Biopolymer Lignin Research Articles

Catalytic Hydrogenolysis of Lignin into Serviceable Products.

ConspectusLignin, a major component of lignocellulosic biomass, accounts for nearly 30% of organic carbon on Earth, making it the most abundant renewable source of aromatic carbon. The valorization of lignin beyond low-value heat and power has been one of the foremost challenges for a long time. On the other hand, aromatic compounds, constituting a substantial segment of the chemical industry and projected to reach a market value of $382 billion by 2030, are predominantly derived from fossil resources, contributing to increased CO2 emissions. Integrating lignin into the aromatic chemical supply chain will offer a promising strategy to reduce the carbon footprint and boost the economic viability of biorefineries. Thus, depolymerizing lignin biopolymers into aromatic chemicals suitable for downstream processing is an important starting point for its valorization. However, owing to lignin's complexity and heterogeneity, achieving efficient and selective depolymerization that yields desirable, isolable aromatic monomers remains a significant scientific challenge.The structure of lignins varies significantly in terms of subunits and linkages across plant species, leading to considerable differences in their reactivity, in the distribution of resulting monomers, and in their subsequent utilization. In this context, this Account highlights our recent studies on the catalytic hydrogenolysis of lignin into serviceable products for preparing valuable materials, fuels, and chemicals. First, we designed a series of catalytic systems for lignin hydrogenolysis specifically tailored to the structural features of lignin from wood, grass, and certain seed coats. To reduce reliance on expensive commercial catalysts like Pd/C, Ru/C, and Pt/C, we advanced heterogeneous metal catalysts by shifting from high-loaded nanostructured metals to low-loaded, atomically dispersed metals and replacing precious metals with nonprecious alternatives. This approach significantly reduces the cost of catalysts, enhances their atomic economy, and improves their catalytic activity and/or selectivity. Then, using the developed catalysts, phenolic monomers tethering a distinct side chain were selectively generated from the hydrogenolysis of lignin (from various plants), achieving yields close to the theoretical maximum. The high selectivity allowed the separation and purification of monomeric phenols from lignin reaction mixtures readily. To gain deeper insights into the cleavage of lignin C-O bonds, we designed deuterium-incorporated β-O-4 mimics (dimers and one polymer) for a mechanistic study, which excluded the pathways involving the loss of linkage protons and led to the proposal of a concerted hydrogenolysis process for β-O-4 cleavage. Finally, to enable the utilization of depolymerized lignin phenolic monomers, unconventional feedstocks in the current chemical industry, we developed a series of methods to transform them into valuable bioactive molecules, functional materials, and high-energy fuels. Overall, these contributions opened new avenues for converting lignin into serviceable products, encompassing upstream processing and downstream applications.

Effect of Various Stabilizers on the Characteristics of a Nitrate Esters-Double Base Propellant under Thermal Aging

ABSTRACT The current study examined the stabilizing effect of lignin biopolymer in comparison to traditional 2-nitrodiphenylamine (2-NDPA) and 1,3-Dimethyl-1,3-diphenylurea (C-II) stabilizers on the stability of double-base nitrocellulose (NC)/diethylene glycol dinitrate (DEGDN) propellant during artificial aging (at 338.65 K for 60 days). Various spectroscopic techniques, including Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction (XRD), were used, along with traditional stability tests like the Bergmann-Junk (BJ) test and isothermal thermogravimetric analysis (TGA). Experimental results confirmed that FTIR and XRD provided valuable insights into chemical changes during aging. Particularly, lignin-stabilized NC/DEGDN exhibited comparable stability to C-II and 2-NDPA at all stages of aging, as evidenced by the amount of the released nitrous gases measured by BJ test and thermal stability assessed by TGA. Additionally, multivariate data analysis using principal component analysis (PCA) of FTIR spectra successfully differentiated between aged and unaged samples and highlighted trends in stability. Overall, the findings suggest that lignin offers a comparable stabilizing effect for NC/DEGDN propellants relative to traditional stabilizers.

Аэрогели на основе диоксида кремния и лигносульфоната

Currently, there is considerable interest in the synthesis of aerogels based on natural polymers. The use of biopolymers is due to their physical and chemical properties, availability, non-toxicity, and the renewable nature of the raw materials needed for their production. These characteristics are possessed by lignosulfonates – sulfonates of the natural biopolymer lignin, formed as a result of sulfite (bisulfite) delignification of wood. Composite aerogel materials attract special attention by combining the properties of both organic and inorganic components. The incorporation of biopolymers into the matrix of nanocomposite aerogels can improve their consumer properties. The aim of this work has been the synthesis of aerogels based on silicon dioxide and sodium lignosulfonate, the study of gelation in the “sodium lignosulfonate – silicon dioxide” system and the assessment of the influence of synthesis conditions on the formation of the structure of aerogel materials based on them. Hydrogels based on components of various chemical natures of sodium lignosulfonate and silicon dioxide, have been obtained by sol-gel synthesis. It has been shown that strong elastic gels are formed at silicon dioxide concentrations above 175 g/l. It has been established that modification of sodium lignosulfonates with silicon dioxide leads to particle aggregation and an increase in their size. Aerogel materials based on sodium lignosulfonate and silicon dioxide, obtained at different molar ratios of componets (the mass fraction of lignosulfonate in the system), have a developed inner surface, the specific surface area is 250...452 m2/g, the total pore volume varies from 0.84 to 2.00 cm3/g. It has been shown that with an increase in the mass fraction of lignosulfonate in the system, the textural characteristics of synthesized composite aerogel materials change: an increase in the specific surface area and pore volume of the obtained materials is observed. With a sodium lignosulfonate content of 6…25 % in the system, the specific surface area of composite aerogels is 250…325 m2/g; with an increase in the proportion of sodium lignosulfonate in the system to 33...50 %, it reaches 357…452 m2/g. The synthesized materials can be used as sorbents, sensor devices, and catalyst carriers.

Assessing the Impact of Various Industrial Wastes on the Volumetric and Mechanical Properties of Warm Mix Asphalt (WMA)

In recent decades, sustainable practices in pavement construction have been studied to promote circular economy principles and protect the environment. This research seeks to determine the potential benefits of using three different industrial waste materials in formulating warm mix asphalt (WMA). WMA mixes were prepared using ground granulated blast furnace slag (GGBFS) from steel production and biomass fly ash (FA) from the paper industry as virgin filler replacement, and an industrial waste rich in lignin biopolymer (LB) from the hardboard industry as a partial substitute for binder. The study analyzed their volumetric and mechanical properties, including moisture damage resistance, resilient modulus, fatigue resistance, permanent deformation, and abrasion resistance, which were compared with those of a control WMA mix (without any waste). The findings provide insights into an important gap in the literature on the use of GGBFS and LB in WMA. GGBFS-2 mix (75% GGBFS) exhibited the best fatigue performance but the highest axial deformation and rut depth. LB-1 mix (5% LB) performed slightly worse than the optimum control WMA in all tests.

Morphological and dynamic mechanical properties of biobased epoxy composites with anisotropic, green carbon aerogels as reinforcement

Hierarchically porous, anisotropic, and green carbon aerogels (CAs) prepared from second most abundant and underutilized biopolymer lignin is used together with biobased epoxy resin to prepare green composite materials with superior mechanical properties. Green and facile preparation route involving ice-templating, lyophilization followed by carbonization was followed for the preparation of CAs. Ice-templating cooling rate is an important parameter in determining the porous structure of the CAs and by choosing a slower cooling rate bigger macropores can be achieved which facilitate the capillary impregnation of the epoxy resin through the CA structure. Hence in this study a cooling rate of 5 K/min was used and the CAs were prepared at 1000 °C from lignin/CNF suspensions containing 3, 5 and 7 wt% of total solid contents. Composites prepared using these CAs as reinforcements showed interesting morphologies which were analyzed using scanning electron microscopy and X-Ray microtomography. Prepared composites contained a mass fraction of 5–9 wt% of CAs. Composites showed remarkable 72 % higher dynamic mechanical properties compared to neat epoxy. Thus, this study introduces new synthesis strategy for carbon composites with completely biobased anisotropic CAs as oriented and strong reinforcements.

Modeling the Production Process of Lignin Nanoparticles Through Anti-Solvent Precipitation for Properties Prediction.

Global warming has recently intensified research interest in renewable polymer chemistry, with significant attention directed towards lignin nanoparticle (LNP) synthesis. Despite progress, LNP industrial application faces challenges: (1) reliance on kraft lignin from declining raw biomass processes, (2) sulfur-rich and condensed lignin use, (3) complex lignin macroparticles to LNP conversion, using harmful and toxic solvents, and, above all, (4) lack of control over the LNP production process (i.e., anti-solvent precipitation parameters), resulting in excessive variability in properties. In this work, eco-friendly LNPs with tailored properties were produced from a semi-industrial organosolv process by studying anti-solvent precipitation variables. Using first a parametric and then a Fractional Factorial Design, predictions of LNP sizes and size distribution, as well as zeta-potential, were derived from a model over beech by-products organosolv lignin, depending on initial lignin concentration (x1, g/L), solvent flow rate (x2, mL/min), antisolvent composition (x3, H2O/EtOH v/v), antisolvent ratio (x4, solvent/antisolvent v/v), and antisolvent stirring speed (x5, rpm). This novel chemical engineering approach holds promise for overcoming the challenges inherent in industrial lignin nanoparticle production, thereby accelerating the valorization of lignin biopolymers for high value-added applications such as cosmetics (sunscreen or emulsion) and medicine (encapsulation, nanocarriers), a process currently constrained by significant limitations.

Formation of Nanodiamonds during Pyrolysis of Butanosolv Lignin.

The preparation of artificial diamonds has a long history driven by decreased costs compared to naturally occurring diamonds and ethical issues. However, fabrication of diamonds in the laboratory from readily available biomass has not been extensively investigated. This work demonstrates a convenient method for producing nanodiamonds from biopolymer lignin at ambient pressure. Lignin was extracted from Douglas Fir sawdust using a butanosolv pretreatment and was pyrolyzed in N2 at 1000 °C, followed by a second thermal treatment in 5% H2/Ar at 1050 °C, both at ambient pressure. This led to the formation of nanodiamonds embedded in an amorphous carbon substrate. The changes occurring at various stages of the pyrolysis process were monitored by scanning electron microscopy, Fourier transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy. High resolution transmission electron microscopy revealed that nanodiamond crystallites, 4 nm in diameter on average, formed via multiple nucleation events in some carbon-containing high density spheres. It is proposed that highly defected graphene-like flakes form during the pyrolysis of lignin as an intermediate phase. These flakes are more deformable with more localized π electrons in comparison with graphene and join together face-to-face in different manners to form cubic or hexagonal nanodiamonds. This proposed mechanism for the formation of nanodiamonds is relevant to the future fabrication of diamonds from biomass under relatively mild conditions.

Development of CuS/C composite for microwave absorption using lignin biopolymer

In recent decades, electronic devices have become a crucial component of everyday life and an increasingly important aspect of national security. However, despite their convenience, the emission of electromagnetic (EM) radiation from these devices has created a pollution issue that demands urgent attention. In this study, the properties and performance of CuS/C composites as EM wave-absorbing materials were examined. The main technique employed involved modifying the surface structure and properties of a lignin biopolymer via a fiber laser to derive porous carbon as a microwave absorber in the X-band range. Flower-like CuS microspheres were integrated into the porous carbon to improve the electrical conductivity and promote internal reflections. In addition, multilayer microwave absorbers were developed using CuS/C/epoxy composites with varying weight percentages, which were fabricated through refluxing and annealing techniques. The return losses of the absorbers in single- and multi-layer modes were optimized by modified local particle swarm optimization (MLPSO). The minimum average return loss improved to −15 dB (96.8%) by optimization in the 4-layer mode with a thickness of 1.8 mm. The optimum absorption peak in the 3-layer structure was −54.52 dB at a frequency of 8.83 GHz. The shielding effectiveness assessments indicated that the CuS/C/epoxy composite significantly improved the shielding capabilities of porous C and CuS, resulting in an increase of the shielding effectiveness threshold (SET) from less than 2 dB in lignin to more than 10 dB in CuS/C/epoxy.

Unveiling the mechanism of triphos-Ru catalysed C–O bond disconnections in polymers

Ruthenium complexes with facially coordinating tripodal phosphine ligands are privileged catalysts for a broad range of (de-)hydrogenation-based transformations. Among these, C–O bond hydrogenolysis holds potential for the depolymerisation of both the biopolymer lignin and epoxy resins applied in wind turbine blades, aircrafts and more. However, this methodology is poorly understood in mechanistic terms. Here, we present a detailed investigation on the triphos-Ru catalysed C–O bond scission on a molecular level. A combination of experimental, spectroscopical and theoretical studies elucidates the reactivity of the ruthenium trimethylenemethane precatalyst, revealing the key roles of ruthenium phenolates in both catalyst activation as well as the catalytic cycle itself. Furthermore, a Ru(0)/Ru(II) oxidative addition into the C–O bond is disclosed, with a triphos-Ru(0) dihydrogen complex as entry point. With the molecular nature of the operating triphos-Ru species and the thermodynamics and kinetics of the catalysis unravelled, improvements of established methods as well as design of related transformations may become possible.

The Impact of Lignin Biopolymer Sources, Isolation, and Size Reduction from the Macro- to Nanoscale on the Performances of Next-Generation Sunscreen.

In recent years, concerns about the harmful effects of synthetic UV filters on the environment have highlighted the need for natural sun blockers. Lignin, the most abundant aromatic renewable biopolymer on Earth, is a promising candidate for next-generation sunscreen due to its inherent UV absorbance and its green, biodegradable, and biocompatible properties. Lignin's limitations, such as its dark color and poor dispersity, can be overcome by reducing particle size to the nanoscale, enhancing UV protection and formulation. In this study, 100-200 nm lignin nanoparticles (LNPs) were prepared from various biomass by-products (hardwood, softwood, and herbaceous material) using an eco-friendly anti-solvent precipitation method. Pure lignin macroparticles (LMPs) were extracted from beech, spruce, and wheat straw using an ethanol-organosolv treatment and compared with sulfur-rich kraft lignin (KL). Sunscreen lotions made from these LMPs and LNPs at various concentrations demonstrated novel UV-shielding properties based on biomass source and particle size. The results showed that transitioning from the macro- to nanoscale increased the sun protection factor (SPF) by at least 2.5 times, with the best results improving the SPF from 7.5 to 42 for wheat straw LMPs and LNPs at 5 wt%. This study underscores lignin's potential in developing high-quality green sunscreens, aligning with green chemistry principles.

One-pot molten strategy to synthesize tough bio-derived lignin-based photothermal elastomers for photoelectric driven and programmable shape memory

Utilizing renewable biomass as an alternative to petroleum-based products for the development of smart materials emerges as a pivotal strategy for sustainable development. However, the straightforward, rapid, and cost-effective deployment of biomass for novel smart material synthesis remains a formidable challenge. Herein, we employ a facile solvent-free one-pot strategy to develop a multifunctional smart biomass photothermal elastomer, which synthesized from the natural small molecule of α-lipoic acid (LA) and renewable lignin biopolymer without any chemical modification. The incorporation of lignin confers to the obtained elastomers superior mechanical strength, photothermal responsiveness, photothermal self-healing, and adhesive capabilities. Notably, the photothermal elastomers can be fully recycled and reused by simple thermal remodeling. As a proof of concept, the temperature difference generator can be driven to generate electricity utilizing the excellent photothermal effect of elastomers, highlighting its excellent light-heat-electricity conversion capability. Intriguingly, the photothermal elastomers exhibit light-driven shape memory effect, enabling to grasp objects by shape-programmed four-arm soft gripper under selective irradiation. This pioneering work not only demonstrates significant progress in high-value utilization of bio-derived lignin, but also opens up a new avenue for sustainable and innovative applications in advanced energy management devices and soft actuators.

Novel sustainable corrosion inhibitors for enhancing carbon steel corrosion resistance based on clay and lignin biopolymer extracted from raw Alfa fibers

Novel sustainable corrosion inhibitors for enhancing carbon steel corrosion resistance based on clay and lignin biopolymer extracted from raw Alfa fibers

Characterization of vinyl ester–based biocomposites using grape stalk lignin biopolymer and Celosia cristata stem fibers: a characterization study

Characterization of vinyl ester–based biocomposites using grape stalk lignin biopolymer and Celosia cristata stem fibers: a characterization study

Mitigation of Soil Erosion and Enhancement of Slope Stability through the Utilization of Lignin Biopolymer.

Human activities have had a profound impact on the environment, particularly in relation to surface erosion and landslides. These processes, which are natural phenomena, have been exacerbated by human actions, leading to detrimental consequences for ecosystems, communities, and the overall health of the planet. The use of lignin (LIG) as a biopolymer soil additive material is regarded as an eco-friendly solution against soil erosion and slope failure which holds immense promise. However, significant research gaps currently hinder a comprehensive understanding of its mechanisms and effectiveness. Experimental studies offer a robust platform to address these gaps by providing controlled conditions for assessing soil stability, exploring mechanisms, and evaluating adaptability. Bridging these research gaps will contribute to the development of innovative and sustainable strategies for mitigating soil erosion and preventing slope failure, thereby promoting environmental resilience and resource conservation. This study aimed to investigate the effect of the LIG biopolymer on mitigation of soil erosion, slope failure and the enhancement of soil strength by conducting laboratory tests (UU triaxial, unconfined compressive strength (UCS), and soaking) as well as flume experiments under uniform rainfall events. The alterations in the engineering characteristics and erosion resistance of silty soil mixed with a LIG additive at concentrations of 1% and 3.0% by weight have been examined. The results show that the LIG-treated samples demonstrated an enhanced resistance to surface erosion and an enhanced prevention of slope failure, as well as improved shear stress, cohesion, stiffness, and resistance to water infiltration.

Dimensionally stable and durable wood by lignin impregnation

Cracking, warping, and decaying stemming from wood's poor dimensional stability and durability are the most annoying issues of natural wood. There is an urgent need to address these issues, of which, sustainable and green chemical treatments are favorably welcomed. Herein, we developed a facile method through the incorporation of environmentally friendly biopolymer lignin into wood cells for wood dimensional stability and durability enhancement. Enzymatic hydrolysis lignin (EHL) was dissolved into various solvents followed by impregnation and drying to incorporate lignin into wood cells. Impregnation treatment was developed to incorporate into wood to improve its dimensional stability, durability, and micromechanics. The anti-swelling efficiency reached up to 99.4 %, the moisture absorption decreased down to 0.55 %, the mass loss after brown rot decay decreased to 7.22 %, and the cell wall elasticity as well as hardness increased 8.7 % and 10.3 %, respectively. Analyses acquired from scanning electron microscopy, fluorescent microscopy, and Raman imaging revealed that the EHL was successfully colonized in cell lumen as well as in cell walls, thus improved wood dimensional stability and durability. Moreover, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy confirmed EHL interaction with the cell wall components, thus the wood mechanical property was not impaired significantly, whereas nanoindentation data indicated even slight mechanical enhancement on the cell walls. This facile approach can improve the wood properties in multiple aspects and remarkably enhance the outdoor performance of modified wood products. In addition, using lignin as a natural modifying agent to improve wood performance will have a great positive impact on the environment.

Efficient isomerization of glucose to fructose over Al-loaded functional lignin biopolymer

Al-loaded functional lignin biopolymer (Alx-Lbp) catalysts were synthesized using H2O2 oxidized alkali lignin and aluminum acetate via mechanochemical modification without post-calcination treatment. The Alx-Lbp catalysts exhibited higher hydrophilicity and lower surface energy than lignin-free Al-activated carbon catalysts. Unprecedented high yields (58.5 %) of fructose from glucose were obtained over Al1-Lbp in ethanol at 140 ºC in 30 min reaction time. Al1-Lbp catalyst had Lewis acid sites (47.2 μmol/g), Brønsted acid sites (6.9 μmol/g) and a surface energy of 39.1 mN/m that facilitated glucopyranose ring-opening and gave a glucose isomerization activation energy of 65.2 kJ/mol, which was lower than values reported for Lewis acid-catalyzed systems. Active sites of Al2O3 and Al(OH)3 formed on the Al1-Lbp catalyst in ethanol promoted the formation of an enediol intermediate as confirmed with isotope experiments to achieve efficient isomerization of glucose to fructose. The Al1-Lbp catalyst demonstrated recyclability and maintained its initial activity for eight times reuse.

Harnessing Atomically Dispersed Cobalt for the Reductive Catalytic Fractionation of Lignocellulose.

The reductive catalytic fractionation (RCF) of lignocellulose, considering lignin valorization at design time, has demonstrated the entire utilization of all lignocellulose components; however, such processes always require catalysts based on precious metals or high-loaded nonprecious metals. Herein, the study develops an ultra-low loaded, atomically dispersed cobalt catalyst, which displays an exceptional performance in the RCF of lignocellulose. An approximately theoretical maximum yield of phenolic monomers (48.3 wt.%) from lignin is realized, rivaling precious metal catalysts. High selectivity toward 4-propyl-substituted guaiacol/syringol facilitates their purification and follows syntheses of highly adhesive polyesters. Lignin nanoparticles (LNPs) are generated by simple treatment of the obtained phenolic dimers and oligomers. RCF-resulted carbohydrate pulp are more obedient to enzymatic hydrolysis. Experimental studies on lignin model compounds reveal the concerted cleavage of Cα-O and Cβ-O pathway for the rupture of β-O-4 structure. Overall, the approach involves valorizing products derived from lignin biopolymer, providing the opportunity for the comprehensive utilization of all components within lignocellulose.

Retraction Note: Recent advances and future perspectives of lignin biopolymers

Retraction Note: Recent advances and future perspectives of lignin biopolymers

Eco-friendly conversion between n- and p-type carbon nanotubes based on rationally functionalized lignin biopolymers

We strategically modify lignin as effective p- and n-dopants for nanocarbon materials, offering promising alternatives to chemical dopants from fossil-fuels.

Assessment of the effect of lignin biopolymer on the thermal stability of energetic nitrocellulose/diethylene glycol dinitrate composite

AbstractThis study explored the stability and thermo‐kinetic features of double base nitrocellulose (NC)/diethylene glycol dinitrate (DEGDN) propellant supplemented with Kraft lignin. For this purpose, the impact of 2‐nitrodiphenylamine (2‐NDPA), 1,3‐dimethyl‐1,3‐diphenylurea (C‐II) and lignin stabilizers on the molecular structure, morphology, and thermokinetic behavior of NC/DEGDN composite were thoroughly analyzed. Experimental results showed that lignin exhibits promising stabilizing efficiency comparable to that of the conventional 2‐NDPA and C‐II. In addition, thermal findings highlighted that the incorporation of 2‐NDPA, C‐II, and lignin has improved the thermal decomposition temperature of NC/DEGDN propellant. The investigation of the thermolysis kinetics of stabilized NC/DEGDN composites demonstrated an increase in the Arrhenius parameters with respect to the NC/DEGDN baseline. Above all, this investigation contributes to the ongoing efforts to develop new environmentally friendly stabilizers for nitrate esters‐based composites.