Additive manufacturing techniques are under constant further development since their introduction in the 1980s. Developments are moving in the direction of more complex and functional 3D printed objects. A potential way of fabrication of 3D parts with varied mechanical properties is multi-material additive manufacturing. The objective of the present thesis is to utilize a dual-wavelength vat photopolymerization approach to enable spatial control of the mechanical properties of 3D printed objects. A multicomponent photocurable resin was developed, which consists of both acrylate- and epoxide-based monomers. Those components are cured following two different photoreactions. The employed digital light processing (DLP) printer operates at two different wavelengths, one in the visible light spectrum and the other in the UV light spectrum. Visible light irradiation should initiate radical polymerization of the acrylate. UV light irradiation should lead to the formation of a hybrid network consisting of radically cured acrylates and cationically cured epoxies.
Suitable initiators to trigger either the curing of the acrylates or the curing of the epoxide monomers in the desired wavelength ranges were selected. Their cure kinetics were investigated using FTIR spectroscopy and verified during initial printing trials. Selective illumination with either light source of the printer should shift stiffness between the soft acrylate and the rather stiff epoxide network. Dynamic mechanical analysis showed a matching glass transition temperature (Tg) of 20 °C for specimen produced both with the pure acrylate and the dual-curing system when irradiated with visible light, thus confirming the selective curing of the acrylate under visible light. The Tg of the dual-curing system shifted to 70 °C for specimen printed by consecutive illumination with both lights. This rise in Tg coincides with the observed increase in stiffness of materials printed with the dual-curing formulation, using both lights. The test specimens underwent thermal post-curing at 120 °C for 2 hours to increase epoxide monomer conversion. Conducted tensile tests displayed no effect of the post-curing routine on the pure acrylate but a significant effect on hybrid samples, illuminated with both wavelengths of light. An increase in maximum stress from 0.5 MPa to 5.9 MPa, as well as an increase in elongation at break from around 9.1 % to approx. 23.7 % occurred. More advanced 3D geometries such as a cube, a box, and a hinge were printed to demonstrate proof of principle of multi-material printing and locally tuning mechanical properties of 3D printed parts.