SwePub
Sök i SwePub databas

  Utökad sökning

Träfflista för sökning "WFRF:(Antunes Luis) "

Sökning: WFRF:(Antunes Luis)

  • Resultat 1-10 av 17
  • [1]2Nästa
Sortera/gruppera träfflistan
   
NumreringReferensOmslagsbildHitta
1.
  • Alves, Luis, et al. (författare)
  • Dissolution state of cellulose in aqueous systems. 1. Alkaline solvents
  • 2016
  • Ingår i: Cellulose. - Springer. - 0969-0239. ; 23:1, s. 247-258
  • 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.
  •  
2.
  • Alves, Luis, et al. (författare)
  • Dissolution state of cellulose in aqueous systems. 1. Alkaline solvents
  • 2016
  • Ingår i: Cellulose (London). - 0969-0239 .- 1572-882X. ; 23:1, s. 247-258
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>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.</p>
  •  
3.
  • Alves, Luis, et al. (författare)
  • Dissolution state of cellulose in aqueous systems. 2. Acidic solvents
  • 2016
  • Ingår i: Carbohydrate Polymers. - Elsevier. - 0144-8617. ; 151, s. 707-715
  • 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.
  •  
4.
  • Alves, Luis, et al. (författare)
  • Dissolution state of cellulose in aqueous systems. 2. Acidic solvents
  • 2016
  • Ingår i: Carbohydrate Polymers. - 0144-8617 .- 1879-1344. ; 151, s. 707-715
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>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.</p>
  •  
5.
  • Alves, Luis, et al. (författare)
  • New Insights on the Role of Urea on the Dissolution and Thermally-Induced Gelation of Cellulose in Aqueous Alkali
  • 2018
  • Ingår i: GELS. - 2310-2861. ; 4:4
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>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.</p>
  •  
6.
  • Alves, Luis, et al. (författare)
  • On the rheology of mixed systems of hydrophobically modified polyacrylate microgels and surfactants : Role of the surfactant architecture
  • 2018
  • Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 513, s. 489-496
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>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. </p>
  •  
7.
  • Alves, Luís, et al. (författare)
  • On the rheology of mixed systems of hydrophobically modified polyacrylate microgels and surfactants : Role of the surfactant architecture
  • 2018
  • Ingår i: Journal of Colloid and Interface Science. - Elsevier. - 0021-9797. ; 513, s. 489-496
  • 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.
  •  
8.
  • Alves, Luis, et al. (författare)
  • On the role of hydrophobic interactions in cellulose dissolution and regeneration: Colloidal aggregates and molecular solutions
  • 2015
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - Elsevier. - 0927-7757. ; 483, s. 257-263
  • 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.
  •  
9.
  • Alves, Luis, et al. (författare)
  • Unusual extraction and characterization of nanocrystalline cellulose from cellulose derivatives
  • 2015
  • Ingår i: Journal of Molecular Liquids. - Elsevier. - 0167-7322. ; 210, s. 106-112
  • Tidskriftsartikel (refereegranskat)abstract
    • Unlike many nanomaterials, nanocrystalline cellulose (CNC) is not synthesized from molecular or atomic components but rather extracted from naturally occurring cellulose. Undoubtedly, the exploitation of CNCs will become a bridge between nanoscience and natural resource products, which could play a major role in reviving the forest industry. In this work, CNC was successfully extracted from unusual sources, hydroxypropyl methylcellulose (HPMC) and carboxymethylcellulose (CMC). The extracted crystallites were purified and further characterized by Fourier transform infrared (FTIR), scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and dynamic light scattering (DLS). The average size of the CNCs extracted from HPMC and CMC was found to be less (and with lower zeta potential) than the ones extracted from microcrystalline cellulose (MCC). On the other hand, FTIR and XRD revealed that native HPMC and CMC are unexpectedly highly crystalline and hence can be used as a source for CNCs. (C) 2014 Elsevier B.V. All rights reserved.
  •  
10.
  • Georgakis, Marios K., et al. (författare)
  • Malignant Central Nervous System Tumors Among Adolescents and Young Adults (15-39 Years Old) in 14 Southern-Eastern European Registries and the US Surveillance, Epidemiology, and End Results Program: Mortality and Survival Patterns
  • 2017
  • Ingår i: Cancer. - WILEY. - 0008-543X .- 1097-0142. ; 123:22, s. 4458-4471
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>BACKGROUND: Unique features and worse outcomes have been reported for cancers among adolescents and young adults (AYAs; 15-39 years old). The aim of this study was to explore the mortality and survival patterns of malignant central nervous system (CNS) tumors among AYAs in Southern-Eastern Europe (SEE) in comparison with the US Surveillance, Epidemiology, and End Results (SEER) program. METHODS: Malignant CNS tumors diagnosed in AYAs during the period spanning 1990-2014 were retrieved from 14 population-based cancer registries in the SEE region (n = 11,438). Age-adjusted mortality rates were calculated and survival patterns were evaluated via Kaplan-Meier curves and Cox regression analyses, and they were compared with respective 1990-2012 figures from SEER (n = 13,573). RESULTS: Mortality rates in SEE (range, 11.9-18.5 deaths per million) were higher overall than the SEER rate (9.4 deaths per million), with decreasing trends in both regions. Survival rates increased during a comparable period (2001-2009) in SEE and SEER. The 5-year survival rate was considerably lower in the SEE registries (46%) versus SEER (67%), mainly because of the extremely low rates in Ukraine; this finding was consistent across age groups and diagnostic subtypes. The highest 5-year survival rates were recorded for ependymomas (76% in SEE and 92% in SEER), and the worst were recorded for glioblastomas and anaplastic astrocytomas (28% in SEE and 37% in SEER). Advancing age, male sex, and rural residency at diagnosis adversely affected outcomes in both regions. CONCLUSIONS: Despite definite survival gains over the last years, the considerable outcome disparities between the less affluent SEE region and the United States for AYAs with malignant CNS tumors point to health care delivery inequalities. No considerable prognostic deficits for CNS tumors are evident for AYAs versus children. (c) 2017 American Cancer Society.</p>
  •  
Skapa referenser, mejla, bekava och länka
  • Resultat 1-10 av 17
  • [1]2Nästa
Åtkomst
fritt online (3)
Typ av publikation
tidskriftsartikel (16)
bokkapitel (1)
Typ av innehåll
refereegranskat (17)
övrigt vetenskapligt (1)
Författare/redaktör
Alves, Luis (14)
Lindman, Björn, (13)
Medronho, Bruno (11)
Antunes, Filipe E. (9)
Topgaard, Daniel, (6)
Antunes, Filipe, (5)
visa fler...
Romano, Anabela (4)
Filipe, Alexandra, (2)
Klotz, Björn, (2)
Böttcher, Axel, (2)
Haake, Hans-Martin, (2)
Zamorano, Jose Luis (1)
Iung, Bernard (1)
Lancellotti, Patrizi ... (1)
Lindman, Bjorn (1)
Davidovich, Irina, (1)
Talmon, Yeshayahu, (1)
Medronho, Bruno F. (1)
Miguel, Maria G. (1)
Fernandez-Garcia, Ma ... (1)
Ventura, Joao (1)
Araujo, Joao P. (1)
Miro, Jose M (1)
Habib, Gilbert (1)
Miguel, Maria, (1)
Sonnenschein, Jonas, (1)
Thuny, Franck (1)
Mundaca, Luis, (1)
Seidl, Roman (1)
Tornos Mas, Pilar (1)
Lopes, Marta, (1)
Snygg-Martin, Ulrika ... (1)
Erba, Paola Anna (1)
Bongiorni, Maria Gra ... (1)
Henggeler Antunes, C ... (1)
Georgakis, Marios K. ... (1)
Price, Susanna, (1)
Casalta, Jean Paul (1)
Papathoma, Paraskevi ... (1)
Ryzhov, Anton, (1)
Zivkovic-Perisic, Sn ... (1)
Eser, Sultan, (1)
Taraszkiewicz, Lukas ... (1)
Sekerija, Mario, (1)
Zagar, Tina, (1)
Antunes, Luis, (1)
Zborovskaya, Anna, (1)
Bastos, Joana, (1)
Florea, Margareta, (1)
Coza, Daniela, (1)
visa färre...
Lärosäte
Lunds universitet (9)
Mittuniversitetet (6)
Göteborgs universitet (1)
Linköpings universitet (1)
Språk
Engelska (17)
Forskningsämne (UKÄ/SCB)
Naturvetenskap (7)
Teknik (7)
Medicin och hälsovetenskap (2)

År

 
pil uppåt Stäng

Kopiera och spara länken för att återkomma till aktuell vy