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Spherical lignin particles offer a versatile platform for the development of advanced materials based on renewable resources. When their production can be coupled to simple protocols such as sonochemistry or innocuous solvent-antisolvent protocols, they become suitable tools for a wide range of biomedical and cosmetic applictions. Here, we describe generation of lignin nanoparticles in a flexible approach that additionally allows for the incorporation of actives. For such applications, another prerequisite is to use lignins with high purity, well-suited organoleptic quality, and biocompatibility. Following these criteria, a novel type of lignin nanoparticles (LNPs) was developed in a solvent-antisolvent approach. Their structural stability profile was investigated, as well as their ability to carry highly hydrophobic actives and release them in a pH-dependent manner. The application of antioxidative lignin particles as carriers for anti-inflammatory drugs is also expected to offer synergistic effects in vivo. Extensive insights into the growth mechanism are presented, that allows fine-tuning for specific applications, and the development of a general formation strategy. Characteristics of the LNPs generated by the the solvent-antisolvent approach are compared to those obtained by using sonochemistry.

Motivation: Traditional pulp and paper processes as well as emerging biorefineries generating cellulosic ethanol from lignocellulosic agricultural waste material lead to large amounts of kraft lignin and side-stream straw lignin.1 Both types of technical lignins, i.e., organosolv lignins and kraft lignins, offer various amounts of different functional groups, mainly aliphatic and phenolic hydroxyl groups and double bonds.2,3 Whereas the hydroxyl groups are normally used for lignin functionalisation, a more versatile type of functionalisation is obtained when leaving the hydroxyl groups intact and creating carbon-carbon bonds. Design of experiment: Lignin modification was thus performed using nascent hydrogen, as well as carbenes of varying reactivity. Exploiting the possibilities for in situ production of the reactive species, various technical lignins were subjected to standardised reactions conditions. Re-isolated modified lignin samples were subjected to GPC analysis,4 FTIR analysis, quantitative 31P NMR after phosphitylation,5 as well as quantitative {13C-1H}-HSQC analyses.6,7 Results: Molar mass distribution effects were noted in the modified lignins. In case of carbenes, detection of new, unexpected cross-peaks in the HSQC spectra area specific for newly emerging C=C bonds were observed, while other ‘typical’ lignin signals in the aromatic region underwent drastic changes. Together with unexpectedly decreased amounts of the respective free phenolic OH groups in the modified lignins, quinone-formation involving G- and H-type aromatic rings of lignins through a Reimer-Tiemann mechanism8 is postulated, among other reactions and rearrangements. In case of treatment of lignins with nascent hydrogen, structural changes lead to yet different, ‘atypical’ lignins.

One crucial component within the efforts aiming at the valorisation of lignin is a rather precise knowledge regarding its structural features in terms of the amounts of aliphatic and phenolic hydroxyl groups, the amount of non-phenolic end groups, and the nature of interunit bonding motifs including their abundances. For achieving a complete characterisation, these data are best to be interpreted in connection with the molecular mass key data describing the oligomeric lignin chains, namely the number average molecular weight Mn, the weight average molecular weight Mw, and the polydispersity PD. Especially the latter one is often referred to when the discussion comes to the quality of polymeric or oligomeric sample: the smaller the PD, the better the polymer with respect to subsequent (chemical) modifications. Within the GPC-based determination of the above-mentioned key data like the PD for a given lignin sample, a meaningful calibration of the instrumentation, as well as the use of suitable detectors, are of paramount importance: a misled estimation of the “expected” molecular weight of a lignin sample might lead to a poor choice of the range of molecular weights of the standards used for calibration; the wrong detector-type lacks sensitivity. The range of the molecular weights covered in the calibration, however, does affect significantly the results obtained in the measurements of the lignin samples especially with respect to the polydispersity, and a non-suitable detector neglects the extremes. So-obtained astonishingly good, or unexpectedly bad polydispersities eventually lead to wrong conclusions and decisions concerning future actions. We have developed a transparent and robust protocol for the gel-permeation chromatography-based characterisation of plant-derived polyphenols in general, and lignins in particular. After systematically evaluating i) the influence of the range of molecular weights used for the calibration of the analytical set-up, ii) the influence of the flow-rate on the molecular mass-related key figures of certain lignin samples, and iii) the influence of the nature of the detector used for recording (UV-based of refractive index-based), we propose a generally applicable method and set-up for determining molecular weight key-figures based on GPC, that correspond to molecular weight data obtained via NMR spectroscopy-based methods.

Lignins were fractionated in a segmented continuous flow fractionation (SCFF) approach using isocratic or gradient elution profiles of different solvent systems at various flow rates and temperatures against adjustable pressure regimes. Superior control of parameters such as temperature and pressure in combination with the possibility of freely combinable solvent gradients allowed facile fractionation and generation of industrially interesting fractions differing in molecular weight properties and/or in physicochemical properties in a process that could be fully remotely controlled for automation and performance. Scale-up of the process was possible in linear and parallel mode. Analyses of the realised fractions by standardised gel permeation chromatography and 31 P NMR spectroscopy protocols showed that the SCFF of lignins delivered fractions that could be similar to conventional batch fractions, as well as novel/altered fractions available by applying overheated solvents in pressurised systems.

Two different organosolv lignins (OSLs), that is, wheat straw and corn stover OSLs, were chemically and enzymatically functionalized. Functional groups were attached via the formation of stable ether bonds exploiting the reactivity of free phenolic OH groups along the lignin backbone. The functional groups introduced a range from compact charged and chargeable building blocks for the generation of surface-active lignins to oligomeric and polymeric species used in lignin block-copolymer productions. Combination of selected functions led to novel charged or chargeable polymeric lignin-based materials. Products could be realized with different degrees of technical loadings in terms of introduced functional groups., Industrially produced wheat straw and corn stover organosolv lignins were chemically and enzymatically functionalized via formation of ether bonds using various surface-active functionals.

Eucalyptus nitens wood samples were subjected to consecutive stages of hydrothermal processing for hemicellulose solubilization and delignification with an ionic liquid, i.e., either 1-butyl-3-methylimidazolium hydrogen sulfate or triethylammonium hydrogen sulfate. Delignification experiments were carried out a 170 C for 10&ndash, 50 min. The solid phases from treatments, i.e., cellulose-enriched solids, were recovered by centrifugation, and lignin was separated from the ionic liquid by water precipitation. The best delignification conditions were identified on the basis of the results determined for delignification percentage, lignin recovery yield, and cellulose recovery in solid phase. The lignins obtained under selected conditions were characterized in deep by 31P-NMR, 13C-NMR, HSQC, and gel permeation chromatography. The major structural features of the lignins were discussed in comparison with the results determined for a model Ionosolv lignin.

Recently reported acetosolv soft- and hardwood lignins as well as ionosolv soft- and hardwood lignins were transformed into monomeric aromatic compounds using either a vanadate or a molybdate-based catalyst system. Monomers were generated with remarkable, catalyst-dependent selectivity and high depolymerisation yields via oxidative exo- and endo-depolymerisation processes. Using the vanadate&ndash, hydrogen peroxide system on acetosolv pine lignin, vanillin and isovanillin were produced as main products with depolymerisation yields of 31%. Using the molybdate system on acetosolv and ionosolv lignin, vanillic acid was the practically exclusive product, with depolymerisation yields of up to 72%. Similar selectivities, albeit with lower depolymerisation yields of around 50% under standardised conditions, were obtained for eucalyptus acetosolv lignin, producing vanillin and syringaldehyde or vanillic acid as products, by using the vanadate- or the molybdate-based systems respectively.

Thymol and the corresponding brominated derivatives constitute important biological active molecules as antibacterial, antioxidant, antifungal, and antiparasitic agents. However, their application is often limited, because their pronounced fragrance, their poor solubility in water, and their high volatility. The encapsulation of different thymol derivatives into biocompatible lignin-microcapsules is presented as a synergy-delivering remedy. The adoption of lignosulfonate as an encapsulating material possessing relevant antioxidant activity, as well as general biocompatibility allows for the development of new materials that are suitable for the application in various fields, especially cosmesis. To this purpose, lignin microcapsules containing thymol, 4-bromothymol, 2,4-dibromothymol, and the corresponding O-methylated derivatives have been efficiently prepared through a sustainable ultrasonication procedure. Actives could be efficiently encapsulated with efficiencies of up to 50%. To evaluate the applicability of such systems for topical purposes, controlled release experiments have been performed in acetate buffer at pH 5.4, to simulate skin pH: all of the capsules show a slow release of actives, which is strongly determined by their inherent lipophilicity.

Lignocellulosic biomass is one of the most important renewable materials to replace carbon-based fossil resources. Solvent-based fractionation is a promising route for fractionation of biomass into its major components. Processing is governed by the employed solvent-systems properties. This review sheds light on the factors governing both dissolution and potential reactivities of the chemical structures present in lignocellulose, highlighting how proper understanding of the underlying mechanisms and interactions between solute and solvent help to choose proper systems for specific fractionation needs. Structural and chemical differences between the carbohydrate-based structural polymers and lignin require very different solvents capabilities in terms of causing and eventually stabilizing conformational changes and consequent activation of bonds to be cleaved by other active components in the. A consideration of potential depolymerization events during dissolution and energetic aspects of the dissolution process considering the contribution of polymer functionalities allow for a mapping of solvent suitability for biomass fractionation. Validerad;2023;Nivå 2;2023-01-16 (sofila)

The moisture resistance of friction-welded wood joints can be improved by applying bio-based bonding additives. Several biomolecules including tannic acid, organosolv lignin from hardwood, kraft lignin from softwood, and derivates thereof, were investigated regarding their applicability as bonding additives in the friction welding process. Welding with kraft lignin showed significantly increased moisture stability after 24 h water immersion. An average wet bond strength of 1.5 MPa compared to 0.38 MPa of untreated spruce was obtained. Modification of kraft lignin through succinylation, acetylation or depolymerisation led to no further improvement in moisture stability. Depolymerised kraft lignin resulted in an even higher delamination rate of the samples during water immersion than untreated samples. Structural analysis of the lignin variations by FTIR-ATR, GPC and P-31 NMR in combination with thermal analysis by TGA and DSC showed the impact of various structural and chemical features on the thermal behaviour and intermolecular interactions of the applied lignin., Journal of Adhesion Science and Technology, ISSN:0169-4243, ISSN:1568-5616

Organosolv pretreatment represents one of the most promising biomass valorization strategies for renewable carbon-based products; meanwhile, there is an overall lack of holistic approach to how extraction conditions affect the suitable end-usages. In this context, lignin extracted from silver birch (Betula pendula L.) by a novel hybrid organosolv/steam-explosion treatment at varying process conditions (EtOH %; time; catalyst %) was analyzed by quantitative NMR (1H-13C HSQC; 13C NMR; 31P NMR), gel permeation chromatography, Fourier transform infrared (FT-IR), Pyr-gas chromatography-mass spectroscopy (GC/MS), and thermogravimetric analysis, and the physicochemical characteristics of the lignins were discussed regarding their potential usages. Characteristic lignin interunit bonding motifs, such as β-O-4', β-β', and β-5', were found to dominate in the extracted lignins, with their abundance varying with treatment conditions. Low-molecular-weight lignins with fairly unaltered characteristics were generated via extraction with the highest ethanol content potentially suitable for subsequent production of free phenolics. Furthermore, β-β' and β-5' structures were predominant at higher acid catalyst contents and prolonged treatment times. Higher acid catalyst content led to oxidation and ethoxylation of side-chains, with the concomitant gradual disappearance of p-hydroxycinnamyl alcohol and cinnamaldehyde. This said, the increasing application of acid generated a broad set of lignin characteristics with potential applications such as antioxidants, carbon fiber, nanoparticles, and water remediation purposes.

Softwood kraft lignin SKL was fractionated using aprotic acetone and protic methanol to yield both previously reported “traditional” fractions and novel refined fractions thereof. Based on differences in mutual H-bonding affinities exerted by the solvents on one side and the OH group characteristics of the lignin oligo- and polymers on the other side, the 85% acetone-insoluble kraft lignin fraction AIKL, for example, could be further fractionated in 16% methanol-soluble and 67% methanol-insoluble parts. Sequential use of the two solvents practically resembled a refinement protocol that shed light on eventual “structural impurities” contained in the traditional fractions, which is not delineable easily in front of the background of a dominating spectroscopic image. Exploiting H-bonding characteristics offers a valid option for the facile generation of truly “structurally purified” lignin fractions. Acetone-insoluble, methanol-soluble MSAIKL, for example, exhibits 25% less aliphatic interunit bonding while being enriched in phenolic groups up to 25%, thus representing condensed, lower-molecular-weight structures with overall H-bond accepting character that was still contained in the overall larger-molecular-weight acetone-insoluble AIKL. More “polyphenylpropanoidic” parts practically free of condensed units, determining the overall structural picture of the unrefined lignins due to their overall abundance, are represented by the globally insoluble fractions like acetone-insoluble, methanol-insoluble MIAIKL. The original fractions and refined fractions generated based on targeting specific H-bonding affinities give a more homogeneous picture with respect to trends in glass transition temperatures, clearly indicating that Tg is dominated by actually both MW and nature of OH groups.

Lignin is the second most abundant polymer in forest biomass after cellulose. Compared to the ubiquitous use of cellulose, lignin is currently simply being wasted. In fact, as a waste product in the cellulose production, it serves mainly for the generation of energy. The reason for this lies in the challenging structural features and the patchy understanding of the correlation between structural features and polymer characteristics displayed by various lignins. This chapter will introduce the general characteristics and peculiarities of lignin as biopolymer and will present techniques for investigating structural issues. Approaches toward a valorization of lignin will be highlighted, showing the possibilities for using lignin in chemistry and material sciences.

Stimuli-responsive behavior of lignin microcapsules (LMCs) has been investigated along with the detailed characterization of their stability profiles. The disassembly of LMCs was found to be salt species-dependent, indicating the specific relevance of inherent kosmotropic and chaotropic characteristics. For the first time, a connection between the Hofmeister series and the stability profile of lignin microscale materials is established. LMCs showed excellent stability in water and under high temperature and pressure (autoclaving conditions). Active release is efficiently triggered by pH changes and balancing chaotropic and kosmotropic effects via salinity tuning.

Nanoencapsulation of active substances with controlled release in harmless matrices has been the subject of numerous scientific efforts mainly due to the significant biomedical potential of such endeavors. Lignin, the environmentally sustainable byproduct of the pulp and paper industry, contains a multitude of phenolic hydroxyl groups, some of which, are known to readily and strongly chelate with iron ions. In this effort we demonstrated that the concerted use of chelation chemistry, oil in water emulsion principles, and low energy sonication, offers a facile, one-pot strategy to assemble lignin nanocapsules (LNCs) of a controlled architecture. Under these conditions capsules are shown to rapidly assemble utilizing two driving forces, the p-stacking propensity of lignin and its metal chelating ability at alkaline pH. Detailed size exclusion chromatographic evidence validates that the formation of capsules is driven mainly by the enumerated physical interactions with no significant chemical modification of the lignin. The developed process was systematically optimized so as to create the foundations for the morphology and the yield of the capsules being modulated as a function of sonication time, power, and surface contact area. Both pure LNCs and Fe-LNCs were synthesized in high yields with size distributions varying from 0.3 to 6 mm and their release efficiencies were evaluated in detail. As anticipated, the complexation effects of the phenolic OH groups offered to the Fe-LNCs, increased stability, reduced shell thickness (allowing for greater loading efficiencies), and lower release kinetics, compared to LNCs.

The mechanism of lignin nanoprecipitation and subsequent self-assembly was elucidated by studying generation of lignin nanoparticles (LNPs) from aqueous ethanol. LNP formation was found to follow a kinetically controlled nucleation–growth mechanism in which large lignin molecules formed the initial critical nuclei. Using this information, we demonstrate entrapment of budesonide in LNPs and subsequent pH-triggered and surfactant-responsive release of this synthetic anti-inflammatory corticosteroid. Overall, our results not only provide a promising intestinal delivery system for budesonide but also deliver fundamental mechanistic understanding for the entrapment of actives in LNPs with controlled size and release properties.

The biotechnological conversion of lignocellulosic biomass is a pivotal aspect in the development of sustainable and environmentally friendly biorefinery and valorization processes for nonfossil biomass. Lipoxygenase, a noncellulolytic oxidizing enzyme normally operating on linoleic acid metabolism, is demonstrated to catalyze the oxidative functionalization of lignin. Lipoxygenase was used for structurally altering the most important types of technical lignins. Noteworthy oxidation is achieved by activation via a radical mechanism leading to both oxygen- and carbon-centered radicals. Since this activation also occurs on the lignin backbone, the ketyl and benzyl radicals generated can be used to functionalize lignins via formation of carbon-carbon bonds.

One of the most daunting challenges when studying lignin relates to analytical chemistry approaches applied to the heterogeneous polymer or epolymerization products. Understanding the structure of lignin in the cell wall alone is a target that remains incredibly challenging. This chapter will cover advances in understanding lignin in planta as well as characterizing isolated lignin or lignin depolymerization products, highlighting the methods and their respective advantages and disadvantages in terms of reliable data acquisition.

The main target of a biorefinery pretreatment process is to break down the lignin-reinforced plant cell wall structure prior to enzymatic hydrolysis of polysaccharides to fermentable sugars. Various physico-chemical alterations occur in lignin during the biomass pretreatment, but effects of those structural changes on subsequent enzymatic hydrolysis have remained ambiguous. We review the reinforcing and detrimental lignin-enzyme interactions and their underlying mechanisms, and use this structure-function information to assess critical features of current and emerging pretreatment technologies. Our perspective is that truly multidisciplinary research is needed to develop pretreatments that render lignin non-inhibiting to enzymes and with high potential for further valorisation.

Two constitutional structural schemes are proposed attempting to unify and rationalize a series of focused NMR and chromatographic determinations aimed at providing an integrated picture for the structure of softwood kraft lignin. The complexity of native softwood lignin when coupled with the complexity of the kraft pulping process is known to lead to a rather heterogeneous material that has eluted us to date. The present work embarks at applying state-of-the-art quantitative 1D and 2D NMR methods on carefully isolated softwood kraft lignin samples and fractions. The accumulated data, when coupled with size exclusion chromatography, mass spectrometric analyses and literature accounts that pertain to the chemistry of kraft pulping, provide the following picture for softwood kraft lignin. Softwood kraft lignin is composed of two distinct fractions that can be separated by using anhydrous acetone. The acetone insoluble fraction is a somewhat branched polymeric material that still contains a variety of native wood lignin bonding patterns, albeit in significantly reduced abundance, as well as new structures induced during the process. The acetone soluble fraction is a significantly more branched and less polymeric material with an abundance of chemical structures that may be created when oligomeric phenols react under kraft pulping conditions. To account for the presence of the various moieties in these two fractions, kraft pulping fragmentation and repolymerization chemistries are extensively invoked, including radical processes initiated by sulfur.

To liberate society from its dependence on fossil‐based fuels and materials it is pivotal to explore components of renewable plant biomass in applications that benefit from their intrinsic biodegradability, safety, and sustainability. Lignin, a byproduct of the pulp and paper industry, is a plausible material for carrying various types of cargo in small‐ and large‐scale applications. Herein, possibilities and constraints regarding the physical–chemical properties of the lignin source as well as modifications and processing required to render lignins suitable for the loading and release of pesticides, pharmaceuticals, and biological macromolecules is reviewed. In addition, the technical challenges, regulatory and toxicological aspects, and future research needed to realize some of the promises that nano‐ and microscaled lignin materials hold for a sustainable future are critically discussed.

A new fractionation protocol for wheat straw organosolv lignin was developed on the basis of the dominating H-bonding orientations of its components. Acetone as H-bond accepting aprotic polar solvent and methanol as H-bond donating and accepting protic polar solvent were used in sequence. Obtained fractions were structurally and thermally analysed. The protocol allowed for the generation of purified lignin fractions and the isolation of a novel, yet unobserved lignin carbohydrate complex (LCC) fraction. This LCC fraction was found to contain exclusively phenyl glycosides and &gamma, esters as LCC motifs.

Driven by the need of a simple method to arrive at rather accurate molecular mass key data for different lignin samples across different laboratories, we revisited thoroughly the different aspects that comprise the determination of molecular weight key data of lignins by means of gel permeation chromatography. We considered setup issues and their effect on calibration, implications emerging from sample preparation, issues connected to data acquisition, and effects of raw data evaluation. Considering identified key issues, we propose a standardized setup in connection with a standardized data treatment that ensures the generation of precise GPC results. The introduction of an additional lignin-type depending correction factor, which is delineated using averaged bidimensional NMR-based advanced structural information obtained for a given lignin type, allows us to account for system-inherent bias, rendering the precise measurements de facto accurate.

Isolation of lignins from hardwood and softwood biomass samples, containing 26.1% and 28.1% lignin, respectively, has been performed with the use of alkaline and organosolv pretreatment methods. The effect of catalyst loading, ethanol content, particle size, and pretreatment time on the yields and properties of the isolated lignins were investigated. Alkaline lignins had higher carbohydrate content - up to 30% - and exhibited higher molecular weights in the range of 3000 Da, with a maximum phenolic hydroxyl content of 1 mmol g−1 for birch and 2 mmol g−1 for spruce. Organosolv lignins, on the other hand, showed high purity - 93% or higher - despite the more extensive biomass dissolution into the pretreatment medium; they also exhibited a lower range of molecular weights between 600 and 1600 Da depending on the source and pretreatment conditions. Due to the lower molecular weight, phenolic hydroxyl content was also increased, reaching as high as 4 mmol g−1 with a simultaneous decrease in aliphatic hydroxyl content as low as 0.6 mmol g−1. Efficient lignin dissolution of 62% for spruce and 69% for birch, achieved at optimal pretreatment conditions, was combined with extensive hemicellulose removal.

In this study, the application of different chemical and enzymatic treatment methods for the fractionation of the birch outer bark components was evaluated. More specifically, untreated and steam exploded, hydrothermally and organosolv treated bark samples were incubated with enzyme mixtures that consisted of cellulases, hemicellulases and esterases, and the effect of enzymes was analyzed with 31P NMR and {13C-1H} HSQC. The biocatalysts performed the cleavage of ester bonds resulting in reduction of methoxy and aliphatic groups in the remaining solid fraction, whereas the aromatic fraction remained intact. Moreover, the suberin and lignin fraction were isolated chemically and their properties were characterized by gas chromatography (GC-MS), 31P NMR, {13C-1H} HSQC and gel permeation chromatography (GPC). It was demonstrated that the lignin fraction was enriched in guaiacyl phenolics but still contained some associated aliphatic acids and carbohydrates, whereas the suberin fraction presented a polymodal pattern of structures with different molecular weight distributions. This work will help in getting a deeper fundamental knowledge of the bark structure, the intermolecular connection between lignin and suberin fractions, as well as the potential use of enzymes in order to degrade the recalcitrant bark structure toward its valorization. Validerad; 2016; Nivå 2; 2016-11-02 (andbra)

A pH- and light-responsive polymer has been synthesized from softwood kraft lignin by a two-step strategy, which aimed at incorporating diazobenzene groups. Initially, styrene oxide was reacted with the phenolic hydroxyl groups in lignin, to offer the attachment of benzene rings, thus creating unhindered reactive sites for further modifications. The use of advanced spectroscopic techniques (1H and 31P NMR, UV and FTIR) demonstrated that the reaction was quantitative and selective towards the phenolic hydroxyl groups. In a second step, the newly incorporated benzene rings were reacted with a diazonium cation to form the target diazobenzene motif, whose formation was again thoroughly verified. As anticipated, the diazobenzene-containing kraft lignin derivatives showed a pH-dependent color change in solution and light-responsive properties resulting from the cis-trans photoisomerization of the diazobenzene group.

Two distinct functionalization schemes for Kraft lignin (KL) were developed to selectively incorporate furan and/or maleimide motifs as chain ends. The incorporation of furan functionalities was carried out by the selective and quantitative reaction of the lignin’s phenolic OH groups with furfuryl glycidyl ether (FGE). Maleimide groups were introduced by esterifying the lignin’s aliphatic and phenolic OH groups with 6 maleimidohexanoic acid (6-MHA), offering a high loading despite a somewhat incomplete conversion. Furan- and maleimide-functionalized lignins were subsequently combined to generate crosslinking via the Diels–Alder (DA) [4 + 2] cycloaddition reaction. The formation of the DA adduct was confirmed by 1H NMR. Under appropriate conditions, the formation of a gel was apparent, which turned back into the liquid state after performing the corresponding retro-DA reaction upon heating to 120 °C. This study reveals the significant versatility and potential of the developed strategy for the utilization of lignin-based recyclable networks.

This study has shown that ultrafiltration allows the selective extraction from industrial black liquors of lignin fraction with specific thermo-mechanical properties, which can be matched to the intended end uses. Ultrafiltration resulted in the efficient fractionation of kraft lignin according to its molecular weight, with an accumulation of sulfur-containing compounds in the low-molecular weight fractions. The obtained lignin samples had a varying quantities of functional groups, which correlated with their molecular weight with decreased molecular size, the lignin fractions had a higher amount of phenolic hydroxyl groups and fewer aliphatic hydroxyl groups. Depending on the molecular weight, glass-transition temperatures (Tg) between 70 and 170C were obtained for lignin samples isolated from the same batch of black liquor, a tendency confirmed by two independent methods, DSC, and dynamic rheology (DMA). The Fox-Flory equation adequately described the relationship between the number average molecular masses (Mn) and T g's-irrespective of the method applied. DMA showed that low-molecular-weight lignin exhibits a good flow behavior as well as high-temperature crosslinking capability. Unfractionated and high molecular weight lignin (Mw >5 kDa), on the other hand, do not soften sufficiently and may require additional modifications for use in thermal processings where melt-flow is required as the first step.

Lignin is the second-most abundant polymer after cellulose within the biomass of our planet. Structurally, it displays random oligomeric units without fixed repetition schemes beyond the stage of dimers. Quantitative 1H-3C HSQC measurements have recently greatly facilitated lignin analyses. In some cases, however, long acquisition times needed for obtaining quantitative HSQCs are not compatible with the chemical integrity of (a potentially functionalised) lignin sample. We thus compared different methods that were developed for more time-efficient quantitative HSQC measurements with respect to their usefulness in lignin analyses: reliable and reproducible results were obtained using both the QQ-HSQC and the HSQC0 method. © 2013 Sette et al. Licensee: Computational and Structural Biotechnology Journal. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly cited.

Lignin is the second most abundant natural polymer. Its use and targeted functionalisation within biomass refinery processes, however, still needs to be further explored and developed. The oxidative functionalisation, and thus valorisation of lignin, is a very promising way to go, since it holds the possibilities to yield highly functionalised, monomeric or oligomeric products that can serve as starting materials for other valorisation processes in the chemical and pharmaceutical industries. Gaining a profound knowledge about the structure of lignin, being able to analyse structural features, and understanding the mechanisms that guide the reactions leading to the oxidative derivatisation, depolymerisation and functionalisation of lignin samples from different renewable sources are key requirements for developing successful valorisation protocols for lignin. In this review, we wish to revisit, and set into context, some important achievements in the field of oxidatively upgrading lignin. We will focus on organometal catalyses (MTO, salen complexes, POMs), biomimetic catalyses (porphyrins), and enzymatic catalyses (laccase, peroxidase) for upgrading lignin and lignin model compounds. Details of mechanistic implications and means of potential manipulations of reaction outcomes are discussed.

This study demonstrates the effects of structural variations of lignins isolated via an organosolv process from different woody and herbaceous feedstocks on their thermal stability profiles. The organosolv lignins were first analysed for impurities, and structural features were determined using the default set of gel permeation chromatography, FT-IR spectroscopy, quantitative 31 P NMR spectroscopy and semi-quantitative 1 H- 13 C HSQC analysis. Pyrolysis-, O 2 - and CO 2 -reactivity of the organosolv lignins were investigated by thermogravimetric analysis (TGA), and volatile formation in various heating cycles was mapped by head-space GC-MS analysis. Revealed reactivities were correlated to the presence of identified impurities and structural features typical for the organosolv lignins. Data suggest that thermogravimetric analysis can eventually be used to delineate a lignin character when basic information regarding its isolation method is available.