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Probing cellulose–solvent interactions with self-diffusion NMR: Onium hydroxide concentration and co-solvent effects
Publication . Medronho, Bruno; Pereira, Ana; Duarte, Hugo; Gentile, L.; Rosa Da Costa, Ana; Romano, A; Olsson, U.
The molecular self-diffusion coefficients were accessed, for the first time, in solutions of microcrystalline cel-lulose, dissolved in 30 wt% and 55 wt% aqueous tetrabutylammonium hydroxide, TBAH (aq), and in mixtures of 40 wt% TBAH (aq) with an organic co-solvent, dimethylsulfoxide (DMSO), through pulsed field gradient stim-ulated echo NMR measurements. A two-state model was applied to estimate alpha (i.e., average number of ions that "bind" to each anhydroglucose unit) and Pb (i.e., fraction of "bound" molecules of DMSO, TBAH or H2O to cellulose) parameters. The alpha values suggest that TBA+ ions can bind to cellulose within 0.5 TBA+ to 2.3 TBA+/ AGU. On the other hand, the Pb parameter increases when raising cellulose concentration for TBA+, DMSO and water in all solvent systems. Data suggests that TBAH interacts with the ionized OH groups from cellulose forming a sheath of bulky TBA+ counterions which consequently leads to steric hindrance between cellulose chains.
Revisiting the dissolution of cellulose in H3PO4(aq) through cryo-TEM PTssNMR and DWS
Publication . Alves, Luis; Medronho, Bruno; Filipe, Alexandra; Romano, Anabela; Rasteiro, Maria G.; Lindman, Bjorn; Topgaard, Daniel; Davidovich, Irina; Talmon, Yeshayahu
Cellulose can be dissolved in concentrated acidic aqueous solvents forming extremely viscous solutions, and, in some cases, liquid crystalline phases. In this work, the concentrated phosphoric acid aqueous solvent is revisited implementing a set of advanced techniques, such as cryo-transmission electronic microscopy (cryo-TEM), polarization transfer solid-state nuclear magnetic resonance (PTssNMR), and diffusing wave spectroscopy (DWS). Cryo-TEM images confirm that this solvent system is capable to efficiently dissolve cellulose. No cellulose particles, fibrils, or aggregates are visible. Conversely, PTssNMR revealed a dominant CP signal at 25 degrees C, characteristic of C-H bond reorientation with correlation time longer than 100 ns and/or order parameter above 0.5, which was ascribed to a transient gel-like network or an anisotropic liquid crystalline phase. Increasing the temperature leads to a gradual transition from CP to INEPT-dominant signal and a loss of birefringence in optical microscopy, suggesting an anisotropic-to-isotropic phase transition. Finally, an excellent agreement between optical microrheology and conventional mechanical rheometry was also obtained.
Lignin enhances cellulose dissolution in cold alkali
Publication . Costa, Carolina; Medronho, Bruno; Eivazi, Alireza; Svanedal, Ida; Lindman, Björn; Edlund, Håkan; Norgren, Magnus
Aqueous sodium hydroxide solutions are extensively used as solvents for lignin in kraft pulping. These are also
appealing systems for cellulose dissolution due to their inexpensiveness, ease to recycle and low toxicity. Cellulose dissolution occurs in a narrow concentration region and at low temperatures. Dissolution is often
incomplete but additives, such as zinc oxide or urea, have been found to significantly improve cellulose dissolution. In this work, lignin was explored as a possible beneficial additive for cellulose dissolution. Lignin was found to improve cellulose dissolution in cold alkali, extending the NaOH concentration range to lower values.
The regenerated cellulose material from the NaOH-lignin solvents was found to have a lower crystallinity and
crystallite size than the samples prepared in the neat NaOH and NaOH-urea solvents. Beneficial lignin-cellulose interactions in solution state appear to be preserved under coagulation and regeneration, reducing the tendency of crystallization of cellulose.
Sustainable extraction of polyphenols from vine shoots using deep eutectic solvents: influence of the solvent, vitis sp., and extraction technique
Publication . Duarte, Hugo; Aliaño-González, María José; Cantos-Villar, Emma; Faleiro, Leonor; Romano, Anabela; Medronho, Bruno
Vine shoots are the main by-products of grapevine pruning with no added value. In the present study, deep
eutectic solvents (DESs) were used as alternatives to traditional chemical solvents, for the extraction of phyto chemicals from grapevine shoots. Three levulinic acid-based DESs were tested for the first time, and their per formance was compared to methanol (a standard chemical solvent) regarding the extraction of phenolic
compounds from thirteen Vitis sp. shoots. Two extraction methods have been applied: ultrasound-assisted
extraction and solid-liquid extraction. A total of eleven polyphenols which belongs to four families (proantho cyanins, stilbenes, hydroxycinnamic acids, and flavonols) have been identified and quantified in the extracts.
The statistical analysis shows that the levulinic acid-based DES systems are novel and important alternatives to
chemical solvents due to favourable eco-friendly properties and remarkable extraction performance of poly phenols. On the other hand, the ultrasound-assisted extraction technique has significantly increased the
extraction rate in comparison to the solid-liquid extraction method with p-values lower than 0.05 for most
compounds. The genetic factor has been shown to play an important role in the content of extracted polyphenols,
being V. riparia pubescente the one that presented the highest concentrations of extracted polyphenols. Finally,
the polyphenol-enriched extracts have proven important properties such as antioxidant activity and significant
delay in bacteria growth against both gram-positive and gram-negative bacteria. It is important to note that, to
the best of our knowledge, this is the first time that deep eutectic solvents have been used for the extraction of
bioactive compounds from vine shoot residues.
Revisiting lignin: a tour through its structural features, characterization methods and applications
Publication . Melro, Elodie; Filipe, Alexandra; Sousa, Dora; Medronho, Bruno; Romano, Anabela
Lignin is a complex organic polymer found in the plant cell wall with important biological functions, such as water transport, mechanical support, and resistance to various stresses. It is considered the second most abundant biopolymer on earth and the largest natural source of aromatics. Despite being annually co-produced in massive amounts, during cellulose fragmentation in the pulp industry and ethanol biorefinery, it is clearly undervalued; most of it is discarded or burned as fuel for energy production and, so far, only ca. 1-2% of lignin has been utilized as a high-value product. This underuse makes lignin the future resource of choice to produce green fuels and a wide range of added-value biomaterials and chemicals, which can contribute to the transition to more sustainable industries. However, its great variability between plant families combined with its complex and chemically inert structure is challenging researchers who seek for strategies regarding its valorization. With this scope, several different approaches have emerged regarding the development of better and efficient isolation methods, purification and characterization techniques, and improved methodologies for lignin chemical modification and blending with other compounds. These improvements represent important opportunities for the creation of value-added lignin-based biopolymers and materials and some have already shown potential to be scaled up. All these aspects are pedagogically introduced and discussed in this review.
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Funding agency
Fundação para a Ciência e a Tecnologia
Funding programme
CEEC IND 2018
Funding Award Number
CEECIND/01014/2018/CP1540/CT0002