This article studied the carboxylation of technical lignin and subsequent use as emulsion stabilizer. Oxidation was conducted with hydrogen peroxide under alkaline conditions. As both titration and Fourier-transform infrared spectroscopy (FTIR) showed, phenolic units were converted to carboxyl groups by oxidation. The treatment was most effective for soda lignin from Arkansas/straw, but also had significant effect on the softwood kraft lignin and softwood soda lignin. An increase in molecular weight by size-exclusion chromatography was further noted, which was less pronounced for the Arkansas/straw lignin. It was argued that one contributing mechanism was the monolignol composition, as the lignin from annual plants also contained S-units in addition to the G-units that mostly made up the softwood lignin. Moreover, purification prior to oxidation, i.e., removal of inorganic components in the lignin, showed no significant effect on the carboxylation process. Emulsion stabilization was studied with respect to the pH using three oxidized kraft lignins. Here, lower pH yielded better emulsion stabilization, unless the lignin precipitated, which switched the stabilization mechanism from interfacial adsorption to particle stabilization. It was argued that the degree of ionization played a key role, as a lower degree of ionization corresponded with better emulsion stability at the same ionic strength. At last, measurements of interfacial tension and interfacial rheology found that oxidized lignin behaved similar to water-soluble lignosulfonates and created viscoelastic interface layers. 

Wood-derived TEMPO-oxidized cellulose nanofibrils (CNFs) have potential as scaffolding for bone tissue engineering. Although biocompatible, the material lacks osteoconductive and appropriate mechanical properties. Incorporation of nano-hydroxyapatite (nHA) and modification of scaffold preparation methods could improve applicability. In this study, freeze-dried porous scaffolds were prepared using a range of nHA (0, 20, 33, 50%) and CNF compositions. Not only the microarchitecture but also the chemical composition of the scaffolds was studied. Osteoblast-like osteosarcoma derived cells (Saos-2) were cultured on the scaffolds and their responses (viability, attachment, proliferation, and osteogenic phenotype) to the different scaffolds were documented. The results show that incorporation of nHA influenced the microarchitecture, mechanical stiffness and surface properties of the scaffolds. Moreover, biological characterization demonstrated good cell viability in all the groups. However, the increase of nHA concentration beyond 20% does not offer further advantages. It is concluded that the incorporation of 20% nHA resulted in the widest and most biomimetic pore size distribution, increased surface roughness and improved protein adsorption. These changes in material properties enhanced cell spreading and the osteogenic gene expression of osteoblast-like cells seeded on the scaffolds. Moreover, 20% nHA warrants further investigation as a potential scaffolding material for bone tissue engineering. Graphical abstract: (Figure presented.).

This article provides a concise insight into the thermoforming of airlaid CTMP pulp. First, the airlaid process was studied, showing that fiber fractionation and the retention of fines occurred in the forming head. Then, the effect of temperature and pressure during thermoforming was investigated. Harsher conditions, i.e. higher temperature and pressure, yielded greater densification of the substrate and higher tensile strength. The maximum strength was found at the highest settings tested, that is, 100 MPa and 200°C. The screening of thermoforming conditions was also compared to previously published results on wetforming. Next, the effect of softwood CTMP pulp was delineated, which on average showed the best mechanical properties at elevated freeness and high degrees of bleaching. At last, a comparison between dry forming and wetforming was made for one selected pulp quality. Here, the dryformed substrates were stiffer at low elongation, yet the wetformed substrates yielded a greater extensibility and higher tensile strength. In conclusion, dryformed pulp mostly relies on temperature and pressure for bond formation during thermoforming, which produces materials that are distinctly different from wetformed molded pulp. 

In this paper, the potential of esterified Kraft lignin as a novel oil-soluble surfactant was examined. The lignin was chemically modified by esterification with lauric or stearic acid, making it soluble in solvents such as toluene or n-decane. Adsorption at the oil-water interface was then studied by the Du Noüy ring-method. The oil-soluble lignin behaved similar to water-soluble lignin surfactants, both the qualitative and quantitative progression of interfacial tension. Modeling revealed a surface excess of 7.5-9.0 × 10-7 mol/m2, area per molecule of 185-222 Å2, and a diffusion coefficient within the range 10-10 to 10-14 m2/s; all of which are in line with existing literature on water-soluble lignosulfonates. The data further suggested that the pendant alkyl chains were extended well into the paraffinic solvent. At last, bottle tests showed that the oil-soluble lignin was able to stabilize oil-in-water emulsions. The emulsion stability was affected by the concentration of lignin or NaCl as well as the oil phase composition. Aromatic oils exhibited lower emulsion stability in comparison to the aliphatic oil. In conclusion, a new type of surfactant was synthesized and studied, which may contribute to developing green surfactants and novel approaches to valorize technical lignin.

This article tested a novel concept for synthesizing green wax inhibitors. Four technical lignins were reacted with stearoyl chloride to produce esterified C18 esterified lignin. The effect of the reaction on the lignin molecular weight, characteristic FTIR spectra, and thermal degradation was surveyed. In addition, wax inhibition testing was performed by rheology on model waxy oils. The grafting reactions increased the mass-average molecular weight of the lignin and in some cases also the polydispersity index. FTIR analysis confirmed the success of esterification reactions as the O-H stretching band decreased, whereas the C-H and C═O stretching bands significantly increased. The thermal degradation was further found to occur at temperatures above 170 °C, indicating that the lignin wax inhibitors were thermally stable enough for crude oil production. The effect on waxy gelation was varied, showing that the low molecular weight waxes benefited more than the high molecular ones. A gelation point reduction of up to 6 °C was found after lignin addition. After the wax type, wax concentration, lignin concentration, and lignin type were varied, it was found that C18 esterified Kraft lignin exhibited the most beneficial effect. The results from viscometry agreed with the observations from the rheometric gelation point. Cross-polarized microscopy was used to map the effect on the wax crystal morphology. A difference was found only in the case of one esterified Kraft lignin, which yielded smaller and more finely dispersed wax crystals. In conclusion, a new wax inhibitor was synthesized by reacting technical lignin with stearoyl chloride. This lignin showed wax inhibitor activity in some of the tested cases. At this point, the length of the pendant alkyl chains (C18) is likely a limiting factor. However, this study attributes the potential for a new concept to synthesize green wax inhibitors. 

Purity of technical lignin is one of the main obstacles in the utilization of lignin to value-added chemicals, products, and materials. The objective of this study was to investigate and compare single and two stage purification methods for obtaining soda lignin with high purity. Extensive washing and extraction with water was found effective, increasing the abundance of acid insoluble lignin while reducing its ash content. Extraction with organic solvents was conducted with 2-propanol or blends of n-heptane/1-butanol or cyclohexane/acetone. These solvents were shown to have little effect on the total lignin content, as determined by wet-chemical methods. Two-stage treatments (washing with water followed by solvent extraction) were hence not better than single stage water extraction in terms of the lignin purity. Still, selective removal of low molecular weight components after solvent extraction was noted, reducing the overall polydispersity of the lignin. Evaporation at 40 °C also showed little effect, whereas calcination at 150 °C significantly increased the molecular weight of the soda lignin. The latter effect was explained by thermally induced cross-linking. In addition, the UV absorbance of the calcinated lignin increased, which is likely related to changes in the aromatic structure. Such effect also entailed that UV/vis spectrophotometry was found less reliable in determining the total lignin content. At last, a mathematical model was adapted to predict the total lignin content from FTIR spectrometry. In conclusion, the tested procedures can be used to purify soda lignin and adjust its molecular weight.

Active Principal Ingredient (API) encapsulation through adsorption and physical entrapment onto TEMPO-oxidized cellulose nanofibrils (toCNFs) is possible, but challenges such as burst release and use of low water-soluble API such as sulfadiazine (SD) are yet to be addressed. The objective of this study is to assess the release property and antibacterial activity of toCNF/β-Cyclodextrin (β-CD)/SD materials in the form of films. Release in sink conditions was achieved with result highlighting the importance of the toCNF network structure, which is tightened at acidic pH for toCNFs due to its carboxylic content, reducing the burst effect phenomena. Antibacterial activity against Staphylococcus aureus and Escherichia coli was assessed and the results showed a clear beneficial impact of using β-CDs. An antibacterial effect for toCNF/SD films is confirmed for 3 successive applications whereas an antibacterial effect for a toCNF/CMβCD/SD film is prolonged up to 7 successive applications. The improvement of the topical release of a prophylactic agent with these materials are making them promising for biomedical applications such as wound dressing. Graphic abstract: [Figure not available: see fulltext.] © 2023, The Author(s)

Cellulose-based materials represent a renewable, biodegradable, and environmentally friendly alternative to plastic from fossil resources. Nanopaper is a strong and lightweight material formed from cellulose nanofibrils (CNFs). Paper and nanopaper have been considered as excellent alternatives to plastics for use in agriculture and for packaging applications. However, common for both paper and nanopaper is their hydrophilic character, and consequently, poor water-resistance properties. ORMOCER®s are a class of inorganic–organic polymers with excellent barrier and protective properties used for a range of coating applications. Here we present ORMOCER®-coated paper and nanopaper. The coated papers and nanopapers are characterized, both in terms of their morphology, hydrophobicity, and mechanical properties. We demonstrate that the pressure used during the pressing and drying of paper and nanopaper influence their tear and tensile—properties, and that the morphology of the coated nanopaper differs significantly from that of the coated paper. While the ORMOCER® was impregnated within the porous network of the paper, a well-defined two-layered morphology was obtained with the coated nanopaper. Further, the biodegradability of the nanopaper with and without coating was assessed. The degradation study demonstrated that both the pressure used during the pressing and drying of the nanopaper, and the composition of the ORMOCER®, influenced the rate of degradation. Taken together, ORMOCER®-coated paper and nanopaper are promising for the preparation of materials that are both water-resistant, renewable, and biodegradable. © 2022, The Author(s).

Cellulose nanofibrils (CNFs) are multiscale hydrophilic biocompatible polysaccharide materials derived from wood and plants. TEMPO-mediated oxidation of CNFs (TO-CNF) turns some of the primary hydroxyl groups to carboxylate and aldehyde groups. Unlike carboxylic functional groups, there is little or no information about the biological role of the aldehyde groups on the surface of wood-based CNFs. In this work, we replaced the aldehyde groups in the TO-CNF samples with carboxyl groups by another oxidation treatment (TO-O-CNF) or with primary alcohols with terminal hydroxyl groups by a reduction reaction (TO-R-CNF). Rat mesenchymal stem/stromal cells (MSCs) derived from bone marrow were seeded on polystyrene tissue culture plates (TCP) coated with CNFs with and without aldehyde groups. TCP and TCP coated with bacterial nanocellulose (BNC) were used as control groups. Protein adsorption measurements demonstrated that more proteins were adsorbed from cell culture media on all CNF surfaces compared to BNC. Live/dead and lactate dehydrogenase assays confirmed that all nanocellulose biomaterials supported excellent cell viability. Interestingly, TO-R-CNF samples, which have no aldehyde groups, showed better cell spreading than BNC and comparable results to TCP. Unlike TO-O-CNF surfaces, which have no aldehyde groups either, TO-R-CNF stimulated cells, in osteogenic medium, to have higher alkaline phosphatase activity and to form more biomineralization than TCP and TO-CNF groups. These findings indicate that the presence of aldehyde groups (280 ± 14 μmol/g) on the surface of TEMPO-oxidized CNFs might have little or no effect on attachment, proliferation, and osteogenic differentiation of MSCs. © 2023 The Authors.

In this work, we aimed to tune cellulose nanocrystals (CNCs) properties by introducing different functional groups (aldehyde, carboxyl, silane, and ammonium groups) on the surface through different chemical modifications. These functional groups were obtained by combining: the periodate oxidation with TEMPO-oxidation, aminosylation or cationization. CNCs produced and their films were characterized to elucidate their performances. The results showed that the properties of obtained CNCs varied depending on the grafted functionalities on the surface. The results reveal that after each modification a colloidal stability is preserved. Interestingly, Periodate oxidation of cellulose nanocrystals results in film components that interact through intra- and intermolecular hemiacetals and lead to films with a tensile strength of 116 MPa compared to the pristine CNCs, in contrast the subsequent modifications led to lower tensile strength. Of note, remarkable thermal stability has been achieved after modifications reaching a maximum of 280 °C. The oxygen barrier properties of the films after modifications varied between 0.48 and 0.54 cm3μm/(m2d*kPa) at 50 % RH.