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In this study, the development of lignin-based resins for wood adhesion applications was demonstrated. We investigated two lignin fractions: commercial Protobind 1000 lignin and methanol-soluble Protobind 1000 lignin fraction after mild solvolysis. Although lignin has previously been incorporated into various cross-linked systems, this is the first report on lignin-based thermosets obtained via thiol–yne “click” chemistry. In this approach, lignin was functionalized with terminal alkyne groups followed by cross-linking with a multifunctional thiol, resulting in polymeric network formation. The influence of the curing conditions on the resin characteristics and performance was studied, by varying the amount of reactive monomeric diluents. Additionally, a post-curing strategy utilizing the Claisen rearrangement was investigated. These resins were tested as a wood adhesive and were proven to possess a desirable performance, comparable to the state-of-art phenol-formaldehyde resins. Lignin-based thiol–yne resins turn out to be an alternative to phenol-formaldehyde resins, currently used as adhesives and coatings. Although it is possible to use lignin in phenol-formaldehyde resins, lignin addition is compromising the resin’s performance. The main benefits over the phenol-formaldehyde approach are that higher lignin loadings are possible to achieve, and no volatiles are emitted during the resin processing and use.

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

There is an environmental concern regarding the use of petroleum-based lubricants, which are generally toxic and nonbiodegradable. Biobased lubricants, such as vegetable oils, are the alternative: they show excellent lubricity, are readily biodegradable and nontoxic. However, a major disadvantage of using vegetable oils in lubricant applications is their lack of thermo-oxidative stability, which can be improved by antioxidant additives. Here, we propose the use of lignin-based additives in biolubricant formulations to improve this feature, based on lignin’s known antioxidant properties. To ensure a stable dispersion in vegetable oil, lignin was partially esterified. Antioxidant properties of lignin before and after palmitoylation were demonstrated in a 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. Four different lignin-based fractions, commercial Protobind P1000 soda lignin from straw, solvolytically fractionated Protobind P1000 lignin and two lignin fractions from reductively catalyzed fractionation (RCF) of native birch wood, were tested in biolubricant formulations with castor oil as base oil. Those lignin fractions exhibited excellent performance compared to butylated hydroxytoluene (BHT), a commonly used petroleum-based antioxidant. Formulations of modified lignin in castor oil possess improved thermo-oxidative stability, as illustrated by their increased oxidation induction time. Additionally, rheological and tribological tests demonstrate similar, or in some cases improved, lubricating properties compared to castor oil. This study showcases the successful incorporation of lignin-based antioxidants in biolubricant formulations, tackling the major disadvantage of vegetable oils as environment-friendly lubricants.

Lignin, a major constituent of lignocellulosic biomass, is the largest natural source of aromatic molecules and thus is an attractive feedstock for renewable chemical production. Direct incorporation of isolated lignin into materials has long been researched due to the idea's simplicity and the scheme's potentially high atom economy. However, due to its high chemical reactivity lignin is difficult to isolate without having it undergo uncontrolled condensation and repolymerization, which greatly hinder its ease of incorporation into polymers and other materials. Therefore, controlled chemical modifications have been and are being developed to increase lignin's compatibility with existing materials. This review presents the latest advances in lignin extraction and functionalization and their potential for improving the production of lignin-based materials.

Lignin is an abundant natural feedstock that offers great potential as a renewable substitute for fossil-based resources. Its polyaromatic structure and unique properties have attracted significant research efforts. The advantages of an enzymatic over chemical or thermal approach to construct or deconstruct lignins are that it operates in mild conditions, requires less energy, and usually uses non-toxic chemicals. Laccase is a widely investigated oxidative enzyme that can catalyze the polymerization and depolymerization of lignin. Its dual nature causes a challenge in controlling the overall direction of lignin-laccase catalysis. In this Review, the factors that affect laccase-catalyzed lignin polymerization were summarized, evaluated, and compared to identify key features that favor lignin polymerization. In addition, a critical assessment of the conditions that enable production of novel lignin hybrids via laccase-catalyzed grafting was presented. To assess the industrial relevance of laccase-assisted lignin valorization, patented applications were surveyed and industrial challenges and opportunities were analyzed. Finally, our perspective in realizing the full potential of laccase in building lignin-based materials for advanced applications was deduced from analysis of the limitations governing laccase-assisted lignin polymerization and grafting.

Refining of industrial lignin to produce homogeneous fractions is essential for high-value applications. However, the understanding of key interactions between a variety of solvents with lignin polymer is still uncertain. In this work, single-step fractionation of industrial hardwood kraft lignin (HKL) using organic solvents of different polarities - ethanol, acetone, diethyl ether and hexane - was investigated by combining an experimental and theoretical approach. Experimental results revealed that higher polarity solvents (ethanol and acetone) exhibited higher solubility yield compared to moderate and low polarity solvents. The chemical differences between lignin fractions were proven by pyrolysis gas chromatography mass spectrometry and near infrared spectroscopy. Density functional theory (DFT) results indicated that ethanol presented higher interaction energy followed by acetone, diethyl ether and hexane, which was consistent with experimental findings. Hydrogen bond and non-covalent interaction results from DFT demonstrated that the predominant interaction was found for high polarity of ethanol over other solvents and gamma-OH in the lignin model is the key site. The authors gratefully acknowledge the European Commission for funding the InnoRenew project [Grant Agreement #739574] under the Horizon2020 Widespread-Teaming program, the Republic of Slovenia (investment funding from the Republic of Slovenia and the European Union European Regional Development Funds) and infrastructural ARRS program IO-0035. Additionally, O.G. is grateful for the financial support received from the University of the Basque Country (post-doctoral grant DOCREC18/29) and R.H. acknowledges to the Department of Education of the Basque Government (post-doctoral grant INGVTCL4-D00112-7).

International audience; The objective of this communication is to present and discuss different strategies for the recovery of lignin-based antioxidants. Lignins are phenolic polymers constitutive of plant cell-walls. Their multi-functionality confers them with a key role in plant mechanical support, water transport and resistance to biological attacks. During most lignocellulose biorefinery processes, native lignins are converted into heterogenous by products, technical lignins, more or less depolymerized and contaminated by carbohydrates. Whatever their origin, technical lignins show antioxidant properties along with other properties of interest, such as antimicrobial, anti-UV, cross-linking and flame-retardant properties, which make them potential valuable ingredients for plastics, building materials, or cosmetics. In order to develop markets for lignin-biobased ingredients, an integrated value-chain approach from plant to end-product is necessary. Indeed, the composition and properties of technical lignins can be controlled both by selection of both the plant feedstock and the lignocellulose processing parameters. Grass lignins recovered by soda delignification process are good candidate to substitute commercial synthetic antioxidant. With a radical scavenging power of the same order as that of BHT, they might be used as additive in polyolefins or bio-based plastics such as poly (lactic acid). Higher-value applications could be targeted by applying solvent extraction combined with mild selective depolymerization yielding fractions with increased functionalities.

The viability of several technical lignins as a source for biobased platform chemicals was investigated via hydrotreatment using a cheap Fe-based limonite catalyst and without using a solvent. In general, high-quality oils (up to 29 wt% total monomers) with an average relative composition of 55% alkylphenolics and 27% aromatics were obtained. Detailed structural investigations showed that the S-G aromatic unit content of the lignins was the most important factor positively affecting overall oil yields. A second parameter was the lignocellulose processing method. Even though alkaline lignin isolation provides more recalcitrant lignins, their lower aliphaticity and methoxy group content partially limit char and gas formation. Finally, enhanced monomer yields could be obtained irrespective of the ether linkage content, and a high amount of beta-O-4 linkages actually showed a slightly negative effect on monomer yields. Overall, the results demonstrate that this route is particularly suitable for processing residual lignin streams.

Technical lignins are structurally heterogeneous and polydisperse. This work describes the use of a simple and green method for lignin fractionation, using different proportions of acetone (40 and 60%) in water. Lignins from three different sources (wheat straw organosolv lignin, wheat straw soda lignin and softwood kraft lignin) were used in this fractionation protocol. The obtained fractions showed different molar mass and functional groups. The lower molar mass fractions showed more phenolic hydroxyl groups and carboxylic acid moieties than higher molar mass fractions, which also possessed much higher amounts of carbohydrates. The chemical characterization of these fractionated lignins showed that the PREC fraction was exceptionally pure and homogeneous lignin. Its total lignin content was >96% for all three lignins and it was practically free from carbohydrates and inorganics (ash). Furthermore, PREC fraction possessed the highest carbon content for the three lignin samples (63.05–69.26%). These results illustrate that the proposed aqueous acetone fractionation protocol could indeed produce pure and uniform lignin fraction and it was applicable for lignins from different sources.

The goal of this work was to study the use of Eutectic Solvents (ESs) for wood fractionation aiming at their application on pulping processes, in the biorefinery framework. To achieve this purpose, fundamental studies were performed to better understand the solubility of lignin monomer model compounds (syringaldehyde and syringic, vanillic and ferulic acids) and technical lignins (kraft and organosolv) in ESs and their aqueous solutions. Particularly, aqueous solutions of propionic acid:urea (2:1) at 50 or 75 wt % of concentration and 353.15 K improved lignin solubility by two orders of magnitude in comparison to water and conventional lignin solvents [solubility enhancement of (228.3 ± 8.2)- and (474.7 ± 2.7)-fold for kraft and organosolv lignin, respectively]. Furthermore, maximum solubilization of lignin monomer model compounds was achieved using ethylene glycol:tetrabutylphosphonium chloride (2:1) aqueous solutions at 50 or 75 wt % of concentration and 323.15 K [(34.9 ± 6.7)-, (116.6 ± 1.6)-, (58.6 ± 0.4)- and (202.5 ± 16.9)-fold, respectively]. It should be highlighted the fundamental role of water, which allows a hydrotropic effect on lignin (and their monomers) solubility in these ESs aqueous solutions. The best ESs to enhance the solubility of lignin in water was used to develop a new wood delignification process. Therefore, delignification of Eucalyptus globulus wood catalyzed by mineral or organic acids in ESs aqueous solutions was studied. The results obtained confirmed that the wood delignification using ESs aqueous solutions requires the addition of acid catalyst in order to enhance lignin removal. Two different ESs aqueous systems were identified as the best to delignify E. globulus wood under mild conditions: (i) the 50 wt % aqueous solution of propionic acid:urea (2:1) in the presence of 25 wt % of p-toluenesulfonic acid as catalyst (8 h, 363.15 K and atmospheric pressure). This system led to the production of a solid fraction yield of 59.50 ± 0.51 wt %, containing a residual Klason lignin of 3.86 ± 0.10 wt % with preserved cellulose fibers, when compared to conventional E. globulus kraft pulp; and (ii) the 50 wt % aqueous solution of ternary-ESs mixture (sodium p-toluenesulfonate:p-toluenesulfonic acid:choline chloride) at optimal molar ratio of (0.393:0.376:0.232) that allowed producing 46.60 ± 2.70 wt % of solid fraction yield, containing a residual Klason lignin of 2.74 ± 0.08 wt % under milder conditions (3 h, 363.15 K and atmospheric pressure). Moreover, the chemical structural analysis of both isolated lignins revealed that fewer transformations are induced by these systems, when compared to E. globulus kraft, and other ESs reported in literature. Finally, promising preliminary results show the feasibility for scaling the ES wood delignification process using both ESs. Este trabalho teve como objectivo estudar o uso de solventes eutécticos (SEs) no fraccionamento de madeira, com vista à sua aplicação em processos de produção de pasta, no âmbito de uma biorrefineria. Nesse sentido, foi desenvolvido um estudo fundamental que permitisse compreender a solubilidade de lenhinas técnicas (kraft e organosolv) e dos seus monómeros (siringaldeído e ácidos siríngico, vanílico e ferúlico) nos SEs puros e respetivas soluções aquosas. Mostrou-se que, soluções aquosas de ácido propiónico:ureia (2:1) com concentrações de 50 ou 75 % m/m a 353.15 K aumentam a solubilidade da lenhina em duas ordens de grandeza relativamente à sua solubilidade em água pura ou solventes orgânicos convencionais usados normalmente para a solubilização de lenhina [aumento de solubilidade de (228.3 ± 8.2)- e (474.7 ± 2.7)-vezes para as lenhinas kraft e organosolv, respectivamente]. Além disso, foi possível obter uma solubilização máxima dos monómeros de lenhina usando uma solução aquosa de etileno glicol:cloreto de tetrabutilfosfónio (2:1) com concentrações de 50 ou 75 % m/m a 323.15 K [(34.9 ± 6.7)-, (116.6 ± 1.6)-, (58.6 ± 0.4)- e (202.5 ± 16.9)-vezes, respectivamente]. É de salientar o papel fundamental da água que permite o efeito hidrotrópico na solubilização da lenhina e seus monómeros nas soluções aquosas dos SEs estudados. De seguida, os melhores SEs foram usados no processo de deslenhificação de madeira de Eucalyptus globulus como prova de conceito. O efeito da adição de catalizadores ácidos foi igualmente estudado. Os resultados obtidos confirmaram que a adição de um catalizador ácido às soluções aquosas de SEs promovem a extração de lenhina. Neste estudo, dois sistemas aquosos de SEs (50 % m/m) apresentaram resultados excelentes na deslenhificação da madeira de E. globulus: (i) ácido propiónico: ureia (2:1) na presença de 25 % m/m de catalisador ácido ptoluenosulfónico (8 h, 363.15 K e pressão atmosférica). Este sistema resultou num rendimento de fração sólida de 59.50 ± 0.51 % m/m, contendo 3.86 ± 0.10% m/m de lenhina Klason residual. A análise da pasta resultante permitiu concluir que as fibras de celulose foram preservadas quando comparadas com a pasta kraft de E. globulus; e (ii) mixtura ternária (p-toluensulfonato de sódio: ácido p-toluenosulfónico:cloreto de colina) numa razão molar óptima de (0.393:0.376:0.232) nas condições óptimas de operação de 3 h, 363.15 K e pressão atmosférica. Este sistema resultou num rendimento de fração sólida de 46.60 ± 2.70 % m/m, contendo 2.74 ± 0.08 % m/m de lenhina Klason residual. As análises químicas estruturais realizadas às lenhinas isoladas revelaram menos modificações induzidas pelos sistemas propostos, quando comparados com a lenhina kraft de E. globulus ou outros sistemas SEs reportados na literatura. Por fim, estudos preliminares de aumento de escala usando os SEs propostos revelaram-se promissores. Programa Doutoral em Engenharia Química

Biorefineries need cost-efficient pretreatment processes that overcome the recalcitrance of plant biomass, while providing feasible valorization routes for lignin. Here we assessed aqueous ammonia for the separation of lignin from hydrothermally pretreated wheat straw prior to enzymatic saccharification. A combined severity parameter was used to determine the effects of ammonia concentration, treatment time and temperature on compositional and physicochemical changes [utilizing elemental analysis, cationic dye adsorption, FTIR spectroscopy, size-exclusion chromatography (SEC), and P-31 nuclear magnetic resonance (NMR) spectroscopy] as well as enzymatic hydrolysability of straw. Pretreatment at the highest severity (20% NH3, 160 degrees C) led to the maximum hydrolysability of 71% in a 24 h reaction time at an enzyme dosage of 15 FPU/g of pretreated straw. In contrast, hydrolysabilitiac remained low regardless of the severity when a low cellulase dosage was used, indicating competitive adsorption of cellulaseson nitrogen-containing lignin. In turn, our results showed efficient adsorption of cationic, anionic and uncharged organic dyes on nitrogen-containing lignin, which opens new opportunities in practical water remediation applications.

This work investigates the valorization of sodium lignosulfonate, kraft, and organosolv lignins from South America. A detailed characterization of the lignins and their chemical modification by hydroxymethylation through its reaction with formaldehyde were performed. The characterization included measurements of moisture, ash, carbohydrate contents, elemental and thermogravimetric analysis, and functional groups, molar mass distributions by Fourier transform infrared spectroscopy, and size exclusion chromatography, respectively. Also, reactive aromatic hydrogens ( HAr) were quantified by the measurement of phenolic hydroxyl groups (P-OH) content by UV–Vis spectroscopy. The different initial formaldehyde/lignin weight ratios (0.07, 1.47), temperatures (40, 50, and 70 C), and pHs (9, 11); and the following of hydroxymethylation reactions by UV–Vis spectroscopy were investigated. All lignins resulted attractive for the use as replacement of phenol in phenolic resins, but sodium lignosulfonate was the most appropriate due to its water solubility. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47712. Fil: Taverna, María Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina. Universidad Tecnológica Nacional; Argentina Fil: Felissia, Fernando Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; Argentina Fil: Area, Maria Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; Argentina Fil: Estenoz, Diana Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Nicolau, Verónica Viviana. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Tecnológica Nacional; Argentina

A grass soda technical lignin (PB1000) underwent a process combining solvent fractionation and treatment with an ionic liquid (IL), and a comprehensive investigation of the structural modifications was performed by using high‐performance size‐exclusion chromatography, 31P NMR spectroscopy, thioacidolysis, and GC–MS. Three fractions with distinct reactivity were recovered from successive ethyl acetate (EA), butanone, and methanol extractions. In parallel, a fraction deprived of EA extractives was obtained. The samples were treated with methyl imidazolium bromide ([HMIM]Br) by using either conventional heating or microwave irradiation. The treatment allowed us to solubilize 28 % of the EA‐insoluble fraction and yielded additional free phenols in all the fractions, as a consequence of depolymerization and demethylation. The gain of the combined process in terms of antioxidant properties was demonstrated through 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH.) radical‐scavenging tests. Integrating further IL safety‐related data and environmental considerations, this study paves the way for the sustainable production of phenolic oligomers competing with commercial antioxidants., Technical lignin refinement: A cascade biorefinery process is presented that enables upgrading of technical lignins and sustainable production of phenolic oligomers of interest as substitutes for commercial antioxidants.

Lignocellulose is a widely available carbon source and a promising feedstock for the production of advanced second‐generation biofuels. Nonetheless, lignin, one of its major components, is largely underutilized and only considered an undesired byproduct. Through catalytic hydrotreatment, the highly condensed lignin can be partially depolymerized into a range of monomers. However, its recalcitrance and the presence of aromatic fragments linked by C-C bonds require extensive cracking, which is challenging to achieve. Here, a two‐step strategy is reported in which an initial pretreatment step with ozone is used prior to catalytic hydrotreatment to boost lignin depolymerization. Three types of lignin (Kraft, pyrolytic, and Fabiola organosolv) are used as feedstocks and the ozonation step is performed under ambient conditions with either methanol or ethanol as the solvent. The pretreatment is shown to have a positive effect on the subsequent hydrotreatment reaction (Pd/C, 350 °C, 100 bar H2) and gives product oils with significantly lower Mw (up to 43% lower), higher volatility, and improved calorific values (up to 45.3 MJ kg−1) compared to a direct hydrotreatment.

We present a simple method for solubilising lignin using liquid ammonia. Unlike water, which requires harsh conditions, ammonia can solubilise technical lignins, in particular kraft lignin. A commercial pine wood Kraft lignin (Indulin AT) was solubilized instantaneously at room temperature and 7–11 bars autogeneous pressure, while a commercial mixed wheat straw/Sarkanda grass soda lignin (Protobind™ 1000) was solubilized within 3 h at ambient temperature, and 30 min at. 85 °C. Hydroxide salts were not required. Wheat straw, poplar and spruce organosolv lignins, as well as elephant grass native lignin (MWL) were also solubilized, albeit at lower values. Different sequences of solubilisation and extraction were tested on the Protobind™ 1000 lignin. The remaining lignin residues were characterized by FTIR, size exclusion chromatography (SEC), elemental analysis (ICP), 2D-NMR and 31P NMR. Liquid ammonia is not an innocent solvent, as some nitrogen was incorporated in the residual lignin which then rearranged to higher molecular weight fractions. Nevertheless, the mild solubilisation conditions make liquid ammonia an attractive candidate as a solvent for lignin in future biorefinery processes.

Lignin preparations from kraft and sulfite pulping, steam explosion, and enzyme saccharification processes were assessed as substrates for lignin polymerization catalyzed by Trametes hirsuta laccase (ThL). Oxygen consumption associated with laccase catalyzed oxidation of the selected lignins was measured using a microplate-based oxygen assay. Laccase-induced changes in the molecular masses of the lignin polymers were assessed with aqueous-alkaline size exclusion chromatography (SEC) and changes in monomeric phenolics by reverse-phase high pressure liquid chromatography (HPLC). Obtaining consistent results in the lignin-laccase assay system required careful pH monitoring and control. All lignin preparations were oxidized by ThL, the rate being highest for steam-exploded eucalypt and lowest for enzyme-saccharified lignin. Comparing lignins, higher lignin-laccase reactivity was correlated with lower lignin molecular mass and higher amounts of monomeric phenolics. Solubility was not an indicator of reactivity. Steam-exploded and lignosulfonate-treated pine preparations were further fractionated by ultrafiltration to determine what molecular mass fractions were the most reactive in ThL catalyzed oxidation. Both retentate (> 3kDa), and to a lesser degree permeate (

The new organosolv process of wheat straw fractionation elaborated by Compagnie Industrielle de la matiere Vegetale (France) corresponds to the biorefinery approach, which allows separating cellulose, hemicelluloses, and lignin. The straw lignin (Biolignin™) is an attractive product, for which new applications are sought. In the present work, straw lignin (L) was converted into liquid lignopolyols via a batch reaction with propylene oxide (PO). The effects of the lignin content (L%) in the initial reaction mixture (L/(L+PO) on the oxypropylation process and the properties of whole lignopolyols and L/PO copolymers were studied. Almost complete disappearance of L-OHphen and L-COOH groups in copolymers was accompanied by an increase in the L-OHaliph groups’ content therein. The polydispersity (M w /M n ) of all copolymers obtained decreased essentially compared to the reference. The extent of PO grafting onto OH groups increased with decreasing lignin content in the initial reaction mixture. At a lignin content of 15–30% in the initial reaction mixture, the lignopolyols fulfil the requirements of polyol polyethers for rigid polyurethane foam production. The further increase in the lignin content leads to the appearance of the non-liquefied fraction and the undesirable increase in the viscosity of the liquefied part.

Technical hydrolysis lignin (THL) was micronized by grinding in a rotary-jet mill to obtain a fraction of approximately 5 mm. Both initial and milled THLs were liquefied by thermal alkaline treatment at 220°C for 2 h. Upgraded THLs that were nonmilled (L1) and milled (L2) were desalted by treatment with cation-exchanged resin and were dried. Micronization affected the course of hydrothermal alkaline treatment and the structure and composition of the obtained lignin. Thus, L2 contained much less concomitant polysaccharides and extractives than L1 and was more condensed. The molecular weights of L1 and L2 were 1100 and 1000 Da, respectively, as determined by size-exclusion chromatography. Structural characterization carried out by employing tandem electrospray ionization-mass spectrometry and 1D and 2D nuclear magnetic resonance spectroscopy revealed that small amounts of β-O-4 (∼6 mol.%), β-5, and β-β structures still remained in L1 and L2. Overall, upgraded lignins are oligomers (trimers-pentamers) with highly degraded propane chains and possess polyconjugated condensed aromatic structures. Upgraded THL seems to be a promising raw material for polymeric formulations.

Non-purified lignins resulting from ethanol-based organosolv fractionation of wheat straw were characterized for the presence of impurities (carbohydrates and ash), functional groups (hydroxyl, carboxyl and methoxyl), phenyl-propanoid structural moieties, molar mass distribution and thermal behavior. In accordance with its herbaceous nature, the syringyl/guaiacyl-ratio of the wheat straw lignins was substantially lower than of Alcell lignin. In addition, the content of p -hydroxyphenyl and carboxyl groups is substantially higher for the wheat straw lignins. The non-purified organosolv lignins had a high purity with 0.4–5.2% carbohydrate impurities, both originating from lignin to carbohydrate complexes and residual organosolv liquor. The use of H 2 SO 4 in the organosolv process improved the lignin yield, but at low acid doses increased the carbohydrate impurities. For applications where a low amount of carbohydrates is important, lignin from a high-temperature autocatalytic organosolv process was found to be preferred. The highest content of total hydroxyl groups was determined when lignins were produced using 30 mM H 2 SO 4 as catalyst or 50% w/w aqueous ethanol as solvent for the organosolv process. Aliphatic hydroxyl groups, the most predominant type of hydroxyl groups present originating for a substantial part from residual carbohydrates, were found to decrease with reaction time and ethanol proportion of the organosolv solvent. The correlations between organosolv process conditions and lignin characteristics determined can facilitate the use of organosolv lignins in value-added applications such as in polymers and resins and as a feedstock for bio-based aromatics.

Ingeniería técnica Industrial. Especialidad en Química industrial

Development of eco-friendly binders with no harmful emission during its complete life cycle is of high interest for the wood-based industry. In this paper, a fully renewable binder based on activated lignin and poly-furfuryl alcohol and a partly renewable lignin based phenol-formaldehyde (PF) binder were evaluated. Activation of kraft and soda lignins, isolated respectively from softwood and non-woods, by periodate oxidation was performed to improve lignin reactivity and application in wood adhesives. Periodate oxidation of lignin leads to higher lignin acidity, formation of quinonoid groups under more severe conditions, higher molar mass and higher reactivity towards the curing of furfuryl alcohol within a temperature range currently used in industry. Comparison of a 100% furan-based glue with a furan-based glue substituted by 10% lignin yields comparable product properties. However, periodate-activated lignin leads to lower wood failure, which might be caused by incompletely solubilised lignin particles in the acidic formulation disturbing crosslinking of the furan resin. Unmodified softwood kraft lignin performs well in a PF resin formulation at substitution levels up to 30% (w/w). Periodate oxidation of soda lignins enhances the glue performance because higher wood failure is attained. The higher molar mass after periodate treatment could be an important parameter for development of a stronger wood binder.