In an interesting research, overlooked by most industry media, researchers from Kansas State University, SUNY Buffalo and Purdue University demonstrated the first three-dimensional printed graphene oxide (GO) complex structures by stereolithography (SLA).
Graphene is seen as a very interesting area of exploration in several 3D printing technologies, including thermoplastic filament extrusion (FDM/FFF) and plastic powder bed laser sintering (SLS). Now it seems this material could prove useful in photopolymerization based technologies as well by improving the quality of the resin materials.
Since properties of polymer-based nanocomposites rely on distribution, concentration, geometry and properties of nanofillers in the polymer matrix, increasing the concentration of carbon-based nanomaterials, such as graphene or CNTs, in the polymer matrix often results in stronger but more brittle material.
The resulting composite material presented a good combination of increased strength and ductility. Adding only 0.2% of graphene oxide to EnvisionTEC’s Pic100 castable resin material, the tensile strength of the composite was increased by 62.2% and elongation increased by 12.8%. To achieve the ideal dispersion of the GO particles into the polymer matrix, the scientists used the solution intercalation method, where the graphene is dispersed in solvent before addition of the polymer resin. The 3D printing process was carried out by bottom-up Mask Projection Based Stereolithography (MPSL), which is more commonly known as DLP stereolithography in the commercial sphere.
This bottom-down approach provided several advantages associated with the nanocomposite 3D printing process, enabling a much smaller layer thickness which can consequently compensate the reduced curing depth due to the increased diffraction index of the nanoparticles. As the vat depth is independent of the part height, a shallow vat can be used to reduce the required volume of the liquid resin as well as the nanoparticles, allowing for testing of multiple nanomaterial concentration without the need of contamination and material waste. Furthermore recoating was achieved by constraining the resin between the previously cured layer and resin vat, hence no additional sweeping was needed to flatten the surface, which in turn dramatically improved the fabrication speed.
Transmission electron microscope (TEM) results showed that the graphene oxides were randomly aligned in the cross section of the polymer. Investigating the strengthening mechanism of the 3D printed structure in terms of tensile strength and elastic modulus (stress vs strain), the researchers found that an increase in ductility of the 3D printed nanocomposites is related to increase in crystallinity of GO reinforced polymer. Although commercial applications of the graphene composite are yet unclear, due to the costs of both the graphene and the streolithography systems.