What is PTFE microporous film? What is the waterproofing mechanism of PTFE microporous membrane? What is the waterproof principle of PTFE composite fabric?
What is PTFE microporous film? What is the waterproofing mechanism of PTFE microporous membrane? What is the waterproof principle of PTFE composite fabric?
1. PTFE Micro Waterproofing Mechanism of Porous Film
Polytetrafluoroethylene film In the capillary formed by micropores, the liquid-gas interfacial tension of the meniscus surface will be attached to the capillary liquid column. According to Lapus equation, additional pressure P is:
P=YLG (1/p1+1/p2)
Formula: YLG The surface energy or liquid-gas interfacial tension at the interface between liquid and gas, usually called surface tension, 200C water is 0.0725N/M;
P1, P2 Curvature of the two axial directions of the curved surface Semimenstrual period.
For cylindrical capillary holes, p= P1= P2 Then there are:
P=2yLG / P
Due to: p=r/cos
Where: r-capillary equivalent semi-meridian;
θ-the advancing contact angle between the inner wall of the capillary tube and the liquid, The value of PTFE is 1180.
P is positive outward, so there is:
P =2yLG cos / r
What is obtained is a polytetrafluoroethylene film The micropores in are simplified to the cylindrical capillary model formula. 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 polytetrafluoroethylene with a pore diameter of 1um The theoretical pressure resistance value of ethylene microporous film 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.
From the above formula, it can be found that the influence of polytetrafluoroethylene The main factors that determine the resistance of microporous films to water pressure are the diameter r of the micropores and the contact angle. When 900﹤ ﹤1800, the larger it is, the higher the water pressure resistance is. 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 is 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 the hole diameter is smaller than that of small raindrops, which cannot directly penetrate.
In addition, the surface energy of PTFE microporous film is very Low, the contact angle of water on the surface of the PTFE microporous film is around 1200, so its wettability is extremely poor; the PTFE film itself has a certain mechanical strength and is slightly weak when subjected to pressure. The holes are not easily squeezed, which is beneficial to improving water pressure resistance.
Theoretically, water pressure resistance has nothing to do with film thickness, but in practice On the other hand, 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 accumulation on the film surface (the same order of magnitude as the thickness of the PTFE microporous membrane) can be ignored.
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