Additive manufacturing of high-performance vinyl ester resin via direct ink writing with UV-thermal dual curing

Vinyl ester (VE) resin is widely used as a thermosetting polymer for structural materials because of its high mechanical properties and excellent chemical resistance. Using additive manufacturing to produce high-performance VE structures with dimensional scalability and material efficiency has gained interest from both research and industry, however it is challenging due to the limitations of current techniques. In this work, a modified setup of direct ink writing (DIW) with ultraviolet (UV)-thermal dual curing is made compatible with commercially available VE resins thickened by 4 wt% fumed silica to fabricate three-dimensional structures with outstanding mechanical properties. The in-situ UV curing during DIW partially solidifies the resin to provide the structural shape, and subsequent thermal curing allows for a high degree of crosslinking. The printed and dual cured VE nanocomposites have a Young's modulus of 3.7 GPa and a tensile strength of approximately 80 MPa, which outperforms conventionally molded neat VE cured with methyl ethyl ketone peroxide (MEKP) by about 10% and also indistinguishable from the tensile properties of molded VE nanocomposites with the same composition. The fracture toughness of the printed and dual cured VE nanocomposites is also 16% higher than the molded neat VE with MEKP curing due to the superior interfacial bonding between DIW infill paths and the additional 4 wt% fumed silica for toughening, and similar to the molded VE nanocomposites with the same composition. Along with the outstanding mechanical properties, the scalability and resolution of the DIW technique with dual curing is demonstrated by printing a 100 mm long wrench and a microscale lattice, thus showing the potential of this technique in additive manufacturing of high-performance VE structures.