Lignin Sources Research Articles

Obtaining Lignin from Nutshells under Mild Extraction Conditions and Its Use as a Biostimulant in Tomato Seedlings

Biostimulants are an important alternative to improve and promote higher efficiency in cropping systems. Although the biostimulant industry has been developing for several years, there are still areas of opportunity for new sources of biostimulants as well as new ecofriendly extraction techniques that allow for a circular economy and the reuse of waste. Lignin is a heteropolymer that constitutes about 40% of the plant cell wall. A great source of lignin is agrowastes, giving it added value. Recently, its use has been tested in agronomy as a carrier of nutrients and pesticides. Walnuts are produced on a large scale in Northern Mexico, and the shell represents between 15 and 40% of its total weight. However, to obtain this biopolymer, to date, non-environmentally friendly techniques have been used; for this reason, it is necessary to find extraction alternatives to make this proposal sustainable. In this work, the obtaining and characterization of lignin through mild extraction conditions from nutshells and its evaluation as a biostimulant on the growth of tomato seedlings are reported. Lignin was extracted by hydrolysis with a mixture of acetic acid and distilled water (65:35 v/v). The results showed that it was possible to obtain 15% (w/w) lignin using mild solvents, evidenced by thermogravimetric analysis (TGA), proton magnetic nuclear resonance (H-RMN), and infrared (IR). Subsequently, lignin solutions were prepared at different concentrations, 0, 10, 50, and 100 ppm, and applied via foliar weekly to tomato seedlings. A greater fresh weight of the stem was found with 10 and 50 ppm, and the height and the fresh biomass increased with the three concentrations (10, 50, and 100 ppm), concluding that lignin extracted from nutshells using mild conditions can act as a plant biostimulant.

Quantitative 13C-IS pyrolysis-GC-MS lignin analysis: Overcoming matrix effects in animal feed and faeces

Recently, a pyrolysis-GC-MS methodology for specific lignin quantification and structural characterisation was developed, relying on the use of uniformly 13C-labeled polymeric lignin isolate as internal standard (IS). The 13C-IS py-GC-MS method has been validated for grasses, woods, and applied in various showcases. To study the fate of lignin in animals, this method still requires careful validation in animal feeds and, especially complex faecal samples, hence the aim of this work. Hereto, faecal material was collected from pigs fed with wheat straw as lignin source and subjected to the py-GC-MS analytical platform for thorough examination of IS pyrolysis behaviour in terms of response and structural features. Next, 13C-ISpy-lignin contents and corrected Klason lignin contents were compared. Most importantly, we revealed that pyrolysis behaviour of 13C-IS lignin and 12C-sample lignin was differently affected in the faecal matrix, resulting in the ultimate underestimation of 13C-ISpy-lignin contents. In-depth examination and evaluation of matrix constituents showed that predominantly matrix ash was responsible for the effects observed. We further demonstrated that said matrix effects can be overcome by water extraction of the samples prior to analysis. Our validation and approach extend the use of the specific 13C-IS py-GC-MS methodology for accurate quantitative lignin analysis to biomass samples with complex matrices like pig faeces, and now call for application in future digestibility studies.

Capability lignin from Acacia crassicarpa black liquor as an environmentally benign antibacterial agent to produce antibacterial and hydrophobic textiles

Recently, the growing health awareness of society on the utilization of fabrics has led to an increasing demand for natural-based antibacterial textiles. Lignin, a generous polyphenol compound in nature, is capable of preventing bacterial growth; in particular, it dwells bacteria closely together on human skin, such as Staphylococcus epidermidis, Bacillus subtilis, Propionibacterium acnes, and Staphylococcus aureus. However, the antibacterial properties of lignin are limited by factors such as the lignin concentration, source, and type of bacteria. This study aimed to evaluate the potency of lignin as an antibacterial agent for textiles. Moreover, the thermal properties and wettability of the textile after lignin coating were also investigated. This study showed that lignin isolation methods significantly contributed to the inhibition of bacterial growth in the clear zone diameter. In addition, the lignin structure, lignin concentration, and type of bacteria had notably different antibacterial effects. SEM images showed that lignin was successfully coated on the fiber, and the antibacterial textile was successfully fabricated with clear zones in the range of 0.1–0.5 cm against four different bacteria. Lignin did not significantly improve the thermal stability of the textile, as proven by the TGA results. After the HDTMS coating by dispersion method, the wettability of the lignin-textile improved to that of the hydrophobic material, with a contact angle greater than 119.05° with excellent antibacterial properties (clear zone of 0.1–0.43 cm).

Isotopic analysis (δ13C and δ2H) of lignin methoxy groups in forest soils to identify and quantify lignin sources

The relative apportion of above and below ground carbon sources is known to be an important factor in soil organic matter formation. Although lignin is the most abundant aromatic plant material in the terrestrial biosphere, our understanding of lignin source contributions to soil organic matter (SOM) is limited due to the complex molecular structure and analysis of lignin. In this study, we novelly apply the dual isotopic analysis (δ13C and δ2H values) of lignin methoxy groups (LMeO) with the Bayesian mixing model, MixSIAR, to apportion lignin sources in two contrasting soil types, a podzol and a stagnosol. Results of the isotopic analysis of LMeO demonstrate the ability of δ2H LMeO values to discriminate between above and below ground lignin sources, while δ13C LMeO values discriminated between photosynthesising and non-photosynthesising tissues. In the stagnosol subsurface horizons, a decreasing proportion of the leaf litter lignin was observed with increasing organic matter degradation, cumulating in the Ah horizon being dominated by lignin from roots. The podzol sites indicated a similar reduction in leaf litter lignin with an increase in organic matter degradation and depth. However, the Ah horizon was shown to accumulate lignin from the above ground woody material. Furthermore, given the significant abundance of LMeO groups in the terrestrial biosphere and the extremely depleted δ13C LMeO values in leaf litter, we employed a mass balance approach to determine the extent in which the 13C bulk enrichment generally associated with isotopic fractionation during organic matter decomposition can be attributed to the shift in lignin sources. Analysis reveals that 14 % and 11 % of bulk 13C enrichment can be attributed to the transition in LMeO sources from leaf litter to roots in the stagnosol and podzol, respectively. Thus, models relying on 13C enrichment with depth as an indicator of carbon turnover may be partially overestimating rates.

Pickering emulsion via interfacial assembly of lignin particles and cationic surfactant: Formation of robust anchoring layer

Lignin, a byproduct of the paper and pulp industry, shows promise as stabilizers for emulsions, offering potential value-added applications to direct disposal. However, utilizing particulate lignin directly as stabilizers is challenging due to limited emulsion stability. In this study, co-stabilization of Pickering emulsions is investigated by combination of lignin particles and cationic surfactants (CTAB and DDAB), wherein lignin source and oil types are optimized with a focus on emulsion stability. A battery of characterization methods, including visual appearance, microstructure, droplet size, zeta potential, etc., is employed to evaluate emulsion stability. The findings reveal that kraft lignin nanospheres (LNS) are the optimal stabilizing particles. The incorporation of cationic surfactants via electrostatic adsorption enhances the stabilizing effect of LNS, and the use of DDAB is found to significantly enhance emulsion stability compared to CTAB, attributing to higher charge shielding capability of DDAB, as well as the formation of a more robust and compact nonpolar anchoring layer. The surfactant-assisted LNS can be used to stabilize a range of oil types, with tridecane as the optimal oil. This research presents a straightforward, efficient, and scalable approach for producing highly stable lignin-based Pickering emulsions, showing potential applications in recycling and value enhancement of waste lignin.

Lignin-incorporated Co-MOFs-derived catalysts for selective hydrodeoxygenation of lignin-derived phenols into cyclohexanols

Lignin accounted for the second largest amount in biomass, and was regarded as an important carbon source and important renewable source for value-added chemicals. Herein, a series of lignin-derived carbon-based heterogeneous catalyst was synthesized through a simple hydrothermal method, using Co-MOFs as template. Lignin was introduced as a carbon material into MOF catalysts. Through some characterizations, it has been proven that lignin has been successfully introduced into MOF materials and significantly improved the catalyst performance. Then, lignin-MOF derived catalysts (Co/C-EL-X) were successfully introduced into the catalytic hydrodeoxygenation of lignin-derived phenols. The addition of enzymatic hydrolysis lignin (EL) in catalysts, calcination temperature and some other factors were investigated in detail, considering the catalytic performance during the HDO of vanillin and other typical lignin-derived phenols. Co/C-EL-0.5(500) exhibited the best catalytic performance for the conversion of different kinds of lignin-derived phenols to either 2-methoxy-4-methylphenol (MMP) or cyclohexanol. Under the optimal conditions of 240 °C, 0 MPa N2, and 2 h, the conversion rate of vanillin reached 100 %, and the yield of 4-methyl-2-methoxyphenol (MMP) was up to 92 %. Furthermore, vanillin could also be converted into 4-methylcyclohexanol (MCYL) by changing the initial nitrogen pressure. Also, Co/C-EL-0.5 (500) exhibited high activity for the conversion of other lignin-derived phenols into cyclohexanol (COL). This work provided a novel strategy for the catalytic valorization of lignin sources.

Investigation of synergistic effects incorporating esterified lignin and guar gum composite aerogel for sustained oil spill cleanup

The recently developed aerogel demonstrates a high capacity for pollutant absorption, making it an environmentally friendly option for oily water treatment. In an effort to reduce the adverse effects of the black liquor accumulation in the pulp industry, this study focused on utilizing the mentioned abundant bio-resource lignin, which can be applied to various high-value applications such as 3D porous materials for oil spill cleanup. Lignin, precipitated from the black liquor, was esterified using maleic anhydride as the esterifying reagent to enhance the hydrophobicity. Then, the composite aerogel fabricated from esterified lignin and guar gum (GG) was successfully prepared through the facile freeze-drying, using glutaraldehyde (GA) as the cross-linker. The resulting aerogel exhibited high porosity values exceeding 95%, low density (27.4 mg/cm3), and an impressive absorption capacity of 32.5 g/g for sunflower oil. These results demonstrate the potential of black liquor utilization as a bio-waste source of lignin and highlight the cost-effective guar gum-esterified lignin composite aerogel, which exhibits remarkable oil absorption capabilities and environmental sustainability promotion.

Preparation and Characterization of Lignin Nanoparticles from Different Plant Sources.

This article presents new research on producing lignin nanoparticles (LNPs) using the antisolvent nanoprecipitation method. Acetone (90%) served as the lignin solvent and water (100%) as the antisolvent, using five types of lignins from various sources. Comprehensive characterization techniques, including NMR, GPC, FTIR, TEM, and DLS, were employed to assess both lignin and LNP properties. The antioxidant activity of the LNPs was evaluated as well. The results demonstrated the successful formation of spherical nanoparticles below 100 nm with initial lignin concentrations of 1 and 2%w/v. The study highlighted the crucial role of lignin purity in LNP formation and colloidal stability, noting that residual carbohydrates adversely affect efficiency. This method offers a straightforward, environmentally friendly approach using cost-effective solvents, applicable to diverse lignin sources. The innovation of this study lies in its demonstration of a cost-effective and eco-friendly method to produce stable, nanometric-sized spherical LNPs. These LNPs have significant potential as reinforcement materials due to their reinforcing capability, hydrophilicity, and UV absorption. This work underscores the importance of starting material purity for optimizing the process and achieving the desired nanometric dimensions, marking a pioneering advancement in lignin-based nanomaterials.

Copper-catalyzed C–C bond cleavage coupling with C[tbnd]N bond formation toward mild synthesis of lignin-based benzonitriles

N-participated lignin depolymerization is of great importance for the transformation of waste lignin into value-added chemicals. The vast majority of developed strategies employ organic amines as nitrogen source, and considerable methods rely on excessive use of strong base, which suffers severe environmental issues. Herein, benzonitrile derivatives are synthesized from oxidized lignin β-O-4 model compounds in the presence of solid nitrogen source (NH4)2CO3 under mild, base-free conditions over commercially available copper catalyst. Mechanism studies suggest the transformation undergoes a one-pot, highly coupled cascade reaction path involving oxidative C-C bond cleavage and in-situ formation of CN bond. Of which, Cu(OAc)2 catalyzes the transfer of hydrogen from Cβ (Cβ-H) to Cα, leading to the cleavage of Cα-Cβ bonds to offer benzaldehyde derivative, this intermediate then reacts in-situ with (NH4)2CO3 to afford the targeted aromatic nitrile product. Tetrabutylammonium iodide (TBAI), acting as a promoter, plays a key role in breaking the Cα-Cβ bonds to form the intermediate benzaldehyde derivative. With this protocol, the feasibility of the production of value-added syringonitrile from birchwood lignin has been demonstrated. This transformation provides a sustainable approach to benzonitrile chemicals from renewable source of lignin.

Selective production of phenolic monomer via catalytic depolymerization of lignin over cobalt-nickel-zirconium dioxide catalyst

The utilization of lignin, an abundant and renewable bio-aromatic source, is of significant importance. In this study, lignin oxidation was examined at different temperatures with zirconium oxide (ZrO2)-supported nickel (Ni), cobalt (Co) and bimetallic Ni-Co metal catalysts under different solvents and oxygen pressure. Non-catalytic oxidation reaction produced maximum bio-oil (35.3 wt%), while catalytic oxidation significantly increased the bio-oil yield. The bimetallic catalyst Ni-Co/ZrO2 produced the highest bio-oil yield (67.4 wt%) compared to the monometallic catalyst Ni/ZrO2 (59.3 wt%) and Co/ZrO2 (54.0 wt%). The selectively higher percentage of vanillin, 2-methoxy phenol, acetovanillone, acetosyringone and vanillic acid compounds are found in the catalytic bio-oil. Moreover, it has been observed that the bimetallic Co-Ni/ZrO2 produced a higher amount of vanillin (43.7% and 13.30 wt%) compound. These results demonstrate that the bimetallic Ni-Co/ZrO2 catalyst promotes the selective cleavage of the ether β-O-4 bond in lignin, leading to a higher yield of phenolic monomer compounds.

Recent Advancement and Emerging Applications of Lignin

Lignin is a significant renewable natural energy resource these days, used as an environmentally acceptable and sustainable alternative fossil fuel feedstock in a huge possibility of value-added products. Lignin is a polymeric molecule that possesses an aromatic unit structure, together with cellulose, and is a main component of the cell walls of plants. It is the byproduct of agriculture residues and biorefinery products and can be extracted from paper-pulp industries. Properties of lignin may differ depending on the extraction method and source and also on an aromatic ring as the main constituent of lignin in the structure. This rare composition of lignin makes it more valuable, allowing for value-added applications such as in the field of storage devices and energy harvesters. This review focuses on derivatives of lignin, structure and composition sources and characteristics, and its sustainable emerging application in various fields are discussed.

A Novel Source of Lignin from Date Palm Leaves as a Reinforcing Agent for Fabrication of Carboxymethyl Cellulose-Based Active Food Packaging Film

A Novel Source of Lignin from Date Palm Leaves as a Reinforcing Agent for Fabrication of Carboxymethyl Cellulose-Based Active Food Packaging Film

Rapid Lignin Thermal Property Prediction through Attenuated Total Reflectance-Infrared Spectroscopy and Chemometrics.

To expedite the valorisation of lignin as a sustainable component in materials applications, rapid and generally available analytical methods are essential to overcome the bottleneck of lignin characterisation. Where features of a lignin's chemical structure have previously been found to be predicted by Partial Least Squares (PLS) regression models built on Infrared (IR) data, we now show for the first time that this approach can be extended to prediction of the glass transition temperature (Tg), a key physicochemical property. This methodology is shown to be convenient and more robust for prediction of Tg than prediction through empirically derived relationships (e. g., Flory-Fox). The chemometric analysis provided root mean squared errors of prediction (RMSEP) as low as 10.0 °C for a botanically, and a process-diverse set of lignins, and 6.2 °C for kraft-only samples. The PLS models could separately predict both the Tg as well as the degree of allylation (%allyl) for allylated lignin fractions, which were all derived from a single lignin source. The models performed exceptionally well, delivering RMSEP of 6.1 °C, and 5.4 %, respectively, despite the conflicting influences of increasing molecular weight and %allyl on Tg. Finally, the method provided accurate determinations of %allyl with RMSEP of 5.2 %.

Investigation of lignin substructures participating in self-assembly for the synthesis of monodisperse lignin spherical particles

The intricate structure of lignin, characterized by a mix of hydrophilic components and hydrophobic structures from its aliphatic and aromatic constituents, poses challenges in creating monodisperse particles. This is due to the need for precise modulation of self-assembly kinetics. Herein, we explore a correlation between the substructure of lignin and its capacity for self-assembly. We have conducted an in-depth investigation into the interactions between hydrophilic groups, such as phenolic and aromatic-OH, and monolignols with interunit linkages that are involved in the formation of lignin particles (LPs). A high degree of hydrophilicity with a condensed structure is crucial for high supersaturation levels, which in turn determines the growth phase and leads to small LPs. An approach based on tailoring the supersaturation level which is contingent on the structural characteristics of extracted organosolv lignin was used to obtain remarkably uniform LPs with mean diameters of approximately 230 and 480 nm. The results of this study have the potential to serve as a foundation for the preparation of monodisperse LPs derived from various lignin sources as well as for the development of methods to extract lignin containing a specific chemical substructure.

Modification of plywood with phenol–formaldehyde resin: substitution of phenol by pyrolysis cleavage products of softwood kraft lignin

The modification by impregnation of veneers for the production of plywood with phenol–formaldehyde resins is a well-known method to improve the dimensional stability and fungal resistance. Because phenol is obtained from non-renewable resources, finding substitutes has been a topic of research. Due to similarities in chemical structure and availability, lignin cleavage products present a promising alternative. In this study, microwave-assisted pyrolysis cleavage products of softwood kraft lignin have been used to substitute 30% of phenol in phenol–formaldehyde resins. Scots pine veneers were impregnated with the resin, and five-layered plywoods were produced. The influence of the substitution on the bonding quality, the dimensional stability, and the leaching of resin from the specimens were studied. Mechanical properties such as the bending strength, the modulus of elasticity, as well as the dynamic impact bending strength of the plywood were analyzed. Both treatments led to plywood with good dimensional stability, and the resin was stable against leaching. The substitution of phenol with lignin cleavage products led to slightly reduced brittleness of the specimens compared to pure phenol–formaldehyde resin. This study presents a method to reduce the use of non-renewable resources, increase the use of currently underutilized lignin sources, and produce plywood with promising properties for exterior applications.

Preparation of TiO2/Lignin Composites with Agave sisalana Residue for Bisphenol-A Removal

Composites prepared from metal oxides and materials derived from agroforestry residues have been successfully applied to remove emerging contaminants. The lignin properties, high surface area and number of functional groups, are beneficial in the preparation of TiO2 composites. In the present work, sisal residue was used as a source of lignin, and after extraction, the lignin was applied in the preparation of an adsorbent composite with TiO2 to remove bisphenol-A. The optimal conditions for lignin extraction resulted in a lignin purity of 73%. Characterization proved that the synthesized composites have a high surface area (> 100 m2 g-1), homogeneous distribution of TiO2 particles and stable surface charge. Such characteristics resulted in a lignin/TiO2 composite with a maximum adsorption capacity of 13.7 mg L-1, capable of removing up to 97% of bisphenol-A. The adsorbent can be used in six cycles, removing over 70% by the third cycle, which indicates good stability.

Development and Characterization of Edible Packaging Film Using Lignin Extracted from Coffee Silverskin

In this study, edible packaging films were developed by solvent casting method using lignin extracted from Costa Rican or Kenyan coffee silverskin and their barrier properties were investigated. Anise or cinnamon essential oil, glycerol or sorbitol or polyethylene glycol, and sodium alginate effects on the film properties were compared. The moisture content, swelling index and water vapor transmission rate analyses of the produced edible films were realized. Chemical structure analysis was done using Fourier Transform Infrared Spectroscopy device. Edible films plasticized with glycerol, have higher moisture content (23.21%), low swelling index (28.44%) and low water vapor transmission rate (0.7991*10-8(g/cm2.s)), than the films plasticized with sorbitol and polyethylene glycol. As a result, it was observed that coffee processing waste coffee silverskin, plasticized in preference with glycerol and mixed with anise or cinnamon essential oil, can be successfully used as a cost-effective lignin source for edible packaging film production.

UTILIZAREA LIGNINEI PENTRU ÎNDEPĂRTAREA PARTICULELOR DE MICROPLASTIC DIN APĂ

The focus of the research was to evaluate the use of lignin from different sources as an agent for the removal of diverse types of microplastics when present in wastewater. Organosolv lignin was obtained from three different sources (Miscanthus sp., pine bark and solid anaerobic digestates from Organic Fraction of Municipal Solid Wastes) by an ethanol-based organosolv treatment carried out in a pressurized stirred-tank reactor. The lignins obtained were evaluated as an adsorbent for diverse types of microplastics: High-density polyethylene (HDPE), Polystyrene (PS), Expanded Polystyrene (EPS), and Polypropylene (PP). All lignins used had the capacity to capture plastic particles from all plastic types, but a differential absorbance potential was found both for plastic types and lignin samples. EPS was the least adsorb type for all lignin sources, with the remaining plastics presenting equivalent results. Pine bark lignin was the best adsorbent among the tested feedstocks, always presenting the best performance for all plastic types. The direct utilization of organosolv hydrolysates, avoiding lignin recovery presented a similar behaviour. These results open the possibility to develop new natural, plant-based, adsorbents for microplastic removal from contaminated wastewater.

Endocrine-disrupting chemicals (EDCs), their sources, health concerns and biodegradation of EDCs using laccase

At present, the presence of endocrine disruptor chemicals in the environment are important factors that are affecting the functioning of environmental systems and the health of individuals. Endocrine-disrupting chemicals are present in a wide variety of consumer products and interfere with the functioning of hormones and causing growth and development-related problems in exposed individuals. Laccase is a copper-containing enzyme that has shown its potential to degrade Endocrine-disrupting chemicals. The microbial production of laccase requires a rich source of lignin along with cellulose, hemicelluloses, and other proteins. Thus, lignocelluloses rich wastes may be considered as good substrates for the production of laccase using microorganisms. In this article, we have discusses the fate of endocrine disruptors, and role of laccase in the biodegradation of endocrine disruptors.

Enhancing Carbon Fiber Properties through Lignin-Cellulose Composites: A Comparative Study of Hardwood Vs. Softwood Lignin Sources

Carbon fibers are integral to a wide range of applications, including automotive, construction, packaging, textiles, and emerging fields such as energy storage electrodes like flexible supercapacitors. However, concerns related to limited availability and environmental impact associated with fossil-based carbon fiber production have sparked growing interest in sustainable alternatives, particularly those derived from lignin and cellulose composites. This conference work presents a comparative analysis of the mechanical properties of lignin-cellulose composite carbon fibers derived from hardwood and softwood lignin sources, elucidating the significant influence of lignin origin on fiber performance.Our study focuses on the advantages and disadvantages of utilizing a composite of hardwood lignin vs. softwood lignin with cellulose in carbon fiber production, comparing these materials to commercially available carbon fibers. We emphasize the mechanical performance of these composite fibers, specifically highlighting the tensile strength and tensile modulus as a key metric. Notably, our results demonstrate that carbon fibers derived from hardwood lignin/cellulose composites exhibit superior mechanical strength compared to those from softwood lignin/cellulose composites. To gain fundamental insights into the reasons behind this mechanical disparity, we employed Raman spectroscopy to analyze the carbon structures within the fibers. Our findings revealed that carbon fibers produced from hardwood lignin exhibited a higher degree of graphitization, helping in achieving of typically desirable pre-graphite turbostractic carbon structures. These structural enhancements significantly contributed to the improved mechanical characteristics observed. In summary, our research underscores the critical importance of lignin source selection in the production of lignin-cellulose composite carbon fibers. The mechanical performance of these fibers is closely linked to the carbon morphology influenced by the lignin source. Therefore, understanding and controlling the lignin source from hardwood or softwood is pivotal for tailoring carbon fiber properties to meet specific application requirements. This study not only advances the knowledge in sustainable carbon fiber production but also offers valuable insights into achieving desirable properties for a wide range of applications, including advanced energy storage systems and structural materials.