## 3 Composite Matrices and Applications
### Metals  
Metals are a class of elements characterized by their high electrical and thermal conductivity, malleability, ductility, and typically lustrous appearance. Metals such as aluminum, titanium, and magnesium are used in automotive, aerospace, and marine applications due to their strength-to-weight ratios, improving fuel efficiency and performance. However, sometimes, virgin metal alloys are not able to live up to expectations as technology progresses rapidly and requires high specific strength, elastic modulus, and stiffness in addition to enhanced functional characteristics [89; 90; 91; 92; 93]. As a response, the use of metal matrix composites (MMCs) has been at the forefront of many new applications, and there have been numerous research studies on the improvement of the mechanical properties of MMCs with micro- and nanofillers [94; 95; 96; 97; 98]. Due to their high carrier mobility (80,000 cm\({}^{2}\)V\({}^{-1}\)s\({}^{-1}\)) and a current carrying capacity that reaches \(10^{9}\) A cm\({}^{-2}\) (\(10^{3}\) times more than copper), CNTs have been utilized to synthesize metal nanocomposites for commercial use [99; 100]. CNTs can be combined with metals using methods such as powder metallurgy and ball milling. Powder metallurgy preserves the structural integrity of CNTs by avoiding damage caused by the high energy forces present in ball milling [101; 102; 103; 104; 105; 106]. This technique led \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
** Composites** & **Formulation** & **Output** \\ \hline PA12 & Pure polymer, no fillers & Moderate tensile strength and low flame resistance \\ \hline PA12/3C & PA12 with 3\% CNTs & 9.5\% increase in tensile strength and slight flame resistance improvement \\ \hline PA12/3C/1W & PA12 with 3\% CNTs and 1\% WS2 & 19.4\% improvement in tensile strength and enhanced flame resistance \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Fire safety and mechanical properties of PA12 nanocomposites. (Summary of the study of [PERSON] et al. [88]). \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
** Composites** & **Formulation** & **Output** \\ \hline PVDF composite & PVDF without fillers & Minimal thermal conductivity \\ \hline p-MWCNTs/GE/PVDF & Pristine MWCNTs and graphene & Moderate thermal conductivity Improvement \\ \hline a-MWCNTs/GE/PVDF & Acidified MWCNTs and graphene & Better dispersion and enhanced thermal conductivity \\ \hline s-MWCNTs/GE/PVDF & Silanized MWCNTs and graphene & Highest thermal conductivity improvement (711.1\%) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Thermal conductivity enhancement in PVDF Composites with MWCNTs and graphene. (Summary of the study of [PERSON] et al. [79]). \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
** Composites** & **Formulation** & **Output** \\ \hline CNT-MIPs & CNTs mixed with polymer components for MIPs & Increased crystallinity and improved shape accuracy \\ \hline CNT-MIPs/PPS & CNT-MIPs added to PPS filaments & Enhanced tensile strength and flexural modulus \\ \hline CNT-MIPs/PPS (0.9 wt\% CNTs) & Higher CNT content & Improved friction coefficient and wear resistance \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Study on CNT-MIPs/PPS for 3D printing. (Summary of the study of [PERSON] et al. [85]). to increased tensile strength and corrosion reduction in metals and opened new doors for applications for metal-CNT composites. Nevertheless, it is important to note that at high temperatures, CNTS may deform due to thermal stress. To avoid this, preventive measures can be applied, such as adjusting the heating rate and controlling the process environment [101; 102; 103; 104; 105; 106].