Waterproof fabric is a new type of textile fabric. Its composition is made of polymer waterproof and breathable material (PTFE film) and fabric composite material.
Definition of Fabric
The main functions of waterproof and breathable fabrics are waterproof, moisture permeability, air permeability, insulation, windproof and warmth preservation. In terms of manufacturing technology, the technical requirements of waterproof and breathable fabrics are much higher than those of ordinary waterproof fabrics, and in terms of quality, waterproof and breathable fabrics also have functional characteristics that other waterproof fabrics do not have. Waterproof breathable fabrics can enhance the air tightness and water tightness of the fabric, at the same time, its unique vapor permeability can make the water vapor inside the structure expel quickly, avoid the structure breeding mildew, and keep the human body dry all the time. It perfectly solves the problems of ventilation and windproof, waterproof and warmth preservation. It is a new type of healthy and environmental protection fabrics.
Real waterproof fabrics can also withstand seepage pressure in humid climatic environment for a long time without seepage. For example, walking outdoors for a long time in the wind and rain, kneeling or sitting on the wet ground, will not seep.
Under the condition of water vapor, water particles are very small. According to the principle of capillary movement, water particles can penetrate into the capillary to the other side smoothly, thus the phenomenon of vapor permeation occurs. When water vapor condenses into water droplets, the particles become larger. Because of the surface tension of water droplets (water molecules are “pulling and competing” with each other), water molecules can not escape from the water droplets and penetrate to the other side smoothly, that is to say, water penetration is prevented, so that the permeable film has the function of waterproof.
How to resist water
1. Young’s Formula
A drop of liquid droplets on a solid surface is assumed to be ideally flat, the droplet gravity is concentrated at one point, and the amount of field is neglected. Due to the interaction of fiber surface tension (Ys), liquid surface tension (YL) and also the interfacial tension (YLS) of the firmware, droplets will form various shapes (from cylindrical to completely flat). Except for the complete de-leveling at night, when the droplet is in equilibrium on the solid surface, point A receives the effect of dispersive gravity.
Angle 0 is called contact angle, when 0 = 00, droplets on the solid surface mianpu screen, which is the limit state of solid surface wetted by the field; when 0 = 1800, droplets are cylindrical, which is an ideal non-wetting behavior. In water repellent finishing, the surface tension of droplets can be regarded as a constant. Therefore, whether the field can wet the solid surface or not, all the contact tension between the solid surface and the dead lotus leaf in the bank. It is said that the larger the contact angle is, the better the rolling loss of water droplets, that is to say, the smaller the contact angle is.
2. Fabric Adhesion Work
Because Ys and YLS can hardly be measured directly, contact angle 0 or cos0 is usually used to evaluate wettability directly. However, the contact angle is not the reason for wetting, but the actual result is that some people have the adhesion work to indicate the relationship between them and the parameters of wetting degree.
YL and cos0, which indicate the work of adhesion, can be measured, so the formula has practical significance. Similarly, the work required to divide the liquid droplets per unit area on the interface into two droplets is 2YL, which can be called the cohesive work of the liquid. It can be seen from the formula that the contact angle decreases when the work of adhesion increases. When the work of adhesion equals the work of cohesion, the contact angle is zero. This is because the liquid is completely flat on the solid surface. Because cos 0 can not exceed 1, the contact angle remains unchanged even if the work of adhesion is greater than 2YL. WSL = YL, then 0 is 900. When the contact angle is 180 degrees, WSL=O indicates that there is no viscous interaction between liquid and solid. However, due to some adhesion between the two sides, the case of contact angle equal to 180 degrees has never been found. At most, some approximate cases can be obtained, such as 160 degrees or larger angles.
3. Critical Surface Tension of Fabric
Because the surface tension of solid is almost impossible to measure, in order to understand the wettability of solid surface, someone has measured its critical surface tension. Although the critical surface tension can not directly express the surface tension of the solid, but the size of Ys-YLS, it can indicate the difficulty of wetting the solid surface. But it should be
It should be noted that the determination of critical surface tension is an empirical method and the range of measurement is very narrow.
Except cellulose, the critical surface tension of other substances is low, so they all have certain water repellency. Obviously, the better water repellent effect can be obtained for the material seats with larger contact and smaller critical surface tension.
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