What environmental factors are related to the porosity of ePTFE membranes?

1. Processing conditions:
Processing conditions, especially temperature and stretching rate, are key factors in determining the porous microstructure of the expanded material. Products stretched at high temperatures and high strain rates have more uniform structures, smaller and denser nodes, and are connected by more fibers.
2. Heat treatment:
Heat treatment has a significant effect on the performance of ePTFE microporous membranes. Studies have shown that when the temperature is higher than the melting point of PTFE, the heat treatment time will affect the pore size, pore size distribution, porosity and surface morphology of the ePTFE microporous membrane, resulting in a decrease in porosity.
3. PTFE resin properties:
Suitable resin crystallinity is crucial for the production of ePTFE. In order to improve the crystallinity of PTFE resins, several technologies have been developed, such as heat treatment (annealing) at high temperatures slightly below the melting point. These methods have been shown to enhance the performance of the resin during the expansion process.
4. Stretch ratio:
The stretch ratio in both directions has a significant effect on porosity and pore size. Unidirectional stretching will elongate the nodes so that the long axis of each node is perpendicular to the stretching direction. In the stretched material oriented in the MD and TD directions, the nodes are at a 45-degree angle to the MD.
5. PTFE powder particle size:
The microporous structure of the ePTFE membrane can be optimized to achieve high oil-water separation performance by controlling the particle size of the PTFE fine powder. Smaller powders lead to reduced pore size, but still maintain high porosity in the stretched membrane.
6. Surface free energy:
The water pressure test provides a relative method to measure the size of the membrane pores. Factors affecting water pressure resistance include pore size, liquid surface tension, surface free energy of the membrane, and the size of the maximum opening.
7. Ambient temperature and humidity:
Ambient temperature and humidity may affect the porosity and air permeability of the ePTFE membrane. For example, in a high temperature and high humidity environment, the air permeability of the ePTFE membrane may increase because high temperature can increase the movement speed of gas molecules, thereby increasing air permeability.