| 1. |
- Duarte, T. A. G., et al.
(författare)
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A Glance at Novel Ionanofluids Incorporating Silk-Derived Carbon Dots
- 2024
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 36:3, s. 1136-1152
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Tidskriftsartikel (refereegranskat)abstract
- One of the hallmarks of the current efforts in the field of thermal energy is heat transfer enhancement. Ionanofluids (INFs), a combination of nanomaterials and ionic liquids (ILs), are an appealing category of thermal fluids. In this work, we introduce sustainable INFs composed of carbon dots derived from Bombyx mori silk fibroin (SF) dispersed in a mixture of 1-butyl-3-methylimidazolium chloride (IL1) and 1-(4-sulfobutyl)-3-methylimidazolium triflate (IL2). The syntheses were performed at mild conditions, with reaction times of 3, 4, and 5 h, and without purification steps. The INFs display room-temperature emission in the visible spectral range with quantum yield values up to 0.09 and are essentially viscous fluids (G″ > G′). A marked shear thinning behavior is observed at high shear rates, particularly for the systems SFIL1IL2-3h and SFIL1IL2-4h. The INFs demonstrate relatively high heat capacity and thermal conductivity values in comparison to state-of-the-art INFs. Under suitable illumination conditions, the INFs can convert light into heat in an efficient manner, with photothermal conversion efficiencies of up to 28%, similar to other reported INFs. SFIL1IL2-5h exhibits remarkable stability over time within the range of working temperatures. This work paves the way for the development of new thermal fluids for enhanced heat transfer technologies using sustainable synthesis routes and natural raw precursor materials.
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| 2. |
- 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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| 3. |
- Fernandes, C., et al.
(författare)
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New deep eutectic solvent assisted extraction of highly pure lignin from maritime pine sawdust (Pinus pinaster Ait.)
- 2021
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Ingår i: International Journal of Biological Macromolecules. - : Elsevier BV. - 0141-8130 .- 1879-0003. ; 177, s. 294-305
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Tidskriftsartikel (refereegranskat)abstract
- Lignocellulosic biomass is a renewable and sustainable feedstock, mainly composed of cellulose, hemicellulose, and lignin. Lignin, as the most abundant natural aromatic polymer occurring on Earth, has great potential to produce value-added products. However, the isolation of highly pure lignin from biomass requires the use of efficient methods during lignocellulose fractionation. Therefore, in this work, novel acidic deep eutectic solvents (DESs) were prepared, characterized and screened for lignin extraction from maritime pine wood (Pinus pinaster Ait.) sawdust. The use of cosolvents and the development of new DES were also evaluated regarding their extraction and selectivity performance. The results show that an 1 h extraction process at 175 °C, using a novel DES composed of lactic acid, tartaric acid and choline chloride, named Lact:Tart:ChCl, in a molar ratio of 4:1:1, allows the recovery of 95 wt% of the total lignin present in pine biomass with a purity of 89 wt%. Such superior extraction of lignin with remarkable purity using a “green” solvent system makes this process highly appealing for future large-scale applications.
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| 4. |
- Kihlman, Martin, et al.
(författare)
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Cellulose Dissolution in an Alkali Based Solvent : Influence of Additives and Pretreatments
- 2013
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Ingår i: Journal of the Brazilian Chemical Society. - : SOC BRASILEIRA QUIMICA, Brazil. - 0103-5053 .- 1678-4790. ; 24:2, s. 295-303
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Magalhaes, Solange, et al.
(författare)
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Acacia Wood Fractionation Using Deep Eutectic Solvents : Extraction, Recovery, and Characterization of the Different Fractions
- 2022
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 7:30, s. 26005-26014
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Tidskriftsartikel (refereegranskat)abstract
- The selective extraction and recovery of different lignocellulosic molecules of interest from forestry residues is increasing every day not only to satisfy the needs of driving a society toward more sustainable approaches and materials (rethinking waste as a valuable resource) but also because lignocellulosic molecules have several applications. For this purpose, the development of new sustainable and ecologically benign extraction approaches has grown significantly. Deep eutectic solvents (DESs) appear as a promising alternative for the processing and manipulation of biomass. In the present study, a DES formed using choline chloride and levulinic acid (ChCl:LA) was studied to fractionate lignocellulosic residues of acacia wood (Acacia dealbata Link), an invasive species in Portugal. Different parameters, such as temperature and extraction time, were optimized to enhance the yield and purity of recovered cellulose and lignin fractions. DESs containing LA were found to be promising solvent systems, as the hydrogen bond donor was considered relevant in relation to lignin extraction and cellulose concentration. On the other hand, the increase in temperature and extraction time increases the amount of extracted material from biomass but affects the purity of lignin. The most promising DES system, ChCELA in a ratio of 1:3, was found to not significantly depolymerize the extracted lignin, which presented a similar molecular weight to a la-aft lignin. Additionally, the P-31 NMR results revealed that the extracted lignin has a high content of phenolic OH groups, which favor its reactivity. A mixture of ChCl:LA may be considered a fully renewable solvent, and the formed DES presents good potential to fractionate wood residues.
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| 6. |
- Magalhães, Solange, et al.
(författare)
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Brief overview on bio-based adhesives and sealants
- 2019
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Ingår i: Polymers. - : MDPI AG. - 2073-4360. ; 11:10
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Tidskriftsartikel (refereegranskat)abstract
- Adhesives 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.
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| 7. |
- Magalhães, S., et al.
(författare)
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Eco-Friendly Methods for Extraction and Modification of Cellulose : An Overview
- 2023
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Ingår i: Polymers. - : MDPI. - 2073-4360. ; 15:14
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Forskningsöversikt (refereegranskat)abstract
- Cellulose 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.
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| 8. |
- Medronho, Bruno, et al.
(författare)
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Silk Fibroin Dissolution in Tetrabutylammonium Hydroxide Aqueous Solution
- 2019
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 20, s. 4107-4116
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Tidskriftsartikel (refereegranskat)abstract
- Bombyx mori L. silk fibroin (SF) is widely used in different areas due to its ability to form durable and resilient materials with notable mechanical properties. However, in some of these applications the dissolution of SF is required, and this is not often straightforward due to its inability to be dissolved in the majority of common solvents. This work reports a novel approach to dissolve SF using 40 wt % aqueous tetrabutylammonium hydroxide, TBAOH(aq), at mild temperature. A thorough rheological study combined with small-angle X-ray scattering is presented to correlate the SF state in solution with changes in the rheological parameters. The scattering data suggest that the SF conformation in TBAOH(aq) is close to a random coil, possibly having some compact domains linked with flexible random chains. The radius of gyration (Rg) and the molecular weight (Mw) were estimated to be ca. 17.5 nm and 450 kDa, respectively, which are in good agreement with previous works. Nevertheless, a lower Mw value was deduced from rheometry (i.e., 321 kDa) demonstrating a low degree of depolymerization during dissolution in comparison to other harsh processes. The transition from a dilute to a semidilute regime coincides with the estimated critical concentration and is marked by the presence of a shear-thinning behavior in the flow curves, violation of the empirical Cox-Merz rule, and an upward increase in the activation energy. This work paves the way toward the development of advanced high-tech SF-based materials. © 2019 American Chemical Society.
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| 9. |
- Melro, E., et al.
(författare)
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Engineering novel phenolic foams with lignin extracted from pine wood residues via a new levulinic-acid assisted process
- 2023
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Ingår i: International Journal of Biological Macromolecules. - : Elsevier. - 0141-8130 .- 1879-0003. ; 248
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Tidskriftsartikel (refereegranskat)abstract
- Phenolic foams are typically produced from phenolic resins, using phenol and formaldehyde precursors. Therefore, common phenolic foams are non-sustainable, comprising growing environmental, health, and economic concerns. In this work, lignin extracted from pine wood residues using a “green” levulinic acid-based solvent, was used to partially substitute non-sustainable phenol. The novel engineered foams were systematically compared to foams composed of different types of commercially available technical lignins. Different features were analyzed, such as foam density, microstructure (electron microscopy), surface hydrophilicity (contact angle), chemical grafting (infrared spectroscopy) and mechanical and thermal features. Overall, it was observed that up to 30 wt% of phenol can be substituted by the new type of lignin, without compromising the foam properties. This work provides a new insights on the development of novel lignin-based foams as a very promising sustainable and renewable alternative to petrol-based counterparts.
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| 10. |
- Melro, E., et al.
(författare)
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On the Development of Phenol-Formaldehyde Resins Using a New Type of Lignin Extracted from Pine Wood with a Levulinic-Acid Based Solvent
- 2022
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Ingår i: Molecules. - : MDPI AG. - 1431-5157 .- 1420-3049. ; 27:9
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Tidskriftsartikel (refereegranskat)abstract
- Resole resins have many applications, especially for foam production. However, the use of phenol, a key ingredient in resoles, has serious environmental and economic disadvantages. In this work, lignin extracted from pine wood using a “green” solvent, levulinic acid, was used to partially replace the non-sustainable phenol. The physicochemical properties of this novel resin were compared with resins composed of different types of commercial lignins. All resins were optimized to keep their free formaldehyde content below 1 wt%, by carefully adjusting the pH of the mixture. Substitution of phenol with lignin generally increases the viscosity of the resins, which is further increased with the lignin mass fraction. The addition of lignin decreases the kinetics of gelification of the resin. The type and amount of lignin also affect the thermal stability of the resins. It was possible to obtain resins with higher thermal stability than the standard phenol-formaldehyde resins without lignin. This work provides new insights regarding the development of lignin-based resoles as a very promising sustainable alternative to petrol-based resins.
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