Tribophysical phenomena on sliding surfaces of polyester composites evaluated by spectroscopic and thermal analysis

Abstract

Polyethylene terephthalate/polytetrafluoroethylene (PET/PTFE) composites were slid under different temperatures or contact pressures and surfaces are scanned with Raman spectroscopy to examine orientation and crystallisation effects induced by frictional stresses and flash temperatures. Characteristic absorption bands at 996 cm−1 and 857 cm−1 or 2,908 cm−1 and 2,960 cm−1 are used for quantification of amorphous, crystalline and rigid-amorphous phases after sliding. With almost an identical amount of total trans conformation either obtained after sliding at high temperatures or normal loads, the orientation of the molecular backbone is mainly concentrated in the formation of a crystalline phase during sliding at high temperatures. When sliding under high normal loads, orientation is concentrated in the rigid-amorphous phase with a stress-induced transition from rigid-amorphous phase into crystalline phase above 25 MPa, yielding a reduced slope in a wear rate versus normal load plot. Visual and thermal analysis of the wear debris shows that degradation under low normal loads is attributed to wear of the amorphous phase with long resident times of debris in the sliding interface. The formation of a load-carrying transfer film is attributed to a post-polymerisation reaction of the wear debris at low contact pressures.