How to detect the porosity and thickness of ePTFE membrane?

Porosity detection method:
1. Bulk density method:
Porosity is determined by measuring the volume density of ePTFE membrane. Volume density refers to the mass per unit volume of a material. The porosity can be calculated by measuring the volume density of non-porous PTFE (about 2.15 g/cm³) and the volume density of ePTFE membrane. There is a direct correlation between fiber length (internode distance) and volume density. The greater the mechanical expansion, the longer the fiber length and the lower the volume density.
2. Bubble point method (ASTM F-316):
The bubble point method is an indicator for evaluating the maximum pore size of ePTFE membrane. This method stipulates that the material is immersed in a liquid (such as isopropyl alcohol) until it is completely soaked, and gas pressure is gradually applied. The critical pressure when the first bubble appears and bubbles continuously is the bubble point, which can be used to characterize the pore size.
3. Gas adsorption method:
The pore volume is obtained based on low-temperature nitrogen adsorption, thereby obtaining the porosity. This method is mainly suitable for pore volume measurement of pore structures with a size of less than 200nm.
4. Mercury intrusion method:
Use pressure to press mercury into the "pores" of various structures of the membrane, and obtain the pore volume and size data of the membrane based on the pressure and volume of the injected mercury. This method is more suitable for analyzing rigid materials and may produce large errors for elastic materials.
Thickness detection method:
1. Thickness gauge:
Use a thickness gauge to test the thickness of the ePTFE waterproof and breathable membrane. During the test, it is necessary to lay the sample flat on a horizontal platform to avoid being affected by external forces. The test results are recorded in microns.
2. Density method:
By calculating the density of the membrane raw material and the apparent density of the membrane, the porosity can be calculated, and then the thickness information of the membrane can be indirectly obtained. The apparent density can be obtained through the apparent volume and mass.