Factors Affecting Fabric Permeability

- Mar 15, 2019-

The breathability of the fabric is directly related to the comfort of the fabric, and it is also related to the health problems of the consumers. Therefore, the breathability of the textile fabric is very important, and is an important feature to ensure the breathable insulation and comfort of the fabric. To this end, it is very important to understand and study the permeability of fabrics. This article focuses on the factors affecting the permeability of fabrics.

 

Temperature and humidity conditions of the fiber:

Experiments have shown that under the same conditions of the fabric structure (including the proportion of the fabric in the fiber), the fiber type has little effect on the fabric fabric resistance. Hollis's comparative experiments on hydrophilic treated polyester fabrics and untreated polyester fabrics also showed that under low-humidity conditions, the transfer of water vapor was not significantly related to the fiber types in the fabric.

 

In fact, under low-humidity conditions, the fiber itself has less moisture absorption, and the diffusion coefficient of air is much larger than that of the fiber. The water vapor diffuses through the pores between the fabrics to the side with lower water vapor pressure, indicating the transfer of water vapor in the fabric and the type of fiber. Little relationship. At this time, the thickness and porosity of the fabric or the fabric structure are the main factors determining the moisture permeability of the fabric.

 

On the other hand, the moisture absorption of the fiberboard is also related to temperature. In the process of listening to wetness, the fiber should be desorbed with a certain amount of heat, so that the temperature of the fiber aggregate is increased, the partial pressure of water vapor inside the fiber is increased, and the gradient of the internal and external water concentration of the fiber is reduced, so that the fiber The moisture absorption rate and diffusion moisture permeability are slowed down. The diffusion coefficient of the fiber increases exponentially with increasing temperature, and this increase is more pronounced when moisture is absorbed. Therefore, the increase in temperature and humidity will enhance the moisture transmission capacity of the fibers in the fabric. From the point of view of the speed of moisture absorption or dehumidification, it generally appears to start faster, gradually slows down with the increase of moisture absorption or moisture release, and finally reaches the moisture absorption balance. However, the time required to reach equilibrium is related to the moisture absorption capacity of the fiber itself and the tightness of the fiber assembly. In addition, the thermal conductivity of the fiber after moisture absorption will increase.

 

Fiber type and filling rate:

In the case of high humidity or tight fabric structure, the water vapor is no longer transmitted only through the pores in the fabric but by the fibers themselves. At this time, the type of the fiber becomes an important factor affecting the fabric transmission. On the one hand, the fiber itself absorbs moisture to cause swelling, the fabric is more tight, the permeability of the fabric is weakened, and the moisture diffusion effect is reduced by the pore diffusion; on the other hand, the surface area of the fiberboard is a considerable amount of the amount compared with the cross-sectional area of the fabric. When the fiber absorbs a large amount, the wicking effect of moisture diffusion through the surface of the fiber, that is, capillary, is strengthened, which becomes the main aspect of moisture transmission of the fabric. The decrease of the porosity of the fabric causes the decrease of diffusion and moisture permeability to become a secondary contradiction. Therefore, as long as the moisture regain rate of the fibers in the fabric reaches a certain level, although the reduction of the pores reduces the amount of moisture transported by the air medium in the fabric, the wet resistance is likely to decrease due to the substantial increase in the moisture transmission of the fibers themselves.

 

Therefore, for a fabric with a loose structure and a high void ratio, in the case where the relative humidity of the air is low, whether the fiber is hygroscopic or not, the moisture permeability is mainly through the diffusion between the fibers and the gap between the yarns; The degree is affected by the type of fiber. In the case of high relative humidity of the air, the fibers with good hygroscopicity are woven into a compact fabric, and the fibers are hygroscopically expanded to reduce the gap between the fibers, and the proportion of diffusion and moisture permeability is reduced. The ratio of capillary permeability in the capillary is increased, and capillary moisture permeability is the main factor.

 

Fabric thickness and coverage factor:

The thickness of the fabric is similar to its wet resistance. Generally, the thicker the fabric, the greater the moisture resistance of the fabric. This is because the thicker the fabric, the longer the water vapor travels through the pores between the fabrics. In addition, experiments have shown that the effect of fabric porosity changes on fabric moisture resistance is significant.

 

Fabric finishing:

Fabric finishing such as coating or impregnation increases the moisture resistance of the fabric. Because it increases the path of water vapor through the fabric or blocks the gaps in 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.

 

Other factors:

Generally, the liquid water transport speed of the fabric is greater than the liquid surface evaporation rate, and the inner side of the fabric has a small gap hole which makes it easy to condense into liquid water for transport, forming a differential capillary effect, and a large gap hole on the outer side to easily satisfy the evaporation condition. It is good for wetting. The evaporation ability of liquid water on the surface of the fabric is not closely related to the thickness and porosity of the fabric, but it is closely related to the surface irregularity of the fabric surface, especially the size and depth of the surface pit. In general, the larger the opening area of the pit, The larger the radius of curvature, the higher the evaporation efficiency. The details of the pit, wind speed, temperature difference, etc. also have a significant impact.