Constructing fully carbon-based fillers with a hierarchical structure to fabricate highly thermally conductive polyimide nanocomposites

A novel kind of fully carbon-based filler (f-MWCNT-g-rGO) is constructed by a reaction between melted urea functionalized multi-walled carbon nanotubes (f-MWCNTs) and graphene oxide (GO) followed by chemical reduction. The corresponding highly thermally conductive polyimide (f-MWCNT-g-rGO/PI) nanocomposites are then fabricated through the combined method of in situ polymerization, electrospinning and hot pressing. An improved thermal conduction model is also proposed and established considering the filler/matrix interfaces, filler dispersion and alignment, etc. The f-MWCNT-g-rGO fillers have a hierarchical "line-plane" structure. The fabricated f-MWCNT-g-rGO/PI nanocomposites possess an outstanding thermal conductivity coefficient (λ), and excellent thermal stabilities and mechanical properties. Specifically, the f-MWCNT-g-rGO/PI nanocomposites reach the maximum λ of 1.60 W m^-1 K^-1 at a relatively low loading of f-MWCNT-g-rGO fillers (10 wt%, the mass ratio of rGO to f-MWCNT is 2:1). In addition, the theoretical λ value calculated by our established thermal conduction model is more in line with the experimental λ values compared with other traditional models. Owing to the high thermal conductivities while preserving good mechanical properties and thermal stabilities at a relatively low loading of f-MWCNT-g-rGO filler, the f-MWCNT-g-rGO/PI nanocomposites are expected to be used as thermal pads in light emitting diode (LED) substrates and liquid crystal displays.