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Innovative bionanocomposite foams based on precipitated Kraft lignin (Lig) and Kraft black liquor (BL) loaded with sepiolite (Sep) were prepared. BL/Sep bionanocomposites were synthesized by emulsion templating and Lig/Sep bionanocomposites were prepared by freeze-drying, resulting in stable and rigid foams. BL/Sep bionanocomposites displayed a closed cell structure, a specific area between 19 and 35 m2/g and macropores of varying sizes. The porosity in this technique is achieved by the mechanical agitation of the emulsion. On the other hand, freeze-dried Lig/Sep bionanocomposites showed open cell morphology with surface areas ranging from 1 to 4 m2/g and uniform macropores due to the ice-templating process. The presence of sepiolite in both types of bionanocomposite foams improved their stiffness, with Young's moduli ranging from 0.21 to 9.6 MPa. The capacity of the foams to adsorb metals, drugs and dyes was evaluated and it was found that the synthesized bionanocomposite foams exhibiting similar adsorption capacities as that reported for lignin. Sepiolite significantly improved the adsorption of Cu(II), Cd(II), acetaminophen (ACT), and methylene blue (MB) in BL/Sep bionanocomposites. Meanwhile, the Lig/Sep bionanocomposites demonstrated superior adsorption capacities for the Cr(VI) anion and aromatic ring compounds, including ACT and MB. In this respect, these lignin-sepiolite foams can be considered as promising materials for the removal of pollutants in aqueous solution.

Natural and renewable resources from plants or animals are an important source of biomaterials due to their biocompatibility and high availability. Lignin is a biopolymer present in the biomass of plants, where it is intertwined and cross-linked with other polymers and macromolecules in the cell walls, generating a lignocellulosic material with potential applications. We have prepared lignocellulosic-based nanoparticles with an average size of 156 nm that exhibit a high photoluminescence signal when excited at 500 nm with emission in the near-infrared (NIR) region at 800 nm. The advantage of these lignocellulosic-based nanoparticles is their natural luminescent properties and their origin from rose biomass waste, which eliminates the need for encapsulation or functionalization of imaging agents. Moreover, the in vitro cell growth inhibition (IC50) of lignocellulosic-based nanoparticles is about 3 mg/mL, and no in vivo toxicity was registered up to 57 mg/kg, which suggests that they are suitable for bioimaging applications. In addition, these nanoparticles can circulate in the blood and are excreted in urine. The combined high luminescence signal in NIR, small size, low in vitro toxicity, low in vivo toxicity, and blood circulation support the potential of lignin-based nanoparticles as a novel bioimaging agent.

A novel strategy for pre-treated biomass detoxification combining emerging green solvents and low environmental impact extraction technologies was evaluated. Steam-exploded biomass was subjected to microwave-assisted or orbital shaking extraction using bio-based or eutectic solvents. The extracted biomass was enzymatically hydrolysed. The potential of this detoxification methodology was studied in terms of phenolic inhibitors extraction and sugar production improvement. The effect of adding a post-extraction water washing step before hydrolysis was also evaluated. Excellent results were achieved when steam-exploded biomass was subjected to the microwave-assisted extraction combined with the washing step. The highest sugar production was achieved when ethyl lactate was used as extraction agent (49.80 ± 3.10 g total sugar/L) over the control (30.43 ± 0.34 g total sugar/L). Results suggested that a detoxification step based on green solvents would be a promising option to extract phenolic inhibitors, which can be revalorized as antioxidants, and improve the sugar production from the extracted pre-treated biomass.

Kraft lignin, a side-stream from the pulp and paper industry, can be modified by laccases for the synthesis of high added-value products. This work aims to study different laccase sources, including a bacterial laccase from Streptomyces ipomoeae (SiLA) and a fungal laccase from Myceliophthora thermophila (MtL), for kraft lignin polymerization. To study the influence of some variables in these processes, a central composite design (CCD) with two continuous variables (enzyme concentration and reaction time) and three levels for each variable was used. The prediction of the behavior of the output variables (phenolic content and molecular weight of lignins) were modelled by means of response surface methodology (RSM). Moreover, characterization of lignins was performed by Fourier-transform infrared (FTIR) spectroscopy and different nuclear magnetic resonance (NMR) spectroscopy techniques. In addition, antioxidant activity was also analyzed. Results showed that lignin polymerization (referring to polymerization as lower phenolic content and higher molecular weight) occurred by the action of both laccases. The enzyme concentration was the most influential variable in the lignin polymerization reaction within the range studied for SiLA laccase, while the most influential variable for MtL laccase was the reaction time. FTIR and NMR characterization analysis corroborated lignin polymerization results obtained from the RSM.

Although hydroxypropyl methylcellulose (HPMC) has been proposed as renewable substitute for traditional plastic, its barrier and active properties need to be improved. Thus, the combination of an organic residue such as kraft lignin (0-10% w/w) and a natural clay such as montmorillonite (3% w/w) by application of ultrasound can significantly improve HPMC properties. This is most likely due to the close interaction between lignin and montmorillonite, which leads to delamination of the clay and improves its dispersion within the HPMC matrix. Specifically, the addition of kraft lignin to the bionanocomposite films provided them with UV-shielding, antioxidant capacity and antibacterial activity. The incorporation of 3% montmorillonite resulted in reductions of 65.8% and 11.4% in oxygen (OP) and water vapor permeabilities (WVP), respectively. Moreover, a reduction of 43.8% in WVP was achieved when both lignin (1%) and montmorillonite (3%) were incorporated, observing a synergistic effect. Thus, the HPMC bionanocomposite with 1% lignin and 3% montmorillonite, presented good thermal stability and mechanical strength with significantly improved gas barrier permeability, as well as UV-shielding (maintaining a good transparency), antioxidant and antibacterial activities.

This work focuses on the structural features and physicochemical properties of different Kraft lignins and how they can influence the electrospinning process to obtain nanostructures. Structural features of Kraft lignins were characterized by nuclear magnetic resonance, size exclusion chromatography, fourier-transform infrared spectroscopy, and thermal analysis, whereas chemical composition was analyzed by standard method. The addition of cellulose acetate (CA) improves the electrospinning process of Kraft lignins (KL). Thus, solutions of KL/CA at 30 wt% with a KL:CA weight ratio of 70:30 were prepared and then physicochemical and rheologically characterized. The morphology of electrospun nanostructures depends on the intrinsic properties of the solutions and the chemical structure and composition of Kraft lignins. Then, surface tension, electrical conductivity and viscosity of eucalypt/CA and poplar/CA solutions were suitable to obtain electrospun nanostructures based on uniform cross-linked nanofibers with a few beaded fibers. It could be related with the higher purity and higher linear structure, phenolic content and S/G ratios of lignin samples. However, the higher values of electrical conductivity and viscosity of OTP/CA solutions resulted in electrospun nanostructure with micro-sized particles connected by thin fibers, due to a lower purity, S/G ratio and phenolic content and higher branched structure in OTP lignin.

Oil-in-water bitumen emulsions stabilized by biobased surfactants such as lignin are in line with the current sustainable approaches of the asphalt industry involving bitumen emulsions for reduced temperature asphalt technologies. With this aim, three lignins, derived from the kraft pulping and bioethanol industries, were chemically modified via the Mannich reaction to be used as cationic emulsifiers. A comprehensive chemical characterization was conducted on raw lignin-rich products, showing that the kraft sample presents a higher lignin concentration and lower molecular weight. Instead, bioethanol-derived samples, with characteristics of non-woody lignins, present a high concentration of carbohydrate residues and ashes. Lignin amination was performed at pH = 10 and 13, using tetraethylene pentamine and formaldehyde as reagents at three different stoichiometric molar ratios. The emulsification ability of such cationic surfactants was firstly studied on prototype silicone oil-in-water emulsions, attending to their droplet size distribution and viscous behavior. Among the synthetized surfactants, cationic kraft lignin has shown the best emulsification performance, being used for the development of bitumen emulsions. In this regard, cationic kraft lignin has successfully stabilized oil-in-water emulsions containing 60% bitumen using small surfactant concentrations, between 0.25 and 0.75%, which was obtained at pH = 13 and reagent molar ratios between 1/7/7 and 1/28/28 (lignin/tetraethylene pentamine/formaldehyde).

The development of nanocellulose-clay materials resulted of great relevance, as it opened up the applications of nanocellulose, but it still requires new approaches that could contribute to improve the preparation procedures and the features of this type of biohybrid materials. In this context, nanocellulose-sepiolite (NC-S) biocomposite foams and films have already been successfully tested for some applications. However, the influence of the nanocellulose properties on sepiolite-cellulose interactions, and consequently on the final properties and potential applications of NC-S biohybrid materials, has not been previously studied. To address this knowledge gap, four kinds of nanocelluloses produced from elm biomass (non-chemically pretreated lignocellulose and bleached cellulose nanofibers (LCNFs and CNFs, respectively), TEMPO-oxidized cellulose nanofibers (TOCNFs) and cellulose nanocrystals (CNCs)) were characterized and used to develop NC-S nanopapers. A stronger interaction was found between sepiolite and negatively charged nanocelluloses (TOCNFs and CNCs), improving their thermal stability and mechanical properties by increasing the sepiolite content. Furthermore, the type of nanocellulose and the sepiolite content could be adjusted to tune the flammability, water permeability and mechanical and optical properties of the NC-S nanopapers. Graphical abstract: [Figure not available: see fulltext.]

In order to identify new sustainable sources for producing cellulose nanofibers (CNFs), fast-growing poplar (Populus alba L.) wood was evaluated herein. For that purpose, bleached poplar kraft pulp was produced and submitted to TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) mediated oxidation (TEMPO-ox) chemical pretreatment followed by microfluidization. The resulting CNFs were thoroughly characterized, including a rheological study at different pH values. Poplar CNFs showed properties comparable to eucalypt CNFs (reference material for CNFs production), showing high carboxylate content (1048 ± 128 µmol g−1), fibrillation yield (87.3% ± 8.1%), optical transmittance (83% at 700 nm) and thermal stability (up to more than 200 °C). Regarding the rheological study, whereas pH from 4 to 10 did not produce significant changes in rheological behavior, a reduction of pH down to 1 led to an order-of-magnitude increase on the viscoelastic functions. Therefore, poplar CNF shows potential in the pH-sensitive hydrogels application field. Finally, the possible ecotoxicity of poplar CNF was assessed. The decrease in cell viability was very low so that only concentrations causing a 10% cytotoxicity could be calculated for the assay detecting alterations in cell metabolism (10 µg mL−1) and plasma membrane integrity (60 µg mL−1).

Cellulose is the most abundant component of biomass and the one that requires the most activation energy (Ea) for pyrolysis. In this study, the dependence of Ea on the intrinsic cellulose characteristics, such as the degree of polymerization (DP), crystallinity, and crystal size, was studied in different cellulose samples, including samples from Eucalyptus globulus, Ulmus minor, Linun usitatissimum, Olea europaea, Robinia pseudoacacia, and Populus alba. Then, to describe the pyrolytic degradation of cellulose, the Ozawa-Flynn-Wall kinetic method was the most appropriate among the isoconversional models studied. An acceptable quadratic relationship of R-2 > 0.9 between the Ea values of the different cellulose samples with their corresponding DP, crystallinity index, and crystal size values was found. Therefore, low crystallinity and low-to-medium crystal size values are desired to obtain lower Ea values for cellulose pyrolysis. On the other hand, DP did not present a clear effect on Ea in the studied DP range. Keywords

After thermal modification at 210 °C using the Thermowood method, changes in Pinus radiata D. Don wood cell wall components and hygroscopicity were studied for subsequent comparison with recently felled wood of the same species in samples from the same region of provenance (Basque Country, Spain). To this end, samples were characterised by sorption isotherms at 15, 35 and 50 °C fitted to the Guggenheim–Anderson–de Boer (GAB) model, the chemical composition was obtained by high performance liquid chromatography (HPLC) and infrared spectroscopy (FTIR), and crystallinity and structural organisation of cellulose (crystal orientation) were determined using powder and 2D X-ray diffraction (XRD). Heat treatment caused the following changes in the wood: a decrease in the equilibrium moisture content (EMC); a smaller hysteresis area and therefore more hygroscopically stable wood; a decrease in the hemicellulose content; an increase in the relative percentage of cellulose, lignin and extractives; and a higher degree of crystallinity and crystal orientation of the cellulose. The reorganisation of cellulose could be explained by epitaxial growth of cellulose starting from the highly oriented crystalline regions during the recrystallisation process. All these chemical and structural changes induced by heating could explain the reduction in hygroscopic properties of wood, as well as its stability.

TEMPO (2,2,6,6-tetramethylpiperidin-1-oxyl)-oxidized cellulose nanofibers (CNF) were assembled to fibrous clay sepiolite (SEP) by means of a high shear homogenizer and an ultrasound treatment followed by lyophilization using three different methods: normal freezing, directional freezing, and a sequential combination of both methods. Methyltrimethoxysilane (MTMS) was grafted to the foam surface by the vapor deposition method to introduce hydrophobicity to the resulting materials. Both the SEP addition (for the normal and directional freezing methods) and the refreezing preparation procedure enhanced the compressive strength of the foams, showing compressive moduli in the range from 28 to 103 kPa for foams loaded with 20% w/w sepiolite. Mercury intrusion porosimetry shows that the average pore diameters were in the range of 30-45 µm depending on the freezing method. This large porosity leads to materials with very low apparent density, around 6 mg/cm3, and very high porosity >99.5%. In addition, water contact angle measurement and Fourier-transform infrared spectroscopy (FTIR) were applied to confirm the foam hydrophobicity, which is suitable for use as an oil sorbent. The sorption ability of these composite foams has been tested using olive and motor oils as models of organophilic liquid adsorbates, observing a maximum sorption capacity of 138 and 90 g/g, respectively.

Motivated by the negative impact of fossil fuel consumption on the environment, the need arises to produce materials and energy from renewable sources. Cellulose, the main biopolymer on Earth, plays a key role in this context, serving as a platform for the development of biofuels, chemicals and novel materials. Among the latter, micro-and nanocellulose have been receiving increasing attention in the last few years. Their many attractive properties, i.e., thermal stability, high mechanical resistance, barrier properties, lightweight, optical transparency and ease of chemical modification, allow their use in a wide range of applications, such as Paper or polymer reinforcement, Packag-ing, construction, membranes, bioplastics, bioengineering, optics and electronics. In view of the increasing demand for traditional wood pulp (e.g., obtained from eucalypt, birch, pine, spruce) for micro/nanocellulose production, dedicated crops and agricultural residues can be interesting as raw materials for this purpose. This work aims at achieving microfibrillated cellulose production from fast-growing poplar and olive tree pruning using physical pretreatment (PFI refining) before the microfibrillation stage. Both raw materials yielded microfibrillated cellulose with similar properties to that obtained from a commercial industrial eucalypt pulp, producing films with high mechanical properties and low wettability. According to these properties, different applications for cellulose microfibers suspensions and films are discussed.

A prospective methodology aimed to develop totally sustainable oleogels with potential application in lubrication is reported. Oleogels were prepared with cellulose nanofibrils from elm pulps in castor oil. Even at a concentration as low as 1.4 wt%, the oleogels showed rheological behaviors similar to a traditional lithium grease used as reference. In that sense, the high thickening power of cellulose nanofibers was remarked. Never-dried bleached and unbleached elm pulps were mechanically treated with PFI mill refiner and microfluidizer. Moreover, as an alternative way of producing cellulose nanofibrils, the never-dried bleached elm pulp was chemically oxidized using 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO). The three types of nanofibers were characterized and used in the production of oleogels. The great challenge was to remove the high amount of water retained by the nanofibrils during the nanofibrillation treatment before it was incorporated into the vegetable oil-based lubricant. Alternative strategies such as liophilization or drying failed because the nanofibers, with very high specific surface and strong capacity to interact among them by hydrogen bonding, underwent severe aggregation. Instead, the proposed methanol-based solvent exchange method enabled the transfer of the cellulose nanofibrils from the origin hydrogel to the vegetable oil with no detriment of both their aspect ratio and thickening capacity. Chemical considerations are provided with regard to such a solvent-mediated method, which yielded homogeneous and storage-stable oleogels. This work may attract the interest of lubricant manufacturers to produce nanocellulose-based eco-lubricating greases for industrial applications.

Nowadays, the transport sector is one of the main sources of greenhouse gas (GHG) emissions and air pollution in cities. The use of renewable energies is therefore imperative to improve the environmental sustainability of this sector. In this regard, biofuels play an important role as they can be blended directly with fossil fuels and used in traditional vehicles’ engines. Bioethanol is the most used biofuel worldwide and can replace gasoline or form different gasoline-ethanol blends. Additionally, it is an important building block to obtain different high added-value compounds (e.g., acetaldehyde, ethylene, 1,3-butadiene, ethyl acetate). Today, bioethanol is mainly produced from food crops (first-generation (1G) biofuels), and a transition to the production of the so-called advanced ethanol (obtained from lignocellulosic feedstocks, non-food crops, or industrial waste and residue streams) is needed to meet sustainability criteria and to have a better GHG balance. This work gives an overview of the current production, use, and regulation rules of bioethanol as a fuel, as well as the advanced processes and the co-products that can be produced together with bioethanol in a biorefinery context. Special attention is given to the opportunities for making a sustainable transition from bioethanol 1G to advanced bioethanol.

Although the removal of lignin and hemicelluloses from cellulose pulp to produce fully bleached cellulose nanofibrils (B-CNF) is the most common practice, the presence of residual lignin and hemicelluloses in raw materials for the production of lignin containing cellulose nanofibrils (LCNFs) holds several advantages. In this work, we investigated the effect of residual lignin in Eucalyptus globulus cellulose fibers on the properties of the resulting LCNFs. The stability of the colloidal suspensions was assessed by zeta-potential values and charge density analyses. Morphology of the CNFs was studied using scanning electron microscopy and atomic force microscopy. Fibril diameter and diameter distributions for CNFs with different levels of residual lignin showed a decrease on fiber diameter as the lignin content increases. Differences in the chemical composition of the CNFs was evidenced as indicated in the Fourier-transform infrared spectroscopy spectra, particularly in fingerprint region. Thermal behavior of the CNFs was not altered by the presence of lignin, as indicated by thermogravimetric analysis. Finally, the rheological behavior of the samples was evaluated observing a gel-like behavior as well as an increase of the viscosity in LCNFs with higher lignin contents.

This study explores the suitability of residual lignin-containing fractions generated as side-streams in different conversion processes of eucalypt and pine woods as thickening agents in bio-lubricant formulations. These conversion processes included fermentable sugars extraction by autohydrolysis or steam explosion and kraft pulping. Structural properties of lignin fractions were characterized by FTIR, 1H and 13C NMR, two-dimensional NMR, TGA and SEC, whereas their compositions were analysed by standard analytical methods. On the other hand, chemical oleogels were prepared with NCO-functionalized residual lignin fractions, and characterized by means of rheological, tribological and AFM techniques. Hydrolysis lignin fractions exhibited a great content of carbohydrates, especially glucose (46.0-48.5%), xylose (4.3-15.6%) and lignin (32.5-39.9%) with a well-maintained structure, displaying the main inter-unit linkages and low phenolic content. By contrast, kraft lignin fractions presented a lower carbohydrate content, mainly xylose (3.4-4.3%), and higher content (44.9-67%) of severely degraded lignin, showing a dramatic reduction of inter-unit linkages, and thereby high phenolic content. The rheological response of NCO-functionalized lignin fractions-based oleogels is highly influenced by the composition and chemical structure of residual lignin fractions. Moreover, these oleogels presented suitable tribological properties with values of the friction coefficient lower than those typically exhibited by standard lubricating greases.

The potential use of elm wood in lignocellulosic industries has been hindered by the Dutch elm disease (DED) pandemics, which have ravaged European and North American elm groves in the last century. However, the selection of DED-resistant cultivars paves the way for their use as feedstock in lignocellulosic biorefineries. Here, the production of cellulose nanofibers from the resistant Ulmus minor clone Ademuz was evaluated for the first time. Both mechanical (PFI refining) and chemical (TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidation) pretreatments were assessed prior to microfluidization, observing not only easier fibrillation but also better optical and barrier properties for elm nanopapers compared to eucalyptus ones (used as reference). Furthermore, mechanically pretreated samples showed higher strength for elm nanopapers. Although lower nanofibrillation yields were obtained by mechanical pretreatment, nanofibers showed higher thermal, mechanical and barrier properties, compared to TEMPO-oxidized nanofibers. Furthermore, lignin-containing elm nanofibers presented the most promising characteristics, with slightly lower transparencies.

Alginate nanocomposite films incorporating sepiolite (Sep) modified with myrtle berries extract (MBE) rich in polyphenols were prepared by solution casting method. The effects of different extract concentrations on the film properties were determined by measuring physicochemical, mechanical and antioxidant properties of the films. Fourier transform infrared (FTIR) spectra indicated that strong interactions between the polyphenols present in the MBE and sepiolite were involved in the films. The results suggested that incorporation of Sep-MBE hybrids into the films improved elongation at break, tensile strength, water vapor and UV barrier properties compared to the control film. The antioxidant activity of the films was significantly improved and raised with increasing content of MBE. The release kinetics results of MBE polyphenols from the active films into alcoholic food simulant indicated that the addition of Sep-MBE hybrids to alginate film is able to slow the release of MBE polyphenols. This study revealed the benefits of incorporation of Sep-MBE hybrids into the alginate films and their potential application as active packaging films or coating material.

Co-production of sugars and lignin from short rotation white poplar and black locust crops is evaluated. Acid-catalyzed ethanol/water organosolv and dilute acid pretreatments are analyzed. Resulting pretreated materials are hydrolyzed enzymatically for sugar production, whereas solubilized lignins from pretreatment liquors are precipitated, analyzed by analytical standard, and characterized by FTIR spectroscopy, SEC chromatography, and solid-state 13C NMR. Organosolv produces in both materials a high delignification degree (46–50%) and a considerable hemicelluloses removal (62–67%), while acid hydrolysis is more efficient at removing hemicelluloses (86–90%), showing a delignification of 43% (white poplar) and 31% (black locust). Organosolv followed by enzymatic hydrolysis results in 37.8% (white poplar) and 38.2% (black locust) total sugars yields, whereas acid pretreatment and subsequent saccharification show higher sugars yields for white poplar (43.3%) and lower for black locust (29.1%). Regarding lignin samples, higher concentrations are recovered from organosolv liquors of both materials (67.8% and 44.9% yields for white poplar and black locust, respectively) compared to the quantities extracted from acid liquors of white poplar (4.6%) and black locust (6.8%). Organosolv lignins display a lower content of S units and phenols, and higher molecular weights. Contrary, acid lignins consist mainly of phenolic fragments with a higher content of S units and lower molecular weights.

Valorization of lignocellulosic feedstock from a Dutch elm disease tolerant Ulmus minor clone was studied as a new biomass resource. Herein, fermentable sugars and activated carbons from the side-stream lignins were produced. For the sugar extraction organosolv and acid hydrolysis pretreatments prior to enzymatic hydrolysis were compared for the first time for this clone prior to enzymatic hydrolysis; organosolv was more efficient for delignification (49 %), while acid hydrolysis was more efficient at eliminating hemicelluloses (95 %). A high final glucose concentration of 22–23.5 g L−1 was obtained after enzymatic hydrolysis suggesting that this clone can be considered a potential source for glucose-based biofuel production. The side-stream lignins were converted to microporous biochars of high surface area (1220 m2 g−1) and micropore volume (0.42 cm3 g−1). These biochars exhibited excellent properties as electrodes in supercapacitors with a specific capacitance of 118 F g−1 and a high energy density of 14 Wh kg−1 at 7000 W kg−1, while they were also efficient adsorbents in water remediation of model contaminants.

Changes were evaluated in cell wall components, hygroscopicity, and thermodynamic properties of Pinus sylvestris L. wood that had been in contact with salt (NaCl) for 300 years in a former saltworks storehouse in Gerri de la Sal (Lérida, Spain), comparing it with recently felled wood (new wood) of the same species. The wood in contact with salt (salt-covered wood) had higher equilibrium moisture content values except in the first interval of the adsorption isotherm, probably because of mechanical blocking of polar sites by salt crystals. The high fibre saturation point values of this wood are caused by the salt dissolved in water above water activity of about 0.75. More energy is invested in the desorption process, and the values are higher in the salt-covered wood.

A comparison was made of the hygroscopicity, cell wall chemical composition and crystallinity of recently peeled poplar (Populus spp.) wood and wood of the same species subjected to repeated cycles (20, 60 and 80) of vacuum/pressure (85 kPa/600 kPa) and soaking in an autoclave followed by oven drying. The 15 and 35 °C sorption isotherms were obtained using the saturated salt method and fitted with the Guggenheim–Anderson–de Boer model. Chemical composition was determined and the infrared spectra and X-ray powder and 2D diffractograms were obtained to identify differences in the wood with and without cycles. The cycles caused a statistically significant decrease in equilibrium moisture content (EMC) between the wood without cycles and the wood with cycles, a statistically significant lower contribution by the monolayer as the number of cycles increased (in the 15 °C isotherm in adsorption without cycles from 8.12% EMC to 6.16% with 80 cycles, in desorption from 10.23 to 8.13%; in the 35 °C isotherm from 7.45 to 5.57% in adsorption and from 8.86 to 6.54% in desorption), a decrease in the area of the hysteresis loop with significant differences between the wood without cycles and the wood with cycles, a statistically significant decrease in the percentage of cell wall components (in cellulose and extractives, in lignin content between the wood without cycles and wood with 60 and 80 cycles, and in hemicellulose between the wood without cycles and the wood with 80 cycles), a statistically significant increase in crystallinity between the wood without cycles (CRI% 52.1%) and the wood with cycles (CRI% 81.60–92.50%), and reorganisation of the cell wall ultrastructure, as seen in the increased size of the cellulose crystal of the fraction oriented parallel to the fibre.

It is known that large amounts of residual lignin are generated in the pulp and paper industry. A new alternative for Kraft lignin valorization, which consists of first a chemical modification using a diisocyanate and then the efficient dispersion in castor oil to achieve stable gel-like systems, is proposed in this work. Rheological properties and microstructure of these materials were determined by means of small amplitude oscillatory shear tests and viscous flow measurements and atomic force microscopy observations, respectively. Moreover, both standardized penetration tests and tribological assays, usually performed in the lubricant industry, were carried out to evaluate the performance characteristics as lubricating greases. Linear viscoelasticity functions are affected by the lignin/diisocyanate ratio and thickener concentration. The thermorheological response evidenced a softening temperature of around 105 °C. The microstructure of these gel-like dispersions is composed of interconnected thin fibers, homogeneously distributed in castor oil. Moreover, the NCO-functionalized lignin gel-like dispersions studied show lower friction coefficients than traditional lubricating greases.It is known that large amounts of residual lignin are generated in the pulp and paper industry. A new alternative for Kraft lignin valorization, which consists of first a chemical modification using a diisocyanate and then the efficient dispersion in castor oil to achieve stable gel-like systems, is proposed in this work. Rheological properties and microstructure of these materials were determined by means of small amplitude oscillatory shear tests and viscous flow measurements and atomic force microscopy observations, respectively. Moreover, both standardized penetration tests and tribological assays, usually performed in the lubricant industry, were carried out to evaluate the performance characteristics as lubricating greases. Linear viscoelasticity functions are affected by the lign

Olive tree pruning, as one of the most abundant lignocellulosic residues in Mediterranean countries, has been evaluated as a source of sugars for fuel and chemicals production. A mild acid pretreatment has been combined with a fungal pretreatment using either two endophytes (Ulocladium sp.;Hormonema sp.) or a saprophyte (Trametes sp. I-62). The use of endophytes is based on the important role that some of them play during the initial stages of wood decomposition. Without acid treatment, fungal pretreatment with Ulocladium sp. provided a nonsignificant enhancement of 4.6% in glucose digestibility, compared to control. When a mild acid hydrolysis was carried out after fungal pretreatments, significant increases in glucose digestibility from 4.9% to 12.0% (compared to control without fungi) were observed for all fungal pretreatments, with maximum values yielded by Hormonema sp. However, despite the observed digestibility boost, the total sugar yields (taking into account solid yield) were not significantly increased by the pretreatments. Nevertheless, based on these preliminary improvements in digestibility, this work proves the potential of endophytic fungi to boost the production of sugar from olive tree pruning, which would add an extra value to the bioeconomy of olive crops. © 2017 Raquel Martín-Sampedro et al.

In a poplar clonal plantation with different species and hybrids, established at 13,333 cuttings ha−1, biomass production was assessed at the end of the first rotation (3 years) and the potential of the different clones for sugar production was evaluated. The highest biomass production was observed for clones ‘AF2’ and ‘Viriato’ (46.5 and 42 t dm ha−1, respectively). After a mild acid pretreatment and an enzymatic saccharification, the highest sugar digestibility was found for ‘Viriato’ and ‘Unal’. A clear relation between sugar digestibility and xylan removal during pretreatment was observed, while no relation with lignin content was found. Taking into account the results, the highest production of sugars per hectare was estimated for the poplar clone ‘Viriato’, being 18–48% higher than that achieved with the other clones. Therefore, this clone is a promising candidate to be used as feedstock for sugar production in a forest biorefinery. © 2017, Springer-Verlag Berlin Heidelberg.

The hygroscopicity and thermodynamic properties of Pinus canariensis wood buried in volcanic ash, dating from 1100 BC, were studied and compared with recently felled juvenile and mature wood of the same species. The sorption iso_x0002_therms were obtained by the saturated salt method at 35 and 50 _x0003_C. The isotherms were fitted using the Guggenheim–Anderson–de Boer model. The thermodynamic parameters were determined following the Clausius–Clapeyron integration method. To understand the behaviour of each type of wood, the chemical composition, infrared spectra and X-ray diffractograms were determined for each sample. The mature wood has a higher sugar content and lower extractive content than the juvenile and the buried wood. For both temperatures, the isotherm of the mature wood is above the isotherm of the juvenile wood and this, in turn, is above the isotherm of the buried wood, primarily influenced by the higher cellulose and hemicellulose contents and lower extractives content in the mature wood, resulting in a higher number of accessible –OH groups. Degradation of the buried wood due to high temperatures explains why its isotherms are below the isotherms of the recent wood. The energy involved in the desorption process is greater than in adsorption. Similarly, more energy is involved in the mature wood than in the juvenile wood, and the energy involved in the juvenile wood is greater than in the buried wood.

The biobleachability of soda-anthraquinone pulp from orange tree pruning has been evaluated in this study for the first time. Three different laccase-mediator systems (LMS) have been tested: laccase from Trametes villosa (Tv), either in combination with 1-hydroxybenzotriazole (HBT) or with acetosyringone (AS), and laccase from Myceliophthora thermophila (Mt) in combination with AS. After the LMS treatment (L), a standard bleaching sequence, comprising an alkaline extraction (E) and a hydrogen peroxide stage (P), was carried out, altogether resulting in a LEP sequence. The three LMS improved the bleaching sequence, L-Tv+AS being the LMS that provided the highest delignification and improvement of optical properties. In contrast, no significant variations were observed in the viscosity and mechanical properties of the handsheets. In order to boost the optimal L-Tv+AS sequence, a xylanase pretreatment was performed; however, no improvements in delignification, optical properties or brightness stability were observed compared with the same sequence without xylanase retreatment.

The continuous increase in the world energy and chemicals demand requires the development of sustainable alternatives to non-renewable sources of energy. Biomass facilities and biorefineries represent interesting options to gradually replace the present industry based on fossil fuels. Lignocellulose is the most promising feedstock to be used in biorefineries. From a sugar platform perspective, a wide range of fuels and chemicals can be obtained via microbial fermentation processes, being ethanol the most significant lignocellulose-derived fuel. Before fermentation, lignocellulose must be pretreated to overcome its inherent recalcitrant structure and obtain the fermentable sugars. Usually, harsh conditions are required for pretreatment of lignocellulose, producing biomass degradation and releasing different compounds that are inhibitors of the hydrolytic enzymes and fermenting microorganisms. Moreover, the lignin polymer that remains in pretreated materials also affects biomass conversion by limiting the enzymatic hydrolysis. The use of laccases has been considered as a very powerful tool for delignification and detoxification of pretreated lignocellulosic materials, boosting subsequent saccharification and fermentation processes. This review compiles the latest studies about the application of laccases as useful and environmentally friendly delignification and detoxification technology, highlighting the main challenges and possible ways to make possible the integration of these enzymes in future lignocellulose-based industries.

A TCF bleaching sequence consisting of a urea pretreatment stage (U), laccase-mediator system stage (L), alkaline extraction stage (E), and hydrogen peroxide bleaching stage (P) was used to study the effect of five independent variables on the dependent variables pulp properties, hydrogen peroxide consumption, and residual enzyme activity. Results showed that the most influential variable was L stage pulp consistency, followed by mediator and laccase dosages. On the other hand, oxygen pressure did not have a significant effect. The optimal UL partial sequence significantly enhanced the EP bleaching sequence 49.8% vs. 33.4% delignification, up to 65.6% ISO vs. 56.3% ISO bleached brightness, and 50.3% vs. 89.9% peroxide consumption in the P stage. The ULE partial sequence also improved an ECF bleaching sequence (ULED0E1D1) 0.6 vs. 1.0 final kappa number; 82.7% ISO vs. 76.0% ISO brightness; and 54.1 N·m·g-1 vs. 51.9 N·m·g-1 and 3.3 KPa·m2·g-1 vs. 2.7 KPa·m2·g-1, tensile and burst indexes, respectively, when compared to the control D0E1D1 sequence.

A laccase stage can be used as a pre-treatment of a standard chemical bleaching sequence to reduce environmental concerns associated to this process. The importance of each independent variable and its influence on the properties of the bleached pulp have been studied in depth in this work, using an adaptive network-based fuzzy inference system (ANFIS) with four independent variables (laccase, buffer, mediator and oxygen) as input. Eucalyptus globulus kraft pulp was biobleached using a laccase from Pycnoporus sanguineus and a natural mediator (acetosyringone). Later, an alkaline extraction and a hydrogen peroxide treatment were applied. Most biobleaching processes showed a decrease in kappa number and an increase in brightness with no significant impact on the viscosity values, compared with the control. Oxygen was the variable with the smallest influence on the final pulp properties while the laccase and buffer solution showed a significant influence.

Five endophytic fungal strains isolated from Eucalyptus sp.;capable of producing laccase (Neofusicoccum luteum, Ulocladium sp.;Pringsheimia smilacis, Hormonema sp.;and Neofusicoccum australe) were used to pre-treat Eucalyptus globulus wood chips. After the fungal pre-treatment, chips were submitted to kraft or mechanical pulping. All the endophytic fungal strains provided higher delignification during kraft pulping than control sample. The highest increase was achieved by Hormonema sp. (26.7%), which also reduced the NaOH consumption by 11.6% and increased mechanical strength (increases in tensile, tear and burst indices of 28.4%, 15.6% and 43.9%, respectively).Regarding mechanical pulping, only N. australe was able to reduce the energy consumed during the process (8.4%). However, all pulps from fungal pre-treated chips showed higher refining degree and mechanical properties than the control pulp, which would probably allow a lower consumption of energy during mechanical pulping to achieve a specific refining degree. The best mechanical properties and the lowest kappa number were also found when Hormonema sp. was applied. © 2015 Elsevier Ltd.

The hygroscopicity and thermodynamic properties of juvenile and mature wood of Abies alba Mill. were studied through the 15, 35 and 50 °C sorption isotherms. The Guggenheim, Anderson and de Boer-Dent model was used to fit the isotherms. The thermodynamic parameters were obtained from the sorption isotherms by applying the integration method of the Clausius–Clapeyron equation. The chemical composition of both types of wood (extractives, lignin and carbohydrate polymer-cellulose and hemicellulose-content) was determined, and infrared spectroscopy and X-ray diffractograms were used to identify any chemical modifications and changes in the crystal structure of the cell wall. The mature wood has more cellulose and hemicellulose content and less extractives content than the juvenile wood. The shorter crystallite length in the mature wood creates a higher amount of amorphous zones and, as a consequence, a higher number of access areas to the –OH groups. The combination of these phenomena explains the different hygroscopic behaviour between the juvenile and the mature wood, as the latter has higher moisture content in the three isotherms. As regards the thermodynamic properties, the amount of energy involved in the sorption process is greater in the mature wood than in the juvenile wood. © 2015, Springer Science+Business Media New York.

New endophytic fungi are assessed for the first time as pretreatment to enhance saccharification of Eucalyptus globulus wood. The fungi are all laccase-producing ascomycetes and were isolated from eucalyptus trees in Spain. After five endophytes had been assayed alone or in combination with white-rot fungus Trametes sp. I-62, three were pre-selected. To improve sugar production, an autohydrolysis pretreatment was performed before or after fungal treatment. Pretreatment increased sugar production 2.7 times compared to non-pretreated wood. When fungal and autohydrolysis pretreatments were combined, a synergistic increase in saccharification was observed in all cases. Endophytic fungi Ulocladium sp.;Hormonema sp. produced greater enhancements in saccharification than Trametes sp. I-62 (increase in sugar yields of 8.5, 8.0 and 6.0 times, respectively), demonstrating the high potential of these new endophytic fungi for saccharification enhancement. © 2015 Elsevier Ltd.

The amount of residual lignin and hemicelluloses in softwood fibers was systematically varied by SO2-ethanol-water fractionation for integrated biorefinery with nanomaterial and biofuel production. On the basis of their low energy demand in mechanical processing, the fibers were deconstructed to lignocellulose nanofibrils (LCNF) and used as substrate for bioconversion. The effect of LCNF composition on saccharification via multicomponent enzymes was investigated at different loadings. LCNF digestibility was compared with the enzyme activity measured with a quartz crystal microbalance. LCNF hydrolysis rate gradually decreased with lignin and hemicellulose concentration, both of which limited enzyme accessibility. Enzyme inhibition resulted from non-productive binding of proteins onto lignin. Near complete LCNF hydrolysis was achieved, even at high lignin and hemicellulose content. Sugar yields for LCNF were higher than those for precursor SEW fibers, highlighting the benefits of high surface area in LCNF. © 2014 Elsevier Ltd.

Growing interest in alternative and renewable energy sources has brought increasing attention to the integration of a pulp mill into a forest biorefinery, where other products could be produced in addition to pulp. To achieve this goal, hemicelluloses were extracted, either by steam explosion or by steam treatment, from Eucalyptus globulus wood prior to pulping. The effects of both pre-treatments in the subsequent kraft pulping and paper strength were evaluated. Results showed a similar degree of hemicelluloses extraction with both options (32-67% of pentosans), which increased with the severity of the conditions applied. Although both pre-treatments increased delignification during pulping, steam explosion was significantly better 12.9 kappa number vs 22.6 for similar steam unexploded pulps and 40.7 for control pulp. Finally, similar reductions in paper strength were found regardless of the type of treatment and conditions assayed, which is attributed to the increase of curled and kinked fibers. © 2013 Elsevier Ltd.

Steam explosion and steam pre-treatment have proved capable of enhancing enzymatic saccharification of lignocellulosic materials. However, until now, these methods had not been compared under the same operational conditions and using the same raw material. Both pre-treatments lead to increased yields in the saccharification of Eucalyptus globulus; but results have been better with steam pre-treatments, despite the more accessible surface of exploded samples. The reason for this finding could be enzymatic inhibition steam explosion causes a more extensive extraction of hemicelluloses and releases a greater amount of degradation products which can inhibit enzymatic action. Enzymatic inhibition is also dependent on the amount and chemical structure of lignin, which was also a contributing factor to the lower enzymatic yields obtained with the most severe pre-treatment. Thus, the highest yields (46.7% glucose and 73.4% xylose yields) were obtained after two cycle of steam treatment, of 5 and 3. min, at 183. °C. © 2014 Elsevier Ltd.

In modern lignocellulosic-based biorefineries, carbohydrates can be transformed into biofuels and pulp and paper, whereas lignin is burned to obtain energy. However, a part of lignin could be converted into value-added products including bio-based aromatic chemicals, as well as building blocks for materials. Then, a good knowledge of lignin is necessary to define its valorisation procedure. This study characterized different lignins from side-streams produced from olive tree pruning bioethanol production (lignins collected from steam explosion pretreatment with water or phosphoric acid as catalysts, followed by simultaneous saccharification and fermentation process) and alkaline pulping (lignins recovered from kraft and soda-AQ black liquors). Together with the chemical composition, the structure of lignins was investigated by FTIR, 13C NMR, and 2D NMR. Bioethanol lignins had clearly distinct characteristics compared to pulping lignins; a certain number of side-chain linkages (mostly alkyl–aryl ether and resinol) accompanied with lower phenolic hydroxyls content. Bioethanol lignins also showed a significant amount of carbohydrates, mainly glucose and protein impurities. By contrast, pulping lignins revealed xylose together with a dramatical reduction of side-chains (some resinol linkages survive) and thereby higher phenol content, indicating rather severe lignin degradation during alkaline pulping processes. All lignins showed a predominance of syringyl units. © 2017 Elsevier B.V.

This study evaluates the potential of a bacterial laccase from Streptomyces ipomoeae (SilA) for delignification and detoxification of steam-exploded wheat straw, in comparison with a commercial fungal laccase from Trametes villosa. When alkali extraction followed by SilA laccase treatment was applied to the water insoluble solids fraction, a slight reduction in lignin content was detected, and after a saccharification step, an increase in both glucose and xylose production (16 and 6%, respectively) was observed. These effects were not produced with T. villosa laccase. Concerning to the fermentation process, the treatment of the steam-exploded whole slurry with both laccases produced a decrease in the phenol content by up to 35 and 71% with bacterial and fungal laccases, respectively. The phenols reduction resulted in an improved performance of Saccharomyces cerevisiae during a simultaneous saccharification and fermentation (SSF) process, improving ethanol production rate. This enhancement was more marked with a presaccharification step prior to the SSF process.

The effect of lignin as an inhibitory biopolymer for the enzymatic hydrolysis of lignocellulosic biomass was studied; specially addressing the role of lignin in non-productive enzyme adsorption. Botanical origin and biomass pre-treatment give rise to differences in lignin structure and the effect of these differences on enzyme binding and inhibition were elucidated. Lignin was isolated from steam explosion (SE) pre-treated and non-treated spruce and wheat straw and used for the preparation of ultrathin films for enzyme binding studies. Binding of Trichoderma reesei Cel7A (CBHI) and the corresponding Cel7A-core, lacking the linker and the cellulose-binding domain, to the lignin films was monitored using a quartz crystal microbalance (QCM). SE pre-treatment altered the lignin structure, leading to increased enzyme adsorption. Thus, the positive effect of SE pre-treatment, opening the cell wall matrix to make polysaccharides more accessible, may be compromised by the structural changes of lignin that increase non-productive enzyme adsorption. © 2013 Elsevier Ltd.

The production of laccase from Trametes sp. I-62 was optimized, and then it was applied for the first time in biobleaching in order to contribute to solve some problems associated with pulp bleaching. When wheat straw and copper sulfate were used in combination as inductors, the maximum laccase activity was obtained. The resulting enzymatic fluid was applied at optimum pH and temperature jointly with acetosyringone in a pretreatment stage (L) aimed to enhance the subsequent bleaching consisting of an alkaline extraction (E) and a hydrogen peroxide stage (P). Results showed that, even when a significantly lower amount of hydrogen peroxide was consumed in the LEP sequence (41.9% vs 89.9% for EP), higher delignification (40.6% vs 33.4%) and brightness (63.6 vs 56.3% ISO) were achieved. After accelerated aging, the optical properties of the biobleached pulp were found to be less stable but still remained higher than those of control pulps. © 2013 American Chemical Society.

Some pretreatments that swell and/or open the structure of wood fibers could increase the effectiveness of a biobleaching process, allowing for an industrial application. To this end, a chemical pretreatment (urea, U), a physical pretreatment (refining, R), and their combinations (RU and UR) were optimized to evaluate and compare their enhancement of the LE biobleaching sequence (laccase-mediator treatment plus alkali extraction). The urea pretreatment before biobleaching (ULE) provided the highest delignification (37.5%) and the highest increase in brightness (6.1 points % ISO). As expected, adding a refining process before or after the urea pretreatment increased paper strength. However, when the refining was applied after the urea pretreatment (URLE), the delignification was higher than that obtained after RULE. Thus, URLE provided a similar Kappa number and an increase of 97%, 149%, and 98% in the tensile, tear, and burst indexes, respectively, compared with ULE treatment, but it had a reduction of 2.8 points (% ISO) in brightness, caused by the action of refining. Therefore, depending on the final use of the paper (which can require high optical properties or high strength), either ULE or URLE would be the optimal sequence.

Eucalyptus globulus woodchips were subjected to steam explosion under a variety of operational conditions in order to evaluate their effect on a subsequent enzymatic hydrolysis. Steam explosion enhanced the enzymatic hydrolysis of the solid fraction. The application of a laccase-mediator system (LMS) before the enzymatic hydrolysis increased the glucose yield from 24.7 to 27.1%, probably as a result of the detoxification of the substrate. However, when xylanase was used to boost the LMS treatment, the hydrolysis rates did not improve. In order to assess the total amount of sugars obtainable from E. globulus, the liquid fraction obtained from the steam explosion was subjected to hydrolysis too. The enzymatic hydrolysis of the liquid fraction was more efficient than the acid hydrolysis, breaking down 82.7% of the xylooligosaccharide backbone into its monomeric constituent, xylose. The overall yield was 210. g of sugars per kg of raw material. © 2012 Elsevier Ltd.

This study aimed at assessing the biobleachability of soda pulps obtained from olive tree pruning residue. The enzymatic (LMS) pre-treatment was applied prior to a simple totally chlorine free (TCF) bleaching sequence, consisting of an alkaline extraction and a hydrogen peroxide stage. Additionally, the effect of adding xylanase jointly with or prior to LMS was evaluated. All of these enzymatic pre-treatments were associated with an enhancement of the bleaching sequence. The best results were found when both enzymes were applied in the same stage lowest hydrogen peroxide consumption (63 percent); kappa number, 11.6; brightness, 46 percent ISO. The mechanical properties observed were similar to those reported by other authors who have studied pulps from olive tree pruning residue. Finally, bleached pulps were subjected to accelerated ageing in order to assess the evolution of brightness and colorimetric properties. Although biobleached pulps showed lower stability upon ageing, the best optical properties, even after ageing, were observed in pulps treated with both xylanase and laccase.

The aim of this work is to study the reinforcement capacity of pulps obtained from Hesperaloe funifera using a simple and low energy consumption process (chemi refiner mechanical pulping) once they are added in different percentages to recycled pulps from newspaper and from old corrugated containers (OCC). Pinus radiata kraft pulp was used as a referent reinforcement material. H. funifera acted as a reinforcement material in newspaper and OCC recycled pulps, improving their optical and mechanical properties. While a 25% of H. funifera was the optimal amount added to reinforce the OCC pulp, only a 10% was needed for newspaper pulp. However, the OCC optimal mixture was better reinforced as it showed higher increase in all properties than the optimal newspaper mixture, apart from tensile index. Finally, all mixtures with P. radiata kraft pulp produce handsheet with lower properties, apart from tear index, suggesting than H. funifera is a better reinforcement material.

Rapid enzymatic saccharification of lignocellulosic nanofibrils (LCNF) was investigated by monitoring nanoscale changes in mass via quartz crystal microgravimetry and also by measuring reducing sugar yields. In only a few minutes LCNF thin films were completely hydrolyzed upon incubation in multicomponent enzyme systems. Conversion to sugars and oligosaccharides of LCNF dispersed in water occurred in about 4 h (50 °C, pH 5). In contrast, a conversion of only 57% was observed for partially crystalline cellulose (Avicel) after 9 h, under same experimental conditions. Under conditions of high enzyme loading the presence of residual lignin and other macromolecules in the cell wall of LCNF did not appear to affect negatively the recorded high hydrolysis rates. Overall, our findings suggest that deconstruction of the cell wall to nanofibrils is an effective pretreatment to facilitate rapid and complete cellulose bioconversion.

Ultrathin bicomponent films of cellulose and lignin derivatives were deposited on silica supports by spin coating, and after conversion into the respective polymer precursor, they were used as a model system to investigate interfacial phenomena relevant to lignocellulose biocatalysis. Film morphology, surface chemical composition, and wettability were determined by atomic force microscopy, X-ray photoelectron spectroscopy, and water contact angle, respectively. Phase separation of cellulose and lignin produced structures that resembled the cell wall of fibers and were used to monitor enzyme binding and cellulolytic reactions via quartz crystal microgravimetry. The rate and extent of hydrolysis was quantified by using kinetic models that indicated the role of the surface lignin domains in enzyme inhibition. Hydrophobic interactions between cellulases and the substrates and their critical role on irreversible adsorption were elucidated by using acetylated lignin films with different degrees of substitution. Overall, it is concluded that sensors based on the proposed ultrathin films of lignocellulose can facilitate a better understanding of the complex events that occur during bioconversion of cellulosic biomass.