| 1. |
- Alves, Luis, et al.
(författare)
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Dissolution state of cellulose in aqueous systems. 1. Alkaline solvents
- 2016
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 23:1, s. 247-258
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Tidskriftsartikel (refereegranskat)abstract
- The understanding of the state of dissolution of cellulose in a certain solvent is a critical step forward in the development of new efficient solvent systems for cellulose. Nevertheless, obtaining such information is not trivial. Recently, polarization transfer solid-state NMR (PTssNMR) was shown to be a very promising technique regarding an efficient and robust characterization of the solution state of cellulose. In the present study, combining PTssNMR, microscopic techniques and X-ray diffraction, a set of alkaline aqueous systems are investigated. The addition of specific additives, such as urea or thiourea, to aqueous NaOH based systems as well as the use of an amphiphilic organic cation, is found to have pronounced effects on the dissolution efficiency of cellulose. Additionally, the characteristics of the regenerated material are strongly dependent on the dissolution system; typically less crystalline materials, presenting smoother morphologies, are obtained when amphiphilic solvents or additives are used.
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| 2. |
- Alves, Luis, et al.
(författare)
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Dissolution state of cellulose in aqueous systems. 2. Acidic solvents
- 2016
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 151, s. 707-715
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose is insoluble in water but can be dissolved in strong acidic or alkaline conditions. How well dissolved cellulose is in solution and how it organizes are key questions often neglected in literature. The typical low pH required for dissolving cellulose in acidic solvents limits the use of typical characterization techniques. In this respect, Polarization Transfer Solid State NMR (PT ssNMR) emerges as a reliable alternative. In this work, combining PT ssNMR, microscopic techniques and X-ray diffraction, a set of different acidic systems (phosphoric acid/water, sulfuric acid/glycerol and zinc chloride/water) is investigated. The studied solvent systems are capable to efficiently dissolve cellulose, although degradation occurs to some extent. PT ssNMR is capable to identify the liquid and solid fractions of cellulose, the degradation products and it is also sensitive to gelation. The materials regenerated from the acidic dopes were found to be highly sensitive to the solvent system and to the presence of amphiphilic additives in solution.
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| 3. |
- Alves, Luis, et al.
(författare)
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New Insights on the Role of Urea on the Dissolution and Thermally-Induced Gelation of Cellulose in Aqueous Alkali
- 2018
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Ingår i: GELS. - : MDPI AG. - 2310-2861. ; 4:4
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Tidskriftsartikel (refereegranskat)abstract
- The 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 degrees C for a system containing 5wt % 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.
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| 4. |
- Alves, Luis, et al.
(författare)
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On the rheology of mixed systems of hydrophobically modified polyacrylate microgels and surfactants : Role of the surfactant architecture
- 2018
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 513, s. 489-496
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Tidskriftsartikel (refereegranskat)abstract
- Hypothesis The rheological control of suspensions is of key interest in the formulation design. A chemically cross-linked hydrophobically modified poly(acrylic acid) (HMCL-PAA), used as rheology modifier, is pH sensitive and shows swelling behavior above a critical pH due to the ionization of the acrylic acid groups. At low pH, HMCL-PAA suspensions are liquid and turbid. The binding of surfactants to HMCL-PAA, at low pH conditions, can result in significant changes on rheology and transparency of the polymeric suspensions, due to the swelling of the microgel particles. Experiments The influence of surfactants addition on the rheological properties and transparency of HMCL-PAA suspensions was determined. A systematic study was performed using different types of surfactants (ionic, non-ionic and zwitterionic). Findings The gelation efficiency of HMCL-PAA suspensions at low pH is strongly dependent on surfactant architecture: ionic surfactants are found to be much more efficient than non-ionic or zwitterionic surfactants. Ionic surfactants lead to a liquid-to-gel transition accompanied by an increase of transparency of the suspensions. Among the ionic surfactants, anionics show stronger interactions with the polymer. Also the surfactant hydrophobicity is relevant; the more hydrophobic the surfactant, the stronger is the binding to the polymer and thus the larger the particle swelling.
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| 5. |
- Alves, Luis, et al.
(författare)
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On the role of hydrophobic interactions in cellulose dissolution and regeneration: Colloidal aggregates and molecular solutions
- 2015
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 483, s. 257-263
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Tidskriftsartikel (refereegranskat)abstract
- The development of strategies for dissolution and regeneration of cellulose constitutes an increasingly active research field due to the direct relevance for many production processes and applications. A wide variety of suitable solvents for cellulose are already available. However, cellulose solvents are of highly different nature reflecting the great challenges in the understanding of the subtle balance between the different interactions. Here, we report on the effect of two different solvents on the dissolution of cellulose on multiple length scales and its consequences for the characteristics of the regenerated material. While an aqueous tetrabutylammonium hydroxide solution gives rise to what appears to be dissolution down to the molecular level, a sodium hydroxide solution does not dissolve cellulose molecularly but rather leaves aggregates of high crystallinity stable in the cellulose dope. The dramatic difference between a small inorganic cation and an amphiphilic cation indicates a critical role of hydrophobic interactions between cellulose molecules and provides support for the picture that cellulose molecules have pronounced amphiphilic properties. (C) 2015 Elsevier B.V. All rights reserved.
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| 6. |
- Medronho, Bruno, et al.
(författare)
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Probing cellulose amphiphilicity
- 2015
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 30:1, s. 58-66
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose dissolution and regeneration is an increasingly active research field due to the direct relevance for numerous production processes and applications. The problem is not trivial since cellulose solvents are of remarkably different nature and thus the understanding of the subtle balance between the different interactions involved becomes difficult but crucial. There is a current discussion in literature on the balance between hydrogen bonding and hydrophobic interactions in controlling the solution behavior of cellulose. This treatise attempts to review recent work highlighting the marked amphiphilic characteristics of cellulose and role of hydrophobic interactions in dissolution and regeneration. Additionally, a few examples of our own research are discussed focusing on the role of different additives in cellulose solubility. The data does support the amphiphilic behavior of cellulose, which clearly should not be neglected when developing new solvents and strategies for cellulose dissolution and regeneration.
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| 7. |
- Mundaca, Luis, et al.
(författare)
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Behavioural economics for energy and climate change policies and the transition to a sustainable energy use — A Scandinavian perspective
- 2019. - 1st
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Ingår i: Energy and Behaviour : Towards a Low Carbon Future - Towards a Low Carbon Future. - 9780128185674 ; , s. 45-87
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Bokkapitel (refereegranskat)abstract
- The Scandinavian region has been at the forefront of energy and environmental policies for decades. While significant effort has been devoted to the supply side and development of technology markets, our study questions the extent to which policy efforts have effectively and explicitly addressed behavioural factors affecting the adoption and the use of low-carbon energy technologies at the individual and household level. Building upon behavioural economics, we explore behavioural factors and the role of economic and noneconomic aspects affecting energy use and decarbonisation activities in the region. Overall, we argue that greater attention needs to be given to behavioural issues in policy design, implementation, and evaluation. At the same time, behavioural interventions are unlikely to be a panacea that can steer sustainable energy use by itself, and both price and nonprice interventions are required. We conclude that a more stringent, integrated behavioural and technological policymaking approach is needed.
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