Polyethylene terephthalate (PET) is one of the most widely produced polymers, extensively used in packaging and beverage industries. However, its low recyclability leads to significant environmental challenges, with less than 10% of global plastic waste effectively recycled, while the majority accumulates in landfills or the natural environment. Developing efficient chemical recycling strategies is therefore essential to mitigate environmental impact and recover valuable resources. Among these, depolymerization of PET into terephthalic acid (TPA) offers a promising route for generating a monomer that can be reused in the synthesis of advanced functional materials.
In this study, PET waste was depolymerized into TPA using microwave-assisted alkaline hydrolysis. A Taguchi experimental design was employed to optimize key process parameters, including temperature (160–200 °C), reaction time (5–90 min), PET particle size (0.2–2 cm), PET-to-liquid ratio (1:10–1:2), and microwave power (up to 630 W). Kinetic parameters of the hydrolysis reaction were also determined to better understand the depolymerization mechanism. Under the optimized conditions—190 °C, 90 min, 0.2 cm PET particle size, 10% PET-to-liquid ratio, and 630 W—a maximum depolymerization efficiency of 65% was achieved. The influence of process variables was ranked as reaction time > temperature > particle size > solid-to-liquid ratio.
The recovered TPA was subsequently used as an organic linker for the microwave-assisted synthesis of MIL-53(Al). Structural and textural characterization by XRD, FTIR, BET, and SEM confirmed the successful formation of a porous framework, showing that synthesis and activation conditions significantly influenced crystallinity, surface area, and morphology. This study demonstrates a sustainable strategy for PET valorization, combining process optimization with the production of advanced metal–organic frameworks, and contributes to circular economy initiatives.

The production of nanofibrous membranes through electrospinning has traditionally relied on highly effective organic solvents such as dimethylformamide (DMF), chloroform (CHL), and dichloromethane (DCM). Despite their efficiency in dissolving polymers and ensuring processability, these solvents are toxic and potentially carcinogenic, raising serious concerns for both human health and the environment. This long standing technical scientific lock-in has restricted the widespread adoption of sustainable alternatives and hindered the development of safer nanostructured materials for biomedical and environmental applications.

In this work, we demonstrate the complete replacement of hazardous solvents with low toxicity systems, including acetone, acetone/ethanol, and acetone/water mixtures, all fully compliant with current EU regulations. Morphological analyses performed on polycaprolactone (PCL) and polylactic acid (PLA) nanofibrous membranes reveal that green solvent systems not only allow the preservation of standard electrospinning parameters but also enable the generation of a wide range of fibrous morphologies from bead-only to beads-on-string and fully continuous fibers. Importantly, this structural versatility highlights the ability to modulate fiber size and surface features without requiring disruptive changes in the processing setup.

Overall, the findings demonstrate that the transition to green solvent systems effectively overcomes the constraints imposed by traditional toxic solvents. By enabling fine morphological control and expanding application versatility, this approach paves the way for the design of nanostructures that are not only high-performing but also safe, environmentally sustainable, and aligned with the growing demand for greener technologies in advanced material science.

The increasing accumulation of synthetic textile waste, especially poly(ethylene terephthalate) (PET)-based fibers, poses a critical environmental challenge. Conventional recycling techniques are often inefficient. Solvolysis with supercritical CO₂ (scCO₂) emerges as a green and efficient alternative, enabling the depolymerization of polyester chains under mild conditions and facilitating the recovery of platform chemicals with minimal solvent waste. In addition, ionic liquids have been proven to reduce the energy requirements of the solvolysis. This approach aligns with circular economy principles and offers a route toward high-purity monomer production for polymer regeneration. The solvolytic depolymerization of PET-based textile waste was carried out in a high-pressure batch reactor using scCO₂ as co-solvent under fixed conditions of 15 minutes of reaction time and CO₂ pressure up to 120 bar. Experimental variables included temperature (183–217 °C), textile-to-ionic liquid ratio ([Tex]:[IL] = 1.7–6.0), and textile-to-solvent ratio ([Tex]:[Sol] = 14.1–33.0). A specific ionic liquid was used as catalytic co-solvent. The influence of these parameters on depolymerization efficiency and product selectivity was assessed. Under optimal conditions, a conversion rate of up to 99% was achieved. Temperature proved to be the most influential parameter, significantly affecting the extent of depolymerization in both solvolysis methodologies. In contrast, the textile-to-ionic liquid ratio showed a moderate effect, and the textile-to-solvent ratio exhibited negligible influence on the conversion, indicating that the process could be optimized with reduced solvent consumption. The low sensitivity of the process to solvent and ionic liquid ratios, combined with the strong influence of temperature, supports the feasibility of a cost-efficient, greener recycling method adaptable to industrial applications.

In response to the urgent need for sustainable alternatives to fossil products and the promotion of a circular economy, biorefineries offer an effective strategy for biomass valorization. Jatropha curcas L., a drought-tolerant species native to Mexico and Central America, is well known for its oil-rich kernels; however, its seed coat remains largely underutilized, limiting the full exploitation of the crop.

This study presents the first integrated biorefinery model for the comprehensive valorization of JCL seeds, converting both kernels and seed coats into high-value biofuels, materials, and nutritional and chemical co-products through sequential fractionation and conversion.

The kernel was subjected to mechanical oil extraction at 200 °C, followed by transesterification with 1% NaOH to produce biodiesel (ASTM-D6751). Residual protein cake from extraction was refined with isopropyl alcohol to obtain molasses. In parallel, milled seed coat underwent alkaline (NaOH 4.5%, 80 °C, 2 h, 4 cycles) and subsequent bleaching treatment (chloride-based, 80 °C, 4 h, 4 cycles) to disrupt lignin–carbohydrate complexes, yielding lignin- and cellulose-rich fractions. The cellulose-rich fraction was then processed into cellulose nanofibrils by high-pressure homogenization (10000 psi, 10 cycles).

This integrated approach achieved ~85% total biomass seed valorization. Kernels accounted for 69.0 ± 2.8% of seed mass, with oil extraction yielding 45.0 ± 2.5% and residual protein cake 47.3 ± 1.0%. Of this extracted oil, 90.3 ± 3.4% was converted into biodiesel, while 9.4 ± 2.8% remained as glycerol. Molasses were produced for first time from the protein cake, representing ~10% of its mass and leaving ~37% as purified protein. The seed coat represented 30.1 ± 3.1% of seed mass, yielding 21.5 ± 3.4% of lignin-rich fraction from the generated black liquor after alkali treatment, and 44.6 ± 2.4% of cellulose-rich fraction from bleaching. The cellulose-rich fraction was then processed into cellulose nanofibrils of 5 nm of diameter without previous pre-treatment.

These findings demonstrate the potential of JCL as a versatile feedstock for sustainable bio-based industries.

Acknowledgments: RM is grateful for Grant RYC2021-034380-I funded by MCIN/AEI/10.13039/501100011033 and the European Union “NextGenerationEU”/PRTR.

The selective extraction and recovery of different molecules of interest from lignocellulosic materials from forestry residues are increasing every day, driving society towards more sustainable approaches and materials. For this purpose, the development of new sustainable and ecologically benign extraction methodologies has grown significantly. Deep eutectic solvents (DESs) appear as a promising alternative for the processing of biomass [1, 2]. In the present study, cellulose-rich fractions obtained from the fractionation of Acacia wood, an invasive species in Portugal, were used to prepare cationic and hydrophobically modified cationic bioflocculants used for wastewater treatment with a focus on microplastics removal [3].

On the other hand, Eucalyptus bleached pulp was also used to prepare anionic and cationic bioflocculants used to treat effluents from the textile industry [4]. The bioflocculant preparation route follows a two-step process, with the introduction of reactive aldehyde groups in the cellulose molecules, followed by cationization or anionization. The hydrophobic variation was obtained by a third step, by esterification of the C₆ OH groups of cellulose with fatty acids obtained from vegetable oils.

All the obtained bioflocculants revealed high performance, according to the results obtained in Laser Diffraction Spectroscopy, at the same level as or even superior to synthetic alternatives, cationic and anionic polyacrylamides, with lower environmental impact.

1. Magalhães, S., et al., Enhancing Cellulose and Lignin Fractionation from Acacia Wood: Optimized Parameters Using a Deep Eutectic Solvent System and Solvent Recovery. Molecules, 2024. 29(15): p. 3495.
2. Magalhães, S., et al., Acacia Wood Fractionation Using Deep Eutectic Solvents: Extraction, Recovery, and Characterization of the Different Fractions. ACS Omega, 2022. 7(30): p. 26005-26014.
3. Magalhães, S., et al., Tailored cellulose-based flocculants for microplastics removal: Mechanistic insights, pH influence, and efficiency optimization. Powder Technology, 2025. 456: p. 120838.
4. Grenda, K., et al., Environmentally friendly cellulose-based polyelectrolytes in wastewater treatment. Water Science and Technology, 2017. 76(6): p. 1490-1499.

Polyhydroxyalkanoates (PHAs) are microbial-derived biodegradable polymers with significant potential to replace conventional synthetic plastics. This study investigates the novel biosynthesis of PHAs by Paramecium caudatum, a ciliated protozoan, using lignocellulosic waste sugarcane bagasse (SCB) as a low-cost carbon source. Paramecium sp. was isolated from industrial wastewater and identified as P. caudatum via 18S rRNA gene sequencing (GenBank: PQ038083). P. caudatum cultures were incubated separately with SCB at 4% (w/v) and glucose at 3% (w/v) for comparison, under optimal conditions (25°C, pH 7). PHA accumulation was assessed using Sudan Black B and Nile Blue A staining during the log phase. Extracted PHAs were characterized using Fourier-transform infrared spectroscopy (FTIR), gas chromatography–mass spectrometry (GC–MS), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). PHA synthase expression in total cellular protein was assessed via SDS-PAGE, and PHA film biodegradability was evaluated through a soil burial test. PHA yields reached 2.43 g/L with glucose and 2.21 g/L with SCB. FTIR and GC–MS analyses revealed predominant PHA monomers, including 3-hydroxybutyrate ethyl ester (92.6%), hexadecanoic acid ethyl ester (74.4%), and octadecanoic acid ethyl ester (65.9%). TGA showed good thermal stability, with Tmax at 280°C (glucose) and 270°C (SCB). SEM imaging displayed a porous, pseudospherical surface morphology, indicating strong polymer integrity. The PHA films exhibited favorable plasticizing properties and fully biodegraded within 30 days in soil. SDS-PAGE confirmed consistent expression of a ~63 kDa PHA synthase under both carbon source conditions. This is the first study to report P. caudatum as a microbial cell factory for scalable bioplastic production via lignocellulosic waste valorization, contributing to circular bioeconomy goals.

The pursuit of sustainable polymeric materials has driven the development of epoxy systems derived from renewable sources, such as epoxidized soybean oil (ESO). Understanding their curing kinetics is essential for process control and optimisation of final properties. In this study, the curing behaviour of ESO/MTHPA/DEH 35 (epoxidized soybean oil/methyl tetrahydrophthalic anhydride/2,4,6-tris(dimethylaminomethyl) phenol) systems—with and without a tin-based catalyst (Tin) (Tin(II) 2-ethylhexanoate)—was evaluated using the isoconversional Friedman method. Samples were analysed via Differential Scanning Calorimetry (DSC) at heating rates of 5, 10, and 20 °C/min. Data were processed using the differential form of the conversion equation (α) to obtain the apparent activation energy (Ea) as a function of conversion. Model validation was achieved by comparing experimental and calculated conversion values (αexp vs αprev), and by linear regressions of ln(dα/dt) versus 1000/T. The Friedman model adequately described the kinetic behaviour of both systems. The Tin-containing formulation started curing at higher temperatures (~140–150 °C), indicating a greater initial energy barrier. The Ea(α) curve showed high values (~80 kJ/mol) for α < 0.2, attributed to the formation of high-energy catalytic complexes. For α > 0.2, a sharp decrease in Ea (< 20 kJ/mol) indicated the onset of autocatalytic propagation. In contrast, the system without Tin exhibited stable Ea values (~45–55 kJ/mol), suggesting a more homogeneous and thermally controlled process. Regression coefficients (R² > 0.98) and sigmoid fits (deviation < ±10%) confirmed the model’s validity. Overall, the Friedman method proved effective for describing the curing kinetics of these bio-based epoxy systems. The presence of Tin led to a multifaceted and accelerated curing mechanism, while its absence resulted in a simpler, thermally governed process with lower chemical complexity.

Biopolymer-based nanostructures, derived from the self-assembly of proteins and polysaccharides, represent a versatile and sustainable platform for the delivery of bioactive small molecules. Their inherent biocompatibility, biodegradability, nontoxicity, and eco-friendly and sustainable preparation make them ideal candidates for applications in both food technology and biomedicine.

Through light scattering, small-angle scattering, microscopy, and spectroscopy techniques, we investigate the formation and morphology of the protein–polysaccharide nanostructures and the binding, loading capacity, and stability of hydrophobic compounds.

We present our recent works in the preparation and characterization of protein/polysaccharide nanoparticles formed through electrostatic complexation and thermal treatment, using proteins such as bovine serum albumin, trypsin, and hemoglobin and polysaccharides such as chondroitin sulfate, xanthan, and hyaluronic acid. Particular emphasis is placed on the interactions of these nanostructures with low-molecular-weight compounds, including the model nutraceuticals β-carotene and curcumin. The role of nanoparticle composition and structure in modulating the affinity for hydrophobic and amphiphilic molecules is explored.

Our results suggest that fine-tuning the protein-to-polysaccharide ratio, pH, and thermal treatment parameters can optimize nanocarrier stability and small molecule encapsulation. These findings contribute to the rational design of biopolymer-based delivery systems and demonstrate their potential for targeted release of functional compounds in nutraceutical and pharmaceutical formulations.

The use of biomass waste for polymer production is a key component of the global plastic sustainability strategy. Bark contains low molecular weight polyphenolic and carbohydrate compounds rich in hydroxyl groups, making it a potential macromonomer source for plastics. The global annual volume of bark waste is estimated at 300–400 million m³, making it a cheap and highly available raw material.

This study focused on the waste-free processing of pine (Pinus sylvestris) bark into rigid polyurethane (PUR) foam. Extractives, obtained in a yield of 25%, enriched with low molecular weight carbohydrates, were separated via pressurized water extraction at 150 °C. Increasing the extraction temperature above 150 °C significantly reduced both the extractives yield and their hydroxyl content due to carbohydrate dehydration. Extractives were converted into liquid polyols through "green" oxypropylation with propylene carbonate (PC), varying PC/OH ratios. The residual bark was introduced into PUR foam formulation as a filler.

The resulting polyols exhibited viscosities ranging from 8.6 to 210 Pa·s, and hydroxyl values between 580 - 660 mg KOH/g were used to synthesize PUR foams with PMDI at an NCO/OH ratio of 1.1.

In the PUR foam formulations, commercial polyols (Lupranol 3300 and Lupranol 3422) were partially or fully replaced by the bark extractives-based polyols. Key material properties —apparent density, deformation, morphological, and thermal characteristics—were evaluated and compared to foams based on commercial polyols.

Polyol synthesized at a PC/OH ratio of 3 was the most promising for PUR foam production, yielding materials with properties equal to or better than those of foams based on commercial polyols. However by incorporating the residual bark after extraction as a filler led to a slight reduction in mechanical performance.

Acknowledgements:

This research is supported by the project: Innovation in Forest Management and Value Chain for Latvia's Growth: New Forest Services, Products and Technologies (Forest4LV) – Project Nr. VPP-ZM-VRIIILA-2024/2-0002.

The European Commission promotes the increase of recycled plastic in short-term applications as its strategy to introduce plastic products into a circular economy model. However, the mechanical recycling process could reduce the thermal stability and mechanical properties of plastics. In this regard, six (TGA) and tensile tests were performed and case materials assessed included two (PET), two (PP), and two (PE) in their virgin and recycled forms.

The samples were sorted, cleaned, shredded into flakes, and then extruded. So, according to the manufacturer, the samples were processed with the same conditions used for the virgin counterparts. However, additives such as plasticizers and fillers were added in order to increase the thermomechanical properties of the materials, among others.

The TGA curves obtained were similar no matter the origin of the plastic, although a residue of 5% was found in some recyclates—in all except for PET.

Relative to the mechanical properties, the elongation, Young modulus, and ultimate tensile strength for the three polymers PET, PP, and PE were analyzed. In the case of PET, the recyclates showed greater ultimate tensile strength and elongation than the virgin plastics, showing, however, the same young modulus. For the other polymers, the virgin PP material showed better properties by 10% to 15% in all the parameters. Regarding PE, the recyclate had a greater elongation by 5%, and the other properties of the virgin PP were about 35% above the recyclates.

The studies showed a good overall performance of the recycled material thermally and mechanically, which makes the recycled polymers a good replacement for the virgin polymers.