## 2 Materials and Methods
### Impact of Molding Pressure on the Tribological Behavior of PEEK
In addition, the presence of loose fibers on the material's surface can intensify friction and potentially lead to localized heat concentration and wear [30]. Figure 9D-F illustrates how varying proportions of PPTA influence the mechanical and tribological behavior of PEEK under conditions of oil lubrication. Figure 9 indicates that integrating an optimal amount of PPTA into PEEK significantly enhances its wear resistance properties. Specifically, increasing the PPTA proportion from 2 wt% to 6 wt% leads to a significant reduction in the average COE for the PPTA/PEEK composites. Additionally, there is a significant decrease in the severity of wear, evidencing an improvement in wear resistance. The wear depth of the 94 wt% PEEK/6 wt% PPTA composite was reduced by 44% compared to that of the PEEK-only samples. This enhancement can be attributed to the low friction experienced under oil-lubricated conditions and the strong tensile properties of PPTA [31], which resists shear damage effectively. As the PPTA proportion increases, the interaction surface between the fiber and bearing expands, offering enhanced load support. This minimizes the direct contact between PEEK and the steel shaft, decreasing the likelihood of adhesive wear. However, with the increase in PPTA proportion from 6 wt% to 10 wt%, a gradual rise in the coefficient of friction (COF) and an intensification of wear tracks are observed (Figure 9F), indicating a decline in wear resistance. This trend reflects the behavior observed under dry friction conditions, where excessive PPTA levels lead to fiber agglomeration, undermining overall anti-wear characteristics of the composite. Figure 8: Density (**A**) and Shore D hardness (**B**) of PPTA/PEEK composite. Impact of Incorporating PTFE on the Tribological Behavior of PEEK under Varying Lubrication Conditions  
Figure 10A,B demonstrates how varying proportions of PTFE influence the density and hardness of PTFE/PEEK composites. Figure 10 demonstrates a progressive rise in the density of the composites with an increase in PTFE proportion, alongside a concurrent softening of the material. This phenomenon is explained by the higher density of PTFE compared to PEEK, without a corresponding increase in porosity in the material prepared utilizing standard procedures. Therefore, the incorporation of PTFE into PEEK results in denser composites. Moreover, due to the soft nature of PTFE, the hardness of the matrix decreases with an increase in the proportion of PTFE. Figure 9: The COF (**A**), average COF (**B**), and wear depth (**C**) of PPTA/PEEK composites under dry friction. And the COF (**D**), average COF (**E**), and wear depth (**F**) of PPTA/PEEK composites under oil lubrication. Figure 11A-C demonstrates how varying proportions of PTFE impact the tribological performance of PEEK under dry friction conditions. Figure 11 indicates that incorporating a suitable amount of PTFE into PEEK resin significantly lowers the COF of the composite material and enhances its wear resistance. With an increase in the PTFE content from 5 wt% to 25 wt% in the composites, the initial COF of the PTFE/PEEK composites stabilizes, the average COF decreases gradually, and there is a significant reduction in the wear depth. This is attributed to PTFE's exceptionally low COF, making the composite matrix more pliable with added PTFE, which mitigates localized fractures due to the brittleness of PEEK. Therefore, this stabilization allows the frictional force to become more consistent. When subjected to pressure and shearing forces, the softer PTFE material spreads out during friction, forming a sleek lubricating film on the material's surface. By enlarging the contact area between PTFE and the metal friction counterpart, this mechanism diminishes the COF. Nonetheless, composites containing 30 wt% PTFE display a lower COF compared to those with 25 wt% PTFE, albeit with an increase in wear depth. This phenomenon occurs because PTFE's surface energy is extremely low, limiting its bonding strength with PEEK.