Highly flexible biodegradable cellulose nanofiber/graphene heat-spreader films with improved mechanical properties and enhanced thermal conductivity

Thermal management materials with high thermal conductivity and good flexibility are needed for the next generation of flexible electronics. Herein, a flexible graphene/cellulose nanofiber (CNFG) composite film with high thermal conductivity was fabricated via simple vacuum-assisted filtration. The highly ordered hierarchical stacked layer structure of the graphene nanosheets endows the CNFG composite films with excellent heat-spreader performance and good flexibility. The in-plane thermal conductivity of the CNFG composite film loaded with 50 wt% graphene reached 164.7 W m −1 K −1 , and the through-plane thermal conductivity reached 5.0 W m −1 K −1 . More importantly, the thermal conductivities of the CNFG composite films in both the axial and radial directions barely changed after 1000 bending cycles. In addition to the good flexibility, the CNFG composite films exhibited superior mechanical properties compared to common graphene papers and neat cellulose nanofibers. The tensile strength of the CNFG composite film containing 50 wt% graphene was 72.3 ± 5.4 MPa. All these qualities make the CNFG composite films ideal heat spreaders for flexible electronic devices. A highly flexible cellulose nanofiber/graphene composite film with metal-like thermal conductivity and outstanding strength was fabricated via simple vacuum-assisted filtration.