3.4. Thermal conductivity
The uncertainty for the thermal diffusivity, specific heat, and thermal
conductivity of all the samples is shown in Table 4. It is calculated
according to the maximum standard deviation when the testing
temperature changes from 30 °C to 150 °C, while the minimum standard
deviation is 0.000.
The thermal conductivity of modified and unmodified graphite filled
NR composites is shown in Fig. 3. It is observed that the thermal conductivity
of graphite filled rubber composites is three orders of magnitude
below that of the isolated graphite. With modified graphite filling, the
thermal conductivity increases. The maximum value of thermal conductivity
reaches 0.569 W·m−1
·K−1
. The thermal conductivity of all the
samples except 4# is not less than 0.54 W·m−1
·K−1
. Adopting
polyacrylate coating graphite makes the thermal conductivity increase
by 8.61% to 19.54%.
The reason for the great difference in thermal conductivity
between the composites and isolated graphite is analyzed as
follows. The transport of heat in isolated graphite is dominated by
phonons. When graphite is incorporated in a rubber matrix beyond
the back-scattering effect, the further scattering effects, e.g., interfacial
boundary and defect scattering lead to a drastic reduction of
thermal transport properties. In addition, the gap between graphite
particles in the rubber matrix also hinders the transport of phonons
through the graphite network.