Lignin valorization: Status, challenges and opportunities

Fractionated lignin as a green compatibilizer to improve the compatibility of poly (butylene adipate-co-terephthalate) /polylactic acid composites

Blending poly (butylene adipate-co-terephthalate) (PBAT) and polylactic acid (PLA) is a cost-effective strategy to obtain biodegradable plastic with complementary properties. However, the incompatibility between PBAT and PLA is a great challenge for fabricating high-performance composite films. Herein, the ethyl acetate fractionated lignin with the small glass transition temperature and low molecular weight was achieved and incorporated into the PBAT/PLA composite as a compatibilizer. The fractionated lignin can be uniformly dispersed within the PBAT/PLA matrix through a melt blending process and interact with the molecular chain of PBAT and PLA as a bonding bridge, which enhances the intermolecular interactions and reduces the interfacial tension of PBAT/PLA. By adding fractionated lignin, the tensile strength of the PBAT/PLA composite increased by 35.4 % and the yield strength increased by 37.7 %. Owing to lignin, the composite films possessed the ultraviolet shielding function and exhibited better water vapor barrier properties (1.73 ± 0.08 × 10-13 g·cm/cm2·s·Pa). This work conclusively demonstrated that fractionated lignin can be used as a green compatibilizer and a low-cost functional filler for PBAT/PLA materials, and provides guidance for the application of lignin in biodegradable plastics.

Combined hemicellulolytic and phenoloxidase activities of Thermobacillus xylanilyticus enable growth on lignin-rich substrates and the release of phenolic molecules

Major challenge in biorefineries is the use of all lignocellulosic components, particularly lignins. In this study, Thermobacillus xylanilyliticus grew on kraft lignin, steam-exploded and native wheat straws produced different sets of phenoloxidases and xylanases, according to the substrate. After growth, limited lignin structural modifications, mainly accompanied by a decrease in phenolic acids was observed by Nuclear Magnetic Resonance spectroscopy. The depletion of p-coumaric acid, vanillin and p-hydroxybenzaldehyde combined to vanillin production in the culture media indicated that the bacterium can transform some phenolic compounds. Proteomic approaches allowed the identification of 29 to 33 different hemicellulases according to the substrates. Twenty oxidoreductases were differentially expressed between kraft lignin and steam-exploded wheat straw. These oxidoreductases may be involved in lignin and aromatic compound utilization and detoxification. This study highlights the potential value of Thermobacillus xylanilyticus and its enzymes in the simultaneous valorization of hemicellulose and phenolic compounds from lignocelluloses.

Separation of lignin derivatives from hemp fiber using supercritical CO2, ethanol, and water at different temperatures

The process of lignin extraction often involves intricate chemical transformations, influencing its potential for high-value utilization. By investigating the process of lignin derivatives extraction from hemp fibers using supercritical CO2, ethanol, and water, we identified the relationship between the chemical structure of lignin derivatives and temperature. This discovery contributes to controlling the chemical structure of lignin derivatives through temperature modulation. We observed that lignin derivatives extracted within the temperature range of 100-120 °C exhibited the lowest average molecular weight and polydispersity index, presenting a disordered microstructure with the highest hydroxyl content. Lignin derivatives extracted between 140 and 160 °C showed an increase in average molecular weight and polydispersity index, decreased hydroxyl content, and a gradual transformation of microstructure into spherical particles. At 180 °C, the average molecular weight and polydispersity index of lignin derivatives decreased, the microstructure of lignin derivatives showed fewer spherical particles, while its hydroxyl content exhibited a partial recovery. Chemical analysis revealed a lower degree of condensation in lignin derivatives at 100-120 °C. Between 120 and 160 °C, the degree of condensation increased. At 180 °C, extensive degradation occurred in lignin derivatives. This research advances innovative techniques for lignin derivative separation, contributing to their utilization in higher-value applications.

Selective adsorption of Cr(VI) by nitrogen-doped hydrothermal carbon in binary system

Selective adsorption of heavy metal ions from industrial effluent is important for healthy ecosystem development. However, the selective adsorption of heavy metal pollutants by biochar using lignin as raw material is still a challenge. In this paper, the lignin carbon material (N-BLC) was synthesized by a one-step hydrothermal carbonization method using paper black liquor (BL) as raw material and triethylene diamine (TEDA) as nitrogen source. N-BLC (2:1) showed excellent selectivity for Cr(VI) in the binary system, and the adsorption amounts of Cr(VI) in the binary system were all greater than 150 mg/g, but the adsorption amounts of Ca(II), Mg(II), and Zn(II) were only 19.3, 25.5, and 6.3 mg/g, respectively. The separation factor (SF) for Cr(VI) adsorption was as high as 120.0. Meanwhile, FTIR, elemental analysis and XPS proved that the surface of N-BLC (2:1) contained many N- and O- containing groups which were favorable for the removal of Cr(VI). The adsorption of N-BLC (2:1) followed the Langmuir model and its maximum theoretical adsorption amount was 618.4 mg/g. After 5th recycling, the adsorption amount of Cr(VI) by N-BLC (2:1) decreased about 15%, showing a good regeneration ability. Therefore, N-BLC (2:1) is a highly efficient, selective and reusable Cr(VI) adsorbent with wide application prospects.

A green pathway for lignin valorization: Enzymatic lignin depolymerization in biocompatible ionic liquids and deep eutectic solvents

Lignin depolymerization, which enables the breakdown of a complex and heterogeneous aromatic polymer into relatively uniform derivatives, serves as a critical process in valorization of lignin. Enzymatic lignin depolymerization has become a promising biological strategy to overcome the heterogeneity of lignin, due to its mild reaction conditions and high specificity. However, the low solubility of lignin compounds in aqueous environments prevents efficient lignin depolymerization by lignin-degrading enzymes. The employment of biocompatible ionic liquids (ILs) and deep eutectic solvents (DESs) in lignin fractionation has created a promising pathway to enzymatically depolymerize lignin within these green solvents to increase lignin solubility. In this review, recent research progress on enzymatic lignin depolymerization, particularly in a consolidated process involving ILs/DESs is summarized. In addition, the interactions between lignin-degrading enzymes and solvent systems are explored, and potential protein engineering methodology to improve the performance of lignin-degrading enzymes is discussed. Consolidation of enzymatic lignin depolymerization and biocompatible ILs/DESs paves a sustainable, efficient, and synergistic way to convert lignin into value-added products.

A powerful two-dimensional chromatography method for the non-target analysis of depolymerised lignin

BACKGROUND

Lignin is an abundant natural polymer obtained as a by-product from the fractionation of lignocellulosic biomass. In the name of a circular economy, lignin should be valorised into valuable chemicals or biomaterials and utilised instead of petrochemicals. For the development of efficient valorisation processes, the structural characterisation of lignin can be highly beneficial. However, this is an arduous task, as the isolated (and sometimes processed) lignin mainly consists of various neutral monomers but also oligomers. In addition, the material contains isomers, which can be especially problematic to separate and identify.

RESULTS

We present a powerful off-line comprehensive two-dimensional (2D) chromatography method combining liquid chromatography (LC), supercritical fluid chromatography (SFC), and high-resolution mass spectrometry for the non-target analysis of depolymerised lignin. The implementation of a 1-aminoanthracene column in the second dimension enabled a class separation of potential lignin monomers, dimers, trimers, and tetramers with an additional separation based on the number of hydroxyl groups and steric effects. The pentafluorophenyl column in the first dimension additionally improved the separation based on hydrophobicity. The comparison of off-line 2D LC × SFC to 1D SFC showed that besides the overall improved performance, the first method is also superior for the separation of isomers. Advanced data analysis methods (MS-DIAL, SIRIUS, and Feature-Based Molecular Network) were integrated into the non-target workflow to rapidly visualise and study the detected compounds, which proved to be especially beneficial for the characterisation of the separated isomers.

SIGNIFICANCE

The method yielded the first 2D LC plot demonstrating a classification of lignin compounds, which can be applied to compare various lignin sources and processing methods. In addition, the technique demonstrated improved separation of compounds, including isomers, which was especially beneficial as 77 % of the detected compounds had at least one isomer in the same lignin sample.

Study on the catalytic hydrodeoxygenation of lignin dimers: Adsorption properties and linkages cleavage

Production of mono-phenols through hydrodeoxygenation is one of the most promising routes for value-added lignin valorization. However, the adsorption characteristic of key intermediates and hydrodeoxygenation mechanism of key linkages in lignin have received inadequate attentions. In this paper, experiments combined with density functional theory calculations were done to explore the adsorption and catalytic HDO mechanism of lignin dimers. It was found that NiFe(111)-Mo2C(001) had a better ability on linkages activation, and showed stronger adsorption on CO containing intermediates, which was favor for further hydrodeoxygenation. Moreover, the calculation results certificated the cleavage of β-O-4 was prior to the hydrodeoxygenation of CO, and the hydrodeoxygenation of β-O-4 included a H· addition to O atom before the C-O cleavage. Finally, the elementary reactions energy barriers were efficiently reduced by NiFe(111)-Mo2C(001) catalyst during the hydrodeoxygenation reactions, which elucidated the superior performance of NiFe catalyst. This work provides a theoretical basis on efficient lignin utilization.

Preparation of uniform lignin/titanium dioxide nanoparticles by confined assembly: A multifunctional nanofiller for a waterborne polyurethane wood coating

We report a facile synthesis for lignin/titanium dioxide (TiO2) nanoparticles (LT NPs) at room temperature by confining assembly of lignin macromolecules. The LT NPs had a uniform nanosize distribution (average diameter ∼ 68 nm) and were directly employed as multifunctional nanofillers to reinforce a waterborne polyurethane wood coating (WBC). X-ray diffraction, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy revealed the mechanism by which formed TiO2 confined lignin assembly. The LT NPs considerably increased the tensile strength of a WBC film from 16.3 MPa to 28.1 MPa. The WBC-LT NPs exhibited excellent ultraviolet (UV) A and UVB blocking performances of 87 % and 98 %, respectively, while maintaining 94 % transmittance in the visible region. Incorporating LT NPs into the WBC enhanced the coating performance (the hardness, adhesion, and abrasion resistance) on wood substrates. A quantitative color and texture analysis revealed that the LT NPs increased the decorativeness of actual wooden products. After nearly 1800 h of UV irradiation, wood coated with the WBC-LT NPs exhibited good color stability, where the original color remained unchanged or even became brighter. In this study, value-added valorization of lignin is enabled by using organic-inorganic nanofillers and insights are gained into developing multifunctional WBCs.

Functional screening pipeline to uncover laccase-like multicopper oxidase enzymes that transform industrial lignins

Laccase-like multicopper oxidases are recognized for their potential to alter the reactivity of lignins for application in value-added products. Typically, model compounds are employed to discover such enzymes; however, they do not represent the complexity of industrial lignin substrates. In this work, a screening pipeline was developed to test enzymes simultaneously on model compounds and industrial lignins. A total of 12 lignin-active fungal multicopper oxidases were discovered, including 9 enzymes active under alkaline conditions (pH 11.0). Principal component analysis revealed the poor ability of model compounds to predict enzyme performance on industrial lignins. Additionally, sequence similarity analyses grouped these enzymes with Auxiliary Activity-1 sub-families with few previously characterized members, underscoring their taxonomic novelty. Correlation between the lignin-activity of these enzymes and their taxonomic origin, however, was not observed. These are critical insights to bridge the gap between enzyme discovery and application for industrial lignin valorization.

Recent developments in lignin-based fluorescent materials

Biomass-based fluorescent materials are an alternative to plastic-based materials for their multifunctional applications. Lignin, an inexpensive and easily available raw material, demonstrates outstanding environment-responsive properties such as pH, metal ions, dyes sensing, bioimaging and so on. To date, only a little work has been reported on the synthesis of lignin-based fluorescent materials. In this review report, synthetic approaches and light-responsive applications of lignin-based fluorescent carbon dots and other materials are summarized. The results reveal that lignin-based fluorescent carbon dots are prepared by hydrothermal method, exhibit small size <10 nm, reveal significant quantum yield, biocompatibility, non-toxicity, photostability and display substantial tunable emission and can be efficiently employed for sensing, bioimaging and energy storage applications. Finally, the forthcoming challenges, investigations, and options open for the chemical and/or physical modification of lignin into fluorescent materials for future applications are well-addressed. To our knowledge, this is the first comprehensive review report on lignin-based fluorescent materials and their light-responsive applications. In addition, this review will attract remarkable consideration and thrust for the researchers and biochemical technologists working with the preparation of lignin-based fluorescent materials for broad applications.

Flame retardant, heat insulating and hydrophobic chitosan-derived aerogels for the clean-up of hazardous chemicals

Leakage of hazardous chemicals often causes significant casualties, enormous economic losses, and negative social benefits. Presently, fire rescue personnel lack efficient and eco-friendly disposal materials for hazardous chemical leakage accidents. In this study, chitosan (CS) aerogels with excellent flame-retardant performance were prepared via cross-linking by two phosphorus-containing vanillin-based compounds (DV and TV). The as-prepared chitosan aerogels were lightweight and porous. The introduction of DV and TV greatly enhanced the residual char yields of CS at 700 °C and the flame-retardant performance of chitosan aerogels. TCS-5.0 possessed the best flame-retardant performance, indicating that TV was more effective than DV in enhancing the flame-retardant performance of chitosan aerogels. The greatly improved flame-retardant properties could be attributed to TV effectively promoting the residual char formation of chitosan aerogels and reducing the formation of combustible gas phase products. To improve the hydrophobicity of chitosan aerogels, TCS-5.0 was treated with solution immersion to load siloxane molecules on its surface. The water contact angle of HTCS-5.0 was 136.1°. HTCS-5.0 had a high oil absorption multiplicity, absorbing up to 31 times its own weight of chloroform. HTCS-5.0 could continuously absorb organic solvents on the water surface with the assistance of a vacuum pump, indicating that HTCS-5.0 could be used for the clean-up of hazardous chemical leakage accidents.

Engineered co-culture for consolidated production of phenylpropanoids directly from aromatic-rich biomass

Consolidated bioprocesses for the in situ hydrolysis and conversion of biomass feedstocks into value-added products offers great potential for both process and cost reduction. However, to date few consolidated bioprocesses have been developed that target aromatic rich feedstock fractions. Reported here is the development of synthetic co-cultivation for the consolidated hydrolysis and valorisation of corncob hydroxycinnamic acids. Biomass hydrolysis was achieved via a secretion module developed in B. subtilis using a genetically encoded biosensor-actuator to secrete hydrolytic enzymes. Conversion was achieved via a biotransformation module developed in E. coli using a suite of plug-and-play encoded enzymes to convert the released hydroxycinnamic acids into high-value phenylpropanoid target compounds. Finally, employing cellulolytic pre-treatment, extractive fermentation and in situ product recovery multiple aromatic products, coniferol and chavicol, were isolated from the same process in high purity.

Streptomyces spp. as biocatalyst sources in pulp and paper and textile industries: Biodegradation, bioconversion and valorization of waste

Complex polymers represent a challenge for remediating environmental pollution and an opportunity for microbial-catalysed conversion to generate valorized chemicals. Members of the genus Streptomyces are of interest because of their potential use in biotechnological applications. Their versatility makes them excellent sources of biocatalysts for environmentally responsible bioconversion, as they have a broad substrate range and are active over a wide range of pH and temperature. Most Streptomyces studies have focused on the isolation of strains, recombinant work and enzyme characterization for evaluating their potential for biotechnological application. This review discusses reports of Streptomyces-based technologies for use in the textile and pulp-milling industry and describes the challenges and recent advances aimed at achieving better biodegradation methods featuring these microbial catalysts. The principal points to be discussed are (1) Streptomyces' enzymes for use in dye decolorization and lignocellulosic biodegradation, (2) biotechnological processes for textile and pulp and paper waste treatment and (3) challenges and advances for textile and pulp and paper effluent treatment.

Fe3O4-lignin@Pd-NPs: A highly active, stable and broad-spectrum nanocomposite for water treatment

In this work, we report an environmentally friendly renewable nanocomposite magnetic lignin-based palladium nanoparticles (Fe3O4-lignin@Pd-NPs) for efficient wastewater treatment by decorating palladium nanoparticles without using any toxic reducing agents on the magnetic lignin abstracted from Poplar. The structure of composite Fe3O4-lignin@Pd-NPs was unambiguously confirmed by XRD, SEM, TEM, EDS, FTIR, and Zeta potential. After systematic evaluation of the use and efficiency of the composite to remove toxic organic dyes in wastewater, some promising results were observed as follows: Fe3O4-lignin@Pd-NPs exhibits highly active and efficient performance in the removal of toxic methylene blue (MB) (up to 99.8 %) wastewater in 2 min at different concentrations of MB and different pH values. Moreover, except for toxic MB, the other organic dyes including Rhodamine B (RhB), Rhodamine 6G (Rh6G), and Methyl Orange (MO) can also be removed efficiently by the composite. Finally, the easily recovered composite Fe3O4-lignin@Pd-NPs exhibits well stability and reusability, and catalytic efficiency is maintained well after ten cycles. In conclusion, the lignin-based magnetism Pd composite exhibits powerful potential practical application in industrial wastewater treatment.

Synthesis of lignin nanoparticle‑manganese dioxide complex and its adsorption of methyl orange

Lignin nanoparticles (LNPs) were synthesized using an anti-solvent method and subsequently loaded with manganese dioxide (MnO2) via potassium permanganate treatment, resulting in the formation of MnO2@LNPs. An extensive investigation was conducted to elucidate the influence of MnO2@LNPs on the decolorization of methyl orange solution. The LNPs were successfully obtained by adjusting the preparation parameters, yielding particles exhibited average sizes ranging from 300 to 600 nm, and the synthesis process exhibited a high yield of up to 87.3% and excellent dispersion characteristics. Notably, LNPs size was reduced by decreasing initial concentration, increasing stirring rate, and adding water. In the acetone-water two-phase system, LNPs self-assembled into spherical particles driven by π-π interactions and hydrogen bond forces. Oxidation modification using potassium permanganate led to the formation of nanoscale MnO2, which effectively combined with LNPs. Remarkably, the resulting MnO2@LNPs demonstrated a two-fold increase in methyl orange adsorption capacity (227 mg/g) compared to unmodified LNPs. The process followed the Langmuir isotherm model and was exothermic.

From waste to health-supporting molecules: biosynthesis of natural products from lignin-, plastic- and seaweed-based monomers using metabolically engineered Streptomyces lividans

BACKGROUND

Transforming waste and nonfood materials into bulk biofuels and chemicals represents a major stride in creating a sustainable bioindustry to optimize the use of resources while reducing environmental footprint. However, despite these advancements, the production of high-value natural products often continues to depend on the use of first-generation substrates, underscoring the intricate processes and specific requirements of their biosyntheses. This is also true for Streptomyces lividans, a renowned host organism celebrated for its capacity to produce a wide array of natural products, which is attributed to its genetic versatility and potent secondary metabolic activity. Given this context, it becomes imperative to assess and optimize this microorganism for the synthesis of natural products specifically from waste and nonfood substrates.

RESULTS

We metabolically engineered S. lividans to heterologously produce the ribosomally synthesized and posttranslationally modified peptide bottromycin, as well as the polyketide pamamycin. The modified strains successfully produced these compounds using waste and nonfood model substrates such as protocatechuate (derived from lignin), 4-hydroxybenzoate (sourced from plastic waste), and mannitol (from seaweed). Comprehensive transcriptomic and metabolomic analyses offered insights into how these substrates influenced the cellular metabolism of S. lividans. In terms of production efficiency, S. lividans showed remarkable tolerance, especially in a fed-batch process using a mineral medium containing the toxic aromatic 4-hydroxybenzoate, which led to enhanced and highly selective bottromycin production. Additionally, the strain generated a unique spectrum of pamamycins when cultured in mannitol-rich seaweed extract with no additional nutrients.

CONCLUSION

Our study showcases the successful production of high-value natural products based on the use of varied waste and nonfood raw materials, circumventing the reliance on costly, food-competing resources. S. lividans exhibited remarkable adaptability and resilience when grown on these diverse substrates. When cultured on aromatic compounds, it displayed a distinct array of intracellular CoA esters, presenting promising avenues for polyketide production. Future research could be focused on enhancing S. lividans substrate utilization pathways to process the intricate mixtures commonly found in waste and nonfood sources more efficiently.

Two-dimensional chromatography for the analysis of valorisable biowaste: A review

Various everyday areas such as agriculture, wood industry, and wastewater treatment yield residual biowastes in large amounts that can be utilised for the purpose of sustainability and circular economy. Depending on the type of biowaste, they can be used to extract valuable chemicals or converted into alternative fuels. However, for efficient valorisation, these processes need to be monitored, for which thorough chemical characterisation can be highly beneficial. For this aim, two-dimensional (2D) chromatography can be favourable, as it has a higher peak capacity and sensitivity than one-dimensional (1D) chromatography. Therefore, here we review the studies published since 2010 involving gas chromatography (GC) or liquid chromatography (LC) as one of the dimensions. For the first time, we present the 2D chromatographic characterisation of various biowastes valorised for different purposes (chemical, fuels), together with future prospects and challenges. The aspects related to the 2D chromatographic analysis of polar, poorly volatile, and thermally unstable compounds are highlighted. In addition, it is demonstrated how different 2D setups can be applied for monitoring the biowaste conversion processes.

Matching diverse feedstocks to conversion processes for the future bioeconomy

A wide variety of wasted or underutilized organic feedstocks can be leveraged to build a sustainable bioeconomy, ranging from crop residues to food processor residues and municipal wastes. Leveraging these feedstocks is both high-risk and high-reward. Converting mixed, variable, and/or highly contaminated feedstocks can pose engineering and economic challenges. However, converting these materials to fuels and chemicals can divert waste from landfills, reduce fugitive methane emissions, and enable more responsible forest management to reduce the frequency and severity of wildfires. Historically, low-value components, including ash and lignin, are poised to become valuable coproducts capable of supplementing cement and valuable chemicals. Here, we evaluate the challenges and opportunities associated with converting a range of feedstocks to renewable fuels and chemicals.

Alkaline lignins from Morinda citrifolia leaves are potential immunomodulatory, antitumor, and antimicrobial agents

Morinda citrifolia, commonly known as noni, is a plant belonging to the Rubiaceae family. This plant has a high biological potential, which has different biological properties, including antioxidant, antibacterial, antiviral, antifungal, antitumor and anti-inflammatory. In this work, the immunomodulatory, antitumor and antimicrobial activities of lignin isolated from Morinda citrifolia leaves were investigated. The results showed that this lignin was not cytotoxic and that it was able to promote activation and differentiation of immune cells in addition to inducing the production of anti-inflammatory cytokines. Furthermore, it was able to inhibit the growth of different tumor and microbial cells in vitro. This pioneering study on these different activities shows that the lignin isolated in this study can be used as a raw material to obtain biomedical and pharmaceutical products.

Antimicrobial Peptide-Inspired Design of Amino-Modified Lignin with Improved Antimicrobial Activities

A major challenge to make use of lignin as an antimicrobial material is the weak antimicrobial activity of industrial lignin. Inspired by the antimicrobial mechanism of actions of antimicrobial peptides, alkyldiamines were employed as lysine mimics for lignin modifications. Accordingly, aminoalkyl-modified lignins with different degrees of substitution of amino groups and different hydrophobicity were synthesized. The chemical structure, properties, and antimicrobial activities of the as-prepared aminoalkyl lignins were thoroughly characterized with state-of-the-art technologies. The results indicated that aminobutyl lignin showed enhanced antimicrobial activity against S. aureus and E. coli and performed even better than copper ions. The antimicrobial mechanism of action of the as-prepared aminobutyl lignin was similar to that of polylysine, which damaged the cell membrane, leading to the leakage of intracellular molecules and death of the cell. This study provides a feasible approach to afford modified lignin with enhanced antimicrobial performance, which would facilitate the high-value valorization of lignin as biological materials.

Development of novel recombinant peroxidase secretion system from Pseudomonas putida for lignin valorisation

Pseudomonas putida is a promising strain for lignin valorisation. However, there is a dearth of stable and efficient systems for secreting enzymes to enhance the process. Therefore, a novel secretion system for recombinant lignin-depolymerising peroxidase was developed. By adopting a flagellar type III secretion system, P. putida KT-M2, a secretory host strain, was constructed and an optimal secretion signal fusion partner was identified. Application of the dye-decolourising peroxidase of P. putida to this system resulted in efficient oxidation activity of the cell-free supernatant against various chemicals, including lignin model compounds. This peroxidase-secreting strain was examined to confirm its lignin utilisation capability, resulting in the efficient assimilation of various lignin substrates with 2.6-fold higher growth than that of the wild-type strain after 72 h of cultivation. Finally, this novel system will lead efficient bacterial lignin breakdown and utilization through enzyme secretion, paving the way for sustainable lignin-consolidated bioprocessing.

Depolymerization of lignin: Recent progress towards value-added chemicals and biohydrogen production

The need for alternative sources of energy became increasingly urgent as demand for energy and the use of fossil fuels both soared. When processed into aromatic compounds, lignin can be utilized as an alternative to fossil fuels, however, lignin's complex structure and recalcitrance make depolymerization impractical. This article presented an overview of the most recent advances in lignin conversion, including process technology, catalyst advancement, and case study-based end products. In addition to the three established methods (thermochemical, biochemical, and catalytic depolymerization), a lignin-first strategy was presented. Depolymerizing different forms of lignin into smaller phenolic molecules has been suggested using homogeneous and heterogeneous catalysts for oxidation or reduction. Limitations and future prospects of lignin depolymerization have been discussed which suggests that solar-driven catalytic depolymerization through photocatalysts including quantum dots offers a unique pathway to obtain the highly catalytic conversion of lignin.

In Situ Lignin Adhesion for High-Performance Bamboo Composites

Bamboo composite is an attractive candidate for structural materials in applications such as construction, the automotive industry, and logistics. However, its development has been hindered due to the use of harmful petroleum-derived synthetic adhesives or low-bonding biobased adhesives. Herein, we report a novel bioadhesion strategy based on in situ lignin bonding that can process natural bamboo into a scalable and high-performance composite. In this process, lignin bonds the cellulose fibrils into a strong network via a superstrong adhesive interface formed by hydrogen bonding and nanoscale entanglement. The resulting in situ glued-bamboo (glubam) composite exhibits a record-high shear strength of ∼4.4 MPa and a tensile strength of ∼300 MPa. This in situ lignin adhesion strategy is facile, highly scalable, and cost-effective, suggesting a promising route for fabricating strong and sustainable structural bamboo composites that sequester carbon and reduce our dependence on petrochemical-based adhesives.

A Comprehensive Mini-Review on Lignin-Based Nanomaterials for Food Applications: Systemic Advancement and Future Trends

The shift to an environmentally friendly material economy requires renewable resource exploration. This shift may depend on lignin valorization. Lignin is an aromatic polymer that makes up one-third of total lingo-cellulosic biomass and is separated into large amounts for biofuel and paper manufacture. This renewable polymer is readily available at a very low cost as nearly all the lignin that is produced each year (90–100 million tons) is simply burned as a low-value fuel. Lignin offers potential qualities for many applications, and yet it is underutilized. This Perspective highlights lignin-based material prospects and problems in food packaging, antimicrobial, and agricultural applications. The first half will discuss the present and future studies on exploiting lignin as an addition to improve food packaging’s mechanical, gas, UV, bioactive molecules, polyphenols, and antioxidant qualities. Second, lignin’s antibacterial activity against bacteria, fungi, and viruses will be discussed. In conclusion, lignin agriculture will be discussed in the food industries.

A Comprehensive Mini-Review on Lignin-Based Nanomaterials for Food Applications: Systemic Advancement and Future Trends

The shift to an environmentally friendly material economy requires renewable resource exploration. This shift may depend on lignin valorization. Lignin is an aromatic polymer that makes up one-third of total lingo-cellulosic biomass and is separated into large amounts for biofuel and paper manufacture. This renewable polymer is readily available at a very low cost as nearly all the lignin that is produced each year (90-100 million tons) is simply burned as a low-value fuel. Lignin offers potential qualities for many applications, and yet it is underutilized. This Perspective highlights lignin-based material prospects and problems in food packaging, antimicrobial, and agricultural applications. The first half will discuss the present and future studies on exploiting lignin as an addition to improve food packaging's mechanical, gas, UV, bioactive molecules, polyphenols, and antioxidant qualities. Second, lignin's antibacterial activity against bacteria, fungi, and viruses will be discussed. In conclusion, lignin agriculture will be discussed in the food industries.

Macromolecular Hydrodynamics and Fractal Structures of the Lignins of Fir Wood and Oat Husks

The topological structure of the macromolecules of lignins isolated from oat husk and fir wood was studied by means of macromolecular hydrodynamic methods. The macromolecular properties were analyzed by evaluating the intrinsic viscosity and coefficients of the translational diffusion and the sedimentation velocity of the lignins in dilute dimethylformamide solutions. The average molecular weights (MDη) and polydispersity parameters were calculated based on the results of the fractionation, as follows: Mw = 14.6 × 103, Mn = 9.0, and Mw/Mn = 1.62 for lignins from fir wood and Mw = 14.9 Mn = 13.5 and Mw/Mn = 1.1 for lignins from oat husks. The fractal analysis of the lignin macromolecules allowed us to identify the distinctive characteristics of the fractal and topological structures of these lignins. The measurements indicated that the fractal dimension (df) values of the guaiacyl-syringyl lignins from oat husks were between 1.71 and 1.85, while the df of a typical guaiacyl lignin from fir wood was ~2.3. Thus, we determined that the lignin macromolecules of oat husks belong to the diffusion-limited aggregation-type cluster-cluster class of fractals of the Meakin-Kolb type, with a predominance of characteristics common to a linear configuration. The lignins of softwood fir trees exhibited a branched topological structure, and they belong to the diffusion-limited aggregation-type particle-cluster class of fractals of the Witten-Sander type. Lignins from oat husks have the linear topology of macromolecules while the macromolecules of the lignins from fir wood can be characterized as highly branched polymers.

Deriving high value products from depolymerized lignin oil, aided by (bio)catalytic funneling strategies

Lignin holds tremendous and versatile possibilities to produce value-added chemicals and high performing polymeric materials. Over the years, different cutting-edge lignin depolymerization methodologies have been developed, mainly focusing on achieving excellent yields of mono-phenolic products, some even approaching the theoretical maximum. However, due to lignin's inherent heterogeneity and recalcitrance, its depolymerization leads to relatively complex product streams, also containing dimers, and higher molecular weight fragments in substantial quantities. The subsequent chemo-catalytic valorization of these higher molecular weight streams, containing difficult-to-break, mainly C-C covalent bonds, is tremendously challenging, and has consequently received much less attention. In this minireview, we present an overview of recent advances on the development of sustainable biorefinery strategies aimed at the production of well-defined chemicals and polymeric materials, the prime focus being on depolymerized lignin oils, containing high molecular weight fractions. The key central unit operation to achieve this is (bio)catalytic funneling, which holds great potential to overcome separation and purification challenges.

A lignin-derived material improves plant nutrient bioavailability and growth through its metal chelating capacity

The lignocellulosic biorefinery industry can be an important contributor to achieving global carbon net zero goals. However, low valorization of the waste lignin severely limits the sustainability of biorefineries. Using a hydrothermal reaction, we have converted sulfuric acid lignin (SAL) into a water-soluble hydrothermal SAL (HSAL). Here, we show the improvement of HSAL on plant nutrient bioavailability and growth through its metal chelating capacity. We characterize HSAL's high ratio of phenolic hydroxyl groups to methoxy groups and its capacity to chelate metal ions. Application of HSAL significantly promotes root length and plant growth of both monocot and dicot plant species due to improving nutrient bioavailability. The HSAL-mediated increase in iron bioavailability is comparable to the well-known metal chelator ethylenediaminetetraacetic acid. Therefore, HSAL promises to be a sustainable nutrient chelator to provide an attractive avenue for sustainable utilization of the waste lignin from the biorefinery industry.

Lignins as Promising Renewable Biopolymers and Bioactive Compounds for High-Performance Materials

The recycling of biomass into high-value-added materials requires important developments in research and technology to create a sustainable circular economy. Lignin, as a component of biomass, is a multipurpose aromatic polymer with a significant potential to be used as a renewable bioresource in many fields in which it acts both as promising biopolymer and bioactive compound. This comprehensive review gives brief insights into the recent research and technological trends on the potential of lignin development and utilization. It is divided into ten main sections, starting with an outlook on its diversity; main properties and possibilities to be used as a raw material for fuels, aromatic chemicals, plastics, or thermoset substitutes; and new developments in the use of lignin as a bioactive compound and in nanoparticles, hydrogels, 3D-printing-based lignin biomaterials, new sustainable biomaterials, and energy production and storage. In each section are presented recent developments in the preparation of lignin-based biomaterials, especially the green approaches to obtaining nanoparticles, hydrogels, and multifunctional materials as blends and bio(nano)composites; most suitable lignin type for each category of the envisaged products; main properties of the obtained lignin-based materials, etc. Different application categories of lignin within various sectors, which could provide completely sustainable energy conversion, such as in agriculture and environment protection, food packaging, biomedicine, and cosmetics, are also described. The medical and therapeutic potential of lignin-derived materials is evidenced in applications such as antimicrobial, antiviral, and antitumor agents; carriers for drug delivery systems with controlled/targeting drug release; tissue engineering and wound healing; and coatings, natural sunscreen, and surfactants. Lignin is mainly used for fuel, and, recently, studies highlighted more sustainable bioenergy production technologies, such as the supercapacitor electrode, photocatalysts, and photovoltaics.

Photoreforming for Lignin Upgrading: A Critical Review

Photoreforming of lignocellulosic biomass to simultaneously produce gas fuels and value-added chemicals has gradually emerged as a promising strategy to alleviate the fossil fuels crisis. Compared to cellulose and hemicellulose, the exploitation and utilization of lignin via photoreforming are still at the early and more exciting stages. This Review systematically summarizes the latest progress on the photoreforming of lignin-derived model components and "real" lignin, aiming to provide insights for lignin photocatalytic valorization from fundamental to industrial applications. Considering the complexity of lignin physicochemical properties, related analytic methods are also introduced to characterize lignin photocatalytic conversion and product distribution. We finally put forward the challenges and perspective of lignin photoreforming, hoping to provide some guidance to valorize biomass into value-added chemicals and fuels via a mild photoreforming process in the future.

Lignin-based nanomaterials for food and pharmaceutical applications: Recent trends and future outlook

Small particles of size ranging from 1 to 100 nm are referred to as nanoparticles. Nanoparticles have tremendous applications in various sectors, including the areas of food and pharmaceutics. They are being prepared from multiple natural sources widely. Lignin is one such source that deserves special mention due to its ecological compatibility, accessibility, abundance, and low cost. This amorphous heterogeneous phenolic polymer is the second most abundant molecule in nature after cellulose. Apart from being used as a biofuel source, lignin is less explored for its potential at a nano-level. In plants, lignin exhibits cross-linking structures with cellulose and hemicellulose. Numerous advancements have taken place in synthesizing nanolignins for manufacturing lignin-based materials to benefit from the untapped potential of lignin in high-value-added applications. Lignin and lignin-based nanoparticles have numerous applications, but in this review, we are mainly focusing on the applications in the food and pharmaceutical sectors. The exercise we undertake has great relevance as it helps scientists and industries gain valuable insights into lignin's capabilities and exploit its physical and chemical properties to facilitate the development of future lignin-based materials. We have summarized the available lignin resources and their potential in the food and pharmaceutical industries at various levels. This review attempts to understand various methods adopted for the preparation of nanolignin. Furthermore, the unique properties of nano-lignin-based materials and their applications in fields including the packaging industry, emulsions, nutrient delivery, drug delivery hydrogels, tissue engineering, and biomedical applications were well-discussed.

Enhancing cellulosic digestibility of wheat straw by adding sodium lignosulfonate and sodium hydroxide to hydrothermal pretreatment

Surfactant-assisted pretreatment has been widely reported to improve the enzymatic hydrolysis of lignocellulose by promoting removal of xylan and lignin. Hence, this work innovatively proposed the use of sodium lignosulfonate (SL) as an additive of alkaline pretreatment (AP), and evaluated its influence on the cellulosic digestibility of wheat straw (WS). The results displayed that the maximum of 72-h cellulosic digestibility could reach 83.5% as 15 g/L SL was introduced to the AP process (SAP), while the cellulosic digestibility of hydrothermal and alkaline pretreated WS was only 63.6% and 70.2%, respectively. These increments were subsequently attributed to the improvement of 6.5% xylan and 26.8% lignin accelerated by SAP, resulting in positive changes in structural characteristics such as accessibility, specific surface area, and cellulosic crystalline structure. The utilization of lignin-based surfactants in pretreatment has realized the economic feasibility of lignocellulosic biorefining and broadened the application prospect of surfactants.

Fabrication and application of amphiphilic polyoxometalate catalyst (CTA)nH5-nPMo10V2O40 for transformation of lignin into aromatic chemicals

Conversion of renewable lignin into bio-aromatic chemicals offers a sustainable pathway to increase biorefinery profitability. However, the catalytic transformation of lignin into monomers remains a highly challenging task due to the complexity and stability of the lignin structure. In this study, a series of micellar molybdovanadophosphoric polyoxometalate (POM) catalysts, (CTA)_nH_5-nPMo₁₀V₂O₄₀ (n = 1-5), were prepared by the ion exchange method and applied as oxidative catalysts for birch lignin depolymerization. These catalysts showed efficient cleavage of C-O/C-C bonds in lignin, and the introduction of an amphiphilic structure facilitated the generation of monomer products. The best catalytic activity was observed at 150 °C within 150 min under a 1.5 MPa oxygen atmosphere over (CTA)₁H₄PMo₁₀V₂O₄₀, which yielded a maximum lignin oil yield of 48.7 % and lignin monomer yield of 13.5 %. We also employed phenolic and nonphenolic lignin dimer model compounds to explore the reaction pathway and demonstrated the selective cleavage of CC and/or CO lignin bonds. Moreover, these micellar catalysts have excellent recyclability and stability as heterogeneous catalysts, which can be used up to five times. The application of amphiphilic polyoxometalate catalysts facilitates the valorization of lignin, and we expect to develop a novel and practical strategy for harvesting aromatic compounds.

Critical Techniques for Overcoming the Diffusion Limitations in Heterogeneously Catalytic Depolymerization of Lignin

Heterogeneously catalyzed depolymerization of lignin to value-added chemicals is increasingly attractive but highly challengeable. Particularly, the diffusion limitation of lignin macromolecule to the solid catalyst surface is a big barrier, which significantly decreases the yield of monomer while increasing char formation. Therefore, for the potential industrial utilization of lignin, new knowledge focused on the size of lignin particles is of great importance to offer guidance for promoting lignin depolymerization and suppressing condensation in the heterogeneously catalytic systems. In this Review, the size of lignin particles and macromolecules are summarized. Previous approaches for improving the mass diffusion including enhancing the solubility of lignin and exploitation of hierarchical and "solubilized" materials are also discussed. Based on these, a constructive perspective is proposed. Thus, this work provides a new insight on the rational design of heterogeneous catalytic techniques for efficient utilization of the aromatic polymer of lignin.

Thermal stability of extracted lignin from novel millet husk crop residue

Recent alarming tones regarding the environment and energy crises have resulted in an emergent need for the utilization of bio-based materials. The current study aims to experimentally investigate the thermal kinetics and pyrolysis behavior of lignin extracted from novel barnyard millet husk (L-BMH) and finger millet husk (L-FMH) crop residue. The characterization techniques FTIR, SEM, XRD, and EDX were employed. TGA was performed to assess the thermal, pyrolysis, and kinetic behavior using Friedman kinetic model. The average lignin yield was obtained as 16.25 % (L-FMH) and 21.31 % (L-BMH). The average activation energy (E_a) was recorded as 179.91-227.67 kJ mol^-1 for L-FMH while 158.50-274.46 kJ mol^-1 for L-BMH in the conversion range of 0.2-0.8. The higher heating value (HHV) was found to be 19.80 ± 0.09 MJ kg^-1 (L-FMH) and 19.65 ± 0.03 MJ kg^-1 (L-BMH). The results create a possibility for the valorization of extracted lignin in polymer composites as potential bio-based flame retardant in polymer composites.

Optimization of lignin extraction from bamboo by ultrasound-assisted organosolv pretreatment

For a sustainable biorefinery, reduction in the recalcitrance of lignocellulosic biomass is very crucial for the efficient utilization of each fraction. The present work investigated an integrated pretreatment method to recover high-quality lignin along with the cellulose-rich pulp. An optimization study employing response surface methodology investigated the synergistic effects of ultrasound and organosolv pretreatment from Bambusa tulda (bamboo). The optimal condition (180 °C, 55 min, and 30 min sonication) resulted in 65.81 ± 2.40% of lignin yield with 95.37 ± 1.17% purity. A reduction in 7.85% yield and 1.54% purity of lignin with organosolv pretreatment highlighted the efficacy of sonication in lignin extraction. Ultrasound resulted in homolytic cleavage of the lignin-carbohydrate bond that enhanced delignification and increase the cellulose crystallinity. NMR, FTIR, GPC, and TGA of lignin suggested the superiority of sonication in maintaining lignin quality. A significant amount of β-O-4 linkages in extracted lignin is favorable for its subsequent valorization.

Combined Catalysis: A Powerful Strategy for Engineering Multifunctional Sustainable Lignin-Based Materials

The production and engineering of sustainable materials through green chemistry will have a major role in our mission of transitioning to a more sustainable society. Here, combined catalysis, which is the integration of two or more catalytic cycles or activation modes, provides innovative chemical reactions and material properties efficiently, whereas the single catalytic cycle or activation mode alone fails in promoting a successful reaction. Polyphenolic lignin with its distinctive structural functions acts as an important template to create materials with versatile properties, such as being tough, antimicrobial, self-healing, adhesive, and environmentally adaptable. Sustainable lignin-based materials are generated by merging the catalytic cycle of the quinone-catechol redox reaction with free radical polymerization or oxidative decarboxylation reaction, which explores a wide range of metallic nanoparticles and metal ions as the catalysts. In this review, we present the recent work on engineering lignin-based multifunctional materials devised through combined catalysis. Despite the fruitful employment of this concept to material design and the fact that engineering has provided multifaceted materials able to solve a broad spectrum of challenges, we envision further exploration and expansion of this important concept in material science beyond the catalytic processes mentioned above. This could be accomplished by taking inspiration from organic synthesis where this concept has been successfully developed and implemented.

Sustainable Starch/Lignin Nanoparticle Composites Biofilms for Food Packaging Applications

Construction of sustainable composite biofilms from natural biopolymers are greatly promising for advanced packaging applications due to their biodegradable, biocompatible, and renewable properties. In this work, sustainable advanced food packaging films are developed by incorporating lignin nanoparticles (LNPs) as green nanofillers to starch films. This seamless combination of bio-nanofiller with biopolymer matrix is enabled by the uniform size of nanofillers and the strong interfacial hydrogen bonding. As a result, the as-prepared biocomposites exhibit enhanced mechanical properties, thermal stability, and antioxidant activity. Moreover, they also present outstanding ultraviolet (UV) irradiation shielding performance. As a proof of concept in the application of food packaging, we evaluate the effect of composite films on delaying oxidative deterioration of soybean oil. The results indicate our composite film could significantly decrease peroxide value (POV), saponification value (SV), and acid value (AV) to delay oxidation of soybean oil during storage. Overall, this work provides a simple and effective method for the preparation of starch-based films with enhanced antioxidant and barrier properties for advanced food packaging applications.

High-purity alkaline lignin extraction from Saccharum ravannae and optimization of lignin recovery through response surface methodology

Saccharum ravannae, known as "Ekra" in the Northeast region of India, is an elephant grass species that abundantly grows in the natural habitat of Assam. This study aims to utilize this wild grass species and extract alkaline lignin of high purity through KOH-mediated alkaline hydrothermal pretreatment using the Oil bath process. Lignin recovery was optimized using RSM (response surface methodology) combined with a central composite model. Three process parameters, namely KOH concentration (1-3 %), reaction time (50-200 min), and solid loading (5-15 %), varied to optimize the combined effect of these parameters. RSM predicted a maximum lignin recovery of 15.38 g/100 g of raw biomass at optimum conditions (2.4 % KOH, 6.41 % solid loading, 176.57 min). Three experimental runs were performed at optimum conditions, and 15.81 ± 0.32 g/100 g lignin recovery was obtained, thus verifying the predicted result. Maximum 93.7 % purity of extracted lignin was achieved in a different operating condition (3 % KOH, 10 % solid loading, 125 min). The commercial and extracted alkaline lignin with maximum purity was characterized by Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared Spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The extracted lignin shows higher phenolic content and more functional groups than commercial lignin and can be used for future applications.

Depolymerization of lignin using laccase from Bacillus sp. PCH94 for production of valuable chemicals: A sustainable approach for lignin valorization

Lignin is the most abundant aromatic polymer in nature, and its depolymerization offers excellent opportunities to develop renewable aromatic chemicals. In the present study, Bacillus sp. PCH94 was investigated for laccase production and lignin depolymerization. Maximum production of laccase enzyme was achieved within 6.0 h at 50 °C on a natural lignocellulosic substrate. Furthermore, Bacillus sp. PCH94 was used to bioconvert lignin dimeric and polymeric substrates, validated using FT-IR, NMR (¹H, ¹³C), and LCMS. Genome mining of Bacillus sp. PCH94 revealed laccase gene (lac^Bl) as multicopper oxidase (spore coat CotA). Further, lac^Bl from Bacillus sp. PCH94 was cloned, expressed, and kinetically characterized. Lac^Bl enzyme showed activity for substrates ABTS (40.64 IU/mg), guaiacol (5.43 IU/mg), and DMP (11.93 IU/mg). The Lac^Bl was active in higher temperatures (10 to 100 °C) and showed a half-life of 36 and 27 h at 50 and 60 °C, respectively. The purified Lac^Bl was able to depolymerize kraft lignin into valuable products (ferulic acid and acetovanillone), which have applications in the pharmaceutical and food industries. Overall, the current study demonstrated the role of bacterial laccase in the depolymerization of lignin and opened a promising prospect for the green production of valuable compounds from recalcitrant lignin.

Toward optimal use of biomass as carbon source for chemical bioproduction

Biomass is widely identified as a promising, renewable replacement for fossil feedstocks in the production of energy, fuels, and chemicals. However, the sustainable supply of biomass is limited. Economic and ecological criteria support prioritization of biomass as a carbon source for organic chemicals; however, utilization for energy currently dominates. Therefore, to optimize the use of available biomass feedstock, biorefining development must focus on high carbon efficiencies and enabling the conversion of all biomass fractions, including lignin and fermentation-derived CO₂. Additionally, novel technological platforms should allow the incorporation of nontraditional, currently underutilized carbon feedstocks (e.g. manure) into biorefining processes. To this end, funneling of waste feedstocks to a single product (e.g. methane) and subsequent conversion to chemicals is a promising approach.

Lignin-derived polyphenols with enhanced antioxidant activities by chemical demethylation and their structure-activity relationship

Lignin valorization to biobased polyphenols antioxidants is increasingly attractive in the modern industry due to their inherent phenolic structures. Herein, lignin-derived polyphenols with enhanced antioxidant activities were prepared from the most available technical lignin including organosolv lignin (OL), alkali lignin (AL), and enzyme lignin (EL) by iodocyclohexane (ICH) chemical demethylation. The structural evolution of lignin indicated that the C_Ar-OCH₃ group and the C_Ar-O-C_alkyl side-chain could be effectively transformed into the C_Ar-OH group, resulting in a significant increase of the phenolic-OH content and a slight decrease of the molecular weight. The 1,1-diphenyl-2-picrylhydrazyl radical (DPPH·) scavenging activity was in the order of ICHOL-24 > ICHAL-24 > ICHEL-24 ≈ FA > BHT, and the IC₅₀ value of ICHOL-24 was 0.56 times lower than that of BHT. The structure-activity relationship demonstrated the activities were quasi-linearly related to phenolic-OH contents and could be affected by molecular weights. The H/G/S proportions of lignin could be an indicator for accurate screening of efficient lignin-derived polyphenols antioxidants (LPA). It was preliminarily estimated to have economic feasibility for producing LPA from technical lignin by demethylation compared with synthetic or natural antioxidants. This work will help to develop efficient biobased antioxidants for lignin valorization.

FERONIA and wall-associated kinases coordinate defense induced by lignin modification in plant cell walls

Altering the content or composition of the cell wall polymer lignin is a favored approach to valorize lignin toward biomaterial and chemical production in the biorefinery. However, modifying lignin or cellulose in transgenic plants can induce expression of defense responses and negatively affect growth. Through genetic screening for suppressors of defense gene induction in the low lignin ccr1-3 mutant of Arabidopsis thaliana, we found that loss of function of the receptor-like kinase FERONIA, although not restoring growth, affected cell wall remodeling and blocked release of elicitor-active pectic polysaccharides as a result of the ccr1-3 mutation. Loss of function of multiple wall-associated kinases prevented perception of these elicitors. The elicitors are likely heterogeneous, with tri-galacturonic acid the smallest but not necessarily the most active component. Engineering of plant cell walls will require development of ways to bypass endogenous pectin signaling pathways.

Advanced (photo)electrocatalytic approaches to substitute the use of fossil fuels in chemical production

Electrification of the chemical industry for carbon-neutral production requires innovative (photo)electrocatalysis. This study highlights the contribution and discusses recent research projects in this area, which are relevant case examples to explore new directions but characterised by a little background research effort. It is organised into two main sections, where selected examples of innovative directions for electrocatalysis and photoelectrocatalysis are presented. The areas discussed include (i) new approaches to green energy or H2 vectors, (ii) the production of fertilisers directly from the air, (iii) the decoupling of the anodic and cathodic reactions in electrocatalytic or photoelectrocatalytic devices, (iv) the possibilities given by tandem/paired reactions in electrocatalytic devices, including the possibility to form the same product on both cathodic and anodic sides to "double" the efficiency, and (v) exploiting electrocatalytic cells to produce green H2 from biomass. The examples offer hits to expand current areas in electrocatalysis to accelerate the transformation to fossil-free chemical production.

Improvement of UV stability of thermoplastic starch matrix by addition of selected lignin fraction - Photooxidative degradation

This paper examines the additivation of thermoplastic starch (TPS) matrix by selected fractions of kraft lignin (KL) and correlates its structure-performance when exposed to photooxidative degradation. KL from Eucalyptus urograndis wood was refined by a sequential fractionation process in ethyl acetate (EtOAc). Films were prepared by mixing lignin fractions as additive in TPS matrix by casting and pressing. The lignin employed were KL, fraction of KL insoluble in EtOAc (INS) and fraction of KL soluble in EtOAc (SOL). The samples were exposed to accelerated aging with Ultraviolet-C light (UV-C) for 432 h. Structural changes were measured by FTIR (Fourier-Transform Infrared) spectra. Thermal properties, such as melting enthalpy, glass transition temperature and thermal decomposition, were evaluated by DSC (Differential Scanning Calorimetry) and TG (Thermogravimetry). Morphology of the films was obtained by SEM (Scanning Electron Microscopy). Surface property of wettability was measured by contact angle. Mechanical properties were explored before and after exposure to UV-C light. It was observed that the least photodegraded films were those resulting from the addition of the lignin fraction with higher phenolic hydroxyl group content. According to structural and morphological observations, the soluble fraction (TSOL) presented the highest photoprotection and stabilizing effect as an UV-C light blocker additive on TPS matrix.

A review on lignin-based epoxy resins: Lignin effects on their synthesis and properties

Lignin can be used as a sustainable alternative to bisphenol A (BPA) to prepared lignin-based epoxy resins. Lignin effects including molecular weight, phenolic content, G/S unit ratio and flexible/rigid linkage ratio on epoxy synthesis and performance were summarized comprehensively. The incorporation of lignin with a higher molecular weight would lead to the higher rigidity of epoxy crosslinking network. Higher contents of ether bonds in lignin would provide higher structural flexibility of lignin incorporated epoxy thermosets. Lignin with higher contents of phenolic hydroxyls was more beneficial for improving the reactivity of its epoxy products after glycidylation. Due to the excellent charring capacity of lignin, higher contents of residue char can be produced at higher additions of lignin at high temperatures, while the loss of crosslinking density caused by the increasing lignin addition (especially for the macromolecular lignin) would deteriorate the thermal stability of their thermosets. Several applications of lignin-based epoxy resins were also mentioned based on their mechanical, thermal and chemical properties, such as coatings (with anticorrosion and UV-blocking), adhesives (with highly crosslinking network, excellent mechanical, and thermal properties) and flame retardants (with high charring capability).