Highly thermally conductive, electrically insulated and flexible cellulose nanofiber-based composite films achieved via stereocomplex crystallites cross-linked graphene nanoplatelets

Synchronously achieving high thermal conductivity, electrical insulation and excellent mechanical properties in one flexible thermal management material is still a great challenge. In this work, a stereocomplex (SC) crystallites cross-linking method was developed to prepare the graphene nanoplatelets (GNPs) filled cellulose nanofibers (CNFs) composite films. The SC crystallites formed between adjacent GNPs exhibit the physical crosslinking effect, which not only prevents the transmission of electron while maintaining the heat diffusion ability in plane but also intensifies the interaction between GNPs to form the integrated GNP network in the whole composite films, endowing the composite films with excellent strength and toughness. As a consequence, the composite films with nacre-like structure exhibit high in-plane thermal conductivity (9.36 W m −1 K −1 ) and high electrical insulation (3.1 × 10 9 Ω m) with extremely high stability during the repeated bending and heating/cooling measurements. Furthermore, the composite film containing 5 wt% filler exhibits an excellent tensile strength of 111.8 ± 6.1 MPa and high toughness of 24.5 ± 2.0 MJ m −3 , which are 51.1% and 75.0% higher than those of the pure CNFs film, respectively. This work provides a valuable strategy for the fabrication of the CNFs-based composite films with promising properties that have great potential as the next-generation thermal management materials. • The graphene nanoplatelets filled cellulose nanofibers composite films were prepared. • The stereocomplex crystallites between adjacent graphene nanoplatelets were formed. • The films have excellent thermal conductivity, electrical insulation and toughness.