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.