Direct Ink Writing\n3D Printing Elastomeric Polyurethane\nAided by Cellulose Nanofibrils

3D printing of a flexible polyurethane elastomer is highly\ndemandable\nfor its potential to revolutionize industries ranging from footwear\nto soft robotics thanks to its exceptional design flexibility and\nelasticity performance. Nevertheless, conventional methods like fused\ndeposition modeling (FDM) and vat photopolymerization (VPP) polyurethane\n3D printing typically limit material options to thermoplastic or photocurable\npolyurethanes. In this research, a water-borne polyurethane ink was\nsynthesized for direct ink writing (DIW) 3D printing through the incorporation\nof cellulose nanofibrils (CNFs), enabling direct printing of complex,\nmonolithic elastomeric structures at room temperature that can maintain\nthe designed structure. Additionally, a solvent-induced fast solidification\n(SIFS) method was introduced to facilitate room-temperature curing\nand enhance mechanical properties. The 3D-printed WPU structures demonstrated\nstrong interfacial adhesion, exhibiting high ultimate tensile strength\nof up to 22 MPa and an elongation at break of 951%. The 3D-printed\nWPU structures also demonstrated outstanding resilience and durability,\ncapable of enduring more than 100 cycles of compression and tension\nas well as withstanding vehicle crushing and heavy lifting. This method\nalso shows suitability for 3D printing complex structures such as\na vase and an octopus.