Browsing by Author "Lindman, B."
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- Brief overview on cellulose dissolution/regeneration interactions and mechanismsPublication . Medronho, B.; Lindman, B.The development of cellulose dissolution/regeneration strategies constitutes an increasingly active research field. These are fundamental aspects of many production processes and applications. A wide variety of suitable solvents for cellulose is already available. Nevertheless, most solvent systems have important limitations, and there is an intense activity in both industrial and academic research aiming to optimize existing solvents and develop new ones. Cellulose solvents are of highly different nature giving great challenges in the understanding of the subtle balance between the different interactions. Here, we briefly review the cellulose dissolution and regeneration mechanisms for some selected solvents. Insolubility is often attributed to strong intermolecular hydrogen bonding between cellulose molecules. However, recent work rather emphasizes the role of cellulose charge and the concomitant ion entropy effects, as well as hydrophobic interactions. © 2014.
- Cellulose dissolution in an alkali based solvent: influence of additives and pretreatmentsPublication . Kihlman, Martin; Medronho, B.; Romano, Anabela; Germgard, Ulf; Lindman, B.The distinction between thermodynamic and kinetics in cellulose dissolution is seldom considered in the literature. Therefore, herein an attempt to discuss this topic and illustrate our hypotheses on the basis of simple experiments was made. It is well-known that cellulose can be dissolved in a aqueous sodium hydroxide (NaOH/H2O) solvent at low temperature but it is here shown that such an alkaline solvent can be considerably improved regarding solubility, stability and rheological properties as a whole if different additives (salts and amphiphilic molecules) are used in the dissolution stage. This work probes new aqueous routes to dissolve cellulose, thereby improving the potential to commercially dissolve cellulose in an inexpensive and environmentally friendly manner.
- Competing forces during cellulose dissolution: from solvents to mechanismsPublication . Medronho, B.; Lindman, B.Cellulose is a polymer so widely abundant and versatile that we can find it almost everywhere in many different forms and applications. Cellulose dissolution is a key aspect of many processes; the present treatise reviews the main achievements in the dissolution area. In particular, the main solvents used and underlying mechanisms are discussed. As is described, cellulose solvents are of highly different nature giving great challenges in the understanding and analyzing the subtle balance between different interactions. Recent work has much emphasized the role of cellulose charge and the concomitant ion entropy effects, as well as hydrophobic interactions. © 2013 Elsevier Ltd.
- Cyclodextrin-grafted cellulose: physico-chemical characterizationPublication . Medronho, B.; Andrade, R.; Vivod, V.; Ostlund, A.; Miguel, M. G.; Lindman, B.; Voncina, B.; Valente, A. J. M.Cyclodextrins (CDs) can form inclusion complexes with a wide variety of molecules making them very attractive in different areas, such as pharmaceutics, biochemistry, food chemistry and textile. In this communication we will report on the physico-chemical characterization of cellulose modified with CDs by means of infra-red spectroscopy (FTIR), cross polarization magic angle spinning solid state nuclear magnetic resonance (CP-MAS NMR), polarized optical microscopy (POM) and thermal gravimetric analysis (TGA). Both CP-MAS NMR and FTIR indicate that CDs are chemically attached to cellulose backbone through the formation of ester bonds. Furthermore, the CD-grafted cellulose was dissolved in a "superphosphoric" acid solution but, despite the increase of hydrophilicity due to the modification, POM revealed that grafted cellulose was less soluble when compared to the unmodified polymer. The formation of a complex CD-cellulose network is suggested. (C) 2012 Elsevier Ltd. All rights reserved.
- Development of carboxymethyl cellulose-chitosan hybrid micro- and macroparticles for encapsulation of probiotic bacteriaPublication . Singh, P.; Medronho, B.; Alves, L.; da Silva, G. J.; Miguel, M. G.; Lindman, B.Novel carboxymethyl cellulose-chitosan (CMC-Cht) hybrid micro- and macroparticles were successfully prepared in aqueous media either by drop-wise addition or via nozzle-spray methods. The systems were either physically or chemically crosslinked using genipin as the reticulation agent. The macroparticles (ca. 2 mm) formed are found to be essentially of the core-shell type, while the microparticles (ca. 5 tim) are apparently homogeneous. The crosslinked particles are robust, thermally resistant and less sensitive to pH changes. On the other hand, the physical systems are pH sensitive presenting a remarkable swelling at pH 7.4, while little swelling is observed at pH 2.4. Furthermore, model probiotic bacteria (Lactobacillus rhamnosus GG) was for the first time successfully encapsulated in the CMC-Cht based particles with acceptable viability count. Overall, the systems developed are highly promising for probiotic encapsulation and potential delivery in the intestinal tract with the purpose of modulating gut microbiota and improving human health. (C) 2017 Elsevier Ltd. All rights reserved.
- Editorial: Cellulose dissolution and regeneration: systems and interactionsPublication . Lindman, B.; Medronho, B.; Theliander, H.The interest in cellulose dissolution and regeneration is old but this topic has recently attracted strongly renewed attention. This is reflected in both applications- earlier and novel- and scientific controversies. This special issue attempts to connect a renewed fundamental understanding of molecular aspects with practical systems for dissolution and regeneration.
- 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).
- Gels of catanionic vesicles and hydrophobically modified poly(ethylene glycol)Publication . Medronho, B.; Antunes, F. E.; Lindman, B.; Miguel, M. G.The association between hydrophobically modified polyethylene glycol (HM-PEG) and sodium dodecyl sulphate/didodecyldimethylammonium bromide (SDS/DDAB) catanionic vesicles is studied by rheology, (1)H-NMR, and cryo-TEM techniques. Phase behavior studies were performed as a function of polymer weight fraction and vesicle volume fraction. At sufficiently high polymer weight fraction and/or vesicle volume fraction, a gel phase is detected, indicating the presence of a three-dimensional network. Phase separation was also identified, with a dilute solution coexisting with a bluish precipitate ( gel fraction). Vesicle-polymer binding is expected to occur via the insertion of the polymer hydrophobes into the vesicle bilayer. Each vesicle can act as a cross-linking point in the network structure. The size of the vesicles is found to be important in terms of the storage modulus and viscosity of the polymer-vesicle mixed solutions. On the other hand, changes in the vesicle total net charge do not influence the association and the rheological properties. We also address the question of how the length of the hydrophobic modification can influence the rheology of the system and, as expected, larger hydrophobic groups increase the cross-linking and the relaxation time.
- How does a non-ionic hydrophobically modified telechelic polymer interact with a non-ionic vesicle? Rheological aspectsPublication . dos Santos, T.; Medronho, B.; Antunes, F. E.; Lindman, B.; Miguel, M. G.The association between hydrophobically modified polyethylene glycol, HM-PEG, and non-ionic vesicles of tetraethylene glycol monododecyl ether, C12E4, was investigated. HM-PEG is in a triblock form, with an alkyl chain attached to each hydrophilic polymer-end. Such polymer structure is denoted as telechelic. The vesicle average radius was measured by self-diffusion measurements. The system exhibits both a monophasic gel and biphasic regions. The monophasic region was characterized from a theological point of view. We argue that the gel formation is due to the presence. of polymer crosslinks between different surfactant aggregates, once the polymer's hydrophobic moieties may adsorb into the vesicle bilayer. This association is strongly concentration dependent which is reflected in the monotonic increase of the storage modulus, relaxation time and shear viscosity with the addition of surfactant and/or polymer. (C) 2007 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.