Plasmonic Characterization of 3D Printable Metal-Polymer Nanocomposites.

Plasmonic polymer nanocomposites (i.e., polymer matrices containing plasmonic nanostructures) are appealing candidates for the development of manifold technological devices relying on light-matter interactions, provided that they have inherent properties and processing capabilities. The smart development of plasmonic nanocomposites requires in-depth optical analyses proving the material performance, along with correlative studies guiding the synthesis of tailored materials. Importantly, plasmon resonances emerging from metal nanoparticles affect the macroscopic optical response of the nanocomposite, leading to far- and near-field perturbations useful to address the optical activity of the material. We analyze the plasmonic behavior of two nanocomposites suitable for 3D printing, based on acrylic resin matrices loaded with Au or Ag nanoparticles. We compare experimental and computed UV-vis macroscopic spectra (far-field) with single-particle electron energy loss spectroscopy (EELS) analyses (near-field). We extended the calculations of Au and Ag plasmon-related resonances over different environments and nanoparticle sizes. Discrepancies between UV-vis and EELS are dependent on the interplay between the metal considered, the surrounding media, and the size of the nanoparticles. The study allows comparing in detail the plasmonic performance of Au- and Ag-polymer nanocomposites, whose plasmonic response is better addressed, accounting for their intended applications (i.e., whether they rely on far- or near-field interactions).

Chitin Nanocomposites for Fused Filament Fabrication: Flexible Materials with Enhanced Interlayer Adhesion.

In this work, we present a series of nanocomposites for Fused filament fabrication (FFF) based on polycaprolactone (PCL) and chitin nanocrystals (ChNCs). The ChNCs were synthesized by acid hydrolysis using HCl or lactic acid (LA). The approach using LA, an organic acid, makes the ChNCs synthesis more sustainable and modifies their surface with lactate groups, increasing their compatibility with the PCL matrix. The ChNCs characterization by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy revealed that both ChNCs presented similar morphologies and crystallinity, while differential scanning calorimetry and thermogravimetric analysis proved that they can bear temperatures up to 210 °C without degrading, which allows their processing in the manufacturing of PCL composites by twin-screw extrusion. Therefore, PCL composites in the form of filaments containing 0.5-1.0 wt % ChNCs were produced and used as feedstock in FFF, and standard tensile and flexural specimens were printed at different temperatures, up to 170 °C, to assess the influence of the ChNCs in the mechanical properties of the material. The tensile testing results showed that the presence of ChNCs enhances the strength and ductility of the PCL matrix, increasing the elongation at break around 20-50%. Moreover, the vertically printed flexural specimens showed a very different bending behavior, such that the pure PCL specimens presented a brittle fracture at 7% strain, while the ChNCs composites were able to bend over themselves. Hence, this work proves that the presence of ChNCs aims to improve the interlayer adhesion of the objects manufactured by FFF due to their good adhesive properties, which is currently a concern for the scientific community and the industrial sector.

Influence of the Carbon Fiber Length Distribution in Polymer Matrix Composites for Large Format Additive Manufacturing via Fused Granular Fabrication.

Many studies assess the suitability of fiber-reinforced polymer composites in additive manufacturing. However, the influence of the fiber length distribution on the mechanical and functional properties of printed parts using these technologies has not been addressed so far. Hence, in this work we compare different composites based on Acrylonitrile Styrene Acrylate (ASA) and carbon fiber (CF) suitable for large format additive manufacturing (LFAM) technologies based on fused granular fabrication (FGF). We study in detail the influence of the CF size on the processing and final properties of these materials. Better reinforcements were achieved with longer CF, reaching Young's modulus and tensile strength values of 7500 MPa and 75 MPa, respectively, for printed specimens. However, the longer CF also worsened the interlayer adhesion of ASA to a greater extent. The composites also exhibited electrical properties characteristic of electrostatic dissipative (ESD) materials (105-1010 Ω/sq) and low coefficients of thermal expansion below 15 µm/m·°C. These properties are governed by the CF length distribution, so this variable may be used to tune these values. These composites are promising candidates for the design of elements with enhanced mechanical and functional properties for ESD protection elements or molds, so the products can be manufactured on demand.