## 3 Composite Matrices and Applications
### Polymers
The wear rate also significantly decreased with CNT addition, mainly attributed to improved heat transfer, reduced contact area, and lubricating effects of CNTs on the friction surfaces [85]. Similarly, the mechanical properties also demonstrated a relative improvement. Tensile strength and modulus increased significantly with the addition of CNTs, particularly at 0.1 wt%, showing a 26% increase in tensile strength compared to pure PPS. The role of CNTs in load transfer, even at low concentrations, contributed to this enhancement due to their uniform dispersion and high compatibility with the matrix. Bending performance improved with the addition of CNTs up to 0.1 wt%, resulting in a 29% increase in flexural strength and a 37% increase in flexural modulus. However, impact strength showed slight fluctuations with varying CNT content, possibly influenced by changes in crystallinity and the reinforcing effect of CNTs [77]. Figure 8: Schematic diagram of the preparation of MIPs and CNT-MIPs/PPS [85]. Another major drawback of polymers is their high fire hazard susceptibility. As a result, their applications are limited in fields that require high fire safety standards. Research on 3D printing and flame-retardant polymers has grown significantly over the past two decades. Compared to traditional methods, like thermoforming and Fused Deposition Modelling (FDM), Selective Laser Sintering (SLS) is often preferred for creating flame-retardant polymers due to its ability to achieve precise dimensions [86; 87]. In SLS, a laser is employed to manufacture objects from powdered materials by fusing particles on the surface of the object layer by layer [87]. A study led by [PERSON] et al. focused on enhancing the fire safety and mechanical properties of polymer nanocomposites made from polyamide 12 (PA12) by reinforcing them with modified carbon nanotubes (CNTs) and fullerene-like tungsten disulfide (WS2) nanofillers through SLS, as shown in Figure 2:0  
Figure 2:1 (**a**) Schematic diagram of the fabrication of chemically modified multi-wall carbon nanotubes (H-CNTs); (**b**) Schematic diagram of the fabrication of PEGylated inorganic fullerene tungsten sulfide (P-IF-WS2) nanofillers; (**c**) laser sintered PA12/H-CNT/P-IF-WS2 nanocomposites [88]. Figure 2:2 Friction coefficient (**a**) and wear rate (**b**) of CNTs/PPS composites as a function of CNT content [85]. The SEM and TEM analyses show that the shapes of chemically modified MWCNTs and WS2 nanoparticles revealed rough surfaces and spherical/elliptical morphologies, respectively. Thermogravimetric analysis (TGA) shows that modifications led to earlier thermal degradation due to unstable functional groups but improved interfacial compatibility and bond strength, enhancing fire safety performance in laser-sintered composites [88]. The tensile strength of pure PA12 was 42 MPa, with an elongation at a break of 14.5%. When combined with CNTs (PA12/3C), the strength increased to 46 MPa (a 9.5% increase), with elongation rising to 16.7% (a 2.2% increase) [80]. This improvement is attributed to the formation of a network structure between CNTs and PA12, increasing cohesive energy density. However, as the CNT content approaches 5%, strength decreases (44 MPa for PA12/5C) due to hydrogen bond saturation, leading to filler agglomeration and reduced energy dissipation. The introduction of PEGylated IF-WS2 enhances tensile strength further, with PA12/3C/1W showing a 19.4% improvement. IF-WS2's functional groups inhibit stacking, improve dispersion, create hydrogen bonding networks, and enhance mechanical properties. Moreover, hydrogen bonds prevent polymer chain movement, further improving tensile characteristics [88]. The results show that the addition of H-CNTs and P-IF-WS2 increased the materials' flame resistance, evidenced by a decrease in Time to Ignition (TTI) and the Fire Growth Index (FGI). The heat release rate (HRR) and total heat release (THR) also decreased with nanocomposite addition, indicating improved fire safety.