3D printing of cellulose nanofiber monoliths for thermal insulation and energy storage applications

The development of porous three-dimensional (3D) monoliths from natural materials for a wide spectrum of thermal insulation, energy storage and tissue engineering applications has recently gained tremendous interest. However, the lack of 3D structural customization and shape fidelity of monoliths limited their effectiveness in meeting a variety of practical uses. Herein, the material extrusion-based 3D printing technology is used to manufacture a variety of 3D customized monoliths with high shape fidelity that are useful for thermal insulation and energy storage applications. By using sustainable wood-derived cellulose nanofiber (CNF) gels as inks, the 3D printability and shape fidelity are systematically optimized by tailoring the concentration-dependent rheological properties as well as the printing parameters. Benefitted from the high fidelity and self-supporting features, the optimized 3D printed CNF monoliths can be further transformed into porous CNF scaffolds with highly-retained 3D shape using a well-established freeze-drying technique without the use of any specific container. The as-prepared CNF scaffold has porous structure, superior mechanical properties, and low thermal conductivity, demonstrating well heat insulation properties. Furthermore, the porous CNF scaffold can be used as a platform for the in-situ polymerization of aniline (ANi). The resultant CNF-PANi scaffold has a conductivity of 0.334 S•cm −1 , and delivers a high capacitance of 107.9 mF·cm −2 (@0.2 mA·cm −2 ) as a binder-free electrode in supercapacitors. This work provides some guidance for 3D printing of customizable monoliths from sustainable materials by tuning the rheological properties and printing parameters for thermal insulation and energy storage applications. • Cellulose nanofiber gel is used as ink for 3D printing of different monoliths. • The rheological performance and 3D printing process are optimized. • Freeze-drying transforms the 3D printed monoliths into porous scaffolds. • The 3D printed porous scaffolds exhibit good thermal insulation performance. • The 3D printed porous scaffolds can be functionalized as conductive electrodes.