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.

In recent years, three-dimensional (3D) printing of environmentally friendly structures with a high concentration of nanocellulose (NC) has gained much attention because of health and environmental issues. However, there remain challenges due to poor adhesion between printed layers, resulting in low mechanical properties and shape fidelity. This research demonstrates an economical approach to printing environmentally friendly 3D structures by directly extruding high-concentration NC (∼25.5 wt %) paste to deal with the challenges. Different low concentrations (2.5, 5, and 10 wt %) of polyvinyl alcohol (PVA) were mixed with NC as a crosslinker to facilitate the adhesion between the printed layers. A twin-screw extrusion machine was used to eject the high-concentration NC paste for 3D printing. After the printing process, the final structures were dried at a controlled relative humidity of 45% and a temperature of 25 °C. An optimum 5 wt % PVA-crosslinked high-concentration NC paste showed the highest flexural strength of 121 ± 2 MPa (233% improvement) and a flexural modulus of 15.0 ± 0.1 GPa (263% improvement), which are much higher than the previously reported results until now. It suggests that the extremely low content of PVA effectively improved the bilayer adhesion, resulting in high shape fidelity and mechanical strength of the 3D printed structures for environmentally friendly structural applications.

No abstract

Additive manufacturing technology (AMT) has transformed polymer composites’ manufacturing process with its exceptional ability to construct complex products with unique materials, functions, and structures. Besides limiting studies of manufacturing arbitrarily shaped composites using AMT, printed structures with a high concentration of nanocellulose face adhesion issues upon drying, resulting in shape fidelity issues and low mechanical strength. This research demonstrates an economical approach to printing a high-concentration (25.46 wt%) nanocellulose (NC) layer-wise pattern to fabricate structures. Two different composites are fabricated: (1) 3D-printed pure and high-concentration (10, 15, and 20 wt%) polyvinyl-alcohol (PVA)-blended NC structures followed by freeze-drying and impregnation of Epofix resin by varying hardener contents; (2) 3D-printed PVA-blended NC green composites dried at cleanroom conditions (Relative humidity 45%; Temperature 25 °C). Different contents (10, 15, and 20 wt%) of PVA as a crosslinker were blended with NC to assist the printed layers’ adhesions. An optimum PVA content of 15 wt% and an Epofix resin with 4 wt% hardener cases showed the highest bending strength of 55.41 ± 3.63 MPa and elastic modulus of 4.25 ± 0.37 GPa. In contrast, the 15 wt% PVA-blended NC cleanroom-dried green composites without resin infusion showed bending strength and elastic modulus of 94.78 ± 3.18 MPa and 9.00 ± 0.27 GPa, reflecting high interface adhesions as confirmed by scanning electron microscope. This study demonstrated that AMT-based nanocellulose composites could be scaled up for commercial use.

No abstract