The development of affordable and sustainable ink materials from renewable resources is essential to satisfy the growing demand for 3D printing materials and at the same time reduce their environmental impact. In this study, methacrylated soy protein isolate (MSPI) was mixed with cellulose nanofibrils (CNFs) and acrylated epoxidized soybean oil (AESO) to obtain fully bio-based ultraviolet (UV)/thermal dual-curable resins for UV-direct ink writing (UV-DIW) 3D printing. NMR results confirmed the successful methacrylation of SPI. Successful printing of tall objects using MSPI was achieved after adding 10 wt% CNFs to the ink or by in situ UV curing, with the latter being more feasible than the former. The addition of AESO and CNFs had strong effects on the printing fluidity and formability of resins. Different post-curing processes were confirmed by FTIR results. Dual post-cuing and thermal post-curing were found to lead to similarly higher improvements in the mechanical properties and water resistance of 3D printed samples than UV curing. The composition of resin formulations also significantly affected the properties of their 3D printed and thermally post-cured samples, with the formulation MSPI-CNF-20AESO showing the best overall performance in terms of printing accuracy, mechanical properties (dry and wet), and water resistance. The tensile strength, strain, and modulus of MSPI-CNF-20AESO at dry state were 39.8±2.93 MPa, 11.5±2.26%, and 488.06±5.03 MPa, respectively; while those at wet state were 1.26±0.12MPa, 25.04±2.29%, and 4.30±0.20 MPa, respectively. Three prototypes including a square grid, a flower pot, and a 3D benchy that were 3D printed from MSPI-CNF-20AESO resin and were thermally post-cured displayed well-defined shapes, well-preserved details and smooth surface, indicating high printing quality and widely accessible range of geometrical complexity. These results demonstrate the great potential of using the developed fully bio-based dual-curable resins as an alternative to fossil-based resins for UV-DIW 3D printing toward prototyping and modeling applications for both professional and hobby users, and also other applications.

3D printing of dual-curable cellulose nanofibrils-reinforced soy protein resins

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