Special Resins for Stereolithography: In Situ Generation of Silver Nanoparticles

The limited availability of materials with special properties represents one of the main limitations to a wider application of polymer-based additive manufacturing technologies. Filled resins are usually not suitable for vat photo-polymerization techniques such as stereolithography (SLA) or digital light processing (DLP) due to a strong increment of viscosity derived from the presence of rigid particles within the reactive suspension. In the present paper, the possibility to in situ generate silver nanoparticles (AgNPs) starting from a homogeneous liquid system containing a well dispersed silver salt, which is subsequently reduced to metallic silver during stereolithographic process, is reported. The simultaneous photo-induced cross-linking of the acrylic resin produces a filled thermoset resin with thermal-mechanical properties significantly enhanced with respect to the unfilled resin, even at very low AgNPs concentrations. With this approach, the use of silver salts having carbon-carbon double bonds, such as silver acrylate and silver methacrylate, allows the formation of a nanocomposite structure in which the release of by-products is minimized due to the active role of all the reactive components in the three dimensional (3D)-printing processes. The synergy, between this nano-technology and the geometrical freedom offered by SLA, could open up a wide spectrum of potential applications for such a material, for example in the field of food packaging and medical and healthcare sectors, considering the well-known antimicrobial effects of silver nanoparticles

Electrically conductive epoxy nanocomposites containing carbonaceous fillers and in-situ generated silver nanoparticles

An epoxy resin was nanomodified with in-situ generated silver nanoparticles (Ag) and with various amounts of carbon black (CB) and carbon nanofibers (NF), in order to increase the electrical conductivity of the matrix. Differential scanning calorimetry tests revealed how the addition of both CB and NF led to a slight decrease of the glass transition temperature of the material, while electron microscopy evidenced how the dimension of CB aggregates increased with the filler content. Both flexural modulus and stress at yield were decreased by CB addition, and the introduction of Ag nanoparticles promoted an interesting improvement of the flexural resistance. CB resulted to be more effective than NF in decreasing the electrical resistance of the materials down to 103 !·cm. Therefore, a rapid heating of the CB-filled samples upon voltage application was observed, while Ag nanoparticles allowed a stabilization of the temperature for elevated voltage application times

Printing and characterization of 3D high-loaded nanocomposites structures

Additive Manufacturing (AM) technologies are spreading rapidly both in academic research and industrial environments [1]. Nanomaterials have proven to provide new size-dependent properties compared to traditional bulk materials [2]. The integration of nanotechnology into AM opens new and interesting challenges in manufacturing advanced nanocomposite materials with custom-made properties and geometries [3]. Synergy between nanomaterials, such as metal and oxide nanoparticles, and AM can in fact result in improved functional and structural performance of manufactured devices, filling the gap between design and production of a specific tool. For instance, silica nanoparticles (SiO2 NPs) are increasingly used as nanofillers, thanks to their excellent mechanical properties, to fabricate nanocomposites used in a wide range of applications [4]. Stereolithography (SLA) represents one of the most widespread AM technologies used to fabricate 3D engineered structures. The general procedure for building objects with SLA involves photo-polymerization of liquid monomer into solid resin by means of an ultraviolet (UV) laser, which creates targeted cross-linked regions where the light irradiates the matrix [5]. SLA AM of nanocomposites usually involves mixing of ex situ synthesized nanoparticles with commercially available acrylic monomers, followed by an optimized printing process. Stable dispersion of colloidal SiO2 NPs in acrylate monomers or oligomers are commercially available, such as Nanocryl product family commercialized by Evonik. These products are traditionally used in adhesive and electronic applications, such as highly scratchresistant coatings for fiber optic cables, conformal coatings, UV curing adhesives for printed circuit boards and can be successfully employed in AM of high-loaded nanocomposites. The produced 3Dprinted specimens were employed to characterize the nanocomposites microstructure and thermomechanical properties respectively by means of scanning electron microscopy (SEM) and dynamicmechanical analyses (DMA)

Pullout behavior of polypropylene macro-synthetic fibers treated with nano-silica

A study of the effects of nano-silica treatment on the bonding properties of macro synthetic polypropylene fibers embedded in a cement matrix is provided in the present paper as a step to improve interfacial properties of the fiber reinforced cementitious composites (FRCC). Polypropylene fibers were treated by sol\u2013gel technique, allowing to obtain a nano-silica coating. Scanning electron microscopy was used to observe the morphological features of PP fibers surfaces before and after the pullout test. The effects of the treatment were investigated by comparative pullout tests on treated and untreated fibers. An increase in maximum load and energy necessary for the complete extraction of the fiber was observed, as a consequence of the improvement of the interface properties due to the nano-silica hydration activity. These two parameters control the crack-resistance and ductility properties of FRCC and are deeply affected by bonding and friction phenomena. The hydration products act as chemical and physical anchors, thus producing a densification of the interface transition zone (ITZ). The abrasion phenomena occurring on the fiber surface during the pullout test are responsible of hardening behavior, consisting in the increase in the frictional shear stress with the fiber slip and thus in the energy required for fiber extraction

Characterization of biocompatible scaffolds manufactured by fused filament fabrication of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate

We characterize poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) scaffolds for tissue repair and regeneration, manufactured by three-dimensional fused filament fabrication (FFF). PHBH belongs to the class of polyhydroxyalkanoates with interesting biodegradable and biocompatible capabilities, especially attractive for tissue engineering. Equally, FFF stands as a promising manufacturing technology for the production of custom-designed scaffolds. We address thermal, rheological and cytotoxicity properties of PHBH, placing special emphasis on the mechanical response of the printed material in a wide deformation range. Indeed, effective mechanical properties are assessed in both the linear and nonlinear regime. To warrant uniqueness of the material parameters, these are measured directly through digital image correlation, both in tension and compression, while experimental data fitting of finite-element analyses is only adopted for the determination of the second invariant coefficient in the nonlinear regime. Mechanical data are clearly porosity dependent, and they are given for both the cubic and the honeycomb infill pattern. Local strain spikes due to the presence of defects are observed and measured: those falling in the range 70\u2013100% lead to macro-crack development and, ultimately, to failure. Results suggest the significant potential attached to FFF printing of PHBH for customizable medical devices which are biocompatible and mechanically resilient

Short Heat Treatments for the F357 Aluminum Alloy Processed by Laser Powder Bed Fusion

Conventionally processed precipitation hardening aluminum alloys are generally treated with T6 heat treatments which are time-consuming and generally optimized for conventionally processed microstructures. Alternatively, parts produced by laser powder bed fusion (L-PBF) are characterized by unique microstructures made of very fine and metastable phases. These peculiar features require specifically optimized heat treatments. This work evaluates the effects of a short T6 heat treatment on L-PBF AlSi7Mg samples. The samples underwent a solution step of 15 min at 540 °C followed by water quenching and subsequently by an artificial aging at 170 °C for 2-8 h. The heat treated samples were characterized from a microstructural and mechanical point of view and compared with both as-built and direct aging (DA) treated samples. The results show that a 15 min solution treatment at 540 °C allows the dissolution of the very fine phases obtained during the L-PBF process; the subsequent heat treatment at 170 °C for 6 h makes it possible to obtain slightly lower tensile properties compared to those of the standard T6. With respect to the DA samples, higher elongation was achieved. These results show that this heat treatment can be of great benefit for the industry

Application of Zirconia in Dentistry: Biological, Mechanical and Optical Considerations

Aiming to replace the infrastructure of metallic dental prostheses, structural ceramics have been improved and increasingly used in dentistry. Among the dental ceramics, the zirconia has emerged as a versatile and promising material because of its biological, mechanical and optical properties, which has certainly accelerated the routine use of CAD/CAM technology in different types of prosthetic treatment.Routinely, zirconia based ceramics are used in structural applications in engineering as the manufacture of cutting tools, gas sensors, refractories and structural opacifiers. To meet structural demands, zirconia has to be doped with stabilizers to achieve high strength and fracture toughness. The bioceramics nowadays, used in medical and dental care, derived from structural materials used in aerospace and military armor, which were modified to suit the additional requirements of biocompatibility

Printability study by selective laser sintering of bio-based samples obtained by using PBS as polymeric matrix

The emerging request to reduce the environmental impact of plastics encourages scientists to use novel sustainable polymeric materials for many applications fields. The present paper aims to use for the first-time poly (butylene succinate) (PBS), a biodegradable and compostable polymer, for Selective Laser Sintering (SLS) applications. PBS is a flexible semicrystalline aliphatic polyester, which can represent a very good alternative to the traditional thermoplastic polymers obtained by fossil sources. The present work started from a lab-scale production of PBS powders by means of an emulsion solvent evaporation/precipitation method, with the purpose to increase the number of polymeric powders available for SLS. The obtained PBS powders were first characterized by morphological and thermal point of view, and then employed as innovative polymeric material in SLS to realized 3D printed parts with increasing geometrical complexity. To confirm PBS cytocompatibility, cell proliferation and cell viability assays (MTT and Live&Dead) were measured using a lung adenocarcinoma epithelial cell line (H1299). The in vitro cytotoxicity of the 3D printed material was also investigated, showing no harm on cells

bioactive nanocomposites for dental application obtained by reactive suspension method

AbstractHydroxyapatite (HA) filled poly(methyl methacrylate)/poly(hydroxyethyl methacrylate) (PMMA/PHEMA) blends were prepared by reactive suspension method: HA was synthesized by co-precipitation process directly within a HEMA solution and the so-obtained suspension was polymerized in the presence of PMMA. HA particles were obtained in form of nanorods with a length of 50–200 nm and a diameter of 10–30 nm. A significant increase in glass transition temperature was observed in the nanocomposites with respect to the unfilled polymer blends. Dynamic-mechanical thermal analysis showed a significant increase in the storage modulus in the nanocomposites measured in the rubbery region. This increase was unpredicted by Mooney's predictive equation and was attributed to the presence of cross-linking points due to the in situ generated HA particles. An increase in the elastic modulus was also observed at room temperature in compression and three-point bending tests. The presence of HA in the polymer blends resulte..

3D-Printing Nanocellulose-Poly(3-hydroxybutyrate- co -3-hydroxyhexanoate) Biodegradable Composites by Fused Deposition Modeling

Fabrication of new biobased composites with remarkable properties offers an attractive pathway for producing environmentally friendly materials. Here, a reinforcement for poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) with functionalized cellulose nanocrystals (CNCs) is presented and used to successfully 3D-print such composites by fused deposition modeling (FDM). Acetylated CNC content varies from 5 to 20 wt % in order to evaluate the effect of the reinforcing agent on thermal and mechanical properties in the composites. The reinforcing effect of CNC is investigated by dynamic mechanical, thermal, and rheological analysis. Thermogravimetric analysis and infrared spectroscopy allow one to assert the success of chemical functionalization, whereas transmission electron microscopy is used to evaluate the impact of chemical modification on the morphology of the crystals. 3D-printability of biobased composites is proved by developing structures of complex designs with a FDM printer. Finally, the degree of disintegration under composting conditions is studied. Findings from these tests serve as an important step forward toward the development of ecofriendly materials for 3D-printing complex architectures with tailored mechanical properties and functionalities