When the body temperature rises due to various reasons such as high air temperature, high levels of physical activity, intense emotions, it sweats to lower its body temperature. Evaporation of sweat from the skin creates moisture vapor in the area between the clothing and the skin. In order for the wearer to feel comfortable, the worn garment must transmit this sweat in the form of steam to the surrounding air. The ability of the garment to transmit sweat in the form of steam is water vapor permeability, which is one of the important parameters that provide comfort to the garment. Clothes are like a second skin for people, as people wear their clothes all day long. For this reason, clothing features are important for humans. Clothing is generally chosen by taking into account the aesthetic features that affect the appearance of the fabric, such as pattern, model, color, fashion. But lately, there has been an increasing trend towards comfort clothing, where people can feel more comfortable.
In order to maintain the thermal balance of the body, the sweat produced when necessary is transmitted to the environment in the form of steam, and the water vapor permeability of the clothes that wrap the body almost like a second skin is at very good levels, making consumers feel more comfortable.. All of the fiber, yarn and fabric properties, which are in a permanent relationship with each other, affect the water vapor permeability of the fabrics. Thickness and porosity of fabrics, yarn count and raw material type are among the most important parameters affecting water vapor permeability.While fabric thickness is inversely related to water vapor permeability, porosity is in a directly proportional relationship. Different opinions have been obtained in various studies examining the water vapor permeability of fabrics with hydrophilic or hydrophobic character. In order to carry out studies on water vapor permeability in a healthy way, methods based on various standards have been developed for the measurement of this property.
Comfort is defined as “the state of contentment of the physiological, psychological and physical harmony between man and the environment”. Clothing comfort is a complex concept that includes many factors. Clothing comfort is generally classified under two groups as sensory comfort and thermo-physiological comfort;
1-Sensory comfort refers to the neurological perceptions felt during the mechanical contact of the textile material with the skin.
2-Thermo-physiological comfort is related to the ability of the fabric to maintain the thermal balance between the human body and the environment, and covers the heat and moisture transfer mechanisms that occur in the fabric.
Sweating is a mechanism the body uses to lower its temperature when body temperature begins to rise. Especially at high activity levels and high ambient temperatures, sweating occurs in the body to reduce the rising body temperature. During sweating, the sweat formed on the skin surface evaporates. As sweat evaporates, it provides the heat of evaporation from the body, thus cooling the body. The fabric worn should allow the passage of liquid and vapor perspiration. Otherwise, the relative humidity in the clothing increases and this causes an uncomfortable feeling of wetness on the skin. For this reason, humidity control, which is defined as the controlled movement of steam and liquid sweat from the skin to the atmosphere through the fabric, is an important factor that provides the thermo-physiological comfort of fabrics, especially in high temperature and high physical activity conditions, as well as thermal properties. The ability of the fabric to pass sweat in the form of steam is measured as water vapor permeability. Since it adds breathability to fabrics, the ability of fabrics to pass water vapor is now an important feature sought not only in sportswear, daily clothing worn outside of work, but also in all types of clothing. The transmission of water vapor through the textile structure is quite complex and many fiber, yarn and fabric parameters affect the water vapor permeability of fabrics.
The human body is a complex thermodynamic system that constantly produces its energy through its own metabolism. As is known, the body temperature of a healthy person is about 37 °C. The human body wants to maintain this temperature at a constant level, even under different conditions. The heat required for body temperature is provided by body metabolism. Man is constantly in heat exchange with his environment. Different environmental temperatures affect body temperature. When the body temperature is higher than the surrounding air temperature, there is a heat flow from the body to the environment and the person loses heat. Conversely, when the body temperature is lower than the surrounding air temperature, a person gains heat. The body should be kept in thermal balance by ensuring that the heat generated by the metabolism and the heat taken from the external source are equal to the amount of heat lost from the body. If heat gain and heat loss are not in balance, body temperature either rises or falls. The heat and moisture transmission from the human body to the environment with textile materials can be expressed by the thermal equilibrium position equation in the body given below.
The total heat loss from the skin to the environment is due to heat loss carried by conduction, convection, radiation, and heat loss as a result of evaporation.
Under normal atmospheric conditions and during normal activity, the heat generated by the body metabolism is given from the body to the atmosphere through conduction, convection and radiation. However, at high activity levels and high temperatures, heat production increases and the transmission of heat from the body to the atmosphere is not sufficient to keep the body temperature at a comfortable level. In this case, sweat glands act to produce sweat, regulating body temperature. The vapor form of sweat is referred to as non-sensible sweat, and the liquid form of sweat is called sensible sweat.. Under temperate environmental conditions, sweating occurs imperceptibly. Insensible sweating causes about 15% heat loss on the skin.
During high activity, hot climate or environmental conditions, sweating can be felt and sweat produced by the body accumulates on the skin. Turning water into steam requires a large amount of heat energy. 1 calorie increases the temperature of 1 gram of water by 1 °C. In contrast, 1 J (2424 calories) is required to evaporate 580 gram of water at body temperature. During the evaporation of sweat, the necessary heat is taken from the body and in this way cooling occurs in the body. The ambient temperature higher than the skin temperature allows heat loss from the body to occur by evaporation. For this reason, heat transfer by evaporation becomes important especially when there is an increase in ambient temperature in providing thermal equilibrium.
As seen in the figure above, when the human body is covered with clothing, an intermediate zone called microclimate is formed between the skin and clothing. During sweating, primarily moisture and steam occur in this region. Moisture formation and moisture transmission in the microclimate area are shown in the figure below depending on time.
As can be seen from the figure above, while sweating continues, the amount of moisture reaches the highest value in the microclimate region. The water vapor permeability feature of the garment greatly affects the moisture formation in this region. Depending on the temperature and humidity difference in the clothing, the water vapor either leaves the clothing or condenses on the clothing. If the evaporation sweat is lower than the sweat generated by the body, moisture accumulates in the inner layer of the fabric. The formation of moisture in the microclimate area between the sweaty skin and the layer of clothing gives the person an uncomfortable, moist and sticky feeling, especially during the cooling period following sports activities that cause sweating. In addition, wetting the fabric with sweat also reduces the thermal insulation of the fabric, causing an undesirable drop in body temperature. The fabric, which is perceived as comfortable, should transmit the water vapor formed during the body's sweating period. When the body stops sweating, the fabric must release the moisture vapor held in the space to the atmosphere to reduce the moisture in the body. Many parameters affect the moisture formation in the microclimate zone.
Human parameters including physical (body movement), physiological (skin temperature, perspiration, evaporation) and psychological states, environmental parameters including temperature, humidity, air flow, radiation, design parameters including collar, arm openings, clothing tightness/slack, fabric layers and finally, the chemical (fiber type, chemical finishing) and physical (thickness, porosity, bulkiness, knitting structure, etc.) properties of the fabrics.
fabric parameters are the parameters that affect the microclimate zone.
Researchers Yoo, Hu, and Kim;
They investigated the effects of the air layer thickness in the microclimate region and the openings of clothing such as collar, arm and waist on the microclimate region by measuring the vapor pressure formed in the microclimate region depending on time. As the air layer thickness between the fabric and the skin increased, the vapor pressure and thus the water vapor density decreased. However, very high air layer thickness did not cause much change in the water vapor density in the microclimate region, as it reduced the drag force to transmit the water vapor to the air. It is stated that the air thickness of about 12 mm in the microclimate zone is suitable for the comfort of the wearer.
Clothing openings of 10% provided a sudden drop in steam pressure in the microclimate zone. Increasing the garment openings from 20% to 60% again resulted in a decrease in steam pressure in the microclimate region, but the reduction in steam pressure was not as great as the garment openings increased from 0% to 10%. The effect of the fabric on the microclimate zone decreased gradually as the garment opening increased. When the clothing clearance is 60%, it completely lost its effect and approached the non-clothing skin value..
Water vapor is transferred from the fabric layers consisting of fibers in 3 ways as given below:
1-Diffusion (passing, diffusion) of water vapor through the fabric layers.
2- Absorption (absorption), transmission and return (desorption) of water vapor by the fiber.
3- Convection of water vapor by convection.
1-Diffusion Process
In the diffusion process, from one side of the fabric to the other The transmission of moisture takes place with the vapor pressure difference.
Since it consists of many fibers coming together, fabrics have a hollow structure. For this reason, water vapor passes through the fabric structure in two ways: the air spaces between the fibers and the yarns and the fiber itself.
The amount of water vapor passing through the air part of the fabric is instantaneous. However, the passage of water vapor through the fiber part of the fabric is limited. The diffusion coefficient of water vapor through air is approximately 0,239 cm2s-1. The diffusion coefficient through which the water vapor passes through the fiber part of the fabric is between 10-710-9. According to the given diffusion coefficients, the increase in the amount of air in the fabric increases the passage of water vapor through diffusion, since the diffusion coefficient through which the water vapor passes through the fiber-filled part of the fabric is considerably lower than the air passage coefficient.
When it comes to the diffusion of water vapor from the fiber part of the fabric, the water vapor passes from the inner surface of the fabric to the fiber surface, then the water vapor reaches the outer surface of the fabric by moving from the fiber to the fiber surface.
In the case of fabric consisting of hydrophilic fibers, diffusion takes place in 2 stages.
Diffusion occurs according to Fick's rule.
In the first stage, diffusion occurs more slowly than in the first stage, and there is an exponential relationship between the concentration change and the water vapor flow. This is due to fiber swelling caused by water molecules. Because hydrophilic fiber molecules attract water molecules, water molecules enter the fiber and water molecules are absorbed by the fibers. In this way, the diffusion process is slowed down as fiber swelling occurs and the size of the air spaces in the fabric is reduced.
2-Absorption and Return Process
The absorption and return process is important for maintaining the moisture balance in the microclimate zone. Fibers absorb water vapor depending on the internal chemical components and structure of the fiber. The hygroscopic/hydrophilic fabric absorbs the water vapor from the humid air next to the sweaty skin and gives it back to the dry air. The hygroscopic/hydrophilic fabric increases the water vapor flow of water vapor from the skin to the environment compared to the hydrophobic fabric, which does not absorb moisture, and thus reduces the moisture formation in the microclimate area. In the absorption and return process, the absorbent fabric works as a source of moisture given to the atmosphere and also acts as a shield to maintain the constant vapor concentration in the surrounding air.
3-Transfer Process
Convection is the moisture transfer caused by the air flowing over the moisture layer. In the transport process, mass transfer is controlled by the moisture concentration difference between the moisture source and the atmosphere. In particular, convection plays an important role in the transmission of moisture from the skin to the atmosphere in windy weather.
DEFINITION OF WATER VAPOR PERMEABILITY AND MEASUREMENT METHODS
Water vapor permeability is the amount of water vapor passing through the unit area of the fabric in a certain time.. The water vapor permeability of the fabrics is also measured in % with the expression of the relative water vapor permeability. Instead of water vapor permeability of fabrics, water vapor resistance is also used. Water vapor resistance is the resistance of the fabric against the passage of water vapor. Water vapor permeability and water vapor resistance vary inversely. The higher the water vapor permeability and the lower the water vapor resistance, the more comfortable the fabrics are.
There are various methods used in the measurement of water vapor permeability. These methods are described below;
1-Vertical Cup Method (Upright Cup Method)
Measurements are made in accordance with ASTM E96 B standard. The sample is fixed on a vertical container containing pure water with the help of gasket. The environment in which the device is located is kept in an environment of 23 °C temperature, 50% relative humidity and 2,8 m/sec air velocity. During a day, the weight of the container assembly is periodically examined to calculate the water vapor transmission rate.
2-Inverted Cup Method
Measurements are made in accordance with the ASTM E96 BW standard. It is similar to the vertical cup method. The measurement is made by inverting the container in which the sample is placed and the water in it. In order to prevent the container with water from wetting the test sample when it is turned upside down, the mouth of the container is covered with a PTFE membrane and then the sample is placed on the membrane. This test is performed in an environment with 23 °C air temperature, 50% relative humidity and 2,8 m/sec air velocity. The container assembly is weighed periodically during a day and the water vapor transmission rate is calculated as in the vertical container method.
3-Desiccant Inverted Cup Test Method
With this method, measurements are made according to ISO 15496 and ASTM E96 standards. The measuring principle is similar to the inverted cup method. A saturated potassium acetate solution is placed in the measuring cup as a desiccant. The mouth of the container is closed with two membranes, which are waterproof but permeable to water vapor, with a fabric sample between them. The container is placed upside down in another container filled with 23 °C distilled water. The measuring cup is weighed and the water vapor permeability is calculated from the weight change.
4-Sweating Guarded Hot Plate Tests
With this method, water vapor resistance is measured in accordance with ISO 11092 standard. The test device consists of a measuring unit and a water delivery unit. The measuring unit consists of a heated square porous metal plate. With this plate, sweating is simulated. The measuring unit is fixed to the metal block with a heater. The upper side of the porous plate is covered with a cellophane membrane that is impermeable to water but permeable to water vapor. The fabric to be tested is placed on this membrane. The porous metal layer is heated to approximately body temperature. Pure water is fed to the porous metal layer surface. The entire apparatus is placed in a closed environment in order to provide environmental conditions. By controlling the ambient conditions, it is ensured that it reaches a temperature of 35 °C and a relative humidity of 40%. Air velocity is set to 1 m/s. When the stable state is reached, the total evaporation resistance of the fabric is measured.
5-Dynamic Moisture Permeation Cell Test Method
The measurement is made in accordance with the ASTM F 2298 standard. The sample is fixed between 2 identical metal plates fixed by 2 flow channels. Nitrogen gas, one of which is dry and the other saturated with pure water, is passed through the flow channels. The test is carried out at 20 °C and a gas flow rate of approximately 2000 cm3/min. The gas flow rate, air temperature and relative humidity are controlled with the help of a computer, and when the steady state is reached, the water vapor transmission rate is calculated.
6- Evapourative Dish Method
Measurements are made in accordance with the BS 7209-90 standard. Samples placed on containers containing pure water are placed on a rotating platform. In an environment with 65% relative humidity and a temperature of 20 °C, the platform is rotated and the test vessels are weighed in 1-hour periods. The containers placed on the turntable again are weighed again after 5 hours. According to the weighing results, the water vapor permeability index value is calculated.
7-Permetest Method
Measurements are made according to ISO 11092 standard in the Permetest measuring device developed by Hes. Dry and wet human skin is represented in terms of thermal sensation with this test device, which is also called the Skin model. With this test device, the relative water vapor permeability and water vapor resistance values are measured in %.. Before measuring, the measuring head representing the leather pattern is covered with a durable semi-permeable foil or cellophane. The foil prevents the passage of water from the measuring system to the sample to be measured and thus ensures that the sample remains dry. First of all, the heat flow value is measured before the sample is placed, by measuring without sample. Then, the area where the sample will be placed is humidified and exposed to a parallel air flow at an adjustable speed. The sample to be tested is placed on a wet area of 80 mm diameter. In this way, the amount of evaporation heat loss of the wet measuring head covered with the sample is measured. With the help of these values, the relative water vapor and water vapor resistance values are calculated.
FACTORS AFFECTING WATER VAPOR PERMEABILITY OF FABRICS
Many parameters affect the water vapor permeability of fabrics. There are many studies on the factors affecting the water vapor permeability of fabrics in the sources, and these factors are as follows;
1) Fiber properties; fiber type, fiber blend ratio, fiber fineness or fiber number, fiber porosity, fiber cross-section.
2) Yarn properties; yarn count or yarn diameter, yarn twist, protruding fiber ends or hairiness, yarn geometry, yarn packing density (fiber volume ratio per unit length of yarn).
3) Fabric properties; fabric porosity, thickness, fabric density.
In the studies, it has been determined that the diffusion process determines the water vapor transmission of the fabrics as the first among the physical mechanisms that transmit water vapor to a large extent. For this reason, as with the air permeability properties of fabrics, the water vapor permeability of fabrics is determined by the amount of air and fiber in the fabric, which is effective in the diffusion process. As mentioned before, since the diffusion coefficient through which the water vapor passes through the fiber part of the textile material is considerably lower than the air passage coefficient, the decrease in the amount of air in the fabric prevents the passage of water vapor.
Researchers named Yoon and Buckley and Prahsarn, Barker and Gupta stated in their studies that the structural parameters of yarns and fabrics that determine the amount of fiber and air in the fabric are effective in the water vapor transmission of the fabrics, and that the effect of the fiber type affects the water vapor permeability of the fabrics by affecting the structural parameters of the fabrics.
The factors affecting the water vapor permeability of fabrics are explained by classifying them as the structural properties of fabrics, the structural properties of yarns and the effect of fiber properties.
1-The Effect of Structural Parameters of Fabrics on Water Vapor Permeability
Yoon, Buckley and Prahsarn et al. stated that the structural parameters of the fabric, especially fabric thickness and fabric porosity, were more effective on the water vapor transmission properties of fabrics.
Fabric thickness and optical porosity, which are structural parameters of fabrics, determine the water vapor transmission of fabrics. Fabric thickness is important as it determines the distance to which water vapor is transmitted. In addition, fabric thickness affects the porosity of fabrics. As the fabric thickness increases, the vapor diffusion rate decreases, that is, the water vapor permeability decreases.
Water vapor diffusion is also largely dependent on air permeability, which varies in direct proportion to fabric porosity. As the air permeability increases, the porosity of the fabric increases and more steam passes through the air spaces in the fabric.
2-Effect of Yarn Properties on Water Vapor Permeability Properties of Fabrics
It was stated by Yoon and Buckley that the fabric porosity and thickness, which determine the water vapor permeability of fabrics, depend on the yarn diameter, and the yarn diameter is determined by the yarn count and especially the packing density of the fibers in blended yarns. The fiber packing factor in the yarn is defined by the yarn packing density, which is expressed as the fiber volume ratio per unit yarn length. It has been stated that especially in staple yarns, the packing density depends on the cross-section of the fibers, the crimp density of the fibers and the twist level of the yarn.
In the study conducted by Özdil, Marmaralı, Kretzschmar, in which the effects of yarn properties consisting of yarn count, yarn twist coefficient and spinning method (carded and combed) on the water vapor permeability of knitted fabrics were also examined, it was found that the water vapor permeability of the fabrics increases as the yarns become more porous. specified. In the studies conducted by other researchers, knitted fabrics made of fine yarns showed higher water vapor permeability than fabrics made of thicker yarns. Increasing the yarn twist coefficient has increased the water vapor permeability of the fabrics, as it provides less hairy and more porous fabric structure. It has been stated that fabrics made from carded yarns show lower water vapor permeability than fabrics made from combed yarns, since the carded yarns are more hairy and the feathers close the pores in the fabric structure.
In the study conducted by Uzun, in which conventional and compact ring spinning methods also examined the relative water vapor permeability of woven fabrics, it is stated that the spinning methods affect the relative water vapor permeability to some extent. It has been stated that the relative water vapor permeability of fabrics made of compact spun yarn is higher than the relative water vapor permeability of fabrics made of conventional spun yarn.
3-The Effect of Fiber Properties on Water Vapor Permeability Properties of Fabrics
Although it was stated by some researchers such as Yoon and Buckley, Prahsarn et al. that the structural parameters of the fabric affect the water vapor permeability of the fabric rather than the fiber type, it was also stated that different fiber types could affect the water vapor permeability of the fabrics by causing differences in the fiber geometry and thus the fabric geometry. There are many experimental studies examining the effects of different fiber types on the water vapor permeability of fabrics in various sources.
Named Yoo, Hu, and Kim As stated by the researchers, there are different opinions among researchers about how hydrophilic/hygroscopic and hydrophobic fiber properties affect the perception of comfort of fabrics and therefore the water vapor permeability of fabrics. Although some of the researchers stated that the high moisture content of the fiber or the hygroscopic / hydrophilic fiber feature increase the water vapor permeability of the fabrics, the studies conducted by some researchers also showed that hydrophobic fibers showed higher water vapor permeability than hydrophilic fibers. In many studies by Das et al., it has been stated that since water vapor is absorbed by the fibers, transmitted by the fibers and given back to the environment by the fibers, the hygroscopic or hydrophobic feature of the fiber type greatly affects the water vapor permeability of the fabric, especially during the absorption and return phase in the mechanisms that transmit water vapor. . Absorption and rehydration phase are important fiber properties that provide comfort, especially in transitional conditions. Different types of fibers have different effects on water vapor transmission. For example, hydrophilic/hygroscopic fibers such as cotton, viscose and wool absorb moisture, whereas hydrophobic fibers such as polyester and polypropylene do not absorb moisture.. It is stated that hygroscopic fibers that absorb water and have high moisture content pass water vapor more. The hygroscopic fabric absorbs water vapor from the moist air near sweaty skin and releases it in dry air.. Compared to non-hygroscopic fabric, it is stated that the hygroscopic fabric relatively increases the flow of water vapor from the skin to the environment, thus reducing the formation of moisture in the microclimate region between the skin and the fabric.
Yoo et al. measured the steam pressure formed in the microclimate zone between clothing and skin, depending on time, and compared the effects of hydrophilic and hydrophobic fibers on the vapor pressure formed in the microclimate zone. Choosing cotton as hydrophilic fiber and polyester fiber as hydrophobic fiber, woven fabrics with the same weight, thickness and density values were obtained.
Immediately after the first perspiration, higher steam pressure was formed in the microclimate area under the polyester fabric than in the microclimate area under the cotton fabric, then the steam pressure in the polyester fabric remained constant for a while. On the other hand, the steam pressure under the cotton fabric increased continuously. In addition, the maximum steam pressure under the cotton fabric was higher than the maximum steam pressure under the polyester fabric. The time required to reach the maximum steam pressure value is also higher for cotton fabric. When sweating occurs, hydrophilic fibers such as cotton absorb moisture, so the curve obtained for cotton fiber is smoother. If the fibers are hydrophobic, such as polyester, the vapor pressure in the microclimate region increases sharply when sweat is formed, and as a result, the slope of the curve becomes steeper. Then, for both types of fabric, the steam pressure decreases as moisture begins to transfer through the pores between the fibers and yarns. Yoo et al. also examined the steam transmission index values for both fabric types, which are used as the ability of the fabric to transmit water vapor, that is, the ability of the fabric to transmit water vapor, without accumulating sweat on the skin. The vapor transmission index value of polyester was obtained higher than the steam transmission index value of cotton. As the reason for this difference, it has been shown that hydrophilic fibers contain more water molecules and reduce the pores of the fabrics by swelling.
Yoo and friends In the first moments of sweating or in cases where there is not much sweating, cotton fiber feels better because it absorbs moisture, on the other hand, while sweating continues, polyester fiber feels better because it does not hold water molecules in and gives water molecules back to the air. It has been stated that polyester fabric provides a better feeling of comfort than cotton fabric, since the time required to reach the maximum steam pressure value is lower for polyester fabric.
There are many experimental studies on the water vapor permeability of fabrics consisting of hydrophilic fibers such as cotton, viscose, modal, lyocell and hydrophobic fibers such as polyester, acrylic, nylon.
In particular, the water vapor permeability values of fabrics consisting of cotton, polyester and mixtures of these two fibers, which are widely used, have been comparatively examined by many researchers.
In all studies involving these fibers, polyester fabrics showed higher water vapor permeability values than cotton fabrics. Yoon and Buckley It has been stated that cotton fabrics are thicker than polyester fabrics by creating a looser and larger diameter yarn than polyester fibers of the same number due to irregular 3-dimensional folds, and therefore cotton fabrics pass water vapor less than polyester fabrics.
Knight and friends In this study, the water vapor permeability values of fabrics consisting of polyester, nylon and acrylic synthetic fibers with hydrophobic fiber properties and the mixtures of these fibers with cotton fiber, which is a hydrophilic fiber, were comparatively examined. According to the experimental results they published, 100% cotton fabrics showed lower water vapor permeability than all fabrics in which 3 synthetic fibers (polyester, acrylic and nylon) were used at 100%. In fabrics consisting of blends of synthetic fibers with cotton fibers, an increase was observed in the water vapor permeability of the fabrics as the synthetic fiber ratio increased or the cotton fiber ratio decreased. It has been stated that fabrics consisting of synthetic fibers with hydrophobic properties pass water vapor better.. Among the fabrics made from synthetic fiber, polyester fabric showed the highest water vapor permeability. Acrylic fabrics followed polyester fabrics and nylon fabrics showed the lowest water vapor permeability. Hassan et al. stated that the water vapor permeability values of fabrics made of cotton fiber are lower than those of synthetic fibers with hydrophobic properties, indicating that fabrics made from cotton fiber, which is very preferred in sportswear, have some deficiencies in terms of moisture management. Although sweat is absorbed by the cotton fabric, wetness in the fabric can cause an unpleasant feeling or thermal discomfort when the fabric comes into contact with the body. In addition, the fabric, which is completely wet with sweat, begins to lose its thermal resistance.
Apart from these studies, there are other studies in which the water vapor permeability values of fabrics made of cellulose fiber such as cotton fiber and hydrophilic fibers such as viscose and lyocell with high fiber moisture content are comparatively examined and the water vapor permeability of fabrics made of polyester fiber are available in the sources.
Varshney et al. In the study in which the water vapor permeability of woven fabrics consisting of viscose, polyester fibers and mixtures of these fibers was examined, 100% viscose and polyester/viscose mixed fabrics showed lower water vapor transmission than 100% polyester fabrics. In other similar studies examining the water vapor permeability of woven fabrics made of viscose, polyester fibers and mixtures of these fibers, Das et al. Varshney et al. contrary to the results of water vapor It was observed that the water vapor permeability of the fabrics decreased as the polyester ratio increased or the viscose ratio decreased.. It has been stated that as the polyester ratio increases, the moisture content of the fibers decreases and this situation reduces the water vapor transmission by diffusion path and absorption and return process. The results of these authors' studies vary inversely with the water vapor permeability results of cotton and polyester fabrics, as mentioned earlier. In another study examining the water vapor permeability of fabrics made of micro lyocell and micro polyester fibers, the water vapor permeability value of the fabrics increased as the amount of micro lyocell, which is a hydrophilic fiber, increased or the amount of micro polyester fibers decreased.
Cimilli et al. According to the results obtained in the study where they examined the water vapor permeability of fabrics made of cotton, modal, viscose, micromodal, bamboo, chitosan and soy fibers, it was stated that the air permeability of the fabrics and the moisture content of the fibers affected the water vapor permeability of the fabrics made from the mentioned fibers. Chitosan fabrics showed the highest water vapor permeability value due to the highest air permeability and lowest fiber moisture content, and on the contrary, cotton fabrics showed the lowest water vapor permeability value due to the lowest air permeability and highest fiber moisture content. The water vapor permeability values of the fabrics are listed as chitosan, bamboo, soybean, modal, viscose, micro modal and cotton from the highest to the lowest.
Due to its advantageous properties such as being environmentally friendly and abundant in nature, there are many studies on water vapor permeability due to the comfort properties of bamboo fibers, another regenerated cellulose fiber that has been increasingly used recently, and the comfort properties of fabrics consisting of cotton and cotton blends of these fibers. In all of these studies, it has been concluded that these fibers increase the water vapor permeability of the fabrics, due to the fact that the fabrics made of bamboo fibers are thinner, have a lower weight, the yarns are less hairy, and the moisture content of the bamboo fibers is high.
Demiryurek and Uysalturk According to the results of the study in which the relative water vapor permeability of viloft/cotton and viloft/polyester blended knitted fabrics were examined, no statistically significant difference was found between the relative water vapor permeability of both fabric mixtures. The amount of viloft in fabric blends has little, not statistically significant, effect on water vapor permeability.
in the sources from acrylic fiber called high bulk There are studies in which the water vapor permeability of fabrics is examined. High bulk acrylic fibers are obtained by shrinking acrylic fibers with high tensile properties by treating them with boiled water. In these studies, water vapor permeability of woven fabrics consisting of high bulk acrylic, cotton and mixtures of these fibers were examined. As the amount of acrylic fiber increased, the water vapor permeability of the fabrics increased. It has been stated that the shrinkage of the acrylic fibers in the yarn causes the buckling of the cotton fibers and the water vapor permeability increases as small pores are formed in the yarn.
It has been stated that adding elastane in the weft direction reduces the water vapor permeability values by 20% compared to cotton fabrics without elastane, since it causes a decrease in the density values. As in woven fabrics containing elastane, the addition of elastane in knitted fabrics caused a decrease in water vapor permeability of cotton knitted fabrics.
The effect of the polyester fiber fineness value on the water vapor permeability values of the fabrics was investigated, In the study of Hatch et al., Fabric made from polyester fiber with a thinner fiber diameter (1,5 denier) has higher water vapor permeability than fabric made from polyester fiber with a thicker fiber diameter (3,5 denier) has shown.
In the study by Sampath et al.Fabrics consisting of micro polyester fibers showed higher water vapor permeability than fabrics made from polyester fibers of normal fineness. It has been stated that the larger surface area of micro polyester fabrics increases the water vapor transmission.
Varshney and friends investigated the water vapor permeability of polyester fabrics with circular, triangular, clover-shaped fiber profile. Fabrics with non-circular cross-section, especially triangular and clover-shaped fibers, showed higher water vapor permeability than fabrics made from circular cross-section fibers due to high porosity.
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