Effect of macromolecule orientation on the coeficient of friction of thermoplastic polymers

Abstract

During a previous study, focused on the tribological characteristics of PTFE (polytetrafluoroethylene), the possibility that the orientation of carbonic macromolecules might have influence upon the tribological properties of PTFE was raised. The current study proposes to perform an analysis of samples of different polymers, evaluating and quantifying the effect of this characteristic on the different tribological properties of each of these materials. Preliminary scratch tests, followed by characterization, by means of measurements on a rugosimeter and a durometer, were performed on samples of hot rolled, pure PTFE. These tests confirmed the influence of the orientation of the scratch, with respect to the direction of lamination of the samples, upon their tribological properties, as the COF presented reduced values in the longitudinal direction, while a higher degree of wear was suffered. After the validation of the method, samples of PP, HDPE and UHMWPE were also prepared, tested and analysed for result comparison between different materials. The results showed that all the materials, with the exception of UHMWPE had a reduction on the values of friction when it was measured longitudinally to the manufacturing flow direction (alignment direction of the macromolecules), while no significant change in wear was observed.