Sonochemical oxidation of technical lignin to obtain nanoparticles with enhanced functionality

Kraft lignin (KL) was treated by employing mild oxidation conditions enhanced by ultrasound irradiation (US) for obtaining more functionalized particles, avoiding the undesired side reactions of degradation and depolymerization. The aim was to obtain products with plausible value for applications with a greater potential market, enabling the introduction of low-cost bio-based materials for technically advanced applications. In the present work, KL was oxidized in alkaline media, applying low temperatures (30–60 °C), short times (15 to 60 min), and US waves (20 kHz). The influence of incorporating hydrogen peroxide (H2O2) as an oxidizing agent was also studied, as well as the chemical composition, physicochemical, thermal, and morphological properties of the final lignin particles. It was observed from Quantitative Acid Hydrolysis (QAH), Elemental Analysis (EA), and molecular weights (Mw) that oxidized lignin particles (OxL) did not suffer any major degradation. Other techniques used to determine physicochemical properties, such as Fourier Transformed Infrared (FTIR), 31 Phosphorous Nuclear Magnetic Resonance (31P NMR), or Ultraviolet–visible (UV-vis) methods, corroborated oxidation reactions, evident by the increment of carboxylic groups. The most noticeable difference, however, was observed when the stability and morphology of the particles were observed by Dynamic Light Scattering (DLS) and Transmission Electron Microscopy (TEM). Some conditions greatly promoted the formation of more stable and nanosized particles. The best conditions were the mildest but with the highest reaction times (no addition of H2O2, 30 °C and 60 minutes). Moreover, all reactions had good recovery yields, above 70% of the original lignin.The authors would like to acknowledge the Basque Government for the financial support of this research through project IT1498-22 and grant PIF19-183. E. R. wants to acknowledge the tenure track position “BOIS” part of E2S UPPA supported by the “Investissements d'Avenir” French program managed by ANR (ANR-16-IDEX-0002). The authors thank for the technical and human support provided by SGIker (UPV/EHU/ERDF, EU)

Assessment of Bleached and Unbleached Nanofibers from Pistachio Shells for Nanopaper Making

Cellulose and lignocellulose nanofibrils were extracted from pistachio shells utilizing environmentally friendly pulping and totally chlorine-free bleaching. The extracted nanofibers were used to elaborate nanopaper, a continuous film made by gravimetric entanglement of the nanofibers and hot-pressed to enhance intramolecular bonding. The elaborated nanopapers were analyzed through their mechanical, optical, and surface properties to evaluate the influence of non-cellulosic macromolecules on the final properties of the nanopaper. Results have shown that the presence of lignin augmented the viscoelastic properties of the nanopapers by ≈25% compared with fully bleached nanopaper; moreover, the hydrophobicity of the lignocellulose nanopaper was achieved, as the surface free energy was diminished from 62.65 to 32.45 mNm−1 with an almost non-polar component and a water contact angle of 93.52°. On the other hand, the presence of lignin had an apparent visual effect on the color of the nanopapers, with a ΔE of 51.33 and a ΔL of −44.91, meaning a substantial darkening of the film. However, in terms of ultraviolet transmittance, the presence of lignin resulted in a practically nonexistent transmission in the UV spectra, with low transmittance in the visible wavelengths. In general, the presence of lignin resulted in the enhancement of selected properties which are desirable for packaging materials, which makes pistachio shell nano-lignocellulose an attractive option for this field.The authors would like to acknowledge the University of the Basque Country UPV/EHU for financially supporting this work. E.R. wishes to acknowledge the tenure track position “Biobased materials” part of E2S UPPA supported by the “Investissements d’Avenir” French program managed by ANR (ANR-16-IDEX-0002). N.I. wishes to acknowledge the Basque Government for financial support through the PIF19-183 contract

Fine-tune of lignin properties by its fractionation with a sequential organic solvent extraction

[EN] In this work, different lignins were obtained from two different extraction methods (kraft and organosolv) but from the same raw material (Eucalyptus globulus sp.). They were subsequently fractionated to determine the differences of each extraction method and their corresponding physicochemical properties found in fractionation sequence and obtained fractions. The goal of the fractionation was to obtain lignin fractions with narrower molecular weight distribution and lower polydispersity index (PI). The solvent sequence was designed based on the environmental friendly properties, health and safety assessments of the selected organic solvents: (methanol (MeOH), ethanol (EtOH), propan-2-one (DMK), ethyl acetate (EtOAc), propan-1-ol (nPrOH), propan-2-ol (iPrOH), butan-2-one (MEK), and butan-1-ol (tBuOH)). The different fractions obtained were characterised to determine their chemical structure by several analytical techniques, such as Fourier Transformed Infrared Spectroscopy (FTIR), Ultraviolet (UV), Phosphorus-31 Nuclear Magnetic Resonance (P-31 NMR), Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS), Thermogravimetric analysis (TGA), and Differential scanning calorimetry (DSC). In addition, Gel Permeation Chromatography (GPC) was used to obtain the molecular weight distribution. This study showed an effective method for obtaining homogeneous lignins with specific structures and properties depending on the solvent and molecular weight attained. Moreover, the method designed was found to be effective regardless of the lignin extraction process employed; besides, various lignin fractions were obtained which were different from each other, having specific target applications depending on their structure and chemical properties, ranging from small molecules with abundant reactive sites to act as active materials or copolymer reagents for many applications, to larger and more inactive molecules with higher thermal resistivity.The authors would like to acknowledge the Basque Government for the financial support of this research through project IT1008-16 and grant PIF19-183. Furthermore, E. R. wants to acknowledge the tenure track position "BOIS" part of E2S UPPA supported by the "Investisse-ments d'Avenir" French program managed by ANR (ANR-16-IDEX-0002)

Preparation of chitosan/tannin and montmorillonite films as adsorbents for Methyl Orange dye removal

A series of novel chitosan/tannin/montmorillonite (Cs/Tn/MMT) films were synthesised by loading different (from 0.2 to 0.5wt%) and MMT (from 0.5 to 1.5wt%) ratios, to be used as promising low-cost biosorbents for methyl orange (MO) removal from aqueous media. The prepared films were characterised using different techniques such as x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), water contact angle, optical properties, colourimetric measurement, porosity, swelling and thickness. The effects of various parameters, i.e. initial MO concentration, adsorbent dose, pH and temperature, were studied. The Cs/Tn0.2/MMT1 film showed a high removal efficiency of 95.62% and maximum adsorption capacity of 57.37mg/g under the optimum adsorption conditions (initial methyl orange concentration 60mg/L, pH7 and 25°C). The adsorption kinetic followed the pseudo second order kinetic model and the experimental data were a good fit for the Langmuir isotherm indicating a homogeneous and monolayer adsorption process. The thermodynamic parameters suggested physical adsorption and exothermic behaviour. Consequently, Cs/Tn/MMT films showed effective potential for the uptake of anionic dyes.The authors thank the Basque Government (IT1008-16) and Tunis El Manar University for financially supporting this work

Exploring chemical reactions to enhance thermal and dispersion stability of kraft and organosolv lignin

Lignin has been overlooked and used as a waste for long due to its complex and partially hydrophobic structure. Many efforts have been carried out to overcome these deficiencies and apply it as a high-value product, which are insufficient to reach the full potential of lignin in various advanced applications, since they require with procedures for the obtaining of more specific and fine-tuned chemical structures. This work focuses on the obtaining of differently structured hydrophilic lignins derived both from Kraft and organosolv isolation processes. The chemical structures of the different lignin types were studied, and the effect of the structural differences in the modification processes and their subsequent properties analyzed, valorizing their potential application for diverse purposes. The carboxymethylation and sulfomethylation reactions were carried out with the aim of enhancing the polarity of the lignin samples, while the methylation reaction aimed to obtain lignins with higher stability. The physicochemical analyses of the samples, carried out by FTIR, GPC, 31P NMR, 13C NMR, and HSQC NMR, verified the effectiveness of the chemical reactions and conditions selected, obtaining lignins with lower hydroxyl content, due to their substitution and insertion of carboxymetyl, sulfomethyl and methyl groups, therefore obtaining more condensed, aromatic and oxygenated aromatic carbon structures. While the methylation reaction was the most efficient in substituting the OH groups, due to its non-selectivity, OL showed higher modification yields than KL. In terms of the thermal and morphological properties, analyzed by DLS and TGA respectively, it was observed that the modified samples showed lower Z potential values, along with higher conductivity, being the sulfomethylated organosolv lignin the one showing the best results, which was also the one with the smallest particle size and polydispersity index. Finally, all the modified samples showed higher T50% values, suggesting a better stability towards degradation.The authors would like to acknowledge the financial support of the Basque Government for (grant PIF19-183) and Diputación de Gipuzkoa (EZAGUTZ-11/2022). The authors thank for the technical and human support provided by SGIker (UPV/EHU/ ERDF, EU)

Kraft and organosolv lignin-activated carbon composites for supercapacitor electrode materials

Lignin-activated carbon (AC) composites were employed as electrode active materials to develop more environmentally friendly Supercapacitor (SC) materials with enhanced properties. This way, the hydroquinone/quinone moieties present in lignin molecules added Faradaic processes to the system, and the capacitance of the active material increased, making it appropriate for future applications requiring more efficient and sustainable active materials. Lignin, a sustainable biobased aromatic polymer high in carbon content, was deposited on AC surface employing ultrasound (US) system, and for a better deposition, AC was treated with HNO3. Since the composition and properties of lignin can vary depending on their isolation process, two different types of lignin were used: Kraft lignin (KL) and Organosolv lignin (OL), and the effects on the chemical and electrochemical composition were deduced. Physicochemical, morphological, and electrochemical analyses were carried out on the lignin-AC composite to determine the optimum material combination and treatment process. It was observed that the acid treatment was effective in enhancing the functionality and porosity of the surface. Additionally, it improved the deposition of lignin and facilitated the formation of hierarchically porous structures on the surface of treated activated carbon (TAC), with different tendencies depending on the lignin employed. The creation of highly porous structures also resulted in enhanced electrochemical performance in materials. This validated the process, where eco-innovative technologies like US forces and employment of lignocellulosic biomass compounds like lignin were used as sustainable and efficient alternatives for obtaining electrochemically active materials.The authors would like to acknowledge the Basque Government for the financial support of this research through project IT1498-22 and grant PIF19-183). The authors thank for the technical and human support provided by SGIker (UPV/EHU/ERDF, EU), European financial support (FEDER and FSE), and Texture Laboratory of the Scientific and Technical Service of INCAR-CSIC

Fractionation of non-timber wood from Atlantic mixed forest into high-value lignocellulosic materials

[EN] The forestry industry in the Basque Country has experienced an abandonment of small-sized forests in which native and introduced species tend to regrow if unattended; thus, requiring an intervention under which proper forest management is implemented. This paper evaluates the potential fractionation of lignin and cellulose from six tree species coming from such mixed forests as a value-added use of wood discarded by logging within the frame of sustainable forest management. The species used were Northern red oak, common oak, common ash, Iberian white birch, sweet chestnut, and black locust. The different wood samples were treated with an Organosolv treatment and elemental chlorine-free bleaching to fractionate them to their main components, recovering the cellulose and the lignin. Cellulose was defibrillated via high-pressure homogenization to obtain cellulose nanofibers. The resulting lignin and cellulose nanofibers were analyzed. The results support the idea that this process offers the opportunity to treat different raw materials in the same process, with corresponding possible economic benefits.Authors want to acknowledge the University of the Basque Country UPV/EHU, as well as the European Agricultural Fund for Rural Development and the Department of Economic Development and Infrastructure of the Basque Government (project 30.2017-00095) for supporting financially this research. L.S. would like to acknowledge the Department of Economic Development and Infrastructures of the Basque Government (scholarship of young researchers training)

Dielectric characterisation of chitosan-based composite membranes containing fractionated kraft and organosolv lignin

Chitosan-based composite membranes with fractionated kraft and organosolv lignin were prepared by solvent casting. A small lignin fraction (1%) was added to the neat chitosan to obtain a good distribution. The influence of lignin extraction with ethyl acetate and consequently ethanol on the dielectric and conductive properties of the composites was investigated by dielectric thermal analysis (DETA). Overall, the chitosan-lignin composites exhibit three relaxation mechanisms (β, βwet, and α) and two conductivity phenomena (σ and MWS). FTIR analysis showed that the composites with organosolv lignin fractions have fewer hydroxyl groups than those with kraft lignin, which decreases slightly further for both after ethanol extraction. The lignin fractions with lower molecular weight and higher OH content show stronger interactions with chitosan, due to hydrogen bonding. These interactions affect the thermal activation and cooperativity of the β-, βwet, and α-relaxation. Furthermore, the kraft lignin fractions with many polar groups are very compatible with the chitosan matrix, resulting in a more compact structure and higher fragility. The membranes CS OLEA and CS KLE have a lower electron conductivity and a higher proton conductivity. Thus, they have promising conductivity properties for fuel cell applications.This study forms part of the Advanced Materials programme and was supported by the Spanish Ministry of Science and Innovation with funding from the European Union NextGenerationEU (PRTR-C17.11) and by the Generalitat Valenciana as project INNOMAT-H2 (MFA/2022/041). The authors also thank the Spanish Ministry of Universities for the pre-doctoral FPU grant of M.H. Wolf (FPU21/00853), the Basque Government for the grant of N. Izaguirre (PIF19-183) and the Universitat Politècnica de València for the PAID-10-19 SUB.1 grant of R. Teruel-Juanes (SP20190049). The authors are also grateful to Karel Beirnaert for experimental assistance in material characterisation