Impact of sintering temperature and compression load on the crystallinity and structural ordering of polytetrafluoroethylene

Abstract

Polytetrafluoroethylene (PTFE) parts are normally consolidated under multi-tonne presses and sintered, but the separate roles of load and temperature on crystal development remain under-explored. Here, we molded PTFE powder under compressive loads (1.2, 1.8 and 2.4 kN) followed by sintering (320, 330 and 340 °C). The starting powder and molded films were characterised using X-Ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), Small-Angle X-Ray Scattering (SAXS), Dynamic Image Analysis (DIA) and Scanning Electron Microscopy (SEM). Raising the sintering temperature from 320 °C to 340 °C (at 1.8 kN) increased XRD-derived crystallinity from 63.5% to 71.8% and sharpened five hexagonal-phase reflections ((100)–(210)), while the a and c lattice parameters contracted by ∼0.3% and ∼1.1%, respectively, indicating tighter chain packing. SAXS revealed a concomitant 7% reduction in long-period spacing, and FTIR showed intensified CF₂ and C–C bands, signifying enhanced chain alignment. In contrast, elevating the load from 1.2 kN to 2.4 kN at 320 °C trimmed bulk porosity from 33% to 25% without a statistically significant crystallinity change (63.0% → 64.8%). SEM cross-sections established that additional load mainly closes residual inter-particle voids rather than promoting crystal growth. Taken together, the data demonstrates that temperature is the primary driver of phase-IV hexagonal ordering, whereas load chiefly controls densification and has only a minor effect on ordering. This work, therefore, establishes a practical, low-pressure processing window 330 to 340 °C under ∼1.8 kN, which yields highly-ordered (≈72% crystalline), low-porosity (≈25%) PTFE films, providing a cost-effective route for manufacturing PTFE films and components.