## 4 Binary Filler-Based Nanocomposites
Figure 15: SEM images of **(a)** the MWCNTs/urushiol formaldehyde polymer (UFP) and **(b)** the GO/MWCNTs/UFP films **(c)** after its deposition on a silicon substrate (Reprinted from [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Fabrication of Graphene Oxide/Multi-Walled Carbon Nanotube/Urushiol Formaldehyde Polymer Composite Coatings and Evaluation of Their PhysiCo-Mechanical Properties and Corrosion Resistance. _Prog. Org. Coatings_**2019**, 127, 131–139 [47], with permission (2020) from Elsevier). They investigated two ways to produce binary fillers. In the first, two types of carbon nanotubes (either MWCNTs or SWCNTs) were mixed with thermally reduced graphite oxide (TRGO). In the second, an ultrasound-treated suspension of graphite oxide (GO) and SWCNT was freeze-dried and then heated to 900 \({}^{\circ}\)C. The two binary fillers were mixed and sonicated with MAO and toluene. The resulting suspensions were then added in propylene bulk, followed by the addition of the metallocene catalyst to mediate the polymerization (60 \({}^{\circ}\)C). The TEM images confirmed the presence of both graphene nanoplates (TRGO) and small island-shaped carbon nanotubes (MWCNT or SWCNT). [PERSON] et al., also used differential scanning calorimetry (DSC) to examine the thermophysical properties of composites as a function of content nanof fillers. The incorporation of high content carbon nanoparticles led to a widening of the melting peak due to the nucleating step which probably prevented the development of larger crystalline areas and also led to a slight decrease in the enthalpy of melting, which corresponds to a decrease in crystallinity. The TGA data showed that the addition of carbon fillers improved the thermal stability of all the composite materials as well as the thermo-oxidative resistance. This was seen in the comparison of TRGO and nanocarbon particles (MWCNT or SWCNT) compared to the composite PP; specifically, for a TRGO+MWCNT filler content of 4.2 wt%, the oxidation rate was twice as low than for neat PP. Thus, the use of carbon nanotubes enables a better dispersion of graphene particles within the polymer matrix and leads to an increase in the oxidative resistance. an investigation of the mechanical properties of different composites showed that the introduction of anisotropic carbon nanofillers increased the elastic modulus (E) but markedly decreased the elongation of breaks. [PERSON] et al., attributed this decrease to the formation of large pores and aggregates. The effects of content and type of filler on the relationship between conductivity and permittivity as well as the percolation threshold were also investigated. The percolation threshold decreased with the use of binary fillers (Table 2). The conductivity of TRGO/MWCNT or SWCNT-based composite materials was similar to monofiller-based materials at lower concentrations of TRGO nanoparticles. They concluded that SWCNT fillers conduct better than TRGO/MWCNT binary fillers whose conductivities were identical, and that the use of TRGO nanoparticles considerably increased permittivity, which was much higher for composite PP/TRGO/SWCNT than for PP/SWCNT. \begin{table}
\begin{tabular}{c c c c} \hline  & **Hardness** & **Adhesion** & **P.E. (\%)** \\ \hline Neat UFP & 3H & 3 & 91.79 \\ MGO/UFP & 6H & 2 & 99.45 \\ MWCNTs/UFP & 1H & 1 & 99.69 \\ GO/MWCNTs/UFP & 6H & 1 & 99.70 \\ \hline \end{tabular}
\end{table} 
Table 1: Physical-mechanical properties. \begin{table}
\begin{tabular}{c c c c} \hline  & **Elastic Modulus (E, MPa)** & **Break Elongation (\(\varepsilon\)b, \%)** & **Percolation Threshold (\%)** \\ \hline Pure PP & 1220 & 500 & – \\ PP/TRGO & 1555 & 7.8 & 3 \\ PP/TRGO/MWCNTs & 1710 & 5.7 & 2 \\ PP/TRGO/SWCNTs & 1390 & 11.2 & – \\ \hline \end{tabular}
\end{table} 
Table 2: Comparison of mechanical properties.