During kraft pulping of wood, a considerable part of biomass is solubilized, forming a black liquor from which material can be taken out as by-products. Of these, extractive-derived fractions such as tall oil and raw turpentine has long seen technical utilization, and presently, lignin degradation products have garnered a large interest. The carbohydrate degradation products, however, have seen considerably less focus. In this work, we have investigated the structure of a high molecular-weight fraction of the carbohydrate degradation products using nuclear magnetic resonance spectroscopy, finding it to be a conjugated aromatic structure rich in methyl, methylidine, alcohol and carboxylic acid groups. Based on this information, we suggest a structure based on hydroxymethylfurfural as the repeating unit, with sugar acid substituents providing additional functionality. Additionally, UV-vis data of the polymer is compared with data from the kraft cooking of cotton linters and other model systems to corroborate the hypothesis that this polymer is indeed present in black liquor and potentially responsible for some of its characteristic colour. It also reacts in the kappa number analysis, exhibiting 40 % of the permanganate consumption predicted for pure lignin. Finally, the technical significance of these carbohydrate degradation products is discussed based on the structural findings.

Kraft pulping is the predominant technique for producing chemical pulps from wood. It offers low operational costs, versatility, high-quality pulps, and an efficient closed chemical recovery system. However, the process requires significant investment due to the necessity for pressurized environments and the associated costly equipment. This study explores a novel approach by replacing water with glycerol, allowing kraft pulping to occur at atmospheric pressure. However, the higher viscosity of glycerol compared to water partially limits impregnation. This research investigates the impact of temperature, chemical charge, and chip size on this process for both hardwood and softwood sapwood. The results indicate that lignin dissolution is expedited by reducing chip size for both softwood and hardwood. However, decreasing the chemical charge negatively impacts lignin dissolution. Conversely, increasing the temperature accelerates lignin release.

Lignin is one of the most complex biopolymers and is characterized by combination of monomers to form a variety of inter-monomer linkages, which successively build up the racemic polymer. The prevailing theory of lignin formation suggests that monomers are enzymatically oxidized into resonance-stabilized radicals that subsequently couple through radical–radical reactions to generate intermediates that are then stabilized via post-coupling reactions. However, this standard model for lignin formation is challenged by certain lignin structures that cannot be easily explained by this theory. One such structure characterized by a side chain carbon (α or β-position) linked to an aromatic C6 is the focal point of this minireview. The evidence supporting the presence of this structure in softwood lignin is scrutinized, leading to the conclusion that this type of structure is most likely formed during the lignification process. Possible mechanisms for its formation are discussed.

This study investigates the swelling and liquid retention properties of cellulosic pulp from cotton waste, cotton linters and conventional dissolving wood pulp in both neutral (water) and alkaline (sodium hydroxide) conditions in regard to the first phase of the viscose process (mercerization). The swelling of single fibers is investigated by microscopic observation of the diameter increase during immersion in the liquids, which resulted in a logarithmic trend over time. The retention properties are investigated by water and lye retention values, and the latter was coupled to the pressability of mercerized pulp through observation of the trend in press factor with increasing pressing times. The different materials behaved similarly in neutral conditions regarding single fiber swelling and retention properties. Alkaline conditions, on the other hand, resulted in increased swelling and retention properties for all materials compared to neutral conditions, and the cotton-based pulps showed higher single fiber swelling and retention of lye, accompanied by impeded pressability. Thereafter, several material properties were investigated; morphological fiber properties (fiber width, cell wall thickness and fiber coarseness), fines content, carbohydrate monomer composition, and charge density. The results indicate that a thin cell wall and large lumen of the cotton waste fibers affect their higher swelling and retention properties, but further investigation of other morphological, chemical and physical properties of the fibers and fiber networks in pulp sheets is necessary. However, these insights on the behavior of different pulps can already help industries with the optimization of implementation of cotton waste pulps for viscose production.

In pursuit of sustainable alternatives to fossil-based materials, cellulose-based products, such as regenerated cellulose and cellulose derivatives, have attracted increasing attention. These materials offer biodegradability, biocompatibility, and a wide range of adjustable properties. However, their production relies on dissolving pulps, which are significantly more expensive than standard paper-grade pulps due to high raw material and processing costs. In this study, a potential route for converting standard bleached chemical pulps into more reactive cellulose was investigated, targeting applications in cellulose derivatives and regenerated materials. The method is based on acidic treatment followed by cold alkali dissolution and precipitation. Results show increased chemical reactivity and partial hemicellulose removal, suggesting a promising path toward low-cost alternatives to conventional dissolving pulp.

Global fiber demand is rising rapidly, yet less than 1% of discarded textiles are recycled into new materials. Here, cold-alkali swelling followed by acid reprecipitation was investigated as a pretreatment to improve cellulose accessibility and reactivity in textile-waste feedstocks. Two recycled cotton-based textiles were compared with cotton linters and dissolving wood pulp. Swelling was performed in 10 wt% NaOH at –20°C, followed by reprecipitation and washing. Cold-alkali treatment increased water retention value (WRV) for all samples, reaching 3.0 g g−1 for recycled pure-cotton textile, 2.5 g g−1 for the cotton–synthetic blend, and 1.6 g g−1 for both cotton linters and dissolving wood pulp. Initial acid-hydrolysis rates increased from 9.0 to 26.3 mg l−1 min−1 for cotton linters, 10.0 to 27.5 mg l−1 min−1 for dissolving wood pulp, 11.6 to 28.8 mg l−1 min−1 for recycled pure-cotton textile, and 12.9 to 22.4 mg l−1 min−1 for the cotton–synthetic blend. These increases occurred despite moderate intrinsic-viscosity losses of 7-26%, depending on feedstock. X-ray diffraction showed broader and less-resolved diffraction peaks after swelling and reprecipitation, with crystallinity index values decreasing from 90% to 63% for cotton linters, from 78% to 66% for dissolving wood pulp, from 89% to 61% for recycled pure-cotton textile, and from 85% to 50% for the cotton–synthetic blend. Overall, cold-alkali swelling and reprecipitation improved cellulose accessibility and reactivity in textile-derived feedstocks and offer a practical pretreatment route for upgrading low-value cotton-rich waste toward regenerated-cellulose and cellulose-derivative processes.

Matrix polysaccharides in primary and secondary plant cell walls are biochemically diverse and include xylans, glucomannans, β-glucans (i.e., mixed linkage β-glucan and xyloglucan), pectins, and β-galactan. Their composition and molecular structure in specific cell walls depend on the type of plant, type of tissue, and the temporal development of the plant. The supramolecular organization of matrix polysaccharides around the cellulose microfibrils affects the flexibility and strength of the cell wall. However, the molecular level details of the interface between the cellulose microfibrils and the matrix polysaccharides are not fully understood. Here, the interaction of unsubstituted model oligosaccharides with cellulose microfibrils was investigated through molecular dynamics simulations of the adsorption of model oligosaccharides representing their respective backbone motifs. The simulations show that induced conformational changes of the polysaccharide backbone upon adsorption and its alignment with the cellulose microfibril lead to stronger interactions with cellulose. This differentiates typical primary and secondary cell wall hemicelluloses (xylans, glucomannans, and β-glucans) from pectins and β-galactan and explains why mixed-linkage β-glucan can be classified as a hemicellulose. Our study contributes to the development of accurate molecular models for plant cell walls, which will improve our understanding of lignocellulosic biomass and its conversion into functional biobased materials.

The growing interest in sustainable lignin valorization has prompted the exploration of new recovery methods compatible with modern kraft pulp mills. This study investigates the use of ultrafiltration for extracting lignin, referred to as oxlignin, from oxygen-delignification wash liquors. Unlike traditional acid precipitation, ultrafiltration enables lignin concentration and fractionation without disrupting the high-pH conditions required for brown stock washing or interfering with the sodium-sulfur balance of the recovery cycle. The oxlignin also has properties similar to lignosulfonates rather than kraft lignin. Using industrial process streams, ultrafiltration successfully prepared oxlignin, as confirmed by characteristic UV-vis absorbance features at 280 and 340 nm. These results demonstrate the ability to tailor lignin composition and open new opportunities for producing application-specific lignin products, such as dispersants or performance additives in bio-based materials. The retained filtrate could be suitable for reuse in the pulping process, ensuring integration with existing operations. Despite practical challenges such as membrane cost and fouling, the use of robust ceramic membranes offers a technically viable path forward for industrial implementation.

Aqueous redox flow batteries (RFBs) as grid-scale energy storage devices hold great potential to accomodate the rising demand for intermittent renewable energy sources. A significant parameter that enhances the sustainability of RFBs is selecting the appropriate redox species. In this study, we investigated the application of lignosulfonate as a redox species for the negolyte of aqueous RFBs because lignosulfonate is a low-cost, abundant, highly water-soluble material with a high phenol content. To overcome the intrinsic electrochemically irreversible nature of lignosulfonate, herein, oxidative depolymerization was employed to modify the chemical structure in a weakly alkaline media. The modified lignosulfonate exhibited improved electrochemical activity, as indicated by cyclic voltammetry, with distinct redox peaks that correspond to lignin-derived monomers, such as vanillin and 4-hydroxybenzaldehyde. The modified lignosulfonate, as negolyte, paired with ferrocyanide in the counterpart in a lab-based single RFB cell. The RFB utilizing 50 g L⁻¹ modified lignosulfonate showed 80.6 % capacity retention over 50 cycles and nearly 1.5 times higher discharge capacity than the RFB using non-modified lignosulfonate. By increasing the concentration of modified lignosulfonate up to 200 g L⁻¹, the discharge capacity increased threefold; however, the capacity retention dropped to 60 %. This study presents an opportunity to utilize bio-based electrolytes in building novel, cost-effective, and sustainable RFBs.

In the past decades, substantial research efforts have been directed towards increasing the availability of renewable and recycled raw materials. Lignin, one of the most abundant natural polymers, constitutes a vast, renewable, and largely untapped source of aromatic structures. In addition, it is one of the most abundant renewable sources of carbon. Despite the countless research projects aimed at valorizing kraft lignin, the largest source of industrial lignin, relatively few commercial kraft lignin products have emerged. Simultaneously, lignosulfonates represent a commercially successful range of products with a steady and growing global market. This paper reviews the current outlook of technical lignin research, including common misunderstandings, and discusses various factors that have hampered the use of lignin as a renewable source of materials and chemicals.