Brownstock washing, a critical process in cleansing kraft pulp, removes dissolved lignin residues from the pulp after it has passed through the cooking digester. It plays a significant role in kraft pulp mills by enhancing economic efficiency and environmental sustainability. Improved washing efficiency leads to better pulp quality and more effective recovery of cooking chemicals. Our study aimed to better understand the impact of different chemical compositions in washing liquors on washing performance. We tested a range of washing liquors, including neutral solutions (deionized water, 1M NaCl, 3M NaCl, 1M Na2SO4) and alkaline solutions (tap water, washing liquor composed of 0.35M NaOH and 1M Na2SO4, and white liquor with 50 g[OH]/l and 8.77 g[HS]/l). These liquors were evaluated for their efficacy in maximizing lignin extraction. Our findings suggest that salt solutions generally reduce washing efficiency. Deionized water and white liquor proved to be the most efficient washing agents, while high-concentration salts and those with high ionic strength negatively impacted washing efficiency. This suggests that brownstock washing may not be operating at its full potential.

This work has focused on oxygen's role in the delignification process within the context of pulp production. We have investigated the role of oxygen in a complex set of chemical reactions taking place during this process, including both oxidative and non-oxidative reactions. This study explores the impact of pH changes during the oxygen delignification process and the characteristics of the resulting pulps. Additionally, this research examines the effect of oxygen, by comparing conventional oxygen delignification with trials using air and nitrogen. Industrial softwood kraft pulps with a kappa number of 35 were subjected to delignification for 20-120 min under alkaline conditions. The resulting pulps were assessed for kappa number, intrinsic viscosity, fiber charge, and ISO brightness. An important observation from this research is the reduction in lignin molecular weight upon exposure to oxygen and air, suggesting depolymerization reactions facilitated by oxygen species, whereas nitrogen exposure results in less pronounced changes. This finding underscores the impact of oxygen in altering lignin structure, thus informing the selectivity and effectiveness of the delignification process.

Glucuronoxylan is the main hemicellulose in the secondary cell wall of angiosperms. Elucidating its molecular structure provides a basis for more accurate plant cell wall models and the utilization of xylan in biorefinery processes. Here, we investigated the spacing of acetyl, glucuronopyranosyl and galactopyranosyl substitutions on Eucalyptus glucuronoxylan using sequential extraction combined with enzymatic hydrolysis and mass spectrometry. We found that the acetyl groups are preferentially spaced with an even pattern and that consecutive acetylation is present as a minor motif. Distinct odd and even patterns of glucuronidation with tight and sparse spacing were observed. Furthermore, the occurrence of consecutive glucuronidation is reported, which adds to the growing body of evidence that this motif is not only present in gymnosperms but also in angiosperms. In addition, the presence of terminal galactopyranosyl units, which can be released by β-galactosidase, altered the digestibility of the glucuronoxylan by GH30 and GH10 xylanase and appeared to be clustered within the polymeric backbone. These findings increase our understanding of the complex structure of glucuronoxylans and its effect on the extractability and biological degradation of Eucalyptus wood.

Although organosolv processes using high-boiling solvents have been investigated in recent decades for developing novel industrial processes, there are potential benefits of using high-boiling point solvents for traditional sulphate-based cooking processes, both from an industrial perspective and from a laboratory perspective. Using high-boiling solvents, experiments can be done under atmospheric conditions, thus making it easier to continually monitor laboratory experiments and extracting aliquots at desired intervals. Using such a system, alkaline consumption was monitored during impregnation of spruce chips in glycerol media using chemical charges of 1 M NaOH and 0.1 M NaHS, i. e., kraft pulping conditions, and compared to a similar investigation of alkaline consumption in water media using steel autoclaves. The resulting data was fitted to a first order kinetic model, with an apparent activation energy of 22 kJ mol-1 in glycerol media. Finally, a "normal quality pulp"of kappa number 28 and a viscosity of 1113 ml g-1 was successful produced using a cooking process with an impregnation step at 140 °C for 3 h and a cooking step at 160 °C for 4 h. A nuclear magnetic resonance study on the dissolved lignin produced for said experiment showed characteristics typical of other kraft lignins.

Samples of Eucalyptus dunnii with high calcium content have less good pulping properties regarding delignification and polysaccharide degradation, as it was shown by us earlier. In this work, we tested the addition of black liquor and green liquor to the Eucalyptus dunnii chips before kraft pulping, Specific improvements were obtained with both liquors, but the most substantial effect was observed with the green liquor, where even wood with the highest calcium content was pulped with a good result. Delignification was faster, and viscosity losses (degree of polymerization of cellulose) were higher for samples treated with green liquor prior to kraft pulping. Bleaching experiments showed that the bleachability of the green liquor-treated pulp was virtually the same as for a control pulp and that the higher viscosity of the bleached pulp was maintained. Possible chemical explanations for the results obtained are discussed.

Studies have shown that the size of LNP depends on the molecular weight (M-w) of lignin. There is however need for deeper understanding on the role of molecular structure on LNP formation and its properties, in order to build a solid foundation on structure-property relationships. In this study, we show, for similar M-w lignins, that the size and morphology of LNPs depends on the molecular structure of the lignin macromolecule. More specifically, the molecular structure determined the molecular conformations, which in turn affects the inter-molecular assembly to yield size- and morphological-differences between LNPs. This was supported by density functional theory (DFT) modelling of representative structural motifs of three lignins sourced from Kraft and Organosolv processes. The obtained conformational differences are clearly explained by intra-molecular sandwich and/or T-shaped pi-pi stacking, the stacking type determined by the precise lignin structure. Moreover, the experimentally identified structures were detected in the superficial layer of LNPs in aqueous solution, confirming the theoretically predicted self-assembly patterns. The present work demonstrates that LNP properties can be molecularly tailored, consequently creating an avenue for tailored applications.

An ionization difference UV-Vis method (Delta epsilon-spectrum method) is the most potentially simple method for fast quantitation of phenolic hydroxyl groups (ph-OH) in lignin. However, the underestimated results were calculated from the conventional Delta epsilon-spectrum method using one- or two-point wavelengths measurement. In this study, a modified Delta epsilon-spectrum method using multi-point wavelengths measurement was developed and the negative absorbance was also considered. Four main typical lignin models, e.g. vanilla alcohol, 5-5 biphenyl, stilbenoid and vanillin, were applied as the guaiacyl-type (G-type) phenolic models for the determination of ph-OH by the modified Delta epsilon-spectrum method. The 2-methoxyethanol/water/acetic acid = 8/2/0.2 (V/V/V) was used as the acidic solvent system and the 2-methoxyethanol/0.2 M NaOH solution = 1/9 (V/V) was used as the alkaline solvent system. The ph-OH contents in the spruce milled wood lignin (SMWL) and the spruce Kraft lignin (SKL) were respectively quantified by the modified Delta epsilon-spectrum method as 1.078 and 4.348 mmol/g, which were comparable to the counterparts determined by P-31 Nuclear Magnetic Resonance Spectroscopy (P-31 NMR). The results revealed that the modified Delta epsilon-spectrum method can provide more accurate and reliable results compared to the conventional method.

Eucalyptus dunnii is cultivated in Uruguay for kraft pulping purposes. However, depending on the growth site, the kraft pulping properties of the wood vary highly, and in some cases, pulping is difficult. Different batches of wood were chemically characterized and the only significant difference related to the pulping properties was the calcium content. The calcium appears to at least partly be present in the form of crystals in the lumen. Kraft pulping experiments on wood with different calcium contents indicated that high calcium led to slower delignification, and higher yield losses. Hexeneuronic acid formation was not significantly affected. Possible mechanistic explanations for these effects are discussed.

The natural polymer, lignin, possesses unique biodegradable and biocompatible properties, making it highly attractive for the generation of nanoparticles for targeted cancer therapy. In this study, we investigated spruce and eucalyptus lignin nanoparticles (designated as S-and E-LNPs, respectively). Both LNP types were generated from high-molecular-weight (M-w) kraft lignin obtained as insoluble residues after a five-step solvent fractionation approach, which included ethyl acetate, ethanol, methanol, and acetone. The resulting S-and E-LNPs ranged in size from 16 to 60 nm with uniform spherical shape regardless of the type of lignin. The preparation of LNPs from an acetone-insoluble lignin fraction is attractive because of the use of high-M-w lignin that is otherwise not suitable for most polymeric applications, its potential scalability, and the consistent size of the LNPs, which was independent of increased lignin concentrations. Due to the potential of LNPs to serve as delivery platforms in liver cancer treatment, we tested, for the first time, the efficacy of newly generated E-LNPs and S-LNPs in two types of primary liver cancer, hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA), in vitro. Both S-LNPs and E-LNPs inhibited the proliferation of HCC cells in a dose-dependent manner and did not affect CCA cell line growth. The inhibitory effect toward HCC was more pronounced in the E-LNP-treated group and was comparable to the standard therapy, sorafenib. Also, E-LNPs induced late apoptosis and necroptosis while inhibiting the HCC cell line. This study demonstrated that an elevated number of carbohydrates on the surface of the LNPs, as shown by NMR, seem to play an important role in mediating the interaction between LNPs and eukaryotic cells. The latter effect was most pronounced in E-LNPs. The novel S- and E-LNPs generated in this work are promising materials for biomedicine with advantageous properties such as small particle size and tailored surface functionality, making them an attractive and potentially biodegradable delivery tool for combination therapy in liver cancer, which still has to be verified in vivo using HCC and CCA models.

Interaction between xylan and cellulose microfibrils is required to maintain the integrity of secondary cell walls. However, the mechanisms governing their assembly and the effects on cellulose surface polymers are not fully clear. Here, molecular dynamics simulations are used to study xylan adsorption onto hydrated cellulose fibrils. Based on multiple spontaneous adsorption simulations it is shown that an antiparallel orientation is thermodynamically preferred over a parallel one, and that adsorption is accompanied by the formation of regular but orientation-dependent hydrogen bond patterns. Furthermore, xylan adsorption restricts the local dynamics of the adjacent glucose residues in the surface layer to a level of the crystalline core, which is manifested as a three-fold increase in their 13C NMR T1 relaxation time. These results suggest that xylan forms a rigid and ordered layer around the cellulose fibril that functions as a transition phase to more flexible and disordered polysaccharide and lignin domains.