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Glass (GFR) and carbon fiber-reinforced (CFR) dual-cure polymer composites fabricated by UV-assisted three-dimensional (UV-3D) printing are presented. The resin material combines an acrylic-based photocurable resin with a low temperature (140 °C) thermally-curable resin system based on bisphenol A diglycidyl ether as base component, an aliphatic anhydride (hexahydro-4-methylphthalic anhydride) as hardener and (2,4,6,-tris(dimethylaminomethyl)phenol) as catalyst. A thorough rheological characterization of these formulations allowed us to define their 3D printability window. UV-3D printed macrostructures were successfully demonstrated, giving a clear indication of their potential use in real-life structural applications. Differential scanning calorimetry and dynamic mechanical analysis highlighted the good thermal stability and mechanical properties of the printed parts. In addition, uniaxial tensile tests were used to assess the fiber reinforcing effect on the UV-3D printed objects. Finally, an initial study was conducted on the use of a sizing treatment on carbon fibers to improve the fiber/matrix interfacial adhesion, giving preliminary indications on the potential of this approach to improve the mechanical properties of the 3D printed CFR components.

In this work, nanocomposites based on a UV-curable polymeric resin and different inorganic fillers were developed for use in UV-assisted three-dimensional (UV-3D) printing. This technology consists in the additive multilayer deposition of a UV-curable resin for the fabrication of 3D macro structures and microstructures of arbitrary shapes. A systematic investigation on the effect of filler concentration on the rheological properties of the polymer-based nanocomposites was performed. In particular, the rheological characterization of these nanocomposites allowed to identify the optimal printability parameters for these systems based on the shear rate of the materials at the extrusion nozzle. In addition, photocalorimetric measurements were used to assess the effect of the presence of the inorganic fillers on the thermodynamics and kinetics of the photocuring process of the resins. By direct deposition of homogeneous solvent-free nanocomposite dispersions of different fillers in a UV-curable polymeric resin, the effect of UV-3D printing direction, fill density, and fill pattern on the mechanical properties of UV-3D printed specimens was investigated by means of uniaxial tensile tests. Finally, examples of 3D macroarchitectures and microarchitectures, spanning features, and planar transparent structures directly formed upon UV-3D printing of such nanocomposite dispersions were reproducibly obtained and demonstrated, clearly highlighting the suitability of these nanocomposite formulations for advanced UV-3D printing applications

Electroless nickel and copper metallization of 3D printed polymers like polylactic acid and polyethylene terephthalate glycol modified is presented. The plating process is tested on suitable samples, which reproduce the characteristic morphologies used in 3D printing of objects. An alkaline etching is used for both polymers in order to modify the surface properties and to enhance the adhesion and uniformity of the metallic coating. In the case of polylactic acid, a plasma treatment is applied as well to further improve adhesion of the metallic coating. For the activation of the surface, a tin free process involving an immersion in a palladium solution and subsequent reduction to form metallic nuclei is employed. Electrolytes are formulated and selected to operate in temperature ranges comparable with the glass transition temperatures of the polymers. Adherent and uniform layers of NiP (3-4% P wt) and Cu can be easily obtained for esthetic and functional applications, also on flexible substrates. Since its introduction in the early 1980s, 1 3D printing has acquired a great relevance for research and industry. In the beginning this technique, based on the sequential deposition of layers to obtain three dimensional objects from a virtual model, found application in rapid prototyping and custom made machine parts. 2 In the last few years however a new industrial revolution began, as home 3D printers can nowadays be easily purchased on the market. This fact is starting to change the common concept of mass production, since 3D printing has the potential to start a new form of handicraft: the customer can obtain the tridimensional model of the desired object and subsequently print it. The production of some goods can thus be moved from factories to homes, with potential advantages.3 Other recent applications for 3D printing have been found in medicine, where the possibility to 3D print scaffolds, 4 cell cultures 5-7 or even organs 8 has been investigated. Many 3D printing techniques exist, like stereolitography (SLA), 9 selective laser sintering (SLS) 10 or fused deposition modelling (FDM).11 Only the latter is however finding the cited commercial success due to the low cost of the materials and the ease of operation. Objects that are complicate or even impossible to manufacture with conventional techniques, can be produced in reduced time ranges with this technique. It is on the other hand expensive to manufacture metallic objects. Some 3D printing techniques are suitable for direct metal processing, like SLS, 10 while for all the methods it is always possible to print the objects and subsequently cast them in a foundry. These two ways are however difficult to apply if the goal is to keep the process inexpensive and homemade.Another possibility to achieve a metal finishing for 3D printed object is to metallize only the surface of the polymer used in the process. This makes possible to achieve the desired properties of the metals without performing a real bulk metal 3D printing.12 Metallization processes like PVD can a...