Wear-Induced Microstructural and Chemical Changes in Poly[tetrafluoroethylene-<i>co</i>-(perfluoroalkyl vinyl ether)] (PFA)

Abstract

Friction-induced shear stress and wear of poly[tetrafluoroethylene-co-(perfluoroalkyl vinyl ether)], also known as perfluoroalkoxy polymer (PFA), causes microstructural and chemical changes. These changes are essential to understand PFA as a tribological material. Tribological (friction and wear) experimentation coupled with differential scanning calorimetry, X-ray diffraction, and infrared spectroscopy was used to characterize the microstructure and chemical differences in PFA wear debris versus bulk. PFA wear debris transitioned from triclinic to hexagonal crystalline structure at lower temperatures and had increased crystallinity versus bulk PFA. Shear-driven molecular alignment was the likely cause of these microstructural changes. Reduced molecular weight of PFA wear debris was confirmed by the presence of free carboxylic acids. Reduced molecular weight is likely due to shear-driven chain scission of the PFA backbone within the amorphous region of the microstructure. Reduced molecular weight and increased crystallinity are observed in wear of PTFE and support the tribochemically driven mechanism for ultralow wear fluoropolymer–alumina composites.