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- Hydrophobic interactions control the self-assembly of DNA and cellulosePublication . Lindman, Björn; Medronho, Bruno; Alves, Luís; Norgren, Magnus; Nordenskiöld, LarsDesoxyribosenucleic acid, DNA, and cellulose molecules self-assemble in aqueous systems. This aggregation is the basis of the important functions of these biological macromolecules. Both DNA and cellulose have significant polar and nonpolar parts and there is a delicate balance between hydrophilic and hydrophobic interactions. The hydrophilic interactions related to net charges have been thoroughly studied and are well understood. On the other hand, the detailed roles of hydrogen bonding and hydrophobic interactions have remained controversial. It is found that the contributions of hydrophobic interactions in driving important processes, like the double-helix formation of DNA and the aqueous dissolution of cellulose, are dominating whereas the net contribution from hydrogen bonding is small. In reviewing the roles of different interactions for DNA and cellulose it is useful to compare with the self-assembly features of surfactants, the simplest case of amphiphilic molecules. Pertinent information on the amphiphilic character of cellulose and DNA can be obtained from the association with surfactants, as well as on modifying the hydrophobic interactions by additives.
- New insights on the role of urea on the dissolution and thermally-induced gelation of cellulose in aqueous alkaliPublication . Alves, Luis; Medronho, Bruno; Filipe, Alexandra; E. Antunes, Filipe; Lindman, Björn; Topgaard, Daniel; Davidovich, Irina; Talmon, YeshayahuThe gelation of cellulose in alkali solutions is quite relevant, but still a poorly understood process. Moreover, the role of certain additives, such as urea, is not consensual among the community. Therefore, in this work, an unusual set of characterization methods for cellulose solutions, such as cryo-transmission electronic microscopy (cryo-TEM), polarization transfer solid-state nuclear magnetic resonance (PTssNMR) and diffusion wave spectroscopy (DWS) were employed to study the role of urea on the dissolution and gelation processes of cellulose in aqueous alkali. Cryo-TEM reveals that the addition of urea generally reduces the presence of undissolved cellulose fibrils in solution. These results are consistent with PTssNMR data, which show the reduction and in some cases the absence of crystalline portions of cellulose in solution, suggesting a pronounced positive effect of the urea on the dissolution efficiency of cellulose. Both conventional mechanical macrorheology and microrheology (DWS) indicate a significant delay of gelation induced by urea, being absent until ca. 60 °C for a system containing 5 wt % cellulose, while a system without urea gels at a lower temperature. For higher cellulose concentrations, the samples containing urea form gels even at room temperature. It is argued that since urea facilitates cellulose dissolution, the high entanglement of the cellulose chains in solution (above the critical concentration, C*) results in a strong three-dimensional network.
- 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.
- Brief overview on bio-based adhesives and sealantsPublication . Magalhães, Solange; Alves, Luís; Medronho, Bruno; Fonseca, Ana C.; Romano, Anabela; Coelho, Jorge F.J.; Norgren, MagnusAdhesives and sealants (AS) are materials with excellent properties, versatility, and simple curing mechanisms, being widely used in different areas ranging from the construction to the medical sectors. Due to the fast-growing demand for petroleum-based products and the consequent negative environmental impact, there is an increasing need to develop novel and more sustainable sources to obtain raw materials (monomers). This reality is particularly relevant for AS industries, which are generally dependent on non-sustainable fossil raw materials. In this respect, biopolymers, such as cellulose, starch, lignin, or proteins, emerge as important alternatives. Nevertheless, substantial improvements and developments are still required in order to simplify the synthetic routes, as well as to improve the biopolymer stability and performance of these new bio-based AS formulations. This environmentally friendly strategy will hopefully lead to the future partial or even total replacement of non-renewable petroleum-based feedstock. In this brief overview, the general features of typical AS are reviewed and critically discussed regarding their drawbacks and advantages. Moreover, the challenges faced by novel and more ecological alternatives, in particular lignocellulose-based solutions, are highlighted.
- Levulinic acid-based “green” solvents for lignocellulose fractionation: on the superior extraction yield and selectivity toward ligninPublication . Melro, Elodie; Riddell, Alexander; Bernin, Diana; Rosa Da Costa, Ana; Valente, Artur J. M.; Antunes, Filipe E.; Romano, Anabela; Norgren, Magnus; Medronho, BrunoThe high potential use of lignin in novel biomaterialsand chemicalsrepresents an important opportunity for the valorization of the mostabundant natural resource of aromatic molecules. From an environmentalperspective, it is highly desirable replacing the hazardous methodscurrently used to extract lignin from lignocellulosic biomass anddevelop more sustainable and environmentally friendly approaches.Therefore, in this work, levulinic acid (a "green" solventobtained from biomass) was successfully used, for the first time,to selectively extract high-quality lignin from pine wood sawdustresidues at 200 degrees C for 6 h (at atmospheric pressure). Moreover,the addition of catalytic concentrations of inorganic acids (i.e.,H2SO4 or HCl) was found to substantially reducethe temperature and reaction times needed (i.e., 140 degrees C, 2 h)for complete lignin extraction without compromising its purity. NMRdata suggests that condensed OH structures and acidic groups are presentin the lignin following extraction. Levulinic acid can be easily recycledand efficiently reused several times without affecting its performance.Furthermore, excellent solvent reusability and performance of extractionof other wood residues has been successfully demonstrated, thus makingthe developed levulinic acid-based procedure highly appealing andpromising to replace the traditional less sustainable methodologies.
- Eco-friendly methods for extraction and modification of cellulose: an overviewPublication . Magalhães, Solange; Fernandes, Catarina; Pedrosa, Jorge F. S.; Alves, Luís; Medronho, Bruno; Ferreira, Paulo J. T.; Rasteiro, Maria da GraçaCellulose is the most abundant renewable polymer on Earth and can be obtained from several different sources, such as trees, grass, or biomass residues. However, one of the issues is that not all the fractionation processes are eco-friendly and are essentially based on cooking the lignocellulose feedstock in a harsh chemical mixture, such as NaOH + Na2S, and water, to break loose fibers. In the last few years, new sustainable fractionation processes have been developed that enable the obtaining of cellulose fibers in a more eco-friendly way. As a raw material, cellulose’s use is widely known and established in many areas. Additionally, its products/derivatives are recognized to have a far better environmental impact than fossil-based materials. Examples are textiles and packaging, where forest-based fibers may contribute to renewable and biodegradable substitutes for common synthetic materials and plastics. In this review, some of the main structural characteristics and properties of cellulose, recent green extraction methods/strategies, chemical modification, and applications of cellulose derivatives are discussed.
- Emulsion formation and stabilization by biomolecules: the leading role of cellulosePublication . Costa, C.; Medronho, Bruno; Filipe, Alexandra; Mira, I.; Lindman, B.; Edlund, H.; Norgren, M.Emulsion stabilization by native cellulose has been mainly hampered because of its insolubility in water. Chemical modification is normally needed to obtain water-soluble cellulose derivatives. These modified celluloses have been widely used for a range of applications by the food, cosmetic, pharmaceutic, paint and construction industries. In most cases, the modified celluloses are used as rheology modifiers (thickeners) or as emulsifying agents. In the last decade, the structural features of cellulose have been revisited, with particular focus on its structural anisotropy (amphiphilicity) and the molecular interactions leading to its resistance to dissolution. The amphiphilic behavior of native cellulose is evidenced by its capacity to adsorb at the interface between oil and aqueous solvent solutions, thus being capable of stabilizing emulsions. In this overview, the fundamentals of emulsion formation and stabilization by biomolecules are briefly revisited before different aspects around the emerging role of cellulose as emulsion stabilizer are addressed in detail. Particular focus is given to systems stabilized by native cellulose, either molecularly-dissolved or not (Pickering-like effect).
- Tuning the properties of regenerated cellulose: Effects of polarity and water solubility of the coagulation mediumPublication . From, Malin; Larsson, Per Tomas; Andreasson, Bo; Medronho, Bruno; Svanedal, Ida; Edlund, Hakan; Norgren, MagnusIn this study, the effect of different alcohols and esters as a coagulation medium in the regeneration of cellulose dissolved in an aqueous LiOH-urea-based solvent was thoroughly investigated using various methods such as solid state NMR, X-ray diffraction, water contact angle, oxygen gas permeability, mechanical testing, and scanning electron microscopy. It was observed that several material properties of the regenerated cellulose films follow trends that correlate to the degree of cellulose II crystallinity, which is determined to be set by the miscibility of the coagulant medium (nonsolvent) and the aqueous alkali cellulose solvent rather than the nonsolvents' polarity. This article provides an insight, thus creating a possibility to carefully tune and control the cellulose material properties when tailor-made for different applications [GRAPHICS]