the small particles. These results will allow for a stronger foundation in understanding the nucleation and growth of LPs when attempting to develop value-added applications for kraft lignin. [ABSTRACT FROM AUTHOR]

The subject of lignin structure, critical for fundamental and practical reasons, is addressed in this study that includes a review of the methods applied to elucidate macromolecular branching. The recently available approaches for determination of the absolute molecular mass of spruce milled wood lignin (MWL) along with the quantification of terminal groups clearly indicate that MWL is significantly branched and cross-linked (with ∼36% lignin units partaking in these linkages). Results from independent methods imply that about half of the branching and crosslinking linkages involve aromatic rings, predominantly 5–5′ etherified units; meanwhile, a significant number of linkages are located in the side chains. Quantitative 13C NMR analyses suggest that the branches involve different aliphatic ether (alkyl-O-alkyl) types at the α- and γ-positions of the side chain, with intact β-O-4 linkages. While the exact structures of these moieties require further investigation, our results point to the fact that conventional lignification theory disagrees with the presence of such key moieties in softwood MWL and the observed high degree of branching/crosslinking. Potential reasons for the noted discrepancies are discussed. [ABSTRACT FROM AUTHOR]

There is an increased interest in renewable carbon as a source of materials, where lignin is expected to play a prominent role. This stems, partially, from new regulations aiming to achieve a cleaner and safer environment. Lignin, as a polyaromatic plant-derived biomolecule, is not only abundant but widely accessible in industrial streams. Due to recent developments in production scalability as well as promising application prospects, nanoscaled lignin particles have recently generated interest in the research and industrial communities. This review describes the main routes to prepare spherical lignin particles, highlighting aspects associated to their shape and topology as well as performance. We discuss the use of spherical lignin particles as dispersants and in the formulation of coatings, adhesives and composites, focusing on the advantages of the spherical shape and nanoscaled size. The state of the particles is furthermore compared in terms of their applicability in dry and wet forms. Finally, we discuss the sustainability, stability and degradation of lignin particles, which are issues that are critically important for any prospective use. [ABSTRACT FROM AUTHOR]

Nano-lignocellulose (NLC) and lignin-free nanocellulose (nano-holocellulose, NHC) were used in paper coating to investigate their effect on coating layer quality and offset printing. The NLC was produced by microfluidisation of unbleached secondary fibres while the reference NHC was obtained from the same fibre source after lignin removal (OHEPH bleaching), following the same mechanical process. TEMPO-mediated oxidation of the fibres prior to microfluidisation was applied to increase the electrostatic charge and hydrophilicity of the nanofibrils. The coatings, displaying given surface morphology and energy, were applied on Kraft, printing-grade papers at three grammage levels. The structure of the coated and uncoated (reference) papers were accessed (SEM and AFM) and IGT printing was carried out to determine the print density, print gloss, rub-off resistance, surface energy, roughness, ink transfer, dry pick resistance, water interference and set-off. The results highlight the important effect of residual lignin or type of nanocellulose on the coating layer and the development of offset printing properties. It was observed that roughness was a key factor leading to a deterioration of the print properties, predominantly affecting the NLC coating. Considering the lower hydrophilicity of NLC, an alternative dispersion with water-alcohol mixtures is proposed. By using this dispersing medium, tailorable surface coverage, surface smoothness, ink acceptance and improved printability was achieved. We show that under these conditions and compared to NHC, NLC is equally effective as a coating layer.

The bagasse of Agave tequilana Weber is one of the most abundant agroindustrial wastes in the state of Jalisco. However, at the present time, there is no technical use for this waste, and its high availability makes it an environmental problem. The objective of this research was to take advantage of this waste and give it an added value to be used in the elaboration of advanced materials. In this sense, the agave bagasse cellulose was obtained using an organosolv method. To obtain the nanofibrils, the cellulose was passed through 6 cycles of a microfluidizer. The material was classified by FTIR, confirming the presence of the functional groups (O-H, C-H, C-C, and C-O-C), characteristics of cellulose, and the elimination of hemicellulose and lignin present in agave bagasse without treatment. The X-ray diffraction technique allowed the determination of the degree of crystallinity of the cellulose nanofibers, which was 68.5%, with a negative zeta potential of −42 mV. The images from the atomic force microscopy helped for the observation of the degree of fibrillation in the cellulose, and with the software ImageJ, the average diameter of the nanofibers was determined to be 75 ± 5 nm with a relatively uniform length of 1.0–1.2 μm. Finally, by means of thermogravimetric analysis, it was found that the obtained cellulose nanofibers (CNFs) supported high temperatures of thermal decomposition, so it was concluded that due to the diameter of the fibrils, the high resistance to pressure, and elasticity, the nanofibrils obtained in this investigation can be used in the elaboration of advanced materials. [ABSTRACT FROM AUTHOR]

A new chemo-enzymatic treatment is proposed to produce cellulosic fibers suitable for heterogeneous- or homogeneous-phase acetylation. The procedure included enzymatic (laccase-violuric acid) lignin removal from the precursor fibers (unbleached sulfite pulp) followed by hydrogen peroxide treatment. An optional intermediate stage included partial hydrolysis (endoglucanase) to increase fiber reactivity. The obtained “biobleached” fibers were acetylated in the heterogeneous phase with acetic anhydride in nonpolar solvents, yielding various acetyl group contents, depending on the severity of the reaction. The degree of acetylation was highly sensitive to the treatment conditions, mainly the acetic anhydride activity in the system. The results were compared to those obtained after acetylation of commercial, dissolving-grade fibers, used as reference. The effect of the inherent nature of the fibers tested were elucidated as far as hemicellulose content, fiber length, fine content and crystallinity. Acetyl group content of up to 24% were determined after heterogeneous reaction with the chemoenzymatic fibers. The substitution of hydroxyl groups by acetyl moieties resulted in a lower hydrophilicity, as assessed by measurement of the water contact angle. Homogeneous acetylation of the chemo-enzymatic and reference fibers resulted in relatively similar acetyl group content (up to 36 and 33%, respectively). These samples were soluble in acetone and produced transparent films (via solvent casting), with enhanced dry strength and lower hydrophilicity. Overall, it is concluded that the proposed chemo-enzymatic treatment is a feasible alternative for the production of fibers that are suitable for efficient acetylation. [ABSTRACT FROM AUTHOR]

Among the most abundant biopolymers in the biosphere, lignin represents an untapped opportunity to create novel bioproducts. In this article, we discuss possibilities to synthesize nano- and microparticles by harnessing lignin’s inherent tendency to associate and to develop new material compositions and functions by controlling its capacity to assemble into supramolecular structures. Because lignin is biodegradable, antimicrobial, antioxidative, and carbon neutral, inexpensive industrial lignin streams could generate value-added particulate materials that preserve the structure, composition, and colloidal features inherent to this macromolecule. We present available routes for synthesis or isolation of lignin particles, including antisolvent and aerosol processing. Metallic and polymeric lignin particle hybrids for magnetic, antibacterial, catalytic, photonic, and other applications are also discussed. Overall, the facile formation of nano- and microparticles from lignins is expected to open new pathways toward future material development. [ABSTRACT FROM AUTHOR]

We take advantage of the amphiphilic properties of technical lignin macromolecules and their inherent high calorific values to formulate oil-in-water (O/W) fuel emulsions with high internal-phase ratios. For the oil phase, we used a combustible hydrocarbon (kerosene) with a measured equivalent alkane carbon number of 12. To adjust the balance of affinity with the oil and water phases and their surface activity, pine kraft lignins were carboxymethylated to different degrees, as quantified by 13C NMR spectroscopy, potentiometric titrations, and zeta potential measurements. Carboxymethylated lignins (CMLs) with a degree of substitution of 30 % displayed a critical aggregation concentration of 3 %. The salinity and pH of the aqueous phase were chosen as formulation variables and adjusted within the Winsor framework. The O/W emulsions were produced by following standard protocols. The drop-size distributions of emulsions with varying pH, degree of substitution, and composition (water-to-oil ratio, WOR) were determined, and the long-term stabilities and rheological behavior of these emulsions were analyzed. Most of the obtained O/W fuel emulsions showed shear-thinning behavior with a drop size of approximately 2.5 μm and were stable for over 30 days. The combustion of the lignins and their respective emulsions was performed, and their higher heating values (HHVs) were quantified. The HHVs of CML and a high-internal-phase (WOR=30:70) O/W emulsion were 20 and 30 MJ kg−1, respectively. Overall, we propose the stabilization of O/W fuel emulsions by lignin as an important avenue in the utilization of this abundant biomacromolecule. [ABSTRACT FROM AUTHOR]

We elucidate the effect of residual lignin on the interfacial, physical and mechanical properties of lignocellulose nanofibrils (LCNF) and respective nanopapers. Fibers containing ∼0, 2, 4, and 14 wt% residual lignin were microfluidized into LCNF aqueous suspensions and were processed into dry films (nanopapers). A systematic decrease in fibril diameter with increasing residual lignin was observed upon fibrillation, consistent with the radical scavenging ability of the lignin that results in better cell wall deconstruction. The stiff nature of the lignin-containing fibrils made them less able to conform during filtration and improved extensively dewatering, owing to a more open structure. However, the softening of the lignin during hot-pressing of the nanopapers and its amorphous nature enabled a binding effect, filling the voids between the nanofibers (thus reducing the number of micropores) and making the surface of the nanopapers smoother. The interfacial free energy of interaction changed drastically with the increased lignin content: the corresponding water contact angles were 35° and 78° for the lignin-free and for the (14%) lignin-containing nanopaper, respectively, revealing the increase in hydrophobicity. Together with the significantly less porous structure of LCNF nanopapers, lower water absorbency was observed with increased lignin content. Lignin in the nanopapers reduced the oxygen permeability by up to 200-fold. Water vapor permeability, in turn, did not correlate linearly with lignin content but depended most significantly on material density. The tensile strength, modulus, and strain for the LCNF nanopapers were found to be in the range 116–164 MPa, 10.5–14.3 GPa, and 1.7–3.5%, respectively. To a good degree of approximation, these mechanical properties were rather insensitive to lignin content and comparable to those of nanopapers derived from fully bleached CNF. Whilst it might be expected that lignin interferes in hydrogen bonding between fibrils, this was apparently counteracted by the uniform distribution of lignin seemingly aiding stress-transfer between fibrils and thus preserving mechanical properties. Overall, LCNF is demonstrated to be a suitable precursor of nanopaper, especially when reduced polarity and low hydrophilicity are desirable in related bio-products. [ABSTRACT FROM AUTHOR]

The interactions with water and the physical properties of microfibrillated celluloses (MFCs) and associated films generated from wood pulps of different yields (containing extractives, lignin, and hemicelluloses) have been investigated. MFCs were produced by combining mechanical refining and a high pressure treatment using a homogenizer. The produced MFCs were characterized by morphology analysis, water retention, hard-to-remove water content, and specific surface area. Regardless of chemical composition, processing to convert macrofibrils to microfibrils resulted in a decrease in water adsorption and water vapor transmission rate, both important properties for food packaging applications. After homogenization, MFCs with high lignin content had a higher water vapor transmission rate, even with a higher initial contact angle, hypothesized to be due to large hydrophobic pores in the film. A small amount of paraffin wax, less than 10%, reduced the WVTR to a similar value as low density polyethylene. Hard-to-remove water content correlated with specific surface area up to approximately 50 m2/g, but not with water retention value. The drying rate of the MFCs increased with the specific surface area. Hornified fibers from recycled paper also have the potential to be used as starting materials for MFC production as the physical and optical properties of the films were similar to the films from virgin fibers. In summary, the utilization of lignin containing MFCs resulted in unique properties and should reduce MFC production costs by reducing wood, chemical, and energy requirements. [ABSTRACT FROM AUTHOR]

Keywords: Lignin; biorefinery; crystalline cellulose; lignin valorization; nanoparticles EN Lignin biorefinery crystalline cellulose lignin valorization nanoparticles 992 992 1 02/20/21 20210218 NES 210218 B The Cover Feature b shows how lignins and cellolignins (cellulose-containing lignins) are paving the way to successful biorefineries. Lignin, biorefinery, crystalline cellulose, lignin valorization, nanoparticles. [Extracted from the article]

Correction for 'Spruce milled wood lignin: linear, branched or cross-linked?' by Mikhail Balakshin et al., Green Chem., 2020, 22, 3985–4001, DOI: 10.1039/D0GC00926A. [ABSTRACT FROM AUTHOR]

Lignocellulosic nanofibrils (LCNF) are produced from a single source of unbleached, oxidized wood fibers by serial disintegration, high‐pressure microfluidization, and homogenization. Sequential centrifugation enables fractionation by fibril width (≈5, ≈9, and ≈18 nm). LCNF residual lignin of high molecular mass reports together with the finest fraction (LCNF‐fine), whereas the more strongly cellulose‐bound lignin, of relatively lower molecular mass, associates with the coarsest fraction (LCNF‐coarse). Hot pressing softens the amorphous lignin, which fills the interstices between fibrils and acts as an in‐built interfacial cross‐linker. Thus, going from the LCNF‐fine to the LCNF‐course films, it is possible to obtain a range of values for the structural consolidation (density from 0.9 to 1.2 g cm−3 and porosity from 19% to 40%), surface roughness (RMS from ≈6 to 13 nm), and strength (elastic modulus from 8 to ≈12 GPa). The concentration of free hydroxyl groups controls effectively the direct surface interactions with liquids. The apparent surface energy dispersive component tracks with the total surface free energy and appears to be strongly influenced by the higher porosity as the fibril lateral size increases. The results demonstrate the possibility to tailor nanofibril cross‐linking and associated optical and thermo‐mechanical performance of LCNF films. [ABSTRACT FROM AUTHOR]

Carbon particles were produced from kraft lignin through carbonization of perfectly spherical, sub-micron beads obtained by aerosol flow. The structure of the resulting carbon particles was elucidated and compared to that derived from commercially available technical lignin powder, which is undefined in geometry. In addition to the smaller diameters of the lignin beads (<1 µm) compared to those of the lignin powder (100 µm), the former displayed a slightly higher structural order as revealed by X-ray diffraction and Raman spectroscopy. With regard to potential application in composite structures, the sub-micron carbon beads were clearly advantageous as a filler of cellulose nanopapers, which displayed better mechanical performance but with limited electrical conductivity. Compression sensing was achieved for this nanocomposite system. [ABSTRACT FROM AUTHOR]

There is an urgent need to develop materials to prevent bacterial infection and the deleterious effects of endotoxins. In this study, we introduce a one-step electrodeposition method to prepare films composed of chitosan/Ag/polypyrrole and layer-by-layer self-assembly to introduce lignin sulphonate (LS) to obtain chitosan/Ag/polypyrrole/LS films. Antibacterial effects against both E. coli and S. aureus are shown by bacterial growth profiles and observation of bacteriostatic zones. Meanwhile, the addition of self-assembled LS improved the antibacterial effect of the film. For E. coli , the inhibition zone diameter was 0.93 cm, while for S. aureus , the inhibition zone diameter was 0.72 cm. Rapid and efficient endotoxin adsorption effects were shown whereby the electrostatic interactions between chitosan and endotoxin molecules played a major role. After adsorption for 1 h, in initial concentration of 1 EU/mL endotoxin solution, the adsorption efficiency could reach up to 85 %, while in initial concentration of 5 EU/mL endotoxin solution, the adsorption efficiency could reach up to 87.6 %. The results suggest chitosan/Ag/polypyrrole/LS films for their capability as a new type of antibacterial film with intrinsic endotoxin adsorption activity. [ABSTRACT FROM AUTHOR]

We report for the first time on the use of water-continuous emulsions stabilized by a bio-based macromolecule in a compression-ignition diesel engine and compare their performance, combustion and emissions against the base fuels (diesel, biodiesel, and jet fuel). For this purpose, high internal phase ratio emulsions (70:30 fuel-to-water) were produced by mechanical emulsification using carboxymethylated wood lignin as stabilizer. Combusting experiments were performed with the engine operating at 2000 rpm under three loads (0, 1.26 and 3.26 bar brake mean effective pressure, BMEP). Engine performance, in-cylinder combustion, and exhaust emissions were monitored and compared for the fuels tested. At no load condition and when compared to the respective base (single phase) fuels, an increase in the indicated work was observed for diesel and biodiesel emulsions. Compared to the base fuels, the emulsions resulted in higher engine mechanical efficiency at 1.26 and 3.26 bar BMEP except for jet fuel emulsion at 1.26 bar. Additionally, they displayed a lower brake specific fuel consumption (BSFC), if calculated on the basis of effective fuel content discounting emulsion water, and higher brake thermal efficiency. Compared to the base fuel, the respective emulsions generally presented lower peak in-cylinder pressure, lower heat release rates, and longer ignition delays at 1.26 bar and 3.26 bar BMEP; the opposite effect was observed at no-load conditions. Remarkably, a large reduction of nitrogen oxides (NO x ) emissions was noted in the combustion of the fuel emulsions, which was accompanied with a relatively higher carbon monoxide (CO) release at 1.26 and 3.26 bar (at 0 bar BMEP, the emulsions produced less CO emissions). The effect of emulsions on hydrocarbon emissions and smoke opacity depended on the fuel type and the engine load. Overall, it is concluded that while reports on fuel emulsions involve oil-continuous systems, the proposed water-continuous alternative represents an opportunity for diesel engines, whereby the fuel is dispersed as micrometric droplets for improved combustion and reduced emissions. At the same time, the fuel emulsion formulation takes advantage of the surface activity and high calorific value of widely available, inexpensive lignin stabilizers, making the proposed system a viable option towards cleaner or fully bio-based fuels. [ABSTRACT FROM AUTHOR]

Producing hydrogels capable of mimicking the biomechanics of soft tissue remains a challenge. We explore the potential of plant-based hydrogels as polysaccharide tragacanth gum and antioxidant lignin nanoparticles in bioactive multicomponent hydrogels for tissue engineering. These natural components are combined with TEMPO-oxidized cellulose nanofibrils, a material with known shear thinning behavior. Hydrogels presented tragacanth gum (TG) concentration-dependent rheological properties suitable for extrusion 3D printing. TG enhanced the swelling capacity up to 645% and the degradation rate up to 1.3%/day for hydrogels containing 75% of TG. Young's moduli of the hydrogels varied from 5.0 to 11.6 kPa and were comparable to soft tissues like skin and muscle. In vitro cell viability assays revealed that the scaffolds were non-toxic and promoted proliferation of hepatocellular carcinoma HepG2 cells. Therefore, the plant-based hydrogels designed in this work have a significant potential for tissue engineering. [Display omitted] • 3D printed hydrogels made of cellulose nanofibrils, lignin nanoparticles, and tragacanth gum were developed and characterized • Tragacanth gum enhanced rheological properties, swelling ratio, and degradation rate • Hydrogels presented no toxicity and promoted proliferation of HepG2 cells • Potential application of plant-based materials in tissue engineering [ABSTRACT FROM AUTHOR]

Current research targets innovative medical textiles of nanofibrous nature and antibacterial activity to prevent diaper dermatitis. The work is based on electrospun nanofibers from cellulose acetate (CA) and lignin (Lig) polymers. A series of new copper complexes were synthesized and loaded to the CA/Lig solution mix then subjected to electrospinning, giving rise to the tricomponent bioactive mats CA/Lig/Cu-complex. The surface morphology of electrospun nanofiber mats was smooth and homogenous as the concentration of lignin increased in the mixture. The incorporation of lignin improved the electrospinnability of the cellulose acetate; however, it increased the fiber diameter. The water contact angle, absorption underload were significantly improved as lignin content increased. The incorporation of Cu-complex in electrospun CA and CA/Lig fiber mats occurred without any substantial change in the surface morphology, indicating well encapsulation of the complex. The electrospun mats were active against Pseudomonas aeruginosa , Acinetobacter baumannii , Staphylococcus epidermidis , and Streptococcus faecalis. The cytotoxicity, protein leakage, and biological results, together with the above studies, would advocate copper complex loaded CA/Lig nanofibers as a potential candidate for hygienic applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Glucuronoxylans (GX), particularly crude fractions obtained by pressurized hot water extraction of birch wood, act as potent emulsifiers and stabilizers against physical separation and lipid oxidation. Herein, we studied the adsorption of GX on hydrophobic interfaces to correlate their multicomponent character towards the formation of interfacial layers in emulsions. Dynamic interfacial tension (DIFT) and quartz crystal microgravimetry with dissipation monitoring (QCM-D) were applied to various GX fractions and the results compared with those from cellulose-based emulsifiers. The roles of residual lignin and polysaccharides are discussed considering the formation of interfacial layers during emulsification. The DIFT of the different GXs reached quasi-equilibrium faster as the lignin concentration increased, implying a correlation between the rate of adsorption and the residual lignin content. The effect of NaCl addition was more pronounced in polysaccharide-rich fractions, indicating that the polysaccharide fraction modulated the effect of ionic strength. QCM-D showed that despite the fast adsorption exhibited by the lignin-rich GX extract in the DIFT curves, the adsorbed materials were lightweight, suggesting that the polysaccharide fraction built the bulk of the interfacial layer. These results provide a foundation towards understanding the role of GX in interfacial stabilization beyond traditional plant-based counterparts. [Display omitted] [ABSTRACT FROM AUTHOR]

The white rot fungus Trametes elegans was used for direct treatment of spent black liquor from pulping processes with the aim to degrade solubilized lignin which is the primary organic by-product from the chemical digestion of lignocellulosic raw materials. The enzymatic activity of T. elegans and the resulting degradation was confirmed by UV/VIS spectrometric and size-exclusion chromatography (SEC) measurements on incubated and control samples of both industrial and synthetic black liquors.Opposing polymerization and depolymerization reactions occurred after treatment of the black liquor with T. elegans in liquid media. It is noteworthy that these effects, which originate from ligninolytic enzyme systems, occur after the direct treatment of the black liquor even if no nutrients are added. The effect of the suspension pH and incubation time on the lignolytic action of T. elegans is also presented. [Copyright &y& Elsevier]

We introduce Kraft lignin colloids produced by destabilization of a kraft lignin solution by pH shift from 2 to 11. The system includes lignin particles and hydrocolloid aggregates in equilibrium (KLP), which are used to control the emulsifying energy and to stabilize oil-in-water emulsions under high energy at pH 11 and 7, yielding excellent stability (at least three months with no creaming). We investigate emulsify technology (ultrasonication and homogenization), energy input (high energy or low energy), particle desorption, drop size, and rheology on the stability of KLP-based Pickering emulsions according to the system's pH. The ultrasonication leads to fine, stable and homogenous lignin emulsions without observing macroscopic creaming phenomenon, whereas homogenization only limits to alkaline condition. Regarding homogenization process, increasing the energy input helps to reduce the emulsion droplet size and consequently improves emulsion stability. In addition, the emulsion produced at acidic conditions always presented excellent stability, independent of the emulsify parameters. Considering the synergistic effects of emulsification protocol, surface activity, and particle interactions, the results indicate the possibility of extending the applications of kraft lignin as a Pickering stabilizer in neutral and alkaline conditions. It also creates a promising method to control the stability and emulsion microstructure in the industrial KLP based emulsion preparation process. [Display omitted] • Lignin stabilized emulsions were extended from acidic to pH 11. • A synergistic stabilization mechanism at high pH is proposed. • Emulsification process and energy input impact the formation and stability of emulsions. • Emulsions are stable for over three months. • E desorption increases for emulsions stabilized by lignin in the order of pH 11 < 7 < 2. [ABSTRACT FROM AUTHOR]

Acetylated Kraft lignins were evaluated for their ability of structuring vegetable oils into oleogels. Microwave-assisted acetylation was used to adjust lignin's degree of substitution according to reaction temperature (130 to 160 °C), and its effect in improving the viscoelasticity of the oleogels, which was related to the hydroxyl group content. The results were compared with those obtained by Kraft lignins acetylated using conventional methods at room temperature. A higher microwave temperature resulted in gel-like oil dispersions with improved viscoelastic properties, and stronger shear-thinning character, along with enhanced long-term stability. Lignin nanoparticles structured castor oil by enhancing hydrogen bonding between the hydroxyl groups of the oil and the nanoparticles. The oil structuring capacity of the modified lignins enhanced the stability of water-in-oil Pickering emulsions that resulted from low-energy mixing. • Acetylation and nanosize reduction are able to compatibilize lignin with castor oil. • Acetylation tune could be obtained through microwave temperature modification. • Acetylation provided enhanced rheological characteristics of oleogels. • Both systems stabilize water-in-oil emulsions with up to 30 wt% water content. [ABSTRACT FROM AUTHOR]

Polydisperse smooth and spherical biocolloidal particles were suspended in aqueous media and allowed to consolidate via evaporation-induced self-assembly. The stratification of the particles at the solid-air interface was markedly influenced, but not monotonically, by the drying rate. Cross-sectional imaging via electron microscopy indicated a structured coating morphology that was distinctive from that obtained by using particles with a mono- or bimodal distribution. Segregation patterns were found to derive from the interplay of particle diffusion, interparticle forces, and settling dynamics. Supporting our experimental findings, computer simulations showed an optimal drying rate for achieving maximum segregation. Overall, stratified coatings comprising nano- and microparticles derived from lignin are expected to open opportunities for multifunctional structures that can be designed and predicted on the basis of experimental Péclet numbers and computational order. [ABSTRACT FROM AUTHOR]

Kraft and organosolv lignins were subjected to carboxymethylation to produce fractions that were soluble in water, displayed a minimum surface tension as low as 34 mN/m (25 °C) and a critical aggregation concentration of ∼1.5 wt%. The carboxymethylated lignins (CML), which were characterized in terms of their degree of substitution ( 31 P NMR), elemental composition, and molecular weight (GPC), were found suitable in the formulation of emulsions with bitumens of ultra-high viscosity, such as those from the Canadian oil sands. Remarkably, the interfacial features of the CML enabled fuel emulsions that were synthesized in a very broad range of internal phase content (30–70%). Cryo-replica transmission electron microscopy, which was used here the first time to assess the morphology of the lignin-based emulsions, revealed the droplets of the emulsion stabilized with the modified lignin. The observed drop size (diameters < 2 μm) was confirmed by light scattering, which revealed a normal size distribution. Such characteristics led to stable emulsified systems that are amenable for a wide range of applications. Emulsification with CML afforded bitumen emulsions with very high colloidal stability (no change was noted for over one month) and with a strong shear thinning behavior. Both features indicate excellent prospects for storage, transport and spraying, which are relevant in operations for power generation, which also take advantage of the high heating value of the emulsion components. The ability of CML to stabilize emulsions and to contribute in their combustion was tested with light fuels (kerosene, diesel, and jet fuel) after formulation of high internal phase systems (70% oil) that enabled operation of a fuel engine. A significant finding is that under certain conditions and compared to the respective pure fuel, combustion of the O/W emulsions stabilized by CML presented lower NO x and CO emissions and maintained a relatively high combustion efficiency. The results highlight the possibilities in high volume application for lignin biomacromolecules. [ABSTRACT FROM AUTHOR]

Understanding enzyme-substrate interactions is critical in designing strategies for bioconversion of lignocellulosic biomass. In this study we monitored molecular events, in situ and in real time, including the adsorption and desorption of cellulolytic enzymes on lignins and cellulose, by using quartz crystal microgravimetry and surface plasmon resonance. The effect of a nonionic surface active molecule was also elucidated. Three lignin substrates relevant to the sugar platform in biorefinery efforts were considered, namely, hardwood autohydrolysis cellulolytic (HWAH), hardwood native cellulolytic (MPCEL), and nonwood native cellulolytic (WSCEL) lignin. In addition, Kraft lignins derived from softwoods (SWK) and hardwoods (HWK) were used as references. The results indicated a high affinity between the lignins with both, monocomponent and multicomponent enzymes. More importantly, the addition of nonionic surfactants at concentrations above their critical micelle concentration reduced remarkably (by over 90%) the nonproductive interactions between the cellulolytic enzymes and the lignins. This effect was hypothesized to be a consequence of the balance of hydrophobic and hydrogen bonding interactions. Moreover, the reduction of surface roughness and increased wettability of lignin surfaces upon surfactant treatment contributed to a lower affinity with the enzymes. Conformational changes of cellulases were observed upon their adsorption on lignin carrying preadsorbed surfactant. Weak electrostatic interactions were determined in aqueous media at pH between 4.8 and 5.5 for the native cellulolytic lignins (MPCEL and WSCEL), whereby a ~20% reduction in the enzyme affinity was observed. This was mainly explained by electrostatic interactions (osmotic pressure effects) between charged lignins and cellulases. Noteworthy, adsorption of nonionic surfactants onto cellulose, in the form cellulose nanofibrils, did not affect its hydrolytic conversion. Overall, our results highlight the benefit of nonionic surfactant pretreatment to reduce nonproductive enzyme binding while maintaining the reactivity of the cellulosic substrate. [ABSTRACT FROM AUTHOR]

Nanofibers were produced by electrospinning aqueous alkaline solutions containing different mass ratios of soy protein and lignin in the presence of poly(ethylene glycol) coadjutant, all of which presented shear thinning behavior. SEM revealed that the addition of polyethylene oxide as a coadjutant indeed facilitated the formation of defect-free fibers whose diameter increased with lignin concentration, in the range between ≈ 124 and ≈ 400 nm. Favorable interactions between lignin and soy protein were identified from data provided by differential scanning calorimetry. In addition, an increased hydrogen bonding and the loss of secondary structure of the proteins as the lignin concentration increased were observed from the disappearance of amide II (∼1500 cm −1 ) and III (∼1400–1200 cm −1 ) bands and a red shift of amide I band in the FT-IR spectrum. The unfolding of the protein contributed to a better interaction with lignin macromolecules, which further improved the electrospinning process. It is concluded that mixtures of lignin and soy proteins, two major renewable resources with interesting chemical features, are suitable for the development of composite sub-micron fibers. [ABSTRACT FROM AUTHOR]

Highlights: [•] Nanofibrils (LCNF) were produced from softwood after SEW fractionation. [•] The effect of lignin and hemicelluloses on LCNF bioconversion was elucidated. [•] Enzyme binding and activity on LCNF was monitored in situ by QCM-D. [•] Hydrolysis of SEW LCNF produce sugar yields higher than those of fibers. [•] SEW-based biorefinery may integrate nanomaterial and biofuel production. [Copyright &y& Elsevier]

Understanding the enzymatic hydrolysisof cellulose and the influenceof lignin in the process are critical for viable production of fuelsand chemicals from lignocellulosic biomass. The interactions of monocomponentcellulases with cellulose and lignin substrates were investigatedby using thin films supported on quartz crystal microgravimetry (QCM)resonators. Trichoderma reeseiexoglucanase(CBH-I) and endoglucanase (EG-I) bound strongly to both celluloseand lignin but EG-I exhibited a distinctive higher affinity with lignin,causing a more extensive inhibition of the cellulolytic reactions.CBH-I was found to penetrate into the bulk of the cellulose substrateincreasing the extent of hydrolysis and film deconstruction. In theabsence of a cellulose binding domain (CBD) and a linker, the CBH-Icore adsorbed slowly and was not able to penetrate into the film.Conversely to CBH-I, EG-I exhibited activity only on the surface ofthe lignocellulose substrate even when containing a CBD and a linker.Interestingly, EG-I displayed a clearly different interaction profileas a function of contact time registered by QCM. [ABSTRACT FROM AUTHOR]

Abstract: The effect of lignin as an inhibitory biopolymer for the enzymatic hydrolysis of lignocellulosic biomass was studied; specially addressing the role of lignin in non-productive enzyme adsorption. Botanical origin and biomass pre-treatment give rise to differences in lignin structure and the effect of these differences on enzyme binding and inhibition were elucidated. Lignin was isolated from steam explosion (SE) pre-treated and non-treated spruce and wheat straw and used for the preparation of ultrathin films for enzyme binding studies. Binding of Trichoderma reesei Cel7A (CBHI) and the corresponding Cel7A-core, lacking the linker and the cellulose-binding domain, to the lignin films was monitored using a quartz crystal microbalance (QCM). SE pre-treatment altered the lignin structure, leading to increased enzyme adsorption. Thus, the positive effect of SE pre-treatment, opening the cell wall matrix to make polysaccharides more accessible, may be compromised by the structural changes of lignin that increase non-productive enzyme adsorption. [Copyright &y& Elsevier]

Abstract: In this study, the effect of torrefaction on the chemical and structural transformation of lignocellulosic biomass was investigated using complementary analytical tools. It was observed that the acid-insoluble fraction was increased from approximately 30 to 38% and the methoxyl content was decreased to about half after torrefaction at 330°C for 2.5min. These results highlight the formation of condensed structures along with lignin transformation via demethoxylation. Solid-state NMR spectroscopy indicated that upon torrefaction the aromaticity increased from about 36 to 60%. For the sample torrefied at 330°C, the non-protonated aromatic carbon fraction was found to be about 60% of total aromatic carbons, indicating the formation of large aromatic clusters. The complementary analyses used in this study are proposed as a suitable approach for the elucidation of chemical and structural transformation of biomass during thermal treatment. [Copyright &y& Elsevier]

Ultrathin bicomponent films of cellulose and lignin derivativeswere deposited on silica supports by spin coating, and after conversioninto the respective polymer precursor, they were used as a model systemto investigate interfacial phenomena relevant to lignocellulose biocatalysis.Film morphology, surface chemical composition, and wettability weredetermined by atomic force microscopy, X-ray photoelectron spectroscopy,and water contact angle, respectively. Phase separation of celluloseand lignin produced structures that resembled the cell wall of fibersand were used to monitor enzyme binding and cellulolytic reactionsvia quartz crystal microgravimetry. The rate and extent of hydrolysiswas quantified by using kinetic models that indicated the role ofthe surface lignin domains in enzyme inhibition. Hydrophobic interactionsbetween cellulases and the substrates and their critical role on irreversibleadsorption were elucidated by using acetylated lignin films with differentdegrees of substitution. Overall, it is concluded that sensors basedon the proposed ultrathin films of lignocellulose can facilitate abetter understanding of the complex events that occur during bioconversionof cellulosic biomass. [ABSTRACT FROM AUTHOR]

Wood-derived cellulosic fibers prepared in different ways were successfully employed to absorb simulated crude oil, demonstrating their possible use as absorbents in the case of oil spills. When dry fibers were used, the highest sorption capacity (six parts of oil per unit mass of fiber) was shown by bleached softwood kraft fibers, compared to hardwood bleached kraft and softwood chemithermomechanical pulp(CTMP) fibers. Increased refining of CTMP fibers decreased their oil uptake capacity. When the fibers were soaked in water before exposure to the oil, the ability of the unmodified kraft fibers to sorb oil was markedly reduced, whereas the wet CTMP fibers were generally more effective than the wet kraft fibers. Predeposition of lignin onto the surfaces of the bleached kraft fibers improved their ability to take up oil when wet. Superior ability to sorb oil in the wet state was achieved by pretreating the kraft fibers with a hydrophobic sizing agent, alkenylsuccinic anhydride (ASA). Contact angle tests on a model cellulose surface showed that some of the sorption results onto wetted fibers could be attributed to the more hydrophobic nature of the fibers after treatment with either lignin or ASA. [ABSTRACT FROM AUTHOR]

Lignin-based fibers were produced by electrospinningaqueous dispersionsof lignin, poly(vinyl alcohol) (PVA), and cellulose nanocrystals (CNCs).Defect-free nanofibers with up to 90 wt % lignin and 15% CNCs wereachieved. The properties of the aqueous dispersions, including viscosity,electrical conductivity, and surface tension, were examined and correlatedto the electrospinnability and resulting morphology of the compositefibers. A ternary lignin–PVA–water phase diagram wasconstructed as a tool to rationalize the effect of mixing ratios onthe dispersion electrospinability and morphology of the resultingfibers. The influence of reinforcing CNCs on the thermal propertiesof the multicomponent fibers was investigated by using thermal gravimetricanalysis and differential scanning calorimetry. The thermal stabilityof the system was observed to increase owing to a strong interactionof the lignin–PVA matrix with the dispersed CNCs, mainly viahydrogen bonding, as observed in Fourier transform infrared spectroscopyexperiments. [ABSTRACT FROM AUTHOR]

Abstract: Films of microfibrillated celluloses (MFCs) from pulps of different yields, containing varying amounts of extractives, lignin, and hemicelluloses, were produced by combining refining and high-pressure homogenization techniques. MFC films were produced using a casting-evaporation technique and the physical and mechanical properties (including density, roughness, fold endurance and tensile properties) were determined. Homogenization of bleached and unbleached Kraft pulps gave rise to highly individualized MFCs, but not for thermo-mechanical pulp (TMP). The resulting MFC films had a roughness equivalent to the surface upon which the films were cast. Interestingly, after homogenization, the presence of lignin significantly increased film toughness, tensile index, and elastic modulus. The hornification of fibers through a drying and rewetting cycle prior to refining and homogenization did not produce any significant effect compared to films from never-dried fibers, indicating that MFC films can potentially be made from low-cost recycled cellulosic materials. [Copyright &y& Elsevier]

Lignin is demonstrated as an unprecedented reinforcing material that tailors the rheological and cushioning properties of castor oil-based polyurethane elastomers, expanding their viscoelastic moduli by four orders of magnitude. The tensile strain at break was triplicated in the presence of lignin while the Young modulus and the stress at break were enhanced 17- and 7-fold, respectively. Remarkably, in compression tests, lignin addition increased the stresses at break by more than 88-fold, whereas the strain at failure shifted from 50 to 93%. Dynamic mechanical compression tests indicated outstanding cushioning and resistance performance. Overall, the results demonstrate a performance not reached before for biosourced elastomeric materials, fitting the demands of a wide range of applications. Image 1 • Production of bio-based elastomers by combining lignin, castor oil and HDI. • Use of lignin to tailor the mechanical properties of castor oil-based polyurethanes. • Differences of four orders of magnitude in viscoelastic moduli by modifying lignin and HDI content. • Lignin significantly enhances both tensile and compressive performance of elastomers. • Outstanding resistance and cushioning properties measured by dynamic mechanical tests. [ABSTRACT FROM AUTHOR]

• Lignocellulosic nanofibrils (LCNF) are prepared from wood using recyclable p -TsOH. • The residual lignin content in LCNF can be easily tailored by the hydrolysis temperature. • LCNF behavior at the oil-water interface depends on residual lignin concentration. • A higher residual lignin in LCNF results in Pickering emulsions with superior properties. Lignocellulose nanofibrils (LCNF) were used to prepare oil-in-water Pickering emulsions and to assess the role residual lignin in interfacial stabilization. Two LCNF fractions of similar morphology (length ∼700 nm and width ∼8 nm) and structure (polymorphism and crystallinity) were obtained by microfluidization of fibers obtained by hydrothermal treatment of wood with a recyclable organic acid. The LCNF with higher residual lignin was less hydrophilic and, correspondingly, performed better as Pickering stabilizer, producing emulsions of smaller droplet size and higher resistance to creaming. Long-term emulsion stabilization (over 40 days) was achieved with LCNF at concentrations as low as 0.24 (w/v)% based on emulsion volume. We conclude that LCNF-stabilized Pickering emulsions can be finely tuned by varying the residual lignin content, providing a rationale for LCNF selection according to lignin type and concentration as variables affecting stabilization. Complementary considerations include the possible benefits of the residual lignin in LCNF, including antioxidant and UV absorption properties. [ABSTRACT FROM AUTHOR]

We produce balsa-based structures by selective removal of lignin. The changes that occur in the main components of balsa upon delignification, including tracheids, closed pits and tylosis vessels, allow the development of mesopores and a substantial increase in fluid permeability. Such system is ideally suited as a support of phase change materials, PCM. Vacuum-assisted impregnation with polyethylene glycol (PEG, a PCM), results in a form-stable PCM system (FPCM). The FPCM displays a high encapsulating capacity (83.5%) at temperatures above the melting PEG transition, with a latent heat of 134 J/g and low supercooling (12 °C). The results are rationalized by the affinity between the unidirectional mesoporous structure and the PCM polymer, involving capillary forces and hydrogen bonding. The leakage-proof FPCM outperforms available systems (based on PEG or other PCMs) supported on minerals or other wood species. Compared to the latter group, the results obtained with balsa relate to its morphology and the effect of residual hemicelluloses in hierarchically-aligned cellulose nano- and microfibrils. The FPCMs resist compressive loads and performs stably for at least 200 cycles of heating and cooling. An insignificant loss in latent heat is observed compared to that of pure PEG. The phase transition temperature fluctuation and non-leaking characteristics under load make the balsa-based FPCM a superior alternative for passive heating/cooling, especially for uses at high ambient temperatures. The reversible thermoregulatory capacity, low cost, high efficiency, renewability, and operability of the balsa-supported FPCM, indicate an excellent option for thermal energy storage and conversion devices. • A form-stable phase change material (FPCM) is prepared from balsa. • Retention of hemicellulose is critical for FPCM performance. • High PCM loading, compressive strength and stability are obtained. • The observed performance of the FPCM is partially explained by PEG affinity with the support. • Reversible thermoregulation is observed for operation at high room temperatures. [ABSTRACT FROM AUTHOR]

Lignins were isolated from spruce, wheat straw, and eucalyptus by using the milled wood lignin (MWL) method. Functional groups and compositional analyses were assessed via 2D NMR and 31P NMR to realize their effect on enzyme binding. Films of the lignins were fabricated and ellipsometry, atomic force microscopy, and water contact angle measurements were used for their characterization and to reveal the changes upon enzyme adsorption. Moreover, lignin thin films were deposited on quartz crystal microgravimetry (QCM) and surface plasmon (SPR) resonance sensors and used to gain further insights into the lignin-cellulase interactions. For this purpose, a commercial multicomponent enzyme system and a monocomponent Trichoderma reesei exoglucanase (CBH-I) were considered. Strong enzyme adsorption was observed on the various lignins but compared to the multicomponent cellulases, CBH-I displayed lower surface affinity and higher binding reversibility. This resolved prevalent questions related to the affinity of this enzyme with lignin. Remarkably, a strong correlation between enzyme binding and the syringyl/guaiacyl (S/G) ratio was found for the lignins, which presented a similar hydroxyl group content (31P NMR): higher protein affinity was determined on isolated spruce lignin (99% G units), while the lowest adsorption occurred on isolated eucalyptus lignin (70% S units). The effect of electrostatic interactions in enzyme adsorption was investigated by SPR, which clearly indicated that the screening of charges allowed more extensive protein adsorption. Overall, this work furthers our understanding of lignin-cellulase interactions relevant to biomass that has been subjected to no or little pretreatment and highlights the widely contrasting effects of the nature of lignin, which gives guidance to improve lignocellulosic saccharification and related processes. [ABSTRACT FROM AUTHOR]