Characterization and analysis of the molecular weight of lignin for biorefi ning studies (original) (raw)
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Recent innovations in analytical methods for the qualitative and quantitative assessment of lignin
Renewable and Sustainable Energy Reviews, 2015
As the attraction of creating biofuels and bio-based chemicals from lignocellulosic biomass has increased, researchers have been challenged with developing a better understanding of lignin structure, quantity and potential uses. Lignin has frequently been considered a waste-product from the deconstruction of plant cell walls, in attempts to isolate polysaccharides that can be hydrolyzed and fermented into fuel or other valuable commodities. In order to develop useful applications for lignin, accurate analytical instrumentation and methodologies are required to qualitatively and quantitatively assess, for example, what the structure of lignin looks like or how much lignin comprises a specific feedstock's cellular composition. During the past decade, various diverse strategies have been employed to elucidate the structure and composition of lignin. These techniques include using two-dimensional nuclear magnetic resonance to resolve overlapping spectral data, measuring biomass with vibrational spectroscopy to enable modeling of lignin content or monomeric ratios, methods to probe and quantify the linkages between lignin and polysaccharides, or refinements of established methods to provide higher throughput analyses, less use of consumables, etc. This review seeks to provide a comprehensive overview of many of the advancements achieved in evaluating key lignin attributes. Emphasis is placed on research endeavored in the last decade.
Accurate and Reproducible Determination of Lignin Molar Mass by Acetobromination
Journal of Agricultural and Food Chemistry, 2012
The accurate and reproducible determination of lignin molar mass by using size exclusion chromatography (SEC) is challenging. The lignin association effects, known to dominate underivatized lignins, have been thoroughly addressed by reaction with acetyl bromide in an excess of glacial acetic acid. The combination of a concerted acetylation with the introduction of bromine within the lignin alkyl side chains is thought to be responsible for the observed excellent solubilization characteristics acetobromination imparts to a variety of lignin samples. The proposed methodology was compared and contrasted to traditional lignin derivatization methods. In addition, side reactions that could possibly be induced under the acetobromination conditions were explored with native softwood (milled wood lignin, MWL) and technical (kraft) lignin. These efforts lend support toward the use of room temperature acetobromination being a facile, effective, and universal lignin derivatization medium proposed to be employed prior to SEC measurements.
Journal of Agricultural and Food Chemistry, 2001
Lignin content in plant samples was determined by using the spectrophotometric method acetyl bromide soluble lignin. As any spectrophotometric method, a reliable standard was required; in this project, lignin extracted with an acidic solution of dioxane was investigated as a possible standard for quantitatively determining lignin content in plant samples. Acidic dioxane lignins were analyzed for carbohydrate, total protein (these values were discounted from the dioxane lignin weight before building the calibration curve), nitrobenzene oxidation products, and for UV spectral characteristics. Total carbohydrate content of isolated lignins ranged from 2.21 to 5.70%, while protein ranged from 0.95 to 6.06% depending upon the plant source of the original cell wall sample. Nitrobenzene analysis indicated differences in amount of guaiacyl and syringyl units making up the lignins but this did not alter the UV spectrum of lignin solubilized in acetyl bromide. Regression equations developed for the acetyl bromide method using the isolated lignins for all the plant samples were similar to each other. Lignin values obtained by the acetyl bromide method were similar to the lignin values obtained as acid insoluble residues following a Klason lignin procedure.
Analysis of Lignin Using Qualitative and Quantitative Methods
2020
Lignin, the second richest biopolymer on earth, after cellulose and the primary deposition on the secondary cell wall structure of plants is composed of complex phenolic compounds. Its composition makes it an important natural renewable raw material for production of a number of commodity products. Lignin is also commercially produced as kraft lignin during paper manufacturing. Naturally occurring lignin plays significant biological role affecting plant growth, development, stress tolerance and adaptation. Keeping in view their commercial significance and biological role, much research has been directed towards determining the biosynthetic pathways of lignin and its qualitative and quantitative analysis. The present chapter discusses the structural features of lignin, the associated condensation and biosynthetic steps for lignin accumulation in plants, its biological functions and commercial significance. Additionally, the qualitative analysis techniques such as staining and microsc...
Toward a Better Understanding of the Lignin Isolation Process from Wood
Journal of Agricultural and Food Chemistry, 2006
The recently developed protocol for isolating enzymatic mild acidolysis lignins (EMAL) coupled with the novel combination of derivatization followed by reductive cleavage (DFRC) and quantitative 31 P NMR spectroscopy were used to better understand the lignin isolation process from wood. The EMAL protocol is shown to offer access at lignin samples that are more representative of the overall lignin present in milled wood. The combination of DFRC/ 31 P NMR provided a detailed picture on the effects of the isolation conditions on the lignin structure. More specifically, we have used vibratory and ball milling as the two methods of wood pulverization and have compared their effects on the lignin structures and molecular weights. Vibratory-milling conditions cause substantial lignin depolymerization. Lignin depolymerization occurs via the cleavage of uncondensed -aryl ether linkages, while condensed -aryl ethers and dibenzodioxocins were found to be resistant to such mechanical action. Condensation and side chain oxidations were induced mechanochemically under vibratory-milling conditions as evidenced by the increased amounts of condensed phenolic hydroxyl and carboxylic acid groups. Alternatively, the mild mechanical treatment offered by ball milling was found not to affect the isolated lignin macromolecular structure. However, the overall lignin yields were found to be compromised when the mechanical action was less intense, necessitating longer milling times under ball-milling conditions. As compared to other lignin preparations isolated from the same batch of milled wood, the yield of EMAL was about four times greater than the corresponding milled wood lignin (MWL) and about two times greater as compared to cellulolytic enzyme lignin (CEL). Molecular weight distribution analyses also pointed out that the EMAL protocol allows the isolation of lignin fractions that are not accessed by any other lignin isolation procedures.
Comparative Evaluation of Three Lignin Isolation Protocols for Various Wood Species
Journal of Agricultural and Food Chemistry, 2006
Milled wood lignin (MWL), cellulolytic enzyme lignin (CEL), and enzymatic mild acidolysis lignin (EMAL) were isolated from different wood species and characterized by various techniques. The EMAL protocol offered gravimetric lignin yields 2-5 times greater than those of the corresponding MWL and CEL. The purities of the EMALs were 3.75-10.6% higher than those of their corresponding CELs, depending upon the wood species from which they were isolated. Molecular weight analyses showed that the EMAL protocol isolates lignin fractions that are not accessed by the other procedures evaluated, while 31 P NMR spectroscopy revealed that MWL is more condensed and bears more phenolic hydroxyl groups than EMAL and CEL. The yields and purities of EMAL, MWL, and CEL from hardwood were greater than those obtained for the examined softwoods. Structural details obtained by DFRC (derivatization followed by reductive cleavage)/ 31 P NMR revealed different contents of condensed and uncondensed -O-aryl ether structures, dibenzodioxocins, and condensed and uncondensed phenolic hydroxyl and carboxylic acid groups within lignins isolated from different wood species.
Review Engineering Plant Biomass Lignin Content and Composition for
2015
Lignin is an aromatic biopolymer involved in providing structural support to plant cell walls. Compared to the other cell wall polymers, i.e., cellulose and hemicelluloses, lignin has been considered a hindrance in cellulosic bioethanol production due to the complexity involved in its separation from other polymers of various biomass feedstocks. Nevertheless, lignin is a potential source of valuable aromatic chemical compounds and upgradable building blocks. Though the biosynthetic pathway of lignin has been elucidated in great detail, the random nature of the polymerization (free radical coupling) process poses challenges for its depolymerization into valuable bioproducts. The absence of specific methodologies for lignin degradation represents an important opportunity for research and development. This review highlights research development in lignin biosynthesis, lignin genetic engineering and different biological and chemical means of depolymerization used to convert lignin into biofuels and bioproducts.
ANALYTICAL METHODS FOR LIGNIN CHARACTERIZATION.
Lignin characterisation is a very difficult task, if considering its diversity with respect to both origin and method of separation. The heterogeneity of lignin is caused by variations in polymer composition, size, crosslinking, functional groups, and linkage type between the phenyl propane monomers (p–hydroxy phenyl, guaiacyl and syringyl units). The elaboration of well-defined analytical methods for lignin characterization is very important for its industrial applications as a raw material. Two groups of lignin from woody species and annual fiber crops have been studied by FT-IR, UV, fluorescence and 13C NMR spectroscopy. The relative content of the different functional groups (p–hydroxy phenyl, guaiacyl and syringyl units) was appreciated by normalised intensities and deconvolution of the spectral bands. Correlation of the results provided by these methods allows the differentiation between the structural characteristics of the two lignin groups.