Polymer-based materials show to be of increasing interest in replacing metal based

materials in tribological applications due to their low weight, cost and easy manufacturability.

To further reduce the environmental impact of these bearing materials recyclability is becoming

more crucial, stimulating the need for high performing thermoplastic materials. In this study,

polyphenylene sulfide (PPS) composites were prepared in an effort to enhance the polymers’

tribological properties. Short carbon fibres (SCFs), graphene oxide (GO) and nano diamonds (NDs)

as well as polytetrafluoroethylene (PTFE) were used as micro and nano reinforcements. The addition

of SCFs especially decreased the linear coefficient of thermal expansions while enhancing the

micro hardness and wettability of the polymer. Under water lubricated conditions, a decrease

in friction up to 56% and a reduction of wear rate in the order of 103  was observed by the addition

of SCF. The reduction in friction and wear was further enhanced by the addition of NDs, providing

a synergistic effect of the reinforcements in micro and nano scale. By testing the individual

reinforcements under dry conditions, PTFE and SCFs were especially effective in reducing friction

while the release and consequent abrasion of NDs and SCFs increased the wear under a higher

contact pressure.

In this work, the effect of hygrothermal aging on friction and wear of water lubricated, Ultra High Molecular Weight Polyethylene (UHMWPE) hybrid composites were evaluated. Graphene Oxide (GO), Nano Diamonds (ND) and Short Carbon Fibers (SCF) were used as reinforcements as they previously exhibited promising improvements in the tribological behavior of UHMWPE in water-lubricated sliding contacts. Hygrothermal aging and pin-on-disc tribological experiments were performed to evaluate the response of the UHMWPE composites. It was observed that the friction and wear of the composites were not significantly affected by the aging conditions, which was attributed to the structural integrity of the newly developed UHMWPE based hybrid composites.

The present study investigates the influence of hygrothermal ageing on the tribological behaviour of polytetrafluoroethylene (PTFE) polymer composites. Three PTFE composites along with unfilled PTFE were tested in sliding contact against Inconel 625 (a Ni-based alloy) plates in both dry and water-lubricated conditions, utilising a unidirectional pin-on-disc tribometer. The tribo-tests were performed at a constant sliding speed of 0.13 m/s with a normal load of 84N providing an apparent contact pressure of 5 MPa. Hygrothermal conditioning was carried out at two different temperatures, and the water absorption evolution and kinetic parameters were estimated. Various characterisation methods were used to identify the wear mechanisms and influence of hygrothermal ageing on the degradation of the filler/matrix. The different tribological behaviour for different PTFE composites was observed within the ageing timeframe. The wear resistance of the fibre-filled samples was reduced compared to the non-aged ones over the ageing timeframe. However, the friction and wear resistance of the bronze-filled PTFE were enhanced by hygrothermal ageing.

Ultrahigh molecular weight polyethylene (UHMWPE) is a known to be the material of choice for bearing components in joint arthroplasty. However, oxidation wear of UHMWPE components is considered to be a major drawback limiting the lifespan of implants. Vitamin E was considered as a promising antioxidant to prevent long-term oxidation and reduce the wear degradation of UHMWPE material. Nevertheless, there are limited results on the improvements of vitamin E on the mechanical and thermal properties of UHMWPE. In this study, we investigated the incorporation of 0.5–3 wt.% carbon nanoparticles: Multiwalled Carbon Nanotubes (MWCNTs), Graphene (GO) and Nanodiamonds (ND) on the mechanical and thermal properties of UHMWPE blended vitamin E (UHMWPE-E). Surface analysis of the composite powders showed well-dispersed carbon nanoparticles within the UHMWPE-E matrix. Thermogravimetric (TGA) and Differential Scanning Calorimetry (DSC) were used to study the thermal behavior of the nanocomposites. It was found that the addition of GO, MWCNTs and ND improved the thermal stability of the nanocomposites compared to neat UHMWPE-E. However, the addition of carbon nanoparticles had no significant effect on the crystallization parameters of the composites. In addition, the incorporation of MWCNT and ND improved significantly the fracture toughness of the composites. The addition of 0.7 wt.% ND and 1 wt.% MWCNT increased the fracture toughness from 5.93 MPa m^1/2 for neat UHMWPE-E to 7.38 and 9.19 MPa m^1/2 respectively. The enhanced fracture toughness and thermal stability of the nanocomposites could be due to the successful powder processing technique where an optimized mixing and ball milling parameters were used.