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Structures of monolignols: p-coumaryl alcohol (H), coniferyl alcohol (G), and sinapyl alcohol (S)

Structures of monolignols: p-coumaryl alcohol (H), coniferyl alcohol (G), and sinapyl alcohol (S)

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With today’s environmental concerns and the diminishing supply of the world’s petroleum-based chemicals and materials, much focus has been directed toward alternative sources. Woody biomass presents a promising option due to its sheer abundance, renewability, and biodegradability. Lignin, a highly irregular polyphenolic compound, is one of the majo...

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... Lignin is composed of phenolic hydroxyl groups and aliphatic hydroxyl groups, and the catechol structure can be obtained through various modification methods, including physical and chemical treatments [30][31][32]. Liu et al. [33] synthesized lignin with a catechol structure through demethylation. They developed a bio-based adhesive by combining lignin, copper ions, and soy protein, resulting in enhanced water resistance and the reduced viscosity of the produced adhesive. ...
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Soybean meal (SM) adhesive is widely acknowledged as a viable substitute for traditional formaldehyde-based adhesives, given its ability to be easily modified, the utilization of renewable sources, and its eco-friendly characteristics. However, the application of SM adhesive in manufacturing has been impeded due to its restricted bonding capacity and inadequate water resistance. Researchers in the wood industry have recognized the significance of creating an SM-based adhesive, which possesses remarkable adhesive strength and resistance to water. This study endeavors to tackle the issue of inadequate water resistance in SM adhesives. Sodium lignosulfonate (L) was oxidized using hydrogen peroxide (HP) to oxidized lignin (OL) with a quinone structure. OL was then used as a modifier, being blended with SM to prepare SM-based biomass (OLS) adhesives with good water resistance, which was found practically through its utilization in the production of plywood. The influence of the HP dosage and OL addition on plywood properties was examined. The changes in the lignin structure before and after oxidation were confirmed using gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). The curing behavior and thermal stability of OLS adhesives were analyzed using dynamic mechanical analysis (DMA) and thermogravimetric (TG) analysis. The reaction mechanism was also investigated using FT-IR and XPS. The outcomes indicated a decrease in the molecular weight of L after oxidation using HP, and, at the same time, quinone and aldehyde functionalized structures were produced. As a result of the reaction between the quinone and aldehyde groups in OL with the amino groups in SM, a dense network structure formed, enhancing the water resistance of the adhesive significantly. The adhesive displayed exceptional resistance to water when the HP dosage was set at 10% of L and the OL addition was 10% based on the mass of SM. These specific conditions led to a notable enhancement in the wet bonding strength (63 °C, 3 h) of the plywood prepared using the adhesive, reaching 0.88 ± 0.14 MPa. This value represents a remarkable 125.6% increase when compared to the pure SM adhesive (0.39 ± 0.02 MPa). The findings from this study introduce a novel approach for developing adhesives that exhibit exceptional water resistance.
... The challenge lies in dealing with the complexity and variability of lignin's structure, which affects its reactivity and the quality of the resulting biofuels. Advances in catalysis, genetic engineering, and process engineering are contributing to overcoming these challenges and improving the feasibility of lignin-based biofuel production [28][29] . ...
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With increased emphasis on Sustainable Development Goals, Green Economy, Green Energy, Green Chemistry etc it has become imperative for the industrial sectors including pulp and paper to adopt appropriate green/ecofriendly technologies to reduce the energy and environmental footprint. In recent years, biotechnological application has gradually gained acceptability in pulp and paper industry in process operation as well as environmental management. Tailormade enzymatic applications or solutions are now available to reduce chemical consumption, energy consumption, slime formation etc during pulping and paper making process as well as improve product quality. Similarly improved microbial consortiums are now available which has not only reduced/eliminated the chemicals or nutrients requirement in conventional activated sludge process but has also reduced energy consumption required to decompose the organic matter leading to reduced operational costs. Similarly increased interest in installation of biomethanation plants by agro based paper mills can also be attributed to availability of improved microbial consortium with improved shock loading bearing capacity and improved performance efficiency in terms of pollution reduction and biogas generation. In context of RCF based kraft paper mills operating on Zero Liquid Discharge (ZLD), enzymatic applications can play a vital role in reducing the build-up of pollution load including VFA in closed loop as well reducing the Odor in product and environment as well as reduce adverse impact on product quality. To address to raw material shortage, biotechnological application in developing fast growing, high yield, disease resistant tree clonal plantations by R&D institutes as well as leading paper mills have already contributed not only in addressing raw material issues to a major extent but also has contributed significantly in promoting social/agro forestry leading to improvement in rural economy as well as green cover. Conversion of lignin, into value added products and biofuels is a potential area for biotechnological applications with lot of promise specially from circular economy point of view. The paper summarizes the biotechnology routes, techniques available as well as research being carried out in this area so as to contribute to making paper industry environmentally sustainable.
... Lignin is found in vascular plants, together with cellulose and hemicellulose, forming the main structure of the plant skeleton [21][22][23]. Lignin is an amorphous and structurally complex natural Lignin, the primary biobased resource with aromatic structures, is increasingly recognized as a raw material for advanced materials. ...
... Lignin accounts for about 15 to 40% of the dry basis weight of lignocellulosic biomass materials, and is the second largest renewable biomass resource only compared with cellulose [6][7][8]. The pulp and paper and cellulosic ethanol industries produce lignin on the scale of millions of tons each year as a by-product, rich in reserves [9]. Lignin is a kind of aromatic natural high molecular compound, and its basic structural unit is phenylpropane, which contains phenolic hydroxyl, alcohol hydroxyl, carboxyl, methoxy groups, and other functional groups. ...
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... They produce and use enzymes such as laccases, peroxidases such as lignin peroxidase (LiP), manganese peroxidase (MnP), secreted by hyphae, and degrade lignin by oxidative depolymerization [10]. Laccase is capable of catalyze the mono-electronic oxidation of organic substrates, as lignin, while concomitantly reducing molecular oxygen to water [11]. White-rot fungi have received more attention in studies of lignin degradation, as they have a very efficient enzyme system degrading lignin [12]. ...
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... In addition, these depolymerization processes would need highenergy consumption steps such as the pretreatment of lignocellulose. Mushroom ligninolytic enzymes could be potential biocatalysts for the initial depolymerization step, combined with mild condition extraction by organosolv or ionic liquid from lignocellulose [164,165]. Mushroom ligninolytic enzymes are secreted proteins including laccases, LiPs, MnPs, VPs, and other oxidases, in the solid-state fermentation [37]. The enzymatic processes with secreted oxidase proteomes for lignin depolymerization from the solid phase of lignocellulosic biomass could reduce energy consumption and byproducts. ...
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... Lignin, a highly irregular, amorphous, and cross-linked biopolymer [12,13], is composed of three phenylpropanoid units, namely p-coumaryl alcohol (H units), coniferyl alcohol (G units), and sinapyl alcohol (S units), and various functional groups [14][15][16][17], which constitute a highly polar, complex, and heterogeneous biomacromolecule with a large quantity of hydroxyl (-OH) by the random permutation of units and groups that are linked to the major interunit linkages including β-O-4, α-O-4, β-5, β-β, 5-5, β-1, and 4-O-5 [18,19]. The diversity and complexity of lignin and the interconnected structure give rise to the low degree of compatibility and reactivity. ...
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... It is an extremely valuable biopolymer and a renewable resource, but today only 2% of the total lignin extracted is exploited for value-added products, while the rest of it is mostly burned for low-cost energy production. 1 Therefore, there is a need for lignin utilization in the production of value-added materials to make the biorefinery process more profitable. Thanks to advances in valorization of each renewable component of the lignocellulosic biomass, new marketable products are being developed. ...
... Thanks to advances in valorization of each renewable component of the lignocellulosic biomass, new marketable products are being developed. 1,2 Using enzymes to modify lignin-based structures avoids the use of toxic chemicals, thus providing a valid biotechnological approach. 1 Laccases belong to a very broad and diverse superfamily of multicopper oxidases (MCOs): they generally contain a cluster of four copper atoms, which constitute their active site. ...
... 1,2 Using enzymes to modify lignin-based structures avoids the use of toxic chemicals, thus providing a valid biotechnological approach. 1 Laccases belong to a very broad and diverse superfamily of multicopper oxidases (MCOs): they generally contain a cluster of four copper atoms, which constitute their active site. Thanks to their natural origin, nontoxicity, mild operating conditions in which they are active, and the very broad range of oxidized substrates, fungal enzymes like laccases are very valuable tools for industrial applications. ...
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... As one of the main components of this biomass, lignin presents an aromatic backbone, making it the most important renewable source of aromatic structures, elucidating the intensive research activities worldwide. In their native forms, lignin appears to be complex, apparently unordered structures, where the different units, involving coumaryl, coniferyl, and sinapyl [11], are connected by ethers or condensed C-C bonds [12,13]. In recent years, the development of high-performance lignin-based functional materials has attracted comprehensive attention, possessing properties such as antibacterial, antioxidant, or UV-absorbance [14]. ...
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Lignin, a natural amorphous three-dimensional aromatic polymer, is investigated as an appropriate filler for biocomposites. The chemical modification of firsthand lignin is an effective pathway to accomplish acetoacetate functional groups replacing polar hydroxyl (–OH) groups, which capacitates lignin to possess better miscibility with poly(lactic acid) (PLA), compared with acidified lignin (Ac-lignin) and butyric lignin (By-lignin), for the sake of blending with poly(lactic acid) (PLA) to constitute a new biopolymer based composites. Generally speaking, the characterization of all PLA composites has been performed taking advantage of Fourier transform infrared (FTIR), scanning electron microscopy (SEM), dynamic Mechanical analysis (DMA), differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), rheological analysis, and tensile test. Visibly, it is significant to highlight that the existence of acetoacetate functional groups enhances the miscibility, interfacial compatibility, and interface interaction between acetoacetate lignin (At-lignin) and PLA. Identical conclusions were obtained in this study where PLA/At-lignin biocomposites furthest maintain the tensile strength of pure PLA.