Bio-based ester- and ester-imine resins for digital light processing 3D printing: The role of the chemical structure on reprocessability and susceptibility to biodegradation under simulated industrial composting conditions

Four biobased ester and ester-imine photocurable resins were formulated and evaluated for printability by digital light processing 3D printing. The resin formulations consisted of methacrylated eugenol alone or in combination with methacrylated poly(hydroxybutyrate)-oligomers and/or methacrylated vanillin-derived Schiff-base monomers. It was not possible to print methacrylated eugenol alone into coherent thermosets, likely due to the lower reactivity of the allyl-double bond. However, in combination with the other building blocks methacrylated eugenol improved the printability, although some over-curing phenomena were registered especially for the resins composed of methacrylated eugenol and methacrylated poly(hydroxybutyrate)-derived oligomers. The three formulations that were successfully printed to coherent thermosets were further evaluated for their solvent resistance, thermal and mechanical properties, reprocessability and biodegradability under simulated industrial composting conditions. The reprocessing experiments documented the synergic effect of ester and imine dynamic covalent bonds in favoring the preservation of the elastic modulus of the thermosets; while an evidently higher deterioration of the mechanical properties was registered for the ester-thermosets. The biodegradation studies highlighted a clear correlation between the biodegradation rate and the chemical structure of the thermosets, with the aliphatic components and ester and imine bonds increasing the thermosets’ susceptibility to the biodegradation under simulated industrial composting conditions.