Viscosity characterization and flow simulation and visualization of polytetrafluoroethylene paste extrusion using a green and biofriendly lubricant

Abstract

Polytetrafluoroethylene (PTFE) and expanded PTFE (ePTFE) are ideal for various applications. Because PTFE does not flow, even when heated above its melting point, PTFE components are fabricated using a process called paste extrusion. This process entails blending PTFE powder particles with a lubricant to form PTFE paste, which is subsequently preformed, extruded, expanded (in the case of ePTFE), and sintered. In this study, ethanol was proposed as an alternative green lubricant for PTFE processing. Not only is ethanol benign and biofriendly, it provides excellent wettability and processing benefits. Using ethanol as a lubricant, the shear viscosity of PTFE paste and its flow behavior during paste extrusion were investigated. Frequency sweeps using a parallel‐plate rheometer were performed on PTFE paste samples and various grits of sandpaper were used to reduce wall slip of PTFE paste. A viscosity model was generated and a multiphysics software was used to simulate PTFE paste extrusion. The simulated extrusion pressure was compared to experimental data of actual paste extrusion. Flow visualization experiments using colored PTFE layers were conducted to reveal the flow profile of the PTFE paste. The morphology of the expanded ePTFE tubes was examined using scanning electron microscopy and the effect of expansion ratio on ePTFE morphology was quantified.

A double‐expanded polytetrafluoroethylene fabrication method for increased mechanical compliance in tubular vascular graft applications

“…That is, fibrillation happened during the first expansion, whereas the second expansion step was to create Note: A standard sample is prepared using the default fabrication condition of the single-expanded ePTFE grafts as reported in previous experiments. 23 the wavy structure. The fibers would not be able to be expanded to a length longer than the sintering length without plastic deformation.…”

“…To characterize the mechanical response of the fabricated D‐ePTFE grafts, uniaxial tensile tests were conducted to verify the stress–strain response. Each sample was compared to a standard, single‐expanded ePTFE graft prepared using a fabrication method reported previously 23 . The stress–strain response of D‐ePTFE revealed a distinct non‐linear behavior consisting of a low‐stress/high‐strain linear region and a steep, upward linear region, as visually depicted in Figure 6.…”

“…Each sample was compared to a standard, single-expanded ePTFE graft prepared using a fabrication method reported previously. 23 The stress-strain response of D-ePTFE revealed a distinct non-linear behavior consisting of a low-stress/high-strain linear region and a steep, upward linear region, as visually depicted in Figure 6. The initial low-stress/ high-strain region (toe region) was a consequence of the process of straightening the fibers from their wavy configuration.…”

“… Note : A standard sample is prepared using the default fabrication condition of the single‐expanded ePTFE grafts as reported in previous experiments 23 …”

“…The standard sample underwent a PTFE expansion procedure in accordance with established protocols adapted from a previous study. 23 The material was subjected to a temperature of 200 C for at least 5 minutes to ensure its equilibration with the environmental chamber. The material was expanded to a 400% expansion ratio at a rate of 500 mm/min.…”