A study on sliding wear mechanism of ultrahigh molecular weight polyethylene/polypropylene blends

This paper explores anti-wear properties and wear mechanism for ultrahigh molecular weight polyethylene (UHMWPE) and ultrahigh molecular weight polyethylene/polypropylene (UHMWPE/PP) blends, which were prepared by melt extruding through a single-screw extruder, and were conducted sliding wear tests with MM-200 wear tester by sliding against 45# steel ring of a surface roughness about 0.015 μm. Results show that anti-wear properties of UHMWPE are improved notably by blending with appropriated content of polypropylene (PP). The coefficients of friction and wear rate of UHMWPE/PP blend are much lower than those of pure UHMWPE during sliding. Partly oxidized transfer film of UHMWPE is formed on the surface of the steel counterpart. No transfer film but fine powders can be found on the steel ring surface sliding against the UHMWPE/PP blend. Long duration sliding causes fatigue failure of UHMWPE and many big spalls are produced around the counterpart edge, while the amount of debris from UHMWPE/PP blends does not show apparent increase with sliding time. DSC analysis reveals that the surface temperature of UHMWPE is higher than that of UHMWPE/PP blend during sliding. ‘Shish-kebab’ crystal is formed in the worn surface of UHMWPE/PP blend due to the long time shearing, stretching and annealing effect during sliding. The improvement of wear resistance is probably due to the rod shape debris existing between the contact surface of UHMWPE/PP and the counterpart, which helps to reduce the friction and wear efficiently.