Enhancing lignin dissolution and extraction: the effect of surfactants

The 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.FCT: UID/QUI/00313/2020, PTDC/AGR-TEC/4814/2014, PTDC/ASP-SIL/30619/2017, UIDB/05183/2020, CEECIND/01014/2018, SFRH/BD/132835/2017, COMPETEinfo:eu-repo/semantics/publishedVersio

Lignin extraction from waste pine sawdust using a biomass derived binary solvent system

Lignocellulosic 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

Chitosan Films in Food Applications. Tuning Film Properties by Changing Acidic Dissolution Conditions

Food contamination due to the presence of microorganisms is a serious problem. New food preservation systems are being studied to kill or inhibit spoilage and pathogenic microorganisms that contaminate food and reduce the shelf life of products. Chitosan films with potential application to food preservation have witnessed great developments during the last years. Chitosan is a cationic polysaccharide with the ability to form films and possess antimicrobial properties. It is water-insoluble but can be dissolved in acidic solutions. In the present work, three different acids (acetic, lactic and citric) were used in chitosan dissolution and both, the resultant solutions and formed films were characterized. It was observed that chitosan water-acetic acid systems show the highest antimicrobial activity due to the highest chitosan charge density, compared to the mixtures with lactic and citric acid. This system showed also the higher solution viscosity compared to the other systems. Chitosan–acetic acid films were also the ones presenting better mechanical properties; this can be attributed to the fact that lactic and citric acids remain in the films, changing their properties, which does not happen with acetic acid. Films produced from chitosan dissolved in water/acetic acid system are resistant, while very fragile but elastic films are formed when lactic acid is used. It was demonstrated that a good selection of the type of acid not only facilitates the dissolution of chitosan but also plays a key role in the properties of the formed solutions and films

Desenvolvimento de produtos inovadores destinado ao tratamento de superfície de rolhas de cortiça

A rolha de cortiça é o produto mais famoso da indústria corticeira, mas o crescente desenvolvimento de vedantes alternativos tem vindo a ser uma ameaça a este vedante tradicional. O mercado está cada vez mais exigente, e a margem para defeitos está cada vez menor. Um dos grandes problemas das rolhas de cortiça usadas em bebidas espirituosas tem sido a migração do tratamento de superfície para o gargalo da garrafa, deixando-o com um aspeto gorduroso que não é apreciado pelo cliente final. Para que a rolha de cortiça não perca o seu prestígio, e para que volte a entrar no mercado das bebidas espirituosas que tem sido “invadido” pelos vedantes alternativos, é de extrema importância o desenvolvimento de produtos inovadores para o tratamento de superfície de rolhas de cortiça, de forma a eliminar as debilidades dos tratamentos tradicionais cuja evolução tem sido praticamente inexistente nas últimas duas décadas. É importante dar valor à cortiça, de forma competitiva, inovadora e diferenciada. Este projecto visa o estudo de novos revestimentos poliméricos a serem usados como tratamento de superfície nas rolhas de cortiça. Este sistema polimérico deverá ter elevada afinidade com a cortiça, evitando a migração do revestimento para o gargalo e posteriormente para a bebida, deverá ter capacidade de impermeabilização da superfície da rolha, protegendo a rolha do ataque da bebida, deverá possuir inércia química, de forma a minimizar possíveis interações com a bebida e distribuição homogénea, formando uma camada fina sobre toda a rolha. Numa primeira fase foram estudados os tratamentos de superfície atualmente utilizados e caracterizada a superfície da rolha de cortiça. Posteriormente foi realizado um estudo intensivo da relação entre a arquitetura do polímero e a adesão à superfície da rolha em ambiente alcoólico. Neste estudo foram usados essencialmente dois tipos distintos de polímeros, polímeros à base de celulose e polímeros acrílicos. Para perceber o comportamento destes polímeros na adesão à rolha de cortiça foram realizados testes de migração do revestimento e de matéria corante para a solução etanólica, analisada a hidrofobicidade da superfície e caracterizadas as soluções poliméricas. De todos os polímeros testados os que apresentam melhor desempenho para serem usados como tratamento de superfície de rolhas de cortiça foram os polímeros celulósicos com substituição catiónica, os SoftCAT, mais especificamente o SoftCAT SL-100 que possui maior número de substituições hidrofóbicas. Este polímero apresentou uma hidrofobicidade adequada e boa adesão à cortiça, mesmo a baixas concentrações

Revisiting lignin: a tour through its structural features, characterization methods and applications

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.Portuguese Foundation for Science and Technology (FCT)Portuguese Foundation for Science and Technology [PTDC/AGR-TEC/4814/2014, PTDC/ASP-SIL/30619/2017, UIDB/05183/2020, CEECIND/01014/2018]; FCTPortuguese Foundation for Science and TechnologyEuropean Commission [UID/QUI/00313/2020, SFRH/BD/132835/2017]; COMPET

On the Development of Phenol-Formaldehyde Resins Using a New Type of Lignin Extracted from Pine Wood with a Levulinic-Acid Based Solvent

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

Chitosan Films in Food Applications. Tuning Film Properties by Changing Acidic Dissolution Conditions

Food contamination due to the presence of microorganisms is a serious problem. New food preservation systems are being studied to kill or inhibit spoilage and pathogenic microorganisms that contaminate food and reduce the shelf life of products. Chitosan films with potential application to food preservation have witnessed great developments during the last years. Chitosan is a cationic polysaccharide with the ability to form films and possess antimicrobial properties. It is water-insoluble but can be dissolved in acidic solutions. In the present work, three different acids (acetic, lactic and citric) were used in chitosan dissolution and both, the resultant solutions and formed films were characterized. It was observed that chitosan water-acetic acid systems show the highest antimicrobial activity due to the highest chitosan charge density, compared to the mixtures with lactic and citric acid. This system showed also the higher solution viscosity compared to the other systems. Chitosan-acetic acid films were also the ones presenting better mechanical properties; this can be attributed to the fact that lactic and citric acids remain in the films, changing their properties, which does not happen with acetic acid. Films produced from chitosan dissolved in water/acetic acid system are resistant, while very fragile but elastic films are formed when lactic acid is used. It was demonstrated that a good selection of the type of acid not only facilitates the dissolution of chitosan but also plays a key role in the properties of the formed solutions and films

Engineering novel phenolic foams with lignin extracted from pine wood residues via a new levulinic-acid assisted process

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.info:eu-repo/semantics/publishedVersio

Dissolution of kraft lignin in alkaline solutions

Lignins are among the most abundant renewable resources on the planet. However, their application is limited by the lack of efficient dissolution and extraction methodologies. In this work, a systematic and quantitative analysis of the dissolution efficiency of different alkaline-based aqueous systems (i.e. lithium hydroxide, LiOH; sodium hydroxide, NaOH; potassium hydroxide, KOH; cuprammonium hydroxide, CuAOH; tetrapropylammonium hydroxide, TPAOH and tetrabutylammonium hydroxide, TBAOH) is reported, for the first time, for kraft lignin. Phase maps were determined for all systems and lignin solubility was found to decrease in the following order: LiOH > NaOH > KOH > CuAOH > TPAOH > TBAOH, thus suggesting that the size of the cation plays an important role on its solubility. The π∗ parameter has an opposite trend to the solubility, supporting the idea that cations of smaller size favor lignin solubility. Dissolution was observed to increase exponentially above pH 9-10 being the LiOH system the most efficient. The soluble and insoluble fractions of lignin in 0.1 M NaOH were collected and analyzed by several techniques. Overall, data suggests a greater amount of simple aromatic compounds, preferentially containing sulfur, in the soluble fraction while the insoluble fraction is very similar to the native kraft lignin