Structural and Compositional Characteristics of Technical Lignin Derived From Non‐Wood Biomass: Bagasse and Kash

The kraft-based dissolving pulp production process can be a model for the forest biorefinery concept. The objective of this study is to characterize the dissolved lignin present in the pre-hydrolysis liquor (PHL) to facilitate its subsequent use following the forest biorefinery concept. In this work, lignin was isolated from PHL by acidification using dilute H2SO4, followed by purification through dissolution in a dioxane solution (9:1) and re-precipitation with diethyl ether. The characteristics of PHL lignin were compared with those of the dioxane lignin, acetic acid (AA) lignin and ethanosolv (EL) lignin isolated from the same mixed hardwood (maple, poplar and birch wood chips, in a ratio of 7:2:1), which is the raw material used for dissolving pulp production. The obtained lignin samples were characterized by UV, FTIR, 1H-NMR spectroscopy, molecular weight determination, elemental and methoxyl analyses. The results showed that the absorptivity of dioxane lignin at 276 nm was 10.0 l g-1cm-1, while that of PHL lignin was 17.2 l g-1cm-1. The presence of condensed structures in the PHL lignin was also observed in the FTIR spectrum (strong bands at 870 and 890 cm-1), which was also present in the AA and EL lignins. The lignin isolated from PHL had a lower molecular weight and methoxyl group per C9 unit, in comparison with other lignin samples. 1H-NMR analysis indicated a significant increase in the phenolic hydroxyl content in the PHL lignin, caused by cleavage of aryl-ether bonds during the prehydrolysis. Keywords: PHL lignin, Dissolving pulp, Kraft pulping, Characteristics, Phenolic hydroxyl group, Molecular weight, Methoxyl group.

To study the behavior of hardwood sulfuric acid lignin (SAL) during phenolization, we compared the product yield, average molecular weight, methoxy content, and reactions of simple model compounds with those of softwood SAL, focusing on the difference between syringyl and guaiacyl units. The beech SAL reacted with phenol more readily than red pine SAL and yielded a larger soluble fraction of phenolized SAL. To investigate the difference in the phenolization activity of the syringyl and guaiacyl units in beech lignin, we prepared syringyl-nucleus-rich sulfuric acid lignin (S-rich-SAL) and guaiacyl-nucleus-rich sulfuric acid lignin (G-rich-SAL) from beech, which were subjected to phenolization. The results suggest that the syringyl unit in SAL had greater phenolization activity and its phenolized products were more soluble in acidic aqueous medium and introduced less phenol than the guaiacyl unit. Using model compounds, the study also showed that the syringyl unit had higher phenolization reactivity than the guaiacyl unit.

Structural characterization of technical lignins for the production of adhesives: Application to lignosulfonate, kraft, soda-anthraquinone, organosolv and ethanol process lignins

A comparative analysis has been made of the dioxane lignins of the stems, seedling shoots, and seed coats of the cotton plant. The ratio of p-hydroxyaromatic, guaiacyl, and syringyl units in the macromolecules of the lignins has been determined, and so have the amounts of functional groups and bonds. It has been established that the main difference between the dioxane lignins from seedling shoots and seed coats of the cotton plant, on the one hand, and the lignin from the woody stems, on the other hand is a lower content of syringyl and guaiacyl units in the former.

The distribution of guaiacyl and syringyl lignins in the secondary xylem tissues of normal and compression wood of Buxus microphylla var. insularis Nakai was examined by visible light (VL) microspectrophotometry coupled with the Mäule and Wiesner colour reactions and by UV -microspectrophotometry, and compared with normal wood of Betula ermani Cham. Buxus formed compression wood on the lower side of the leaning sterns, and the secondary walls of the vessels and fibre-tracheids showed excessive lignification, resembling the S2 (L) layer of compression wood tracheids in gymnosperms.In normal wood of both species, the Mäule colour reaction indicated that in Betula the secondary walls of fibres contain larger amounts of syringyl units in the lignins than other tissues, and that in Buxus the secondary walls of fibre-tracheids contain both syringyl and guaiacyl units. The vessel walls of both speeies contained higher amounts of guaiacyl units. Heterogeneity of the syringyl-Jignin distribution was found in the secondary walls of Buxus fibre-tracheids.In compression wood of Buxus, on the other hand, the spectra of the secondary walls of the vessels and fibretracheids after the Mäule reaction showed low absorbances compared with the normal wood, whereas, after the Wiesner reaction, their secondary walls gave high absorbances. In addition, the UV -absorption maximum of the secondary fibre walls shifted from 274 nm to 279 nrn, and the UV -absorbances of the vessei and fibre-tracheid walls greatly increased in compression wood. The results obtained in the present study demonstrated that in normal Buxus wood the secondary walls of the vessels and fibre-tracheids contain both guaiacyl and syringyl units, though the syringyl unit is a rninor constituent in the vessel walls, and that both cell types increase their contents of guaiacyl units, especially in the outer parts of the secondary walls during their changes from normal wood to compression wood. The present study also suggested that the Wiesner reaction may be used for examining the content of lignin and the proportion of guaiacyl to syringyl units in lignins.

The presented paper deals with some chemical properties of Caribean pine wood and bark lignin. In order to obtain necessary data, the following operations and analyses were performed: dioxane lignin isolations, determination of Klason lignin, determination of methoxyl, carboxyl and phenolic hydroxyl groups in dioxane lignins and the nitrobenzene oxidation of both compared lignins and of the risidues remaining after dioxane lignins extraction. The oxidation products were analysed by GLC. The experimental data show that there are moderate differences between compared lignins.

Artificial antioxidants are synthesized from fossil sources and are now widely used in the polymer, food, and cosmetics industries. The gradual depletion of fossil resources makes it practically significant and necessary to produce green antioxidants from renewable lignocellulosic resources. Herein, short-time hydrothermal (STH) treatment was developed for production of lignin-derived polyphenol antioxidants (LPAs) from poplar wood under conditions of high temperature and high pressure. LPA yields from 21.5 to 37.6 % on the basis of lignin in untreated wood were obtained by STH treatments as result of lignin depolymerization at 190-200 °C and 10 MPa in 5-8 min. Depolymerization reactions were confirmed by the much lower molecular weight of LPA (1076 g mol-1 ) than that of native lignin (4094 g mol-1 ). NMR spectroscopy revealed the structural features of lignin in the isolated LPA, namely syringyl and guaiacyl units with well-preserved interunit linkages. A Folin-Ciocalteu assay indicated that each LPA molecule contained 5.4 phenolic hydroxyl groups on average, much more than other technical lignins. The remarkable antioxidant ability of LPA was verified by the radical-scavenging index of 53.5-67.3, much higher than 0.2-11.1 of the commercial antioxidants butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA). STH treatment only requires water and heat for production of high-value antioxidant, which provides a green and sustainable method for the utilization of lignocelluloses.

Characterisation of lignins in straw, rumen liquor and faeces of sheep fed untreated and SO 2-treated wheat straw

Independent down-regulation of genes encoding p-coumarate 3-hydroxylase (C3H) and hydroxycinnamoyl CoA:shikimate/quinate hydroxycinnamoyl transferase (HCT) has been previously shown to reduce the recalcitrance of alfalfa and thereby improve the release of fermentable sugars during enzymatic hydrolysis. In this study, ball-milled lignins were isolated from wild-type control, C3H, and HCT gene down-regulated alfalfa plants. One- and two-dimensional nuclear magnetic resonance (NMR) techniques were utilized to determine structural changes in the ball-milled alfalfa lignins resulting from this genetic engineering. After C3H and HCT gene down-regulation, significant structural changes had occurred to the alfalfa ball-milled lignins compared to the wild-type control. A substantial increase in p-hydroxyphenyl units was observed in the transgenic alfalfa ball-milled lignins as well as a concomitant decrease in guaiacyl and syringyl units. Two-dimensional 13C–1H heteronuclear single quantum coherence correlation NMR, one-dimensional distortionless enhancement by polarization transfer-135, and 13C NMR measurement showed a noteworthy decrease in methoxyl group and β-O-4 linkage contents in these transgenic alfalfa lignins. 13C NMR analysis estimated that C3H gene down-regulation reduced the methoxyl content by ~55–58% in the ball-milled lignin, while HCT down-regulation decreased methoxyl content by ~73%. The gene down-regulated C3H and HCT transgenic alfalfa lignin was largely a p-hydroxyphenyl (H) rich type lignin. Compared to the wild-type plant, the C3H and HCT transgenic lines had an increase in relative abundance of phenylcoumaran and resinol in the ball-milled lignins.

The amount of hydroxyl groups, particularly phenolic, is one of the most important parameters in lignins, as it is an indicator of lignin reactivity. Ultraviolet (UV) Spectrophotometry is a simple and inexpensive method for determining phenolic hydroxyls in lignin. Ionization Difference Ultraviolet Spectrophotometry (Δe-method) relies on the analysis of solubilized lignin at neutral and alkaline conditions with a UV spectrophotometer. We added a slope analysis to the ∆e-method and dubbed the resulting method ∆e-IDUS (Ionization Difference UV Spectrophotometry). We assessed the reliability of ∆e-IDUS by studying the well-known Indulin AT lignin. Additionally, ∆e-IDUS was applied to a previously uncharacterized milox lignin. When compared to 13 C-NMR, ∆e-IDUS underestimated the amount of phenolic hydroxyls for Indulin AT, possibly due to neglecting second phenolic hydroxyls in some lignin units, which resist ionization because of steric hindrance. Nevertheless, the results agreed with previously reported values and confirm that ∆e-IDUS is useful to screen lignins based on their phenolic hydroxyl group content.

At present, more than 70 million tons per year of technical lignins are obtained from cellulose pulping and lignocellulosic refineries (e.g., kraft, lignosulfonates, soda, and organosolv lignin). These lignins are commonly incinerated to produce steam and energy, and only a small part is used as an additive in various low volume and niche applications, such as dispersant, in concrete admixtures, as an adhesive and as a binder. Furthermore, the potential of technical lignins is considered to be beyond that of an inexpensive fuel or raw material to produce low added value products. The technical lignins consist of complex polyphenolic polymers that contain numerous chemical functional groups, such as phenolic hydroxyl, carboxylic, carbonyl, and methoxyl groups. The phenolic hydroxyl and methoxyl groups present in lignin reportedly possess various biological activities. The amount of data describing the biological activities of technical lignins has increased in the last 10 years. This review presents the most relevant research concerning the various biological activities (antioxidant, antimicrobial, antimutagenic, and others) of technical lignins. Additionally, the most promising and relevant applications are highlighted.

At present, more than 70 million tons per year of technical lignins are obtained from cellulose pulping and lignocellulosic refineries (e.g., kraft, lignosulfonates, soda, and organosolv lignin). These lignins are commonly incinerated to produce steam and energy, and only a small part is used as an additive in various low volume and niche applications, such as dispersant, in concrete admixtures, as an adhesive and as a binder. Furthermore, the potential of technical lignins is considered to be beyond that of an inexpensive fuel or raw material to produce low added value products. The technical lignins consist of complex polyphenolic polymers that contain numerous chemical functional groups, such as phenolic hydroxyl, carboxylic, carbonyl, and methoxyl groups. The phenolic hydroxyl and methoxyl groups present in lignin reportedly possess various biological activities. The amount of data describing the biological activities of technical lignins has increased in the last 10 years. This review presents the most relevant research concerning the various biological activities (antioxidant, antimicrobial, antimutagenic, and others) of technical lignins. Additionally, the most promising and relevant applications are highlighted.

Lignin obtained from steam explosion of pine was fully characterized. Elemental analysis, GPC, and ultraviolet and 1H and 13C NMR spectra revealed that the obtained lignin contains both guaiacyl and syringyl units. Lignin was dissolved in acetonitrile-ethanol and treated with visible light in the presence of both oxygen and Rose Bengal for different irradiation times. Column chromatography of the residue showed the presence of six compounds: trans-sinapyl alcohol, 4-hydroxy-3,5-dimethoxybenzaldehyde, 4-hydroxy-3,5-dimethoxyphenylacetone, 4-hydroxy-3-methoxybenzaldehyde, cis-sinapyl alcohol, and sinapyl aldehyde. The total amount of fine chemicals increases with the irradiation time. However, it increases rapidly during the first eight hours, but increases slowly after this period. The most important compounds obtained were sinapyl alcohol and 4-hydroxy-3,5-dimethoxybenzaldehyde, but sinapyl alcohol was obtained in the highest amounts after eight hours' irradiation, while the highest amounts of 4-hydroxy-3,5-dimethoxybenzaldehyde were obtained after irradiation for 4 h. After 48 h irradiation comparable amounts of sinapyl aldehyde were obtained. We obtained only compounds derived from the syringyl units in lignin in agreement with the hypothesis that the guaiacyl units are more easily oxidised.

Dioxin lignin of Eucalyptus tereticornis kraft pulps and its oxygen-treated pulps with kappa number 21.32, 12.84; 13.03, 12.18 were isolated and subjected to alkaline nitrobenzene oxidation studies to determine the structural changes during oxygen bleaching. HPLC quantitatively identified eight compounds during nitrobenzene oxidation of dioxin lignin in alkaline media. Lignin obtained from E. tereticornis has syringyl and guaiacyl units. Residual lignin composition in pulps was studied and found that during oxygen delignification, the syringyl unit was degraded more in comparison to guaiacyl and p-hydroxy phenyl unit, i.e., the molar ratio of syringyl unit is lower than guaiacyl and p-hydroxy phenyl unit. The results are adequately described in the research.

Characterization and comparison of lignin derived from corncob residues to better understand its potential applications