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

The development of affordable and sustainable ink materials from renewable resources is essential to meet the growing demand for 3D printing while reducing its environmental footprint. 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) printing. Successful printing of tall objects using MSPI was achieved after adding 10 parts CNFs to the ink or by in-situ UV curing. The printability of the ink and print quality was further improved after integrating AESO into the MSPI-CNF ink. Both UV and thermal post-curing improved the mechanical properties and water resistance of the printed samples, with the thermal method showing much better results. The ink containing 10 parts CNFs and 20 parts AESO was found to show the best overall performance including printing accuracy, mechanical properties (dry and wet), and water resistance. Three prototypes printed using this formulation displayed welldefined shapes, well-preserved details, and smooth surfaces, indicating high printing quality and a wide accessible range of geometrical complexity. These results demonstrate the great potential of this fully bio-based ink in UV-DIW 3D printing applications for both professionals and hobbyists.