Visible light 3D printing with epoxidized vegetable oils

Stereolithography is a 3D printing technique in which a liquid monomer is photopolymerized to produce a solid object. The most widely used materials usually belong to the family of acrylate monomers, and photopolymerization occurs through a radical pathway. Photoinitiators can absorb UV or (less often) visible light, producing radicals for direct decomposition or hydrogen abstraction. Due to the toxicity of acrylates, vegetable oil-derived monomers were used in this study. In fact, vegetable oils contain unsaturations, and thus, they can be exploited as monomers. In particular, linseed oil, tung oil or edible oils (soybean, sunflower or corn) could be good candidates as raw materials. Unfortunately, the photoinduced radical polymerization of these oils either does not occur or is too slow for 3D printing applications. For this reason, the oils were modified as epoxides. Epoxides are monomers that are more reactive than natural oils, and they can be polymerized via a cationic mechanism. The aim of this work was to exploit visible light generated by a common digital projector (like those used in classrooms) as a light source. Since the tested photoacid generators working under visible light are ineffective for the polymerization of epoxidized oils, a multi-component photo-initiating mixture was used.