Lignin has been extensively researched as a cathode active material in secondary batteries. In the present work, the energy storage potential of lignin naturally present in papers made of chemi-thermomechanical pulp (CTMP) is explored. More specifically, effects from CTMP fines on the electrochemical characteristics have been studied. Compared to pulp fibers, fines are higher in lignin content and have higher specific surface area. It was expected that this would be positive for the electrode performance; however, the result points to the opposite. The fines do not significantly contribute to a higher lignin specific capacity, and they deteriorate the cycling stability. Higher fines content was found to result in a higher oxidative activity as well as more abundant competing reactions. These competing reactions are believed to be linked to the cycle stability. Therefore, we hypothesize that the electrochemical stability of lignin can be better understood by studying differences between fines and fiber lignin. As the theoretical specific capacity of this material is about 20 times larger than obtained here, identification of the reasons for this capacity discrepancy is needed to realize the full potential of lignin-based paper batteries.

Reducing the heterogeneity of technical lignin is essential to obtain predictable and high-performance polymeric materials that are suitable for high-value applications. Organic solvents with different polarities and solubilities can be used to fractionate lignin and reduce the complexity and diversity of its chemical structure. Among the various solvents and solvent mixtures, acetone-water mixtures offer an energy-efficient, cost-effective, and environmentally friendly means of lignin fractionation. In the present study, temperature-induced acetone-water fractionation was investigated to refine the properties of a technical softwood Kraft lignin, i.e., LignoBoost™ lignin. Relatively mild operating conditions were tested, namely, temperatures of 70-110°C and autogenous pressure. A factorial experimental design was developed using the Design-Expert® software, and three factors (temperature, time, and acetone concentration) were investigated. It was found that temperature-induced fractionation could increase lignin homogeneity and maintain high lignin solubilization with a short processing time (<1 h). It was also possible to tune the properties of the soluble lignin fraction (yield and weight-average molecular weight) based on the factorial models developed. The techno-economic evaluation confirmed the commercial viability of this fractionation process. 

The continuous flow supercritical water (scH2O) treatment of Birch wood (T=372–382 °C; t=0.3–0.7 s; p=260 bar) followed by alkali extraction of lignin allowed for the isolation of lignin and lignin carbohydrate complexes (LCCs) with a high number of β-O-4 moieties in the range 29–57/100 Ar (evaluated by quantitative 13C NMR analysis) in yields ranging between 13–19 wt % with respect to the initial wood. A “lightning rod effect” of carbohydrates has been claimed to explain the low degradation of β-O-4 bonds during the process. The structure of the isolated lignin was thoroughly elucidated via comprehensive NMR studies (HSQC, 13C and 31P). A low degree of condensation (DC)<5 % was found for all the lignin samples, which was only slightly dependent on the reaction severity. The number of aliphatic −OH, phenolic −OH, and −COOH groups was in the range 3.37–5.25, 1.41–2.31 and 0.39–0.73 mmol/g, respectively. The number of −COOH groups increased with increased severity, suggesting that oxidation can occur during the scH2O treatment. Furthermore, by simply varying the reaction severity, it was possible to tune important lignin properties, like the molar mass and the glass transition temperature (Tg).

Process-integrated, continuous, separation of lignin from kraft pulp mills which results in a ligninwith low ash content (0.05-1 %) is relatively new technology compared to traditional kraft pulping subprocesses,like recovery boilers, lime kilns, white liquor preparation etc. The LignoBoost technology wasdemonstrated in 2007 and the first commercial full-scale process started in 2013, delivered to Domtarby Valmet. This means that this concept now has been in commercial scale operation for almost 10years. There is also an alternative commercialized concept available today from another supplier,NORAM International. The idea to integrate lignin separation into a kraft pulp mill is today quite provencommercial technology.This paper will discuss different learnings, experiences, from the early development of theLignoBoost process, which includes handling of the separated lignin followed by drying. The dustexplosion risk is relatively high for dry kraft lignin due to a high kst value – so the paper will also discussif there are opportunities to reduce this risk. The paper will also briefly discuss promising productsegments for kraft lignin.

The effect of reaction variables on the oxidative ammonolysis of technical lignins was studied in the range of 0.4-0.8 M NH4OH, reaction temperature of 70 - 130°C, oxygen pressure of 0.5 - 1.2 MPa and pH 9- 12.7. The kinetics of nitrogen incorporation consists of two phases, both of which follow a pseudo-first order reaction law. The reaction is 1st and 0.5 order with respect to oxygen and NH4OH concentration, respectively. The effective activation energy of nitrogen incorporation is rather low, 33-43 kJ/mol. The dependence of the reaction rate on pH of the reaction solution goes through a maximum. Linear correlation between nitrogen incorporation and O-demethylation, CO2 formation, oxygen uptake as well as oxygen incorporation were observed. Structural analyses of the soluble N-modified lignins by FTIR and 1H NMR spectroscopic techniques showed only qualitative differences of the spectra obtained under different reaction conditions indicating that the reaction conditions do not affect the reaction pathways. A scheme of possible reaction mechanisms is postulated based on the experimental results. 

Sugar-based biorefineries have faced significant economic challenges. Biorefinery lignins are often classified as low-value products (fuel or low-cost chemical feedstock) mainly due to low lignin purities in the crude material. However, recent research has shown that biorefinery lignins have a great chance of being successfully used as high-value products, which in turn should result in an economy renaissance of the whole biorefinery idea. This critical review summarizes recent developments from our groups, along with the state-of-the-art in the valorization of technical lignins, with the focus on biorefinery lignins. A beneficial synergistic effect of lignin and cellulose mixtures used in different applications (wood adhesives, carbon fiber and nanofibers, thermoplastics) has been demonstrated. This phenomenon causes crude biorefinery lignins, which contain a significant amount of residual crystalline cellulose, to perform superior to high-purity lignins in certain applications. Where previously specific applications required high-purity and/or functionalized lignins with narrow molecular weight distributions, simple green processes for upgrading crude biorefinery lignin are suggested here as an alternative. These approaches can be easily combined with lignin micro-/nanoparticles (LMNP) production. The processes should also be cost-efficient compared to traditional lignin modifications. Biorefinery processes allow much greater flexibility in optimizing the lignin characteristics desirable for specific applications than traditional pulping processes. Such lignin engineering, at the same time, requires an efficient strategy capable of handling large datasets to find correlations between process variables, lignin structures and properties and finally their performance in different applications.

The subject of lignin structure, critical for fundamental and practical reasons, is addressed in this study that includes a review of the methods applied to elucidate macromolecular branching. The recently available approaches for determination of the absolute molecular mass of spruce milled wood lignin (MWL) along with the quantification of terminal groups clearly indicate that MWL is significantly branched and cross-linked (with ∼36% lignin units partaking in these linkages). Results from independent methods imply that about half of the branching and crosslinking linkages involve aromatic rings, predominantly 5-5′ etherified units; meanwhile, a significant number of linkages are located in the side chains. Quantitative 13C NMR analyses suggest that the branches involve different aliphatic ether (alkyl-O-alkyl) types at the α- and γ-positions of the side chain, with intact β-O-4 linkages. While the exact structures of these moieties require further investigation, our results point to the fact that conventional lignification theory disagrees with the presence of such key moieties in softwood MWL and the observed high degree of branching/crosslinking. Potential reasons for the noted discrepancies are discussed.

A reference lignin separated from an industrial softwood kraft black liquor via an improved LignoBoost process was compared to four other lignins derived from the same liquor. The four lignins were produced by using a) pH-fractionation within the LignoBoost process, b) ultrafiltration of black liquor prior to the LignoBoost process, and c) solvent leaching of the reference lignin using methanol and d) ethanol.Lignin compositional characteristics and thermal properties were compared, and monofilament extrusion used to assess their potential for successful melt spinning at the 24 filament scale. The lignin prepared by ethanol leaching of the reference lignin was found to be most appropriate for potential pilot scale fibre production. This was owing to a high purity, lower comparative glass transition temperature (Tg), and good spinning performance.Thermal pretreatments of the ethanol leached lignin gave a selection of enhanced lignins which were characterized for comparison, and melt spun on pilot multifilament equipment. The enhanced lignins could be continuously melt spun giving filaments with diameters as low as 10 μm and with minimal defects. Conversion of selected filaments provided carbon fibres with a tensile strength of 1259 ± 159 MPa, tensile modulus of 67 ± 3 GPa and diameter of 7.3 ± 0.5 μm.

The Plantrose® technology is a promising biorefinery method which enables the production of C5 and C6 sugars from different lignocellulosics using sub- and supercritical water in a two-step process. The lignin rich solids after carbohydrate hydrolysis containing various amounts of residual cellulose are trademarked as OmnoTM polymers. The reactivity and bonding performance of different Omno polymers in direct partial substitution of phenol-formaldehyde adhesive resins (PF) for the manufacture of oriented strand board (OSB) and softwood plywood were evaluated by a fast bench screening test using the Automatic Bond Evaluation System (ABES) and by pilot trials on the production and testing of wood panels. The results showed that about 1/3 of commercial glues could be successfully substituted by Omno polymers without any significant drop in the adhesive reactivity and properties of the resulting wood panels. Selected Omno polymers had superior performance as compared to high-purity pulping lignins (Kraft, soda and organosolv) due to a positive effect of the residual cellulose in the Omnopolymers on the adhesive performance. Hardwood lignins had no disadvantages as compared to various softwood lignins, in strict contrast to the current dogma.