Loading...
8 results
Search Results
Now showing 1 - 8 of 8
- Levulinic acid: a novel sustainable solvent for lignin dissolutionPublication . Melro, Elodie; Filipe, Alexandra; Valente, Artur J. M.; Antunes, Filipe E.; Romano, Anabela; Norgren, Magnus; Medronho, BrunoLignin is a natural, renewable resource with potential to be used in biomaterials. Due to its complex structure, its efficient dissolution is still challenging, which hinders its applicability at large scale. This challenge become harder considering the current need of sustainable and environmentally friendly solvents. To the best of our knowledge, this work reports for the first time the dissolution of kraft lignin in levulinic acid, a "green" solvent, and compares its efficiency with common carboxylic acids and sulfuric acid. It has been found that levulinic acid has a high capacity to dissolve kraft lignin at room temperature (40 wt% solubility), and it efficiency is not compromised when diluting the acid with water (up to 40 wt% water content). the Kamlet-Taft pi* parameter of the different acidic solvents was estimated and found to correlate well with their solubility performance. Lignins previously dissolved in levulinic and formic acids were selected to be regenerated and minor differences were found in thermal stability and morphological structure, when compared to native kraft lignin. However, an increase in the content of the carbonyl groups in the regenerated lignin material was observed. (C) 2020 Elsevier B.V. All rights reserved.
- Enhancing lignin dissolution and extraction: the effect of surfactantsPublication . Melro, Elodie; Valente, Artur J. M.; Antunes, Filipe E.; Romano, Anabela; Medronho, BrunoThe dissolution and extraction of lignin from biomass represents a great challenge due to the complex structure of this natural phenolic biopolymer. In this work, several surfactants (i.e., non-ionic, anionic, and cationic) were used as additives to enhance the dissolution efficiency of model lignin (kraft) and to boost lignin extraction from pine sawdust residues. To the best of our knowledge, cationic surfactants have never been systematically used for lignin dissolution. It was found that ca. 20 wt.% of kraft lignin is completely solubilized using 1 mol L-1 octyltrimethylammonium bromide aqueous solution. A remarkable dissolution efficiency was also obtained using 0.5 mol L-1 polysorbate 20. Furthermore, all surfactants used increased the lignin extraction with formic acid, even at low concentrations, such as 0.01 and 0.1 mol L-1. Higher concentrations of cationic surfactants improve the extraction yield but the purity of extracted lignin decreases.
- Perspectives on the Lindman Hypothesis and cellulose interactionsPublication . Norgren, Magnus; Costa, Carolina; Alves, Luís; Eivazi, Alireza; Dahlström, Christina; Svanedal, Ida; Edlund, Håkan; Medronho, BrunoIn the history of cellulose chemistry, hydrogen bonding has been the predominant explanation when discussing intermolecular interactions between cellulose polymers. This is the general consensus in scholarly textbooks and in many research articles, and it applies to several other biomacromolecules’ interactions as well. This rather unbalanced description of cellulose has likely impacted the development of materials based on the processing of cellulose—for example, via dissolution in various solvent systems and regeneration into solid materials, such as films and fibers, and even traditional wood fiber handling and papermaking. In this review, we take as a starting point the questioning of the general description of the nature of cellulose and cellulose interactions initiated by Professor Björn Lindman, based on generic physicochemical reasoning about surfactants and polymers. This dispute, which became known as “the Lindman hypothesis”, highlights the importance of hydrophobic interactions in cellulose systems and that cellulose is an amphiphilic polymer. This paper elaborates on Björn Lindman’s contribution to the subject, which has caused the scientific community to revisit cellulose and reconsider certain phenomena from other perspectives.
- On the formation and stability of cellulose-based emulsions in alkaline systems: effect of the solvent qualityPublication . Costa, Carolina; Medronho, Bruno; Filipe, Alexandra; Romano, Anabela; Lindman, Björn; Edlund, Håkan; Norgren, MagnusWith amphiphilic properties, cellulose molecules are expected to adsorb at the O/W interface and be capable of stabilizing emulsions. The effect of solvent quality on the formation and stability of cellulose-based O/W emulsions was evaluated in different alkaline systems: NaOH, NaOH-urea and tetrabutylammonium hydroxide (TBAH). The optimal solvency conditions for cellulose adsorption at the O/W interface were found for the alkaline solvent with an intermediate polarity (NaOH-urea), which is in line with the favorable conditions for adsorption of an amphiphilic polymer. A very good solvency (in TBAH) and the interfacial activity of the cation lead to lack of stability because of low cellulose adsorption. However, to achieve long-term stability and prevent oil separation in NaOH-urea systems, further reduction in cellulose's solvency was needed, which was achieved by a change in the pH of the emulsions, inducing the regeneration of cellulose at the surface of the oil droplets (in-situ regeneration).
- From a new cellulose solvent to the cyclodextrin induced formation of hydrogelsPublication . Medronho, Bruno; Duarte, Hugo; Magalhaes, Solange; Alves, Luis; Valente, Artur J. M.; Romano, AnabelaA new efficient solvent for cellulose dissolution was developed based on the mixture of aqueous tetrabutylammonium hydroxide, TBAH(aq) and an organic co-solvent, dimethylsulfoxide (DMSO). Clear cellulose solutions were readily obtained at mild conditions in a few minutes. The viscoeleastic properties of the dopes formed are found to be dependent on the cellulose content and TBAH(aq)/DMSO ratio. Additionally, stiff hydrogels are formed when adding beta-cyclodextrin (beta-CD) to the cellulose dopes. The formation of a host-guest complex between the beta-CD and the tetrabutylammonium cations (TBA(+)), which presumably destabilizes the cellulose solution state triggering the hydrogel formation, is suggested as mechanism. The robust hydrogels formed have been characterized regarding their viscoelasticity, microscopic morphology and release properties. The kinetics and released amount of the TBA(+) from the cellulose gel matrixes are found to be strongly dependent on the balance between average pore diameter, surface area and free volume of the hydrogels. (C) 2017 Elsevier B.V. All rights reserved.
- Microrheology of novel cellulose stabilized oil-in-water emulsionsPublication . Medronho, Bruno; Filipe, A.; Costa, C.; Romano, Anabela; Lindman, B.; Edlund, H.; Norgren, M.Diffusing wave spectroscopy (DWS) is a powerful optical technique suitable to investigate turbid samples in a nondestructive and reproducible way, providing information on the static and dynamic properties of the system. This includes the relative displacement of emulsion droplets over time and changes in the viscoelastic properties. Here, novel and promising cellulose-based oil-in-water (O/W) emulsions were prepared and studied, for the first time, by DWS. Cellulose plays the role of a novel eco-friendly emulsifying agent. The hydrolysis time of cellulose was observed to affect the average size of the emulsion droplets and their stability; the longer the hydrolysis time, the more dispersed and stable the emulsions were found to be. Additionally, a good complementarity between the microrheology (DWS) and macrorheology (mechanical rheometer) data was found. Our work suggests that DWS is a highly attractive method to investigate the stability, aging and microrheology properties of cellulose-based emulsions, providing valuable insights on their microstructure. This technique is thus highly appealing for the characterization and design of novel emulsion formulations. (C) 2018 The Authors. Published by Elsevier Inc.
- Lignin enhances cellulose dissolution in cold alkaliPublication . Costa, Carolina; Medronho, Bruno; Eivazi, Alireza; Svanedal, Ida; Lindman, Björn; Edlund, Håkan; Norgren, MagnusAqueous sodium hydroxide solutions are extensively used as solvents for lignin in kraft pulping. These are also appealing systems for cellulose dissolution due to their inexpensiveness, ease to recycle and low toxicity. Cellulose dissolution occurs in a narrow concentration region and at low temperatures. Dissolution is often incomplete but additives, such as zinc oxide or urea, have been found to significantly improve cellulose dissolution. In this work, lignin was explored as a possible beneficial additive for cellulose dissolution. Lignin was found to improve cellulose dissolution in cold alkali, extending the NaOH concentration range to lower values. The regenerated cellulose material from the NaOH-lignin solvents was found to have a lower crystallinity and crystallite size than the samples prepared in the neat NaOH and NaOH-urea solvents. Beneficial lignin-cellulose interactions in solution state appear to be preserved under coagulation and regeneration, reducing the tendency of crystallization of cellulose.
- Stacking self-gluing cellulose II films: a facile strategy for the formation of novel all-cellulose laminatesPublication . Dahlström, Christina; Duan, Ran; Eivazi, Alireza; Magalhães, Solange; Alves, Luís; Engholm, Magnus; Svanedal, Ida; Håkan Edlund; Medronho, Bruno; Norgren, MagnusCellulose laminates represent a remarkable convergence of natural materials and modern engineering, offering a wide range of versatile applications in sustainable packaging, construction, and advanced materials. In this study, novel all-cellulose laminates are developed using an environmentally friendly approach, where freshly regenerated cellulose II films are stacked without the need for solvents (for impregnation and/or partial dissolution), chemical modifications, or resins. The structural and mechanical properties of these all-cellulose laminates were thoroughly investigated. This simple and scalable procedure results in transparent laminates with exceptional mechanical properties comparable to or even superior to common plastics, with E-modulus higher than 9 GPa for a single layer and 7 GPa for the laminates. These laminates are malleable and can be easily patterned. Depending on the number of layers, they can be thin and flexible (with just one layer) or thick and rigid (with three layers). Laminates were also doped with 10 wt% undissolved fibers without compromising their characteristics. These innovative all-cellulose laminates present a robust, eco-friendly alternative to traditional synthetic materials, thus bridging the gap between environmental responsibility and high-performance functionality.