Effect of filler morphology on cryogenic treatment sintered PTFE nanocomposites

Abstract

Introduction. Polytetrafluoroethylene (PTFE) has outstanding chemical resistance and a low friction coefficient but weak mechanical properties and wear resistance, which restrict its wider use in tribological applications. Thus, the present study aims to investigate the coupled influence of nano-filler geometry and cryogenic treatment on the structure–property evolution of PTFE nanocomposites. Materials and methods. The optimized nanocomposite systems (1.0 wt.% nano-mica and 1.5 wt.% nano-alumina), along with neat PTFE, were produced by cold compression moulding and sintering. The specimens were soaked for 8, 12, and 16 h in liquid nitrogen at −185 °C and then evaluated for mechanical, tribological, and structural properties using XRD, FTIR, and SEM. Results and discussion. Compared to untreated PTFE (~27.6 MPa tensile strength), both nano-fillers enhanced the strength and wear resistance. The composites exhibited a strong geometry-dependent response to cryogenic treatment. The tensile strength of mica-filled PTFE was at a maximum at 8 h (~37.9 MPa), while alumina-filled PTFE reached its peak at 16 h (~36.5 MPa). The same trend was observed for hardness and wear resistance. XRD revealed reordering of crystallinity and improved filler–matrix interaction, while SEM showed more stable interfaces in the alumina composites. Extended treatment caused interfacial heterogeneity and defects in mica-filled PTFE, attributed to its flaky morphology. Conclusion. Filler geometry is a major determinant of the effectiveness of cryogenic treatment in PTFE nanocomposites. Globular nano-alumina exhibited superior tensile strength, hardness, and wear resistance compared to flaky nano-mica after long-term cryogenic treatment. This study presents important structure–property relationships for the development of PTFE-based nanocomposites for advanced tribological applications.