New developments in 3D printing of composites : photocurable resins for UV-assisted processes

The aim of this work is the development of new polymer-based composites specially optimized for use in LDM UV-3D printing technology. Initially UV-curable cationic systems were formulated and their photopolymerization process was investigated. Due to the low conversion efficiency of these systems, the adoption of a dual-cure technique has been necessary. Maleic anhydride was added to the cationic epoxy formulation; gel percentage and FTIR spectroscopy analyses confirmed the effective improvement of conversion. Silica was then added to the dual-cure material to increase its viscosity. Through rheological studies, optimal extrusion condition and printability windows for the developed dispersions were obtained. The formulation with 11% wt of silica was adopted as matrix material for SFR-composites development. Glass, carbon, and bamboo SFR-composite inks were prepared. Drop on glass and photocalorimetric analyses demonstrated that a rapid curing reaction could be achieved only in case of transparent glass fibers. Carbon and bamboo fibers slowed the kinetics of the photopolymerization reaction, due to their chemical nature that shields UV rays. In order to UV-3D print the developed inks, a LDM low cost machine was equipped with a UV-laser. The optimal printing parameters were founded by performing several printing trials, using as specially designed 3D model (SCM). The final part of this work was dedicated to the investigation of the mechanical response of UV-3D printed samples. The resulting mechanical properties demonstrated that the LDM technology is still far from replacing the traditional composite manufacturing techniques. However, tensile tests performed on triangular unit cell composites demonstrated the possibility offered by the UV-3D printing to control the mechanical response by varying the infill percentage and structure design. The main advantages of LDM remain its lower cost, its ability to fabricate complex geometries and the possibility to print a wide range of materials. If the mechanical properties of the printed components can be improved, this technology could become more than an alternative to traditional manufacturing processes.