Impact of stretching conditions on microstructure and filtration efficiency of ePTFE membranes

Abstract

Expanded polytetrafluoroethylene (ePTFE) membranes, produced by stretching extruded preform sheet followed by heat treatment, have been widely utilized in various separation and purification processes, establishing itself as a key standard for eco-friendly and sustainable development. While the process may seem straightforward, fabricating high-quality ePTFE membranes with uniform thickness, proper pore distribution, a large effective surface area, and reproducibility remains a significant challenge. In this study, the effects of key parameters such as stretching ratio, temperature, annealing time, and stretching speed on microstructural changes were systematically examined that are difficult to observe in continuous industrial manufacturing. Using specialized stretching equipment with a real-time monitoring, these parameters impact the microstructures, porosity, thickness, and air permeability of ePTFE membranes were explored. Notably, stretching speed significantly influences the quality of ePTFE membranes, achieving an ultrathin and highly uniform membrane at a stretching speed of 50 mm s^-1 under local heating at 320 °C, resulting in excellent air filtration performance. These findings will provide valuable insights for establishing manufacturing processes for high-quality ePTFE membranes and expanding their application, not only in high-efficiency filtration but also across a variety of industries.