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Biomass Chemistry
Published in Jay J. Cheng, Biomass to Renewable Energy Processes, 2017
In chemical terms, lignin is defined as a highly cross-linked aromatic polymer of phenylpropane units with a molecular weight in excess of 10,000 units. There is considerable debate and research on the overall structure of lignin, and several models have been proposed. Biosynthesis of phenylpropane units, which are the fundamental building blocks of lignin, starts with the conversion of glucose into aromatic amino acids via the shikimic acid pathway. The cinnamic acid pathway then converts these amino acids into three distinct phenylpropane units: p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol. These phenylpropane compounds are called monolignols, as they are the fundamental units of lignin. The structures of these monolignols are shown in Figure 2.26.
Chemical Composition of Biomass
Published in Jean-Luc Wertz, Philippe Mengal, Serge Perez, Biomass in the Bioeconomy, 2023
Jean-Luc Wertz, Philippe Mengal, Serge Perez
Lignin is the generic term for a large group of aromatic polymers resulting from the oxidative combinatorial coupling of 4-hydroxyphenylpropanoids (monolignols).373839 It is the only naturally synthesized polymer with an aromatic backbone.40 The three most abundant monolignols are p-coumaryl (4-hydroxycinnamyl), coniferyl (3-methoxy 4-hydroxycinnamyl), and sinapyl (3,5-dimethoxy 4-hydroxycinnamyl) alcohols (Figure 5.14).
Structure and Biosynthesis of Lignin
Published in Jean-Luc Wertz, Magali Deleu, Séverine Coppée, Aurore Richel, Hemicelluloses and Lignin in Biorefineries, 2017
Jean-Luc Wertz, Magali Deleu, Séverine Coppée, Aurore Richel
During lignin deposition, monolignols are synthesized in the cytoplasm, translocated to the apoplast, and polymerized into lignin.7 Over the last two decades, the biosynthesis of monolignols has been a major focus of research on lignification. The monolignol biosynthetic pathway has been now relatively well elucidated, at least for angiosperms.
Spheronized drug microcarrier system from canola straw lignin
Published in Science and Technology of Advanced Materials, 2023
Liming Zhang, Antonia Svärd, Ulrica Edlund
Lignin is a vastly abundant yet widely underutilized renewable resource with high potential commercial value. However, its efficient utilization, either as a polymer or as a feedstock for lower molecular weight derivatives, is currently problematic because of the irregular morphology and inhomogeneity of lignin. Lignin is an irregularly branched polyphenolic polyether with three primary monolignol building blocks: p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol. Structural units are connected via different kinds of ether linkages (C-O-C) and aromatic/non-aromatic C – C bonds in the lignin polymer, which involve mainly guaiacyl (G) and syringyl (S) units, and, in some plants, smaller amounts of p-hydroxyphenyl (H). Lignin structure and composition vary depending on the biomass origin and extraction method. Grass lignins are quite different from lignin found in perennial plants, such as wood lignin [1]. Moreover, lignin is typically isolated from lignocellulosic biomass in the pulping industry, mostly used for energy recovery and yet a largely untapped byproduct of material valorization. The isolation processes alter the native structure, morphology, and particle size of lignin due to irreversible condensations and the cleavage of chemical linkages [2,3]. Such treatments complicate the structure of native heterogeneous lignins and alter molecular weight distributions.
Chemical pretreatment of corncob for the selective dissolution of hemicellulose and lignin: influence of pretreatment on the chemical, morphological and thermal features
Published in Biofuels, 2023
Alejandro Ramírez-Estrada, Violeta Y. Mena-Cervantes, Ignacio Elizalde-Martínez, Gabriel Pineda-Flores, Raúl Hernández-Altamirano
The lignin content in the raw corncob was 18.6%, and after acid pretreatment, it increased to 31.4% in the solid-AC fraction. However, there was only a low 3.2% percent of dissolution, indicating that significant lignin dissolution did not occur. This is likely because the aromatic groups and aryl-alkyl ether bonds of lignin are insoluble in acidic solutions, resulting in the majority of the lignin remaining in the solid fraction. On the other hand, the percentage of lignin in the solid-ALK fraction decreases to 18.6%, in comparison to 31.4% in Solid-AC fraction. The percent of lignin dissolution, after alkaline pretreatment, was 60.4%, indicating that the alkaline pretreatment is a fairly effective method for removing lignin. Lignin is soluble in alkaline solution due to the presence of phenolic hydroxyl groups on its monolignol units. When lignin is exposed to an alkaline solution, the hydroxyl groups ionize and become negatively charged. These negative charges repel each other, causing the lignin polymer to break apart and dissolve in the solution [53]. It was found that the percentage total of raw lignin dissolution (i.e. the lignin of raw corncob) was 63.3%. Zhang et al. [54] pre-treated corncob with H2SO4 (2% wt.) and NaOH (2% wt.) and obtained the cellulose content of 90–92% after pre-treatment and efficacy of 75% for lignin removal. Sunkar et al. [46] found that 2% NaOH at 55 °C for 4 h lead to a maximum delignification of 83.12%. Zhang et al. [54] revealed 81% delignification when the acid hydrolyzed residue was pretreated with 2% NaOH at 80 °C.
Biocoatings and additives as promising candidates for ultralow friction systems
Published in Green Chemistry Letters and Reviews, 2021
Marcia Gabriely A. da Cruz, Tetyana M. Budnyak, Bruno V. M. Rodrigues, Serhiy Budnyk, Adam Slabon
Lignin is one of the major components in structural cell walls of higher vascular plants and it is considered the main renewable source of aromatics in nature. Large quantities of technical lignins are annually generated from pulping, paper, and biorefinery industries (113, 114). Unlike cellulose, lignin is a heterogeneous and amorphous phenylpropanoid macromolecule, mainly composed of monolignol derived moieties, e.g. syringyl (S), guaiacyl (G), and p-hydroxyphenyl (H) units, linked together to form a complex three-dimensional structure (Figure 7) (73, 113). The macromolecular arrangement of lignin differs according to the biomass feedstock and isolation process. Regarding the monomer composition and content of inter-unit types of linkages, phenolic hydroxyl, alcoholic hydroxyl, carbonyl, carboxyl, methoxyl, and conjugated double bonds are the common factor among all of them (94, 95, 113).