High Content Nanocellulose 3D-Printed and Esterified Structures with Strong Interfacial Adhesion, High Mechanical Properties, and Shape Fidelity

Wood-derived biopolymers such as nanocellulose are an attractive engineering material for 3D printing due to their abundance and environment-friendliness, but their processing into complex structures remains challenging. The most challenging issues in 3D printing high cellulose content structures include printability, interfacial adhesion between layers, mechanical properties, and shape fidelity. Here, a simple and economical approach is presented to manufacture 3D structures by directly extruding high concentration nanocellulose (≈25.94 wt.%) paste cross-linked with different citric acid (CA) contents. The CA, a green cross-linker, is optimized in nanocellulose paste to cross-link between cellulose layers substantially. Furthermore, esterification is achieved by heating the 3D-printed structures at 140 °C for 20 min in a vacuum oven, as confirmed by Fourier transform infrared spectroscopy. The optimum CA content in nanocellulose paste (CNC:CA:CNF = 20:2:1) exhibits the flexural strength of 82.78 ± 2.79 MPa (128% improvement) and Young's modulus of 6.97 ± 0.38 GPa after 3D printing followed by esterification, which is the best achievement in nanocellulose 3D printing. In addition to the high mechanical strength, the shrinkage of the esterified 3D-printed structures is below 9%, which demonstrates their high shape fidelity without any interfacial adhesion issues.