What is PTFE microporous film? What is the waterproofing principle of PTFE microporous membrane?
What is PTFE microporous film? What is the waterproofing principle of PTFE microporous membrane? What is the waterproof principle of PTFE composite fabric? Price of PTFE composite fabric
Waterproofing mechanism of PTFE microporous membrane
In the capillary formed by the micropores of the polytetrafluoroethylene film, the liquid-gas interfacial tension of the meniscus surface will be added to the capillary liquid column. According to the Lapuss equation, the additional pressure P is:
In the formula: YLG The surface energy of the liquid and gas interface or the liquid-gas interfacial tension, usually called surface tension, 200C water is 0.0725N/M;
P1, P2 are the semi-meridians of curvature in the two axial directions of the curved surface.
For the cylindrical capillary hole, p= P1= P2, then there is: P=2yLG/ P Since: p=r/cos where: r-capillary equivalent semi-radius; θ-the advancing contact angle between the inner wall of the capillary and the liquid, the value of PTFE to 1180. P is positive outward, so we have: P =2yLGcos / r
From the above formula, it can be found that the main factors affecting the water pressure resistance of PTFE microporous film are the micropore length r and the contact angle. When 900﹤﹤1800, the larger the value, the higher the water pressure resistance. The advancing contact angle between the inner wall of the micropores of the polytetrafluoroethylene microporous film and water is 1180, the receding contact angle is 910, and the contact angle of 1040 is the largest among various materials; the smaller r, the higher the water pressure resistance. The micropore diameter of PTFE microporous film is very small, only a few tenths of a micron. Therefore, the water pressure resistance is very high, and its pore diameter is smaller than that of small raindrops, which cannot directly pass through.
In addition, the surface energy of the PTFE microporous film is very low. The contact angle of water on the surface of the PTFE microporous film is about 1200, so its wettability is extremely poor. The PTFE film itself has a certain mechanical strength and is subject to The micropores are not easily squeezed under pressure, which is beneficial to improving water pressure resistance.
Theoretically, water pressure resistance has nothing to do with film thickness, but in fact, the thinner the film thickness, the lower the mechanical strength, which can cause a decrease in waterproofness.
The calculation results also show that when the capillary is in a vertical position, the influence of gravity caused by the height of water on the film surface (the same order of magnitude as the thickness of the PTFE microporous membrane) can be ignored.
What is obtained is a model formula that simplifies the micropores in the PTFE film to a cylindrical capillary tube. The formula shows that when the advancing contact angle between the inner wall of the capillary tube and the liquid is greater than 900, the water entering the capillary tube is subject to the liquid-gas interfacial tension to form an additional outward pressure. Therefore, to make water pass through the micropores, a force greater than the resistance caused by surface tension is required. When r=1um, P is calculated to be about 72.5kPa, that is, an external pressure of at least 7.2m of water column is needed to make water pass through the capillary micropores; that is to say, for a polytetrafluoroethylene microporous film with a pore diameter of 1um, theoretically it The pressure resistance value is 72.5kPa. Considering that the micropores in the PTFE microporous film are not actually a straight channel, but the channels form a network structure within the film, the actual test value should be greater than the calculated value from the theoretical model.
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