Factors Affecting the Air Permeability and Moisture Permeability of PVC Composite Fabrics (Part 2) - Guangyuan Ruifeng New Materials

Category: PVC composite fabric

Release Time: 2020-08-11

Summary: In high humidity or when the fabric structure is tight, water vapor is no longer transmitted only through the pores in the fabric but also through the fibers themselves. In this case, the type of fiber becomes an important factor affecting fabric transmission.

3. Fiber Types and Fill Rate

In high humidity or tightly woven fabrics, water vapor is no longer transmitted only through the pores of the fabric but through the fibers themselves. In this case, the type of fiber becomes an important factor affecting fabric transmission. (Crosslinking agent used in PVC composite fabric, crosslinking agent manufacturer, PVC adhesion promoter)

On the one hand, the fiber itself absorbs moisture and swells, making the fabric tighter and reducing its breathability, thus reducing the moisture transmission effect through pore diffusion; on the other hand, compared to the cross-sectional area of the fabric, the surface area of the fiber board is a considerably large quantity. When the fiber moisture absorption is large, the diffusion of water through the fiber surface, i.e., the capillary wicking effect, is enhanced, becoming the main aspect of fabric moisture transmission. The reduction in fabric porosity causing a decrease in diffusion moisture permeability becomes a secondary issue.

Therefore, as long as the fiber regain in the fabric reaches a certain level, even though the reduction in pores reduces the amount of moisture transmission through the air medium in the fabric, the moisture transmission of the fiber itself increases substantially, and the moisture resistance may still decrease.

Both moisture transmission through the fiber itself and capillary wicking are closely related to the hydrophilicity and surface properties of the fiber. Experimental results show the relationship between the water vapor moisture resistance of different types of fibers under the same compactness conditions and the fabric compactness. Obviously, under conditions of lower density, the moisture resistance of various fiber fabrics is not much different. When the density factor reaches 0.4 or higher, for fibers with rough surfaces, irregular cross-sections, and good hygroscopicity, such as cotton and wool, as the fiber collection fill rate increases, the increase in fabric moisture resistance is smaller, and the linear relationship between fabric moisture resistance and fill rate is good.

However, for chemical fibers such as nylon, chlorinated fiber, and glass fiber, when the fill rate is large (porosity is small, capacity is large), such as when the fill rate is greater than 39% or the porosity is less than 61%, and the fabric density is greater than 0.98 g/cm³ (for glass fiber fabrics), the moisture resistance will increase sharply with the increase in density and fill rate (or decrease in porosity). The moisture resistance of cotton and wool fabrics with good hygroscopicity is significantly lower than that of non-hygroscopic fiber fabrics. In other words, the effect of fiber hydrophilicity on fabric moisture permeability is determined by the fabric density. (Crosslinking agent used in PVC composite fabric, crosslinking agent manufacturer, PVC adhesion promoter)

Therefore, for fabrics with a relatively loose structure and high porosity, under conditions of low relative air humidity, regardless of whether the fibers are hygroscopic, moisture permeability is mainly through diffusion through the gaps between fibers and yarns; and to a very small extent, it is affected by the type of fiber. Under conditions of high relative air humidity, for hygroscopic fibers woven into tight fabrics, the fiber absorbs moisture and expands, reducing the gaps between fibers, reducing the proportion of diffusion moisture permeability, and increasing the proportion of capillary moisture permeability in the fibers, making capillary moisture permeability the main factor.

4. Fabric Finishing

Coating or impregnation fabric finishing increases the moisture resistance of the fabric because it increases the path of water vapor through the fabric or blocks the pores of the fabric. However, hydrophilic finishing increases the moisture permeability of the fabric. Water-repellent finishing generally does not affect the moisture permeability of the fabric.

5. Other Factors

Generally, the transmission speed of liquid water in fabrics is greater than the evaporation rate of the liquid surface. The smaller gaps and pores on the inner side of the fabric make it easy to condense into liquid water and transport it outwards, forming a differential capillary effect. The larger gaps and pores on the outer side make it easy to meet the evaporation conditions, which is conducive to moisture dissipation. The evaporation capacity of liquid water on the fabric surface is not closely related to the fabric thickness and porosity, but is closely related to the surface morphology of the fabric, especially the size and depth of the surface pits. In general, the larger the opening area of the pit and the larger the radius of curvature, the higher the evaporation efficiency. The details of the pit, wind speed, and temperature difference also have a significant impact. (Crosslinking agent used in PVC composite fabric, crosslinking agent manufacturer, PVC adhesion promoter)

Keywords: Factors Affecting the Air Permeability and Moisture Permeability of PVC Composite Fabrics (Part 2) - Guangyuan Ruifeng New Materials

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