Lignin has emerged as a sustainable alternative to fossil-based polymers in advanced materials such as photonics. However, current methods for preparing photonic lignin materials are limited by non-benign organic solvents and low production yields. In this work, we present a highly efficient process that enables the production of photonic glasses with yields ranging from 48% to 72%, depending on the size of the lignin nanoparticles obtained from herbaceous soda lignin, softwood kraft lignin, and hardwood organosolv lignin. The hydrodynamic diameter of lignin nanoparticles can be regulated by the rate of water addition to the lignin-ethanol solution. We demonstrate that this control over particle size allows for tailoring the color of the photonic glass across the visible spectrum.

Lignocellulosic biomass is the only sufficiently available resource for the sustainable development of the bioeconomy. Among the main components of lignocellulose, lignin has a tremendous potential to serve as a natural aromatic polymer resource due to the vast amounts of lignin available from industrial processes. However, commercial application of lignin is still limited and represents only a minor fraction of the potential utilization of approximately 20 million tons that can readily be isolated from spent pulping liquors and obtained as a residue from lignocellulosic biorefineries. Industrial processes generally depolymerize lignin into heterogeneous mixtures of low molecular weight macromolecules with a high degree of condensation, which collectively makes it challenging to develop them into high-performance materials. Although often neglected, some of the major limitations of these so-called technical lignins are their low molar mass and high dispersity, which make these lignins have poor mechanical properties. The polymerization of small lignin fragments not only contributes to the development of high-performance and multifunctional advanced materials, but also helps to improve the fundamental theory of lignin polymer chemistry. In this review, the polymerization of lignin via physical (aggregation), chemical (chain extension, cross-linking, and grafting), and biological (enzymatic polymerization) routes is described, its applications are assessed, and prospects for the development of high-performance lignin polymer materials are discussed.

Alkyl levulinates (ALs) represent a family of bio-compounds derived from levulinic acid (LA), a platform chemical obtained from lignocellulosic biomass. Medium- and long-chain ALs (pentyl levulinate or longer) have shown potential as biofuel and fuel additives due to their relatively low oxygen content and resemblance to biodiesel. This study reports a fast and environmentally friendly method for synthesizing ALs via microwave (MW)-assisted LA esterification, laying emphasis on medium- and long-chain ALs. By combining p-toluenesulfonic acid (5 wt % loading) as catalyst and MW radiation as heating source for a short time (5 minutes), excellent yields of ALs (≥89 mol %) were achieved for a wide range of primary and secondary alcohols (2–10 carbons), overcoming the expected lower reactivity of long chain alcohols. Additionally, formation of undesired side products, such as dialkyl ethers or LA aldol condensation products, was significantly minimized. The feasibility of recovering the unreacted alcohol was successfully proved by simple distillation (88 wt % recovery). The green chemistry metrics assessment proved that this approach aligns with the green chemistry principles and the United Nations Sustainable Development Goals, offering a more sustainable pathway for biofuel and fuel additive production.

This article reports the first multistep combination of pulsed electric field (PEF; 3 kV/cm, 100 kJ/kg, 2 Hz, 100 ms) and supercritical fluid extraction (SFE) with CO₂ (10–20 MPa, 25 mL/min [10% EtOH], 50 °C, 60 min) for exhausted grape marc (EGM). This current protocol was mainly created to recover bioactive glycosylated and lipidic compounds. In this regard, total antioxidant capacity (TAC) was enhanced up to 68% after PEF treatment compared to conventional soaking. However, re-extracting PEF-treated EGM after the application of SFE (PEF + SFE) boosted the efficiency by up to 87%. Several polyphenols (kaempferol, luteolin, scutellarin, and resveratrol, among others), together with other glycosylated structures, were identified by liquid chromatography coupled with mass spectrometry analysis. The bioactive lipidic compounds extracted by SFE, along with the carbohydrate fraction (free sugars) favourably extracted by PEF pre-treatment (mainly glucose, but also fructose and sucrose), were concurrently detected by nuclear magnetic resonance. The remaining solid fraction after treatment was also characterised. Different microscopic morphology was observed by scanning electron microscopy (SEM) on untreated, PEF, and PEF + SC–CO₂–treated EGM. Differential thermogravimetric (DTG) curves determined by thermogravimetric analysis (TGA) also suggested alternative and potential means for the valorisation of this matrix.

Electrochemical energy storage technologies offer means to transition toward a decarbonized society and carbon neutrality by 2050. Compared to conventional lithium-ion batteries, aqueous zinc-ion chemistries do not require scarce materials or toxic and flammable organic-based electrolytes to function, making them favorable contenders in the scenario of intensifying climate change and supply chain crisis. However, environmentally benign and bio-based materials are needed to substitute fossil-based battery materials. Accordingly, this work taps into the possibilities of lignin together with chitosan to form gel polymer electrolytes (GPEs) for zinc-ion chemistries. A simple fabrication process enabling free-standing sodium lignosulfonate–chitosan and micellar lignosulfonate–kraft lignin–chitosan GPEs with diameters exceeding 80 mm is developed. The GPEs combine tensile strength with ductility, reaching Young’s moduli of 55 ± 4 to 940 ± 63 MPa and elongations at break of 14.1 ± 0.2 to 43.9 ± 21.1%. Competitive ionic conductivities ranging from 3.8 to 18.6 mS cm^–1 and electrochemical stability windows of up to +2.2 V vs Zn²⁺/Zn were observed. Given the improved interfacial adhesion of the GPEs with metallic Zn promoted by the anionic groups of the lignosulfonate, a stable cycling of the Zn anode is obtained. As a result, GPEs can operate at 5000 μA cm^–2 with no short-circuit and Coulombic efficiencies above 99.7%, outperforming conventional separator–liquid electrolyte configurations such as the glass microfiber separator soaked into 2 M ZnSO₄ aqueous electrolyte, which short-circuits after 100 μA cm^–2. This work demonstrates the potential of underutilized biorefinery side-streams and marine waste as electrolytes in the battery field, opening new alternatives in the sustainable energy storage landscape beyond LIBs.

The inferior thermoplastic properties have limited production of melt-spun fibers from lignin. Here we report on the controlled esterification of softwood kraft lignin (SKL) to enable scalable, solvent-free melt spinning of microfibers using a cotton candy machine. We found that it is crucial to control the esterification process as melt-spun fibers could be produced from lignin oleate and lignin stearate precursors with degrees of esterification (DE) ranging from 20-50%, but not outside this range. To fabricate a functional hybrid material, we incorporated magnetite nanoparticles (MNPs) into the lignin oleate fibers by melt blending and subsequent melt spinning. Thermogravimetric analysis and X-ray diffraction studies revealed that increasing the weight fraction of MNPs led to improved thermal stability of the fibers. Finally, we demonstrated adsorption of organic dyes, magnetic recovery, and recycling via melt spinning of the regular and magnetic fibers with 95% and 83% retention of the respective adsorption capacities over three adsorption cycles. The mechanical recyclability of the microfibers represents a new paradigm in lignin-based circular materials.

The circular economy considers waste to be a new raw material for the development of value-added products. In this context, agroindustrial lignocellulosic waste represents an outstanding source of new materials and platform chemicals, such as levulinic acid (LA). Herein we study the microwave (MW)-assisted acidic conversion of microcrystalline cellulose (MCC) into LA. The influence of acidic catalysts, inorganic salt addition and ball -milling pre-treatment of MCC on LA yield was assessed. Depolymerization and disruption of cellulose was monitored by FTIR, TGA and SEM, whereas the products formed were analyzed by HPLC and NMR spectroscopy. The parameters that afforded the highest LA yield (48 %, 100 % selectivity) were: ball-milling pre-treatment of MCC for 16 min at 600 rpm, followed by MW-assisted thermochemical treatment for 20 min at 190 degrees C, aqueous p-toluenesulfonic acid (p-TSA) 0.25 M as catalyst and saturation with KBr. These optimal conditions were further applied to a lignocellulosic feedstock, namely melon rind, to afford a 51 % yield of LA. These results corroborate the suitability of this method to obtain LA from agroindustrial wastes, in line with a circular economy-based approach.

This work reports the first example of combined sequential extraction by pulsed electric fields (PEF) (3 kV/cm, 100 kJ/kg, 2 Hz, 100 ms) and supercritical (SC) fluid extraction (SFE) (15 MPa, 25 mL/min, 50 degrees C, 60 min) with CO2 (SC-CO2) for the valorisation of almond hull (AH) biomass. PEF+SFE boosted the efficiency of the protocol up to 77% for total antioxidant capacity and 20% in terms of polyphenols recovery compared to the traditional soaking. Triple-TOF-LC-MS-MS analysis provided the phenolic profiles for the PEF and SCCO2 extracts, observing significant differences in the polyphenol profile according to the technology applied. Additionally, NMR analysis detected the presence of the carbohydrate soluble (mainly glucose, fructose and sucrose) and lipidic fractions, both selectively extracted by PEF or SC-CO2, respectively. Finally, the post-extraction residual solid biomass was characterized by several techniques such as TGA, FT-IR and SEM. For the latter, the formation of surface pores after PEF and a high fibre compaction after SFE was observed. On the other hand, DTG curves allowed to firmly propose concurrent valorisation routes for this solid, in agreement with a zero-waste approach. 

Here, we show that lignin-first biorefining of poplar can enable the production of dissolving cellulose pulp that can produce regenerated cellulose, which could substitute cotton. These results in turn indicate that agricultural land dedicated to cotton could be reclaimed for food production by extending poplar plantations to produce textile fibers. Based on climate-adapted poplar clones capable of growth on marginal lands in the Nordic region, we estimate an environmentally sustainable annual biomass production of ∼11 tonnes/ha. At scale, lignin-first biorefining of this poplar could annually generate 2.4 tonnes/ha of dissolving pulp for textiles and 1.1 m³ biofuels. Life cycle assessment indicates that, relative to cotton production, this approach could substantially reduce water consumption and identifies certain areas for further improvement. Overall, this work highlights a new value chain to reduce the environmental footprint of textiles, chemicals, and biofuels while enabling land reclamation and water savings from cotton back to food production.

Microwave (MW) treatment promotes homogeneous heating compared to conventional methods, thus increasing the recovery of high-added-value compounds and leading to a considerably lower amount of both by-products and side reactions. Therefore, the main goal of this work is to valorize almond hull (AH) via microwave (MW)-assisted radiation (0–200 W, 0–300 psi, 100–190 °C, 10–40 min). In this context, two different pathways were evaluated. Firstly, the transformation of AH into levulinic acid (LA), one of the major bio-based chemicals obtained from lignocellulosic biomass. The so-called almond hull extractives-free biomass (AH-EFB) led to the best results after using both Lewis (AlCl₃⋅6 H₂O, 1 mol/L, 87 % molar yield) and Brønsted (p-toluenesulfonic (p-TsOH), 0.25 mol/L, 91 % molar yield) acids, at 190 °C for 20 min. This latter not only provides a sustainable system in contrast to mineral acids such as H₂SO₄ or HCl, but also the possibility of being recovered and recycled for further transformations. In a parallel secondary experiment, the recovery of biologically active compounds (BACs) was studied separately. For this purpose, antioxidant assays and phenolic profiling were carried out, which demonstrated that MW was more efficient than traditional methods (i.e. soaking) based on obtained values in terms of scavenging activity and polyphenols. Overall, this valorization approach involves most of the Green Chemistry principles, thus contributing to the development of almond biorefineries.