Polymers

Agricultural residues offer a source of nanocellulose for developing functional composites. This study examined how biomass source, extraction conditions, and copper loading affect the structural and electrochemical properties of nanocellulose derived from hemp hurds and corn cob. A citric-acid-assisted chemical–mechanical extraction route was investigated using response surface methodology, with extraction cycle number and sonication time as factors and FTIR-derived total crystallinity index and SEM-derived apparent fiber size as responses. The selected conditions were three cycles and 120 min for hemp hurds and three cycles and 75 min for corn cob, yielding measured mean apparent fiber sizes of 83.3 and 100 nm, respectively. Nanocellulose was modified with nominal Cu loadings of 15, 25, 50, and 75 wt%. At 0.1 Hz, impedance magnitude decreased from 274.15 and 247.67 kΩ for the respective bare references to below 10 kΩ for all Cu-modified groups. Cu incorporation also increased cycle-5 passed charge, with the corn-cob series showing its highest mean response at 50 wt%. FTIR, SEM, TGA, and XRD supported cellulose enrichment, nanoscale fibrillation, source-dependent thermal behavior, and crystalline metallic Cu formation. These findings support further evaluation of Cu-modified nanocellulose for electrochemical applications.

The increasing demand for sustainable engineering thermosets, such as unsaturated polyester resins (UPR), together with stricter fire safety requirements, promotes the development of environmentally friendly polymer composites. In this study, UPR synthesized from recycled post-consumer poly(ethylene terephthalate) was modified with casein particles to investigate their effects on thermal, thermomechanical, and fire-related properties. The obtained biocomposites were characterized by thermal analysis, thermomechanical testing, and flammability evaluation. Casein incorporation affected the degradation behaviour of UPR and promoted residue formation at elevated temperatures. Cone calorimetry demonstrated a reduction in peak heat release rate from 600 to 407 kW·m⁻² and total heat release from 86 to 65 MJ·m⁻² for the composite containing 15 wt.% casein. The maximum average rate of heat emission decreased from 345 to 255 kW·m⁻², while combustion residue increased from 0.1 to 3.5%, confirming enhanced char formation. Fire performance also improved, with the Fire Potential Index increasing from 0.053 to 0.071 m²·s·kW⁻¹ and the Fire Retardancy Index reaching 1.77 for UPR+C15. The heat deflection temperature increased from 56.9 to 71.3 °C, whereas the Vicat softening temperature decreased slightly. Overall, casein is a promising bio-based additive for tailoring the properties of sustainable UPR composites.

Melt electrospinning (MES) is a fiber manufacturing technique in which a molten polymer is stretched into ultrafine fibers by an electric field. MES combines the ability to produce very fine fibers with the advantages of solvent-free manufacturing. Its controlled variant, melt electrowriting (MEW), is especially valuable because it allows exceptional architectural precision, making it highly attractive for biomedical applications. This study presents a systematic, single-parameter evaluation of how nozzle-to-collector distance (nozzle height), applied pressure, and collector speed influence the morphological and thermal properties of the resultant poly(lactic acid) (PLA) fibers. Fiber diameter, uniformity, thermal transitions, crystallinity, and thermal stability are analyzed, the former being tuned over a wide controlled range (≈4–42 μm). Larger nozzle heights and higher collector speeds promote fiber drawing, yielding thinner (down to ~4 µm) and more uniform fibers, while increasing pressure results in progressively thicker fibers due to higher melt flow rates (up to ~42 µm). Thinner fibers exhibit higher glass transition temperatures, suggesting enhanced molecular orientation, whereas all fibers remain amorphous due to the rapid quenching applied during processing. Thermal stability improves at intermediate nozzle heights, correlating with the increased morphological uniformity. These results provide a clear, quantitative understanding of the physical mechanisms governing MES processing of PLA, delivering practical guidelines and processing–structure–property relationships for the design of tailored biodegradable scaffolds.