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Fluorescent 4D printing materials, as innovative materials that combine fluorescent characteristics with 4D printing technology, have attracted widespread interest and research. In this study, green lignin-derived carbon quantum dots (CQDs) were used as the fluorescent module, and renewable poly(propylene carbonate) polyurethane (PPCU) was used for toughening. A new low-cost fluorescent polylactic acid (PLA) composite filament for 4D printing was developed using a simple melt extrusion method. The strength of the prepared composite was maintained at 32 MPa, while the elongation at break increased 8-fold (34 % increase), demonstrating excellent shape fixed ratio (∼99 %), recovery ratio (∼92 %), and rapid shape memory recovery speed. The presence of PPCU prevented fluorescence quenching of the CQDs in the PLA matrix, allowing the composite to emit bright green fluorescence under 365 nm ultraviolet light. The composite exhibited shear thinning behavior and had an ideal melt viscosity for 3D printing. The results obtained demonstrated the versatility of these easy-to-manufacture and low-cost filaments, opening up a novel and convenient method for the preparation of strong, tough, and multifunctional PLA materials, increasing their potential application value.

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In this study, we report the development of a sustainable polymer system with 50 wt% lignin content, suitable for additive manufacturing and high value-added utilization of lignin. The plasticized polylactic acid (PLA) was incorporated with lignin to develop the bendable and malleable green composites with excellent 3D printing adaptability. The biocomposites exhibit increases of 765.54 % and 125.27 % in both elongation and toughness, respectively. The plasticizer enhances the dispersion of lignin and the molecular mobility of the PLA chains. The good dispersion of lignin particles within the structure and the reduction of chemical cross-linking promote the local relaxation of the polymer chains. The good local relaxation of the polymer chains and the high flexibility allow to obtain a better integration between the printed layers with good printability. This research demonstrates the promising potential of this composite system for sustainable manufacturing and provides insights into novel material design for high-value applications of lignin.

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MnFe2O4 nanoparticles have been synthesized on a large scale by a simple hydrothermal process in a wild condition, and the RGO/MnFe2O4 nanocomposites were also prepared under ultrasonic treatment based on the synthesized nanoparticles. The absorption properties of MnFe2O4/wax, RGO/MnFe2O4/wax and the RGO/MnFe2O4/PVDF (polyvinylidene fluoride) composites were studied; the results indicated that the RGO/MnFe2O4/PVDF composites show the most excellent wave absorption properties. The minimum reflection loss of RGO/MnFe2O4/PVDF composites with filler content of 5 wt % can reach -29.0 dB at 9.2 GHz, and the bandwidth of frequency less than -10 dB is from 8.00 to 12.88 GHz. The wave absorbing mechanism can be attributed to the dielectric loss, magnetic loss and the synergetic effect between RGO+MnFe2O4, RGO+PVDF and MnFe2O4+PVDF.

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Reduced graphene oxide (RGO)/Co3 O4 nanohybrid particles, composed of reduced graphite oxide and Co3 O4 particles, have been fabricated by an in situ growth method under mild wet-chemical conditions (140 °C). A series of characterization results indicate that the as-prepared Co3 O4 particles with relatively uniform sizes are embedded in RGO layers to form unique core-shell nanostructures. The RGO/Co3 O4 /poly(vinylidene fluoride) composite was found to possess excellent absorption properties. Owing to the effect of the negative permeability, the position of the absorption peaks remains at the same frequency at different thicknesses without shifting to lower frequencies. For the composites with a filler loading of 10 wt %, the maximum peaks can reach -25.05 dB at 11.6 GHz with a thickness of 4.0 mm. These enhanced microwave absorbing properties can be explained based on the structures of the nanohybrid particles.

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A facile and environmentally friendly hydrothermal approach has been employed to synthesize size-controllable quasi-cubic α-Fe2 O3 nanocrystals by using an aqueous solution of FeCl3 without any alkaline materials and stabilizing agent. The as-prepared products were carefully characterized and the growth mechanism is also discussed. This hydrothermal synthesis of such quasi-cubic structures implies a simple and low-cost route to prepare monodisperse nanomaterials on a large scale. The size-controllable synthesis of α-Fe2 O3 is the first achieved successfully from 80 nm to 2 µm with constant structures. The synthesized α-Fe2 O3 materials have different optical properties and stabilities in water, which are caused by the change of their band-gap energy and specific surface areas. Finally, the dielectric properties of synthesized α-Fe2 O3 cubes were also investigated, and the differences caused by the particle sizes are discussed.