Browsing by Author "Melro, Elodie"
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- Engineering novel phenolic foams with lignin extracted from pine wood residues via a new levulinic-acid assisted processPublication . Melro, Elodie; Duarte, Hugo; Antunes, Filipe E.; Valente, Artur J.M.; Romano, Anabela; Norgren, Magnus; Medronho, BrunoPhenolic 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.
- Enhancing lignin dissolution and extraction: the effect of surfactantsPublication . Melro, Elodie; Valente, Artur J. M.; Antunes, Filipe E.; Romano, Anabela; Medronho, BrunoThe dissolution and extraction of lignin from biomass represents a great challenge due to the complex structure of this natural phenolic biopolymer. In this work, several surfactants (i.e., non-ionic, anionic, and cationic) were used as additives to enhance the dissolution efficiency of model lignin (kraft) and to boost lignin extraction from pine sawdust residues. To the best of our knowledge, cationic surfactants have never been systematically used for lignin dissolution. It was found that ca. 20 wt.% of kraft lignin is completely solubilized using 1 mol L-1 octyltrimethylammonium bromide aqueous solution. A remarkable dissolution efficiency was also obtained using 0.5 mol L-1 polysorbate 20. Furthermore, all surfactants used increased the lignin extraction with formic acid, even at low concentrations, such as 0.01 and 0.1 mol L-1. Higher concentrations of cationic surfactants improve the extraction yield but the purity of extracted lignin decreases.
- Levulinic acid-based “green” solvents for lignocellulose fractionation: on the superior extraction yield and selectivity toward ligninPublication . Melro, Elodie; Riddell, Alexander; Bernin, Diana; Rosa Da Costa, Ana; Valente, Artur J. M.; Antunes, Filipe E.; Romano, Anabela; Norgren, Magnus; Medronho, BrunoThe high potential use of lignin in novel biomaterialsand chemicalsrepresents an important opportunity for the valorization of the mostabundant natural resource of aromatic molecules. From an environmentalperspective, it is highly desirable replacing the hazardous methodscurrently used to extract lignin from lignocellulosic biomass anddevelop more sustainable and environmentally friendly approaches.Therefore, in this work, levulinic acid (a "green" solventobtained from biomass) was successfully used, for the first time,to selectively extract high-quality lignin from pine wood sawdustresidues at 200 degrees C for 6 h (at atmospheric pressure). Moreover,the addition of catalytic concentrations of inorganic acids (i.e.,H2SO4 or HCl) was found to substantially reducethe temperature and reaction times needed (i.e., 140 degrees C, 2 h)for complete lignin extraction without compromising its purity. NMRdata suggests that condensed OH structures and acidic groups are presentin the lignin following extraction. Levulinic acid can be easily recycledand efficiently reused several times without affecting its performance.Furthermore, excellent solvent reusability and performance of extractionof other wood residues has been successfully demonstrated, thus makingthe developed levulinic acid-based procedure highly appealing andpromising to replace the traditional less sustainable methodologies.
- Levulinic acid: a novel sustainable solvent for lignin dissolutionPublication . Melro, Elodie; Filipe, Alexandra; Valente, Artur J. M.; Antunes, Filipe E.; Romano, Anabela; Norgren, Magnus; Medronho, BrunoLignin is a natural, renewable resource with potential to be used in biomaterials. Due to its complex structure, its efficient dissolution is still challenging, which hinders its applicability at large scale. This challenge become harder considering the current need of sustainable and environmentally friendly solvents. To the best of our knowledge, this work reports for the first time the dissolution of kraft lignin in levulinic acid, a "green" solvent, and compares its efficiency with common carboxylic acids and sulfuric acid. It has been found that levulinic acid has a high capacity to dissolve kraft lignin at room temperature (40 wt% solubility), and it efficiency is not compromised when diluting the acid with water (up to 40 wt% water content). the Kamlet-Taft pi* parameter of the different acidic solvents was estimated and found to correlate well with their solubility performance. Lignins previously dissolved in levulinic and formic acids were selected to be regenerated and minor differences were found in thermal stability and morphological structure, when compared to native kraft lignin. However, an increase in the content of the carbonyl groups in the regenerated lignin material was observed. (C) 2020 Elsevier B.V. All rights reserved.
- Lignin extraction from waste pine sawdust using a biomass derived binary solvent systemPublication . Magalhães, Solange; Filipe, Alexandra; Melro, Elodie; Fernandes, Catarina; Vitorino, Carla; Alves, Luís; Romano, Anabela; Rasteiro, Maria G.; Medronho, Bruno; MDPILignocellulosic biomass fractionation is typically performed using methods that are somehow harsh to the environment, such as in the case of kraft pulping. In recent years, the development of new sustainable and environmentally friendly alternatives has grown significantly. Among the developed systems, bio-based solvents emerge as promising alternatives for biomass processing. Therefore, in the present work, the bio-based and renewable chemicals, levulinic acid (LA) and formic acid (FA), were combined to fractionate lignocellulosic waste (i.e., maritime pine sawdust) and isolate lignin. Different parameters, such as LA:FA ratio, temperature, and extraction time, were optimized to boost the yield and purity of extracted lignin. The LA:FA ratio was found to be crucial regarding the superior lignin extraction from the waste biomass. Moreover, the increase in temperature and extraction time enhances the amount of extracted residue but compromises the lignin purity and reduces its molecular weight. The electron microscopy images revealed that biomass samples suffer significant structural and morphological changes, which further suggests the suitability of the newly developed bio-fractionation process. The same was concluded by the FTIR analysis, in which no remaining lignin was detected in the cellulose-rich fraction. Overall, the novel combination of bio-sourced FA and LA has shown to be a very promising system for lignin extraction with high purity from biomass waste, thus contributing to extend the opportunities of lignin manipulation and valorization into novel added-value biomaterials.
- New deep eutectic solvent assisted extraction of highly pure lignin from maritime pine sawdust (Pinus pinaster Ait.)Publication . Fernandes, Catarina; Melro, Elodie; Magalhaes, Solange; Alves, Luis; Craveiro, Rita; Filipe, Alexandra; Valente, Artur J. M.; Martins, Gabriela; Antunes, Filipe E.; Romano, Anabela; Medronho, BrunoLignocellulosic 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. ? 2021 Elsevier B.V. All rights reserved.
- On the development of Phenol-Formaldehyde resins using a new type of lignin extracted from pine wood with a Levulinic-Acid based solventPublication . Melro, Elodie; Antunes, Filipe E.; Valente, Artur J. M.; Duarte, Hugo; Romano, A.; Medronho, BrunoResole 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.
- Poly(butylene succinate)-based composites with technical and extracted lignins from wood residuesPublication . Melro, Elodie; Duarte, Hugo; Eivazi, Alireza; Costa, Carolina; Faleiro, Maria Leonor; Rosa Da Costa, Ana; Antunes, Filipe E.; Valente, Artur J. M.; Romano, Anabela; Norgren, Magnus; Medronho, BrunoPoly(butylene succinate) (PBS) has been drawing attention as a reliable biodegradable and sustainable alternative to synthetic petroleum-based polymers. In this study, PBS-lignin composites were developed using a recently extracted lignin (LA-lignin) from pine wood residues employing an innovative sustainable approach. These composites were systematically compared with PBS-based composites formed with commonly used technical lignins. The molecular weight of the lignins was evaluated, along with various structural and performance-related properties. The LA-lignin/PBS composites display a remarkably low water solubility (ca. < 2%), water uptake (ca. 100 degrees). Moreover, the rigidity and thermal stability of the LA-lignin-PBS composites were higher than those of the systems formed with technical lignins. Although all composites studied present remarkable antioxidant features, the novel LA-lignin-PBS systems stand out in terms of antiadhesion activity against both Gram-positive and Gram-negative bacteria. Overall, the systematic analysis performed in this work regarding the impact of various lignins on the formed PBS composites enables a better understanding of the essential structural and compositional lignin features for achieving biobased materials with superior properties.
- Revisiting lignin: a tour through its structural features, characterization methods and applicationsPublication . Melro, Elodie; Filipe, Alexandra; Sousa, Dora; Medronho, Bruno; Romano, AnabelaLignin 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.