Mechanical and thermal properties of cellulose nanofiber composites with nanodiamond as nanocarbon filler

Cellulose nanofibers are green nanomaterials because of their biodegradability and sustainability, they are also attractive structural materials because of their high mechanical performance. For further expansion of their application and acquisition of their reliability, mechanical reinforcement and functionalization of cellulose nanofiber materials are required. In this work, we focused on the mechanical properties and thermal conductivities of composites of cellulose nanofibers and a nanodiamond (ND). Compared with graphene oxides, which are conventional two-dimensional nanocarbon fillers in aqueous media, natural diamond possesses a much larger modulus. It also has the highest thermal conductivity among all the elemental substances. The ND possesses hydrophilic oxygen functional groups at the surface, following a high dispersion in aqueous media and the rigid diamond structure at the core. In this work, the ND resulted in an increased mechanical reinforcement and enhancement of the thermal conductivity of the cellulose nanofiber, while keeping the high visible light transmittance originating from the latter. In particular, 2,2,6,6-tetramethylpiperidine 1-oxyl-oxidized cellulose nanofibers were reinforced more effectively than quaternary ammonium cellulose nanofibers because of the stronger interaction with the ND and higher dispersibility of the ND. Accordingly, it was proved that the cellulose nanofiber/ND composite was a promising high-strength and high-thermal-conductive material. [GRAPHICS]