Organosolv and ionosolv processes for autohydrolyzed poplar fractionation: Lignin recovery and characterization.

Biomass fractionation plays a major role in the search for competitive biorefineries, where the isolation and recovery of the three woody fractions is key. In this sense, we have used autohydrolyzed hemicellulose-free poplar as feedstock to compare two fractionation processes, organosolv and ionosolv, oriented to lignin recovery. The recovered lignins were then characterize by different techniques (NMR, GPC, TGA). Both treatments were tested at different temperatures to analyze temperature influence on lignin recovery and properties. The highest lignin recovery was obtained with the ionosolv process at 135 °C, reaching a solid yield of ~70%. Lignin characterization showed differences between both treatments. Lignins enriched in C-O linkages and G units were recovered with the organosolv process, where increasing temperature led to highly depolymerized lignins. However, lignins with higher C-C linkages and S units contents were obtained with the ionosolv process, producing more thermically stable lignins. In addition, increasing temperature caused lignin repolymerization when employing ionic liquids as solvents. Therefore, this work outlines the most important differences between ionosolv and organosolv processes for biomass fractionation, focusing on lignin recovery and its properties, which is the first step in order to valorize all biomass fractions.

Chitosan-reinforced cellulosic bionogels: Viscoelastic and antibacterial properties.

New chitosan-reinforced cellulosic bionogels were successfully formulated with different chitosan loadings (0.25, 0.5, 0.75, and 1 wt/wt. %). These materials were developed using cholinium lysinate, a bio-ionic liquid, being an ecological alternative to conventional ionogels. The rheological properties of these materials showed that all the studied viscoelastic properties were higher (elastic moduli, G'; loss moduli, G"; and complex viscosity, η*) as the chitosan loading increased. The reinforced bionogels were physical weak gels, and the proposed mechanism of formation was by hydrogen bonds. The bionogel with 1 wt/wt. % chitosan loading exhibited the highest viscoelastic properties (for 4 Hz, G': 552 kPa, G": 99 kPa, and η*: 22 kPa·s). Regarding the antibacterial properties, these gels showed a good inhibitory capacity to S. aureus and E. coli, especially against the latter bacterium. For these reasons, these novel ecofriendly gels are promising in the pharmaceutical/medical and biosensors sectors to develop new functional materials.

Acidic depolymerization vs ionic liquid solubilization in lignin extraction from eucalyptus wood using the protic ionic liquid 1-methylimidazolium chloride.

Protic ionic liquids have been proposed as effective solvents for the selective extraction of lignin from wood. In this work, the protic ionic liquid 1-methylimidazolium chloride has been used to extract lignin at different biomass loadings, temperatures, and times to understand the influence of treatment severity on the lignin dissolution mechanism. The maximum lignin recovery (82.35 g lignin/100 g biomass lignin) was achieved at 10% (w/w) biomass loading, 135 °C, and 6 h. An increase in treatment severity leads to an acid cleavage of ether linkages, which increases the average molecular weight and thermal stability of lignins due to C-C repolymerization. HSQC-NMR analysis showed the effect of operating conditions on the predominant mechanism of lignin depolymerization. At mild conditions, there is a preferential degradation of G units (the typical depolymerization mechanism of ionic liquid treatments); but at the most severe conditions, S units are predominantly removed, as usually occurs in acidic treatments. This work contributes to better understanding the different lignin extraction mechanisms occurring with a protic ionic liquid depending on different operating conditions.

Viscoelastic properties of physical cellulosic bionogels of cholinium lysinate.

Novel ionogels with different cellulose contents, namely, 0.5, 1, 1.5 and 2 wt%, were formulated with cholinium lysinate (ChLys), and the rheological properties were evaluated at 3 and 7 days postgelation. Because of the biobased compounds contained in these ionogels, in this work, they are denoted as bionogels. These materials have great potential to yield functional biomaterials for use in the medical/pharmacological sector. Some knowledge of how cellulose is dissolved in ChLys was necessary to formulate the bionogels. The dissolution time was studied for each bionogel, with the dissolution times being 3, 4, 4.5, and 6.5 h for 0.5, 1, 1.5, and 2% cellulose, respectively. The bionogel with a 2% cellulose load had the highest rheological properties, i.e. elastic modulus (G'), loss modulus (G″) and complex viscosity (η*), on the studied postgelation days: G' (3 days): 0.7-50 kPa, G' (7 days): 1-100 kPa, G″ (3 days): 0.1-10 kPa, and G″ (7 days): 0.2-20 kPa, η* (3 days): 0.2-200 kPa s and η* (7 days): 0.4-300 kPa s. The postgelation time is an important parameter in the formulation of bionogels, since at 3 days postgelation, the networks continued to be constituted. Regarding classification, these bionogels were weak physical gels.

Combining autohydrolysis and ionic liquid microwave treatment to enhance enzymatic hydrolysis of Eucalyptus globulus wood.

The combination of autohydrolysis and ionic liquid microwave treatments of eucalyptus wood have been studied to facilitate sugar production in a subsequent enzymatic hydrolysis step. Three autohydrolysis conditions (150 °C, 175 °C and 200 °C) in combination with two ionic liquid temperatures (80 °C and 120 °C) were compared in terms of chemical composition, enzymatic digestibility and sugar production. Morphology was measured (using SEM) and the biomass surface was visualized with confocal fluorescence microscopy. The synergistic cooperation of both treatments was demonstrated, enhancing cellulose accessibility. At intermediate autohydrolysis conditions (175 °C) and low ionic liquid temperature (80 °C), a glucan digestibility of 84.4% was obtained. Using SEM micrographs, fractal dimension (as a measure of biomass complexity) and lacunarity (as a measure of homogeneity) were calculated before and after pretreatment. High fractals dimensions and low lacunarities correspond to morphologically complex and homogeneous samples, that are better digested by enzyme cocktails.