  Combining various carbon nanofillers with different dimensions can lead to a
synergistic effect through the formation of an efficient conductive network.
Hybrid polyurethane (PU) nanocomposites containing multi-walled carbon
nanotubes (MWCNTs) and graphene nanoplatelets (GNPs) were fabricated to study
experimental and theoretical aspects of thermal conductivity (TC) enhancement.
The optimization of hybrid nanofillers combinations was done to synergically
enhance the TC using various types of GNPs, different nanofillers
concentrations and varied ratios. A synergistic thermal conductivity
improvement with MWCNTs and GNPs was confirmed at low nanofillers contents. The
TC of hybrid nanocomposite at 0.25 wt% is approximately equivalent to the TC of
individual nanofillers at 0.75 wt%. An analytical model for the effective
thermal conductivity of single and hybrid nanocomposites was considered with
variables of volume fraction, interfacial thermal resistance, straightness of
the nanofillers and the percolation effect, in which the predictions of the
modified models agree with the experimental results.
