We have evaluated the effectiveness of compatibilizers in blends and composites produced using a solvent manufacturing process. The compatibilizers were two different types of polyethylene (linear low-density and high-density) grafted with maleic anhydride (MAH) and a highly functionalized, epoxy-based compatibilizer with the tradename Joncryl. The selected material combinations were an ultra-high-molecular-weight polyethylene (UHMWPE) with MAH-based materials as compatibilizers and a polyphenylene sulfide plus polytetrafluoroethylene (PPS-PTFE) polymer blend with an epoxy-based compatibilizer. The findings revealed that while the compatibilizers consistently enhanced the properties, such as the impact strength and hardness of PPS-based compositions, their utility is constrained to less complex compositions, such as fibrous-reinforced PPS or PPS-PTFE polymer blends. For fibrous-reinforced PPS-PTFE composites, the improvement in performance does not justify the presence of compatibilizers. In contrast, for UHMWPE compositions, compatibilizers demonstrated negligible or even detrimental effects, particularly in reinforced UHMWPE. Overall, the epoxy-based compatibilizer Joncryl stands out as the only effective option for enhancing mechanical performance. Thermal and chemical characterization indicated that the compatibilizers function as chain extenders and enhance the fiber–matrix interface in PPS-based compositions, while they remain inactive in UHMWPE-based compositions. Ultimately, the incompatibility of the compatibilizers with certain aspects of the manufacturing method and the inconsistent integration with the polymer are the main reasons for their ineffectiveness in UHMWPE compositions.

This study investigates the impact of graphite, hexagonal boron nitride and short carbon fibers, acting as micro- and nano-fillers, on the tribological performance of ultra-high-molecular-weight polyethylene (UHMWPE) hybrid composites. The tribological performance is evaluated under boundary-lubrication conditions with distilled water at contact pressures in the range from 5 and 15 MPa. The fillers were found to work synergistically, with the best performance recorded when the compositions incorporated fillers of all scales. The most effective composite, consisting of short carbon fibers, micro-scale graphite, micro-scale hBN and nano-scale hBN, reduced the coefficient of friction by 75 %, reaching a value of 0.06, and the specific wear rate by two orders of magnitude to 2 × 10−7 mm3/Nm, compared to pure UHMWPE. The fillers' size also played an important role. Composites with nano-boron nitride led to 40 % lower friction compared to micro-scale fillers only. However, all the fillers reduced the amount of abrasive wear, especially the boron nitride, as a consequence of the tribochemical reaction between the boron nitride and water at the interface. Additionally, the formation of a transfer film was observed on the steel discs, with only short carbon fibers and graphite contributing to its formation from among the fillers used.

Recent advances in the tribology of polymer composites in water-lubricated conditions have focused on achieving a synergistic effect by incorporating multiple fillers into the polymer matrix. This approach requires a comprehensive understanding of how each filler interacts with the other components, something that remains unknown for hard fillers. This study investigates the tribological performance and tribological mechanisms of a hard filler, nano-titanium dioxide, in a short-carbon-fibre-reinforced, ultra-high-molecular-weight-polyethylene (UHMWPE) composite when combined with microfillers that include graphite, hexagonal boron nitride and silicon dioxide. The results reveal that, while composites with nano-titanium dioxide and microfillers improve the friction by 30–53 % compared to basic fibre-reinforced UHMWPE, the nano-titanium dioxide reduced the friction only with boron nitride and silicon dioxide. In these cases, the nano-titanium dioxide contributes to transferred material onto the steel surface where it embeds in a relatively softer layer of material composed of other components transferred from the composite and thereby reduces the friction. In contrast, all the composites have lower wear rates than the basic carbon-fibre-reinforced composite. We present how the nano-titanium dioxide interacts synergistically with all the microfillers, with each filler contributing in its own way to improving the load-bearing capacity and hindering the fibre pullout. Surprisingly, the combination with the graphite microfiller did not reduce the friction, but had the lowest wear rate in this study of 5–8 × 10⁻8 mm³ /Nm. The impact of the contact pressure on the fillers’ interactions and the tribological performance is also highlighted in this study.