Technical Lignins Research Articles

Ambient-pressure lignin valorization to high-performance polymers by intensified reductive catalytic deconstruction.

Chemocatalytic lignin valorization strategies are critical for a sustainable bioeconomy, as lignin, especially technical lignin, is one of the most available and underutilized aromatic feedstocks. Here, we provide the first report of an intensified reactive distillation–reductive catalytic deconstruction (RD-RCD) process to concurrently deconstruct technical lignins from diverse sources and purify the aromatic products at ambient pressure. We demonstrate the utility of RD-RCD bio-oils in high-performance additive manufacturing via stereolithography 3D printing and highlight its economic advantages over a conventional reductive catalytic fractionation/RCD process. As an example, our RD-RCD reduces the cost of producing a biobased pressure-sensitive adhesive from softwood Kraft lignin by up to 60% in comparison to the high-pressure RCD approach. Last, a facile screening method was developed to predict deconstruction yields using easy-to-obtain thermal decomposition data. This work presents an integrated lignin valorization approach for upgrading existing lignin streams toward the realization of economically viable biorefineries.

Cationic modified lignin: Regulation of synthetic microspheres for achieving anti-photolysis and sustained release of the abscisic acid

Lignin is an abundant, renewable natural resource that shows UV resistance and whose amphiphilicity can be modified, which means that it could potentially encapsulate photo-sensitive agrichemicals. However, current technical lignins, e.g., alkaline lignin (AL), tend to form large aggregates, which severely limits its encapsulation performance. In this study, three cationic surfactants were selected for hydrophobic modification of AL, and to produce AL microspheres (AL-MPs) encapsulating abscisic acid (ABA). The surfactants tested were dodecyl tetramethyl ammonium bromide DTAB (single C12 chain), dimethyl behenyl ammonium bromide DDAB (two C12 chains) and cetylpyridinium chloride CPC (single C16 chain). The particle sizes, zeta-potentials, and encapsulation efficiencies of the AL-MPs were modified by changing the type of the surfactant and the weight percentage (wt%) of AL. The range of particle sizes, zeta potentials and encapsulation efficiencies were 232–1226 nm, –56.1–18.7 mV, and 62–78%, respectively. Fourier transform infrared spectroscopy (FTIR) was used to characterize the MPs. The photolysis protection and release of ABA from ABA-loaded MPs (e.g., ABA@AL-DDAB) were studied and a release kinetics model was built to probe the release behaviour. The effects of ABA@AL-MPs on the salt tolerance of rice seedlings under salinity stress were studied, and the mechanism is discussed. ABA@AL-MPs effectively protected the seedlings from growth inhibition by salinity stress. ABA@AL-DDAB was the most effective formulation, outperforming ABA@AL-CTAB and even the no-salt control. DDAB is less cytotoxic than CTAB and has the potential, when combine with lignin to encapsulate ABA and other agrichemicals to produce formulations with photolysis resistance and sustained-release properties.

The Application of Enzymatic Pretreatment with Subsequent Pyrolysis to Improve the Production of Phenols from Selected Industrial (Technical) Lignins

The Application of Enzymatic Pretreatment with Subsequent Pyrolysis to Improve the Production of Phenols from Selected Industrial (Technical) Lignins

Structural Analysis of Lignin-Based Furan Resin.

The global “carbon emission peak” and “carbon neutrality” strategic goals promote us to replace current petroleum-based resin products with biomass-based resins. The use of technical lignins and hemicellulose-derived furfuryl alcohol in the production of biomass-based resins are among the most promising ways. Deep understanding of the resulting resin structure is a prerequisite for the optimization of biomass-based resins. Herein, a semiquantitative 2D HSQC NMR technique supplemented by the quantitative 31P NMR and methoxyl group wet chemistry analysis were employed for the structural elucidation of softwood kraft lignin-based furfuryl alcohol resin (LFA). The LFA was fractionated into water-insoluble (LFA-I) and soluble (LFA-S) parts. The analysis of methoxyl groups showed that the amount of lignin was 85 wt% and 44 wt% in LFA-I and LFA-S fractions, respectively. The HSQC spectra revealed the high diversity of linkages formed between lignin and poly FA (pFA). The HSQC and 31P results indicated the formation of new condensed structures, particularly at the 5-position of the aromatic ring. Esterification reactions between carboxyl groups of lignin and hydroxyl groups of pFA could also occur. Furthermore, it was suggested that lignin phenolic hydroxyl oxygen could attack an opened furan ring to form several aryl ethers structures. Therefore, the LFA resin was produced through crosslinking between lignin fragments and pFA chains.

Conversion of Organosolv and Kraft lignins into value-added compounds assisted by an acidic deep eutectic solvent

The valorisation of technical lignins by conversion is herein demonstrated using an acidic deep eutectic solvent in the absence or presence of a co-catalyst (H2SO4 or H2O2).

Revisiting the Molar Mass and Conformation of Derivatized Fractionated Softwood Kraft Lignin.

The limited utilization of reliable tools and standards for determination of the softwood kraft lignin molar mass and the corresponding molecular conformation hampers elucidation of the structure-property relationships of lignin. At issue, conventional size exclusion chromatography (SEC) is unable to robustly measure the molar mass because of a lack of calibration standards with a similar structure to lignin. In the present work, the determination of the absolute molar mass of acetylated technical lignin was revisited utilizing SEC combined with multi-angle light scattering with a band pass filter to suppress the fluorescence. Fractionated lignin isolated using sequential techniques of solvent and membrane methods was used to enhance the clarity of light-scattering profiles by narrowing the molar mass distribution of lignin fractions. Further information on the molecular conformation of derivatized samples was studied utilizing a differential viscometer, and chemical structures were identified by NMR spectroscopy analysis. Through the help of fractionation, intrinsic viscosity values were determined for the different fractions as a function of molecular weight cut-off membranes. The derivatized acetone-soluble lignin was found to possess a lower molecular weight and an extremely compact structure relative to the derivatized acetone-insoluble fraction based on a significantly lower "α" value in the Mark-Houwink-Sakurada plot (0.15 acetone-soluble vs 0.33 acetone-insoluble). The differences in geometry were supported by the linkage analysis from NMR showing the acetone-soluble part containing fewer native linkages. In both of these examples, kraft lignin behaved like a solid sphere, limiting the ability to provide entanglements between molecular chains. From this standpoint, macroscopic properties of lignin are justified with this knowledge of a dense and extremely compact structure.

Accurate prediction of chemical exergy of technical lignins for exergy-based assessment on sustainable utilization processes

The exergy-based assessment on the sustainable utilization processes of technical lignin is important for potential identify and process optimization. In this study, chemical exergy of technical lignin was evaluated for the first time based on the Gibbs free energy relation. The chemical exergy of technical lignin was from 17653.89 to 33337.92 kJ kg−1.The effects of O/C and H/C ratios on the chemical exergy and standard entropy were investigated by using contour plot analysis. The chemical exergy of technical lignin is more significantly influenced by the O/C ratio, compared with the H/C ratio. Three types of prediction models including artificial neural network model with the input of elemental composition, HHV-based correlation, and element-based correlation were developed. The artificial neural network model has an excellent performance of predicting the chemical exergy of technical lignin, with the prediction relative error of less than ±0.15% under the confidential level of 97%. The prediction relative errors of the HHV-based correlation and the element-based correlation are within ±1.0% and ±2.5%, respectively. This work will provide the basic data for exergy-based assessment on the valorization processes of technical lignin, which is an important aspect of improving the economic level of biorefinery industry.

Structural basis for lignin recalcitrance during sulfite pulping for production of dissolving pulp from pine heartwood

Dissolving pulps are technically produced by prehydrolysis kraft, one-stage or two-stage acid sulfite pulping. Like other pulping methods, the delignification process is incomplete and bleaching is required for complete lignin removal. Here, we explored the molecular aspects of lignin recalcitrance during the pulping, in order to gain insights that could inform future pulping efforts. For this purpose, we adopted a protocol for the controlled fractionation of pulp into soluble fractions that could be analyzed by spectroscopic methods including size exclusion chromatography (SEC) and 2D NMR methods. In addition, lignosulfonates (i.e. technical lignin) was analysed as a reference to gain insights on the structural basis for dissolution. Overall, the results identify a sequence of reactions responsible for the dissolution of lignin. In the first stage, the sulfonation of lignin begins and occurs at the α-carbon of β-O-4 and β-5 sub-structures. In the second stage the cleavage of lignin carbohydrate bonds (LCC) of benzyl ether, gamma ester and phenylglycosides types, all of which were detected in the residual lignin of the earlier phases, occurs and enhances lignin dissolution. Finally, condensation reactions of benzylic cations with activated positions on aromatic ring were detected in lignosulfonates. This suggest that a competing reaction mode to the sulfonation at C-α position in lignin was occurring at prolonged pulping conditions, here considered to be unproductive.

Agricultural utilization of lignosulfonates

Abstract Lignosulfonates (LSs) are by-products of the pulp and paper industry from pulping of lignocellulosic biomass according to the sulfite process. This renewable material already plays a role in low-value applications, such as binding agents for fuel, pellets, as a feed additive, or as a dispersant. Another possible field of application of this technical lignin type is agriculture. It is known that this eco-friendly and cheap material can improve soil quality, fertilizer efficacy and replace or decrease the use of potentially (eco)toxic organic or inorganic substances. The use of LS in agriculture and five main strategies for the implementation of LS in soil are discussed in this review: LS as a complexing agent with micronutrients, co-pelleting of LS with (macro)nutrients, capsule formation with LS for coating of fertilizers or pesticides, LS as a biostimulant, and ammonoxidation of LS. All five ways can be beneficial in fertilizer-related applications, either to slow down the release of nutrients or pesticides, to substitute harmful chemicals, or to inhibit nitrification and modify fertilizer behaviour. Nevertheless, application and long-time studies are often missing, and more research is required for generating products that are economically competitive to commercial bulk products.

Characterization of alkali-lignin-grafted polyacrylamide synthesized by atom transfer radical polymerization

The preparation of value-added, chemically modified lignin-based copolymers for the use of technical lignin is crucial for green and sustainable development. Herein, we synthesized alkali-lignin-grafted polyacrylamide by atom transfer radical polymerization (ATRP). As alkali lignin (AL) has the highest total hydroxyl group content, it was modified with 2-bromoisobutyryl bromide to synthesize a lignin macroinitiator (lignin-Br) at different ratios of [OH group in AL]:[TEA]:[BiBB] = 1:1:1, 1:1.5:1.5, and 1:2:2. Acrylamide was grafted from lignin-Br with the most Br-initiating sites via ATRP. The ratios of monomer to lignin-Br used were 50:1, 100:1, and 200:1, and the synthesized copolymers (L-g-PAM) were denoted as L-g-PAM50, L-g-PAM100, and L-g-PAM200, respectively. These copolymers were characterized by Fourier transform infrared (FT-IR) and 1H nuclear magnetic resonance (NMR) spectroscopies. The FT-IR and 1H NMR results indicated that polyacrylamide was introduced into the lignin backbone of all L-g-PAM copolymers. Gel permeation chromatography of L-g-PAM showed that the M w of L-g-PAM200 was the highest at 427,383 g/mol. Photographs and scanning electron microscopy images of L-g-PAM showed that L-g-PAM appeared as a soft sponge and contained interwoven fibers. The maximum degradation temperature (T max) of L-g-PAM increased with increasing monomer-to-lignin-Br ratio. Moreover, the glass transition temperature (T g) of L-g-PAM was higher than that of AL. The alkali-lignin-grafted polyacrylamide, synthesized by ATRP, in our study has a narrow molecular weight distribution, and its soft sponge properties make it a hydrogel or another surfactant.

Guiding stars to the field of dreams: Metabolically engineered pathways and microbial platforms for a sustainable lignin-based industry

Lignin is an important structural component of terrestrial plants and is readily generated during biomass fractionation in lignocellulose processing facilities. Due to lacking alternatives the majority of technical lignins is industrially simply burned into heat and energy. However, considering its vast abundance and a chemically interesting richness in aromatics, lignin is presently regarded both as the most under-utilized and promising feedstock for value-added applications. Notably, microbes have evolved powerful enzymes and pathways that break down lignin and metabolize its various aromatic components. This natural pathway atlas meanwhile serves as a guiding star for metabolic engineers to breed designed cell factories and efficiently upgrade this global waste stream. The metabolism of aromatic compounds, in combination with success stories from systems metabolic engineering, as reviewed here, promises a sustainable product portfolio from lignin, comprising bulk and specialty chemicals, biomaterials, and fuels.

Monitoring Molecular Weight Changes during Technical Lignin Depolymerization by Operando Attenuated Total Reflectance Infrared Spectroscopy and Chemometrics.

Technical lignins are increasingly available at industrial scale, offering opportunities for valorization, such as by (partial) depolymerization. Any downstream lignin application requires careful tailoring of structural properties, such as molecular weight or functional group density, properties that are difficult to control or predict given the structure variability and recalcitrance of technical lignins. Online insight into changes in molecular weight (M w), to gauge the extent of lignin depolymerization and repolymerization, would be highly desired to improve such control, but cannot be readily provided by the standard ex‐situ techniques, such as size exclusion chromatography (SEC). Herein, operando attenuated total reflectance infrared (ATR‐IR) spectroscopy combined with chemometrics provided temporal changes in M w during lignin depolymerization with high resolution. More specifically, ex‐situ SEC‐derived M w and polydispersity data of kraft lignin subjected to aqueous phase reforming conditions could be well correlated with ATR‐IR spectra of the reaction mixture as a function of time. The developed method showed excellent regression results and relative error, comparable to the standard SEC method. The method developed has the potential to be translated to other lignin depolymerization processes.

Cosolvent enhanced lignocellulosic fractionation tailoring lignin chemistry and enhancing lignin bioconversion

Cosolvent Enhanced Lignocellulosic Fractionation (CELF) is an emerging solvolysis pretreatment to fractionate lignocellulosic biomass. Herein, the bioconversion performance of CELF lignin was fully evaluated for the first time. Results showed that CELF lignin possessed higher content of carboxylic acid OH, lower molecular weight, and disappeared β-O-4 and β-5 linkages compared to other two technical lignins including a conventional ethanol organosolv lignin (EOL) and a kraft lignin (KL). Rhodococcus opacus PD630 cell count from CELF lignin fermentation reached the highest value of 3.9 × 107 CFU/mL, representing a 62.5% and 77.3% improvement over EOL and KL, respectively. Correspondingly, lipid yield reached 143 mg/L from CELF lignin, which was 36.2% and 26.5% higher than from EOL and KL, respectively. Principal component analysis (PCA) revealed that more carboxylic acid groups and lower molecular weight contributed to the enhanced bioconversion performance of CELF lignin. This study demonstrates that CELF lignin is a promising candidate for bioconversion.

Lignin Syngas Bioconversion by Butyribacterium methylotrophicum: Advancing towards an Integrated Biorefinery

Hybrid bio-thermochemical based technologies have the potential to ensure greater feedstock flexibility for the production of bioenergy and bioproducts. This study focused on the bioconversion of syngas produced from low grade technical lignin to C2-/C4-carboxylic acids by Butyribacterium methylotrophicum. The effects of pH, medium supplementation and the use of crude syngas were analyzed. At pH 6.0, B. methylotrophicum consumed CO, CO2 and H2 simultaneously up to 87 mol% of carbon fixation, and the supplementation of the medium with acetate increased the production of butyrate by 6.3 times. In long-term bioreactor experiments, B. methylotrophicum produced 38.3 and 51.1 mM acetic acid and 0.7 and 2.0 mM butyric acid from synthetic and lignin syngas, respectively. Carbon fixation reached 83 and 88 mol%, respectively. The lignin syngas conversion rate decreased from 13.3 to 0.9 NmL/h throughout the assay. The appearance of a grayish pellet and cell aggregates after approximately 220 h was indicative of tar deposition. Nevertheless, the stressed cells remained metabolically active and maintained acetate and butyrate production from lignin syngas. The challenge that impurities represent in the bioconversion of crude syngas has a direct impact on syngas cleaning requirements and operation costs, supporting the pursuit for more robust and versatile acetogens.

Revealing the structure-activity relationship between lignin and anti-UV radiation

As a highly abundant natural and renewable aromatic polymer, lignin has been proven to be a good UV-absorber and natural broad-spectrum sun blocker. The structure-activity relationship of lignin under UV radiation remains unclear due to lignin’s complexity and heterogeneity. Here we report the structure influence of lignin on its anti-UV radiation properties of sun protection factor (SPF), UV absorbance, and antioxidant activity by using different lignin model compounds, including β–O–4, β–β, and β–5 dimers, etc., representing the structures of both native lignins and technical lignins. Meanwhile, UV protection properties of six lignin preparations, including cellulolytic enzyme lignin (CEL), organosolv lignin (OL), and kraft lignin (KL) of pinus kesiya and eucalyptus, were also evaluated for better comparison. SPF values of sunscreen preparations were increased but varied with the same addition of each single model compound into the pure cream or commercial sunscreen. In particular, the SPF value of the sunscreen has been greatly enhanced by the addition of a certain molar concentration of a single model compound (0.0558 mmol, around 2 wt%) into the low SPF commercial sunscreen, which was attributed to the synergistic effects of lignin models and inherent sunscreen agent. By comparing, lignin models containing β–O–4 linkage displayed the least desirable UV protection properties in this work, and side-chain difference, especially the existence of conjugate structure and carboxylic groups, would significantly impact the lignin model compounds’ UV performance. Additionally, the antioxidant activities and UV absorbance of different model compounds and lignin preparations are closely related to their structures. These insights revealed the structure-activity relationship of lignin under UV radiation and will provide a theoretical basis for optimizing lignins or lignin derivatives as the sun-screening agents in sunscreens.

Depolymerization of Technical Lignins in Supercritical Ethanol: Effects of Lignin Structure and Catalyst

Depolymerization of Technical Lignins in Supercritical Ethanol: Effects of Lignin Structure and Catalyst

The Comparative Abilities of a Small Laccase and a Dye-Decoloring Peroxidase From the Same Bacterium to Transform Natural and Technical Lignins.

The relative ability of the small laccase (sLac) and dye-decoloring peroxidase (DyP2) from Amycolatopsis sp. 75iv2 to transform a variety of lignins was investigated using time-of-flight secondary ion mass spectrometry (ToF-SIMS). The enzymes modified organosolv hardwood lignin to different extents even in the absence of an added mediator. More particularly, sLac decreased the lignin modification metric S (S-lignin)/Ar (total aromatics) by 58% over 16h, while DyP2 lowered this ratio by 31% in the absence of exogenous H2O2. When used on their own, both sLac and DyP2 also modified native lignin present in aspen wood powder, albeit to lesser extents than in the organosolv lignin. The addition of ABTS for sLac and Mn2+ as well as H2O2 for DyP2 led to increased lignin modification in aspen wood powder as reflected by a decrease in the G/Ar metric by up to a further 13%. This highlights the importance of exogenous mediators for transforming lignin within its native matrix. Furthermore, the addition of ABTS reduced the selectivity of sLac for S-lignin over G-lignin, indicating that the mediator also altered the product profiles. Finally, when sLac was included in reactions containing DyP2, in part to generate H2O2 in situ, the relative abundance of lignin products differed from individual enzymatic treatments. Overall, these results identify possible routes to tuning lignin modification or delignification through choice of enzyme and mediator. Moreover, the current study expands the application of ToF-SIMS to evaluating enzyme action on technical lignins, which can accelerate the discovery and engineering of industrially relevant enzymes for lignin valorization.

Lignin structure defines the properties of asphalt binder as a modifier

This study aims to further illustrate the relationship between technical lignin structure and asphalt binder performance. Two types of technical lignins (soda lignin and kraft lignins), were prepared and fully characterized. Rheological performance tests were performed to study their effects on the asphalt binder performance. Soda lignin was dominated by linear β-O-4′ aryl ethers and possessed more multiple intermolecular H-bonds, which effectively enhanced the low-temperature performance by weakening the cross-linking between asphaltenes and lignins. Kraft lignin, which exhibited condensed C–C linkages and stronger dimeric intermolecular H-bonds, performed as an effective asphalt binder modifier to improve the high-temperature rutting resistance.

Green Fabrication Approaches of Lignin Nanoparticles from Different Technical Lignins: A Comparison Study.

The production of lignin nanoparticles (LNPs) has emerged as a way to overcome the highly variable and complex molecular structure of lignin. It can offer morphological control of the lignin polymer, allowing the formation of stable LNP dispersions in aqueous media, while increasing the potential of lignin for high‐value applications. However, the polydispersity and morphology of LNPs varies depending on the lignin grade and preparation method, and a systematic comparison using different technical lignins is lacking. In this study, it was attempted to find a green fabrication method with a distinct solvent fractionation of lignin to prepare LNPs using three different technical lignins as starting polymers: BLN birch lignin (hardwood, BB), alkali Protobind 1000 (grass, PB), and kraft LignoBoost (softwood, LB). For that, three anti‐solvent precipitation approaches to prepare LNPs were systematically compared: 70 % aqueous ethanol, acetone/water (3 : 1) and NaOH as the lignin solvent, and water/aqueous HCl as the anti‐solvent. Among all these methods, the acetone/water (3 : 1) approach allowed production of homogeneous and monodisperse LNPs with a negative surface charge and also spherical and smooth surfaces. Overall, the results revealed that the acetone/water (3 : 1) method was the most effective approach tested to obtain homogenous, small, and spherical LNPs from the three technical lignins. These LNPs exhibited an improved stability at different ionic strengths and a wider pH range compared to the other preparation methods, which can greatly increase their application in many fields, such as pharmaceutical and food sciences.

Unraveling the role of reaction environment and catalysts for pyrolysis of technical lignin into different functional bio-oil yield

Catalytic pyrolysis of Kraft Lignin (KL) experiments were carried out at different temperatures (350–500 °C) over base MgO, acidic ZSM-5 and mixture of MgO-ZSM-5 catalysts under different environments (N2 and CO2). Non-catalytic reaction produced maximum bio-oil (35.3 wt%) under CO2 at 450 °C. Upgrading of pyrolysis vapor under different environment with catalysts produced lower bio-oil as it is enhanced cracking and coke formation. Higher intensity peak at 1695–1720 cm-1 was found in up-gradation pyrolysis KL vapor under CO2, which showed that the higher aldehyde/acidic or ketone functionality in bio-oil. The content of monocyclic aromatic hydrocarbons increased whereas phenolic compound decreased with using the catalysts under N2 while acidic functionality increased under CO2 environment. Our results suggest that mixture of catalysts showed synergistic effects which increased the bio-oil quality. Overall, mixture of MgO-ZSM-5 showed the highest yield of aromatic hydrocarbons (ca. 49.2%) under N2. Significant amount oxygen content reduced with the mixture of catalyst (MgO-ZSM-5, 1:1 ratio) under N2 with the increasing of aromatic hydrocarbon. Higher heating value bio-oil was obtained with catalytic up-gradation.