Molecular Weight Lignin Research Articles

The effect of ionic liquid cation and anion combinations on the macromolecular structure of lignins

Imidazolium based ionic liquids (ILs) composed of anions such as chloride, acetate and alkyl phosphate have come to be considered as effective non-derivatizing solvents for cellulose, lignin and lignocellulosic biomass. After dissolution and thermal treatment of three technical lignins (organosolv, alkali and alkali low sulphonate) with an array of ILs, it was shown that these solvents behave as either reactants or catalysts, significantly reducing the molecular mass of these macromolecules and altering their structure. The degree of lignin structural modification is shown to be primarily influenced by the anion. Lignin fragmentation mechanisms were defined and a fragmentation hierarchy of the lignin macromolecule as a function of the IL anion was established. It was determined that sulfates > lactate > acetate > chlorides > phosphates in terms of the relative impact on reducing lignin molecular weight, with evidence of different anions causing cleavage of different linkages within the lignin. Of the ILs studied, sulfate based ionic liquids most comprehensively broke down the largest lignin molecules, resulting in fragments >1000–3000 u (by polysaccharide calibration). The lactate anion, while appearing less capable of breaking down the largest lignin molecules, causes the formation of significant quantities of the smallest sized fragments observed (2000–500 u). The new lower molecular mass species formed from the organosolv lignin are shown to have a more highly conjugated structure than their parent molecules, while a reduction in conjugation was observed in the alkali lignins. Using size exclusion chromatography coupled with UV detection, at least 40% of the original large-lignin molecules, from each of the lignins studied, were observed to remained intact. We hypothesize that fragmentation is effected either viacatalytic means or through nucleophilic attack of inter-lignin β-O-bonds.

Increase in 4-Coumaryl Alcohol Units during Lignification in Alfalfa (Medicago sativa) Alters the Extractability and Molecular Weight of Lignin

The lignin content of biomass can impact the ease and cost of biomass processing. Lignin reduction through breeding and genetic modification therefore has potential to reduce costs in biomass-processing industries (e.g. pulp and paper, forage, and lignocellulosic ethanol). We investigated compositional changes in two low-lignin alfalfa (Medicago sativa) lines with antisense down-regulation of p-coumarate 3-hydroxylase (C3H) or hydroxycinnamoyl-CoA:shikimate hydroxycinnamoyltransferase (HCT). We investigated whether the difference in reactivity during lignification of 4-coumaryl alcohol (H) monomers versus the naturally dominant sinapyl alcohol and coniferyl alcohol lignin monomers alters the lignin structure. Sequential base extraction readily reduced the H monomer content of the transgenic lines, leaving a residual lignin greatly enriched in H subunits; the extraction profile highlighted the difference between the control and transgenic lines. Gel permeation chromatography of isolated ball-milled lignin indicated significant changes in the weight average molecular weight distribution of the control versus transgenic lines (CTR1a, 6000; C3H4a, 5500; C3H9a, 4000; and HCT30a, 4000).

Biological effects of high molecular weight lignin derivatives

A number of high molecular weight (HMW) lignin derivatives possessing varied chemical properties were screened for their biological effects in order to obtain more information on the possible structural features of HMW lignin-related effects. The studied compounds were both commercial and in-house extracted lignin derivatives. Bioassays used include reverse electron transport (RET), Vibrio fischeri, Daphnia magna, and juvenile rainbow trout ( Oncorhynchus mykiss) hepatocytes. The studied lignin derivatives inhibited the in vitro systems and luminescence of V. fischeri bacteria to some extent–daphnids were not affected. It seems that, at least in the RET assay, certain pH-dependent functional groups in lignin may be of importance regarding the biological effects.

Comparison of XAD with other dissolved lignin isolation techniques and a compilation of analytical improvements for the analysis of lignin in aquatic settings

This manuscript highlights numerous incremental improvements in dissolved lignin measurements over the nearly three decades since CuO oxidation of lignin phenols was first adapted for environmental samples. Intercomparison of the recovery efficiency of three common lignin phenol concentration and isolation techniques, namely XAD, C18 with both CH3OH (C18M) and CH3CN (C18A) used independently for priming and elution steps, and tangential flow filtration (TFF) for a range of aquatic samples including fresh, estuarine and marine waters, was undertaken. With freshwater samples XAD8-1, C18M and TFF were all observed to recover ca. 80–90% of the lignin phenols and showed no fractionation effects with respect to diagnostic lignin parameters. With estuarine and marine samples more lignin phenols were recovered with C18M and XAD8-1 than TFF because of the increased prevalence of low molecular weight lignin phenols in marine influenced samples. For marine systems, differences were also observed between diagnostic lignin parameters isolated via TFF vs. C18M and XAD8-1 as a result of the high molecular weight lignin phenols being less degraded than the bulk. Therefore, it is recommended for future studies of marine systems that only one technique is utilized for ease of intercomparison within studies. It is suggested that for studies solely aimed at recovering bulk dissolved lignin in marine environments that C18M and XAD8-1 appear to be more suitable than TFF as they recover more lignin. Our results highlight that, for freshwater samples, all three common lignin phenol concentration and isolation techniques are comparable to whole water concentrated by rotary evaporation (i.e. not isolated) but, that for marine systems, the choice of concentration and isolation techniques needs to be taken into consideration with respect to both lignin concentration and diagnostic parameters. Finally, as the study highlights XAD8-1 to be a suitable method for the isolation of dissolved lignin phenols from aquatic systems (statistically indistinguishable from C18M, P < 0.1), lignin data representative of whole waters can be produced for IHSS reference materials or other XAD sample archives.

Fractionating lignocellulose by formic acid: Characterization of major components

Abstract Treatment of corn (Zea mays L.) cob under mild reaction conditions (60 °C and atmospheric pressure) in 88% formic acid was an effective method for separating cellulose from hemicellulose and lignin components in lignocellulose. Most of the hemicellulose degradation and lignin removal occurred within the first 90 min. After 6 h treatment, the decomposition of hemicellulose and the recovery of lignin were over 85% and 70%, respectively. Multi-level structures of lignin and solid residues were further characterized by FTIR, XRD, TG/DTG, SEM and SEC. Peaks attributable to lignin or hemicellulose disappeared in FTIR spectra, indicating complete removal of these two components. The remaining solid residues had a higher crystalline index. The major pyrolysis temperature of corncob was increased after formic acid treatment; the molecular weight (MW) of cellulose in solid residues was higher than that in intact cobs, whereas the hemicellulose remaining in the pulp had a lower MW than the original. Lignin was extracted in an esterified form designated as formic acid lignin (FAL). FAL had two thermal decomposition temperatures (Td) at 277 °C and 385 °C. The MW of lignin increased following formic acid treatment, which may make it a better starting material for chemical syntheses.

Natural Lignans as Adhesives for Cellulose: Computational Interaction Energy vs Experimental Results

Comparison between the molecular mechanics calculated energy of interaction of lignan dimers and trimers with a cellulose I crystallite and the experimental values of Young's modulus obtained by thermomechanical analysis (TMA) of cellulose paper impregnated with low molecular weight lignins showed good correlation between calculated and experimental results. The oligomer composition of the four low molecular weight lignins tested was obtained by MALDI-TOF mass spectrometry. This showed that these lignins were predominantly composed of dimers and trimers rendering them ideal for correlation testing. The lignan/cellulose crystallite interaction energy is determined by the oligomer molecular weight as well as the type of linkage within the lignan oligomers. Lignans with higher molecular weight in which the units are linked as β–O–4 give interaction energy values indicating stronger attraction with cellulose.

Combined organosolv and ultrafiltration lignocellulosic biorefinery process

Non-woody lignocellulosic feedstock (Miscanthus sinensis L.) was fractionated by a biorefinery process to obtain cellulose, different molecular weight lignin fractions and an hemicelluloses enriched liquor following economically and environmentally sustainable criteria. An integrated process composed by ethanol organosolv pre-treatment followed by a membrane ultrafiltration system was used to extract the different fractions. Products physico-chemical characterization (FTIR, GPC, 1H NMR) was done to evaluate their potential possible industrial applications. Obtained experimental data were used to develop a simulation of the process using Aspen Plus software in order to establish mass and energy balances and optimize the process in terms of yield, solvent recovery and energy consumption. Finally, production costs of the obtained ultrafiltrated lignin were estimated resulting in 52 €/tonne of lignin for the studied process conditions.

Soda–AQ delignification of poplar wood. Part 1: Reaction mechanism and pulp properties

Abstract Soda and soda-anthraquinone (AQ) pulpings of poplar (Populus deltoides) wood performed in a flow-through reactor gives rise to the formation of coniferyl alcohol (1) sinapyl alcohol (2) and other low molecular weight (LMW) compounds in different stages of delignification. During the heating-up period, the formation of these compounds increases until the maximum pulping temperature (t max, 170°C) is reached. Afterward, their concentration in the spent liquor decreases sharply. This effect is accompanied by solubilization of high molecular weight (HMW) lignin fractions. Compared with soda pulping, the soda-AQ pulping shows a higher production of LMW compounds because of the presence of AQ-anthrahydroquinone (AHQ) redox system. During the heating-up period, the formation of 1 and 2 – apparently originated from non-etherified β-aryl-ether moieties in the lignin – is accompanied by solubilization of lignin fragments with relative LMW. Lignin cores, having β-aryl-ether bonds as major hydrolyzable inter-unit linkages, remain in the fiber, and they give rise to solubilized lignin fragments with HMW at later delignification stages. The dissolved fragments, in particular those formed during heating-up period, undergo further degradation in the liquor. The degradation occurs via oligomers at the end of the pulping, while the residual lignin cores are more resistant. Pulps with low kappa number can be produced by maintaining higher alkali concentrations than the usual in the last delignification phase. When the pulping liquor is replaced in this stage with liquors of higher alkali concentration, extended delignification will be the result. As a consequence, less degraded lignin fragments will be deposited on fibers.

Biodegradation of high molecular weight lignin under sulfate reducing conditions: Lignin degradability and degradation by-products

This study is designed to investigate the biodegradation of high molecular weight (HMW) lignin under sulfate reducing conditions. With a continuously mesophilic operated reactor in the presence of co-substrates of cellulose, the changes in HMW lignin concentration and chemical structure were analyzed. The acid precipitable polymeric lignin (APPL) and lignin monomers, which are known as degradation by-products, were isolated and detected. The results showed that HMW lignin decreased and showed a maximum degradation capacity of 3.49 mg/l/day. APPL was confirmed as a polymeric degradation by-product and was accumulated in accordance with HMW lignin reduction. We also observed non-linear accumulation of aromatic lignin monomers such as hydrocinnamic acid. Through our experimental results, it was determined that HMW lignin, when provided with a co-substrate of cellulose, is biodegraded through production of APPL and aromatic monomers under anaerobic sulfate reducing conditions with a co-substrate of cellulose.

Membrane extraction for removal of acetic acid from biomass hydrolysates

Production of bioethanol from lignocellulosic biomass requires pretreatment of the biomass in order to improve the susceptibility of the cellulose to enzymatic hydrolysis to glucose. When dilute acid is used to perform this process, the hemicellulose is also hydrolyzed to its component sugars while simultaneously releasing acetyl groups attached to the hemicellulose backbone. Other compounds from the lignin and sugar degradation products are also produced that inhibit subsequent bioconversion of the solubilized sugars to the desired products. In this work we focused on removal of acetic acid from a dilute sulphuric acid pretreated corn stover hydrolysate. Acetic acid has been extracted into an organic phase at pH values below its p K a. The organic phase diluent consisted of octanol. Alamine 336, a tertiary amine and Aliquat 336 a quaternary amine were used as the aliphatic amine extractants. Our results indicate more than 60% removal of acetic acid using Alamine 336. Extraction rates were much slower for Aliquat 336 probably due to the higher viscosity of the Aliquat 336/octanol phase. The presence of sulphate anions, as a result of dilute sulphuric acid pretreatment, results in the co-extraction of bisulphate anion. Bisulphate anion is preferentially extracted at pH values below its p K a. Consequently the pH of the hydrolysate increases from between 1 and 2 to above 4.0 during extraction. In addition, extraction of low molecular weight lignins and phenolics is also observed. Thus the membrane extraction process developed here may be used not only for removal of acetic acid but also to adjust the pH of the hydrolysate to values that are more compatible for fermentation and to remove other inhibitory compounds.

Plant Defense Proteins

Plants are compelled to withstand stresses of all kinds, be it biotic, abiotic or anthropogenic as a consequence of their immobility. The initial infection process involving adhesion/recognition events between plants and fungal pathogens is essential for the establishment of pathogenesis. The extracellular matrix (ECM) is a biologically active part of the cell surface composed of a complex mixture of macromolecules that, in addition to serving a structural function, profoundly affect the cellular physiology of the organism. During the past two decades it has become evident that the cell wall is a dynamic organization that is essential for cell division, enlargement and differentiation as well as responding to biotic and abiotic stress. ECM is also the source of signals for cell recognition within the same or between different organisms. Cell walls are natural composite structures, mostly made up of high molecular weight polysaccharides, proteins and lignins. Lignins are only found in specific cell types. Arabidopsis thaliana cell wall proteins (CWP) that can be involved in modifications of cell wall components, wall structure and signaling as well as interactions with plasma membrane proteins at the cell surface has been reviewed.

FUNGAL-INDUCED REDISTRIBUTION OF KRAFT LIGNIN MOLECULAR WEIGHT BY MULTI-ANGLE LASER LIGHT SCATTERING

Culture broths from Phanerochaete chrysosporium and Trametes cingulata, combined with co-factors such as hydrogen peroxide, dithiothreitol, copper, iron, and manganese ions were examined for the ability to modify lignin structure. High-performance size exclusion chromatography (HP-SEC) coupled to multi-angle laser light scattering (MALLS) detection was used to determine the effect of several white rot fungi, pH values, enzymes, and co-factors on the molecular weight distribution of treated kraft lignin. The analytical procedure tracked changes in molecular weight distribution, radius of gyration, and hydrodynamic radius. Results showed changes in the molecular weight distribution of lignin components when treated with combinations of factors. The induced cultures showed more lignin depolymerization for the specific lignin samples in which they were initially grown. The distribution in the radius of gyration became narrower with time, indicating that molecular conformation changed to a more uniform molecular shape. H2O2 and DTT showed the most significant changes in lignin molecular weight distribution.

Toward a Better Understanding of the Lignin Isolation Process from Wood

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 beta-aryl ether linkages, while condensed beta-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.

Structural changes in lignin during the deinking of old newsprint with laccase–violuric acid system

Old newsprint (ONP) could be deinked with laccase–violuric acid system (LVS). To study the mechanism of LVS deinking, lignins from the control and LVS-deinked pulp were isolated and characterized by chemical, spectroscopic and chromatographic methods. The molecular weight change of lignin was tracked by gel permeation chromatogram (GPC), and structural changes in lignin extracted from the control and LVS-deinked pulps were characterized by elemental analysis, functional groups measurement, FT-IR, 1H NMR and 1H– 13C correlation 2D NMR. The experimental results showed that the molecular weight of lignin from LVS-deinked pulp was lower than that of lignin from the control pulp. The contents of free phenolic hydroxyl groups and methoxyl groups of lignin from LVS-deinked pulp decreased, while the contents of carboxyl and carbonyl groups increased. Guaiacyl units in lignin were oxidized by LVS. Stilbene and 5–5′ substructures in lignin were stable to LVS treatment, while β-O-4 and β–β substructures were partially destroyed during the LVS deinking. According to structural changes in lignin, the mechanism of LVS deinking was deduced.

Effect of low molecular weight lignin fragments including oxalic acid in alkaline-oxygen stage waste liquor on Al toxicity

Our previous study indicated the existence of some low molecular weight contaminants in separated fractions (F1 to F4) of alkaline-oxygen stage waste liquor by spectroscopic analysis. In the present study, the quantities of these compounds were determined by capillary electropheresis (CE). Substantial amounts of oxalate and acetate were found in F3. The complexes between Al and oxalate as well as F3 were characterized by 27Al-nuclear magnetic resonance (NMR) spectroscopy, and the spectra of Al-oxalate complexes demonstrated the ability of oxalate to chelate Al and to produce different forms of complexes at varied molar ratios. Plant growth experiments in the presence of Al-oxalate complexes suggested that at a proper range, oxalate has a favorable effect on the detoxification of Al toxicity. It can be assumed that oxalate in F3 also plays an important role in the efficiency of removing Al toxicity. 27Al-NMR was proved to be a useful method for the study of complexes between Al and organic compounds without disturbing their equilibrium conditions.

Scission of the Lactyl Ether Bond of N-Acetylmuramic Acid by Escherichia coli “Etherase”

The ubiquitous bacterial cell wall sugar N-acetylmuramic acid (MurNAc) carries a unique D-lactyl ether substituent at the C3 position. Recently, we proposed an etherase capable of cleaving this lactyl ether to be part of the novel bacterial MurNAc dissimilation pathway (Dahl, U., Jaeger, T., Nguyen, B. T., Sattler, J. M., Mayer, C. (2004) J. Bacteriol. 186, 2385-2392). Here, we report the identification of the first known MurNAc etherase. The encoding gene murQ is located at 55 min on the Escherichia coli chromosome adjacent to murP, the MurNAc-specific phosphotransferase system. A murQ deletion mutant could not grow on MurNAc as the sole source of carbon and energy but could be complemented by expressing murQ from a plasmid. The mutant had no obvious phenotype when grown on different carbon sources but accumulated MurNAc 6-phosphate at millimolar concentrations from externally supplied MurNAc. Purified MurQ-His6 fusion protein and extracts of cells expressing murQ both catalyze the cleavage of MurNAc 6-phosphate, with GlcNAc 6-phosphate and D-lactate being the primary products. The 18O label from enriched water is incorporated into the sugar molecule, showing that the C3-O bond is cleaved and reformed by the enzyme. Moreover, an intermediate was detected and identified as an unsaturated sugar molecule. Based on this observation, we suggested a lyase-type mechanism (beta-elimination/hydration) for the cleavage of the lactyl ether bond of MurNAc 6-phosphate. Close homologs of murQ were found on the chromosome of several bacteria, and amino acid sequence similarity with the N-terminal domain of human glucokinase-regulatory protein (GckR or GKRP) was recognized.

Modeling of vanillin production in a structured bubble column reactor

Vanillin is an important flavour. Semi-synthetic vanillin can be produced by the oxidation of lignin. Experimental studies leading to vanillin production in a batch reactor and a structured bubble column reactor (SBCR) lead us to the conclusion that the SBCR could have non-idealities such as dispersion. The radial and axial liquid-phase dispersion within the packed criss-crossing sandwich structures of Mellapak-750Y had been studied. A 2D model accounting for axial and radial velocities and dispersion was formulated and solved. The model predictions were compared with that of an experimental residence time distribution curve. The axial dispersion coefficient of the liquid phase is of the same order of magnitude as the radial dispersion coefficient. The reaction kinetics available in literature is adopted for the present study. Model for the SBCR was formulated and simulated using commercial modeling software. Simulation experiments were conducted in a SBCR. The effect of the following parameters on the yield of vanillin is studied: lignin concentration, lignin molecular weight, oxygen partial pressure and reaction temperature. It can be said that lignin molecular weight is a crucial parameter in vanillin production.

Lignin–polymer blends: evaluation of compatibility by image analysis

This paper opens onto a general discussion on the development of new polymeric materials obtained from lignin blends. The aim is ( i) to look for good polymer candidates to obtain a good compatibility with lignins (that is among semi polar polymers), and ( ii) to look for good lignin candidates to obtain a good compatibility with polymers showing extreme behaviours (very polar, e.g. starch, or apolar, e.g. polypropylene). The compatibility is simply assessed through the blend morphology, as studied by visible microscopy. The morphology of the blends obtained from semi polar polymers is very sensitive to the variation of the solubility parameters. In a low range of polymer solubility parameters ( Δ δ = 1 cal cm − 3 ) , both heterogeneous and homogeneous systems are obtained. These blends could be easily improved by a careful choice in the polymer structure (particularly in the family of biodegradable polyesters); it could be possible also to take advantage of lignin variability to improve the compatibility. Only low molecular weight lignins are compatible with apolar and very polar matrixes. These compounds induce interesting specific properties, and original methods have to be looked for in order to improve their production. To cite this article: C. Pouteau et al., C. R. Biologies 327 (2004).

Continuous nano- and ultra-filtration of kraft pulping black liquor with ceramic filters: A method for lowering the load on the recovery boiler while generating valuable side-products

Ceramic membranes coated with ZrO 2 were used for the continuous separation of a well-defined low molecular weight lignin from softwood and hardwood kraft black liquors on a pilot scale. The membranes used had M w cut-offs of 1000, 5000, and 15,000 Da, respectively. The flux (permeate flow) through the different membranes measured as L/(m 2·h) was studied by varying the inlet pressure and temperature. The black liquor lignins in the permeate from the filters were isolated and studied with GPC and UV spectroscopy. The low molecular weight lignin fraction was highly phenolic and could be polymerised by one-electron oxidation.

Synthesis and characterisation of polyurethanes derived from waste black liquor lignin

Waste black liquor lignin, obtained from bagasse from the small-scale paper industry, can be utilized for the synthesis of polyurethanes (PUs). Several polyurethane samples were prepared from laboratory black liquor (LBL) by reacting varying amounts of lignin ranging from 5 to 70% (w/v) in poly(ethylene glycol) (PEG) (having molecular weights of 200, 600, 1000, 1500 and 4000) with tolylene 2,4-diisocyanate (TDI). The effects of lignin concentration and molecular weight of PEG on mechanical and thermal properties of PUs obtained were investigated. The polyurethanes synthesised were characterized for different properties such as shear strength, adhesion and thermal stability. The shear strength of PU joints with aluminum was found to decrease with increase in both lignin concentration and molecular weight of PEG. Maximum shear strength, i.e. 3.6 N/mm2, was shown by 50% (w/v) lignin in PEG of molecular weight 200.