Analyzing Thermophysiological Comfort and Moisture Management Behavior of Cotton Denim Fabrics

2.1 Materials

Bleaching, resin, and softener treatments were applied to 100% cotton denim fabrics. The samples were woven using 3/1 Z twill weave in three different weights (light, medium, heavy) to show the effect of fabric weight on comfort. Ring spun yarns were used to produce fabrics. To obtain different fabric weights, light weight denim fabrics were produced using 50 tex in the warp yarn and 36 tex in the weft yarn; medium weight denim fabrics were produced using 60 and 62 tex for weft and warp yarns; heavy weight denim fabrics were produced using 65 and 70 tex for warp and weft yarns. Then, fabrics were processed using three different finishing treatments (resin, bleaching, softener).

Samples were conditioned for 48 h in the atmospheric conditions of temperature 20 ± 2°C and relative humidity 65 ± 2%, before the measurements on the samples were taken. The thickness was measured according to standard ASTM D 1777-64 under 20 g/cm² pressure with 0.01 mm precision.

2.2 Method

Table 2 shows the finishing processes for denim fabrics in detail.

Alambeta was used to test thermal absorptivity and thermal resistance of the fabrics [25]. The Alambeta instrument simulates the dry human skin, and its working principle is based on the mathematical processing of time course of heat flow passing through the fabric. The Permetest instrument was used to measure water vapor resistance and water vapor permeability according to the ISO 11092:2014 standard [26]. The air permeability of the samples was measured by using the Prowhite test apparatus according to standard EN ISO 9237:199519 by applying 100 Pa constant air pressure and 20 cm² sample size [27]. As conducted in the study of Fangueiro et al., drying capabilities were evaluated by calculating WERs [28]. The specimens were prepared 200—200 mm in dimensions and weighed. The amount of water was 30% of the dry specimens’ weight, and it was used to wet the specimens. The changes in weights with time were recorded to calculate WER values. Each denim sample was tested five times for all mentioned tests.

3.1 Thermophysiological comfort properties

Heat transfer characteristics of fabrics are very important for thermal comfort and protection against weather conditions. Insulation properties of clothing are caused by the small air pockets separated from each other to prevent air from migrating through the material. Thermal resistance gives thermal insulation property of a fabric. The results of thermal resistance of fabrics are given in Figure 1. It was generally observed that thermal resistance values were increased as the fabric weights increased. Bleaching and softening processes increased the thermal resistance values very much because they increased the fabric thickness values, created more area and air inside the fabric structure, and led to more insulation. Resin application created more stiff fabric structure by decreasing yarn and fabric hairiness and decreased fabric thermal resistance values.

Figure 1

Thermal resistance results of denim fabrics.

Thermal absorptivity of fabrics is influenced by surface smoothness; if the contact area between fabric and skin increases, heat flow increases. As seen from Figure 2, as the fabric thicknesses were increased from lightweight to heavy weight, thermal absorptivity values increased. Rigid denim fabrics made without any prewash had higher thermal absorptivity values because of their stiff fabric structure and smooth surface. Fabric weight had an increasing effect on thermal absorptivity of rigid fabrics. Softening and bleaching applications decreased thermal absorptivity by creating more spacing that is interior. Resin fabric structure with medium and high weights had also the highest level of thermal absorptivity. As a general trend, as the fabrics weight increased from lightweight to medium weight, thermal absorptivity increased, but from medium to heavy weight, no significant change has been observed.

Figure 2

Thermal absorptivity results of denim fabrics.

Air permeability is the tendency to air penetration and affects the thermal insulation of the fabric. In the study, it was observed that due to the compact structures of fabrics with higher weights, air permeability results of fabrics were getting lower as the fabric weights were increased (Figure 3). Denim fabrics with higher fabric weights reduced spaces between yarns and decreased air passage.

Figure 3

Air permeability results of denim fabrics.

Vapor transmission through the fabric structure was mainly influenced by fabric thickness. As shown in Figure 4, as the fabric weight and also fabric thickness values were getting higher, water vapor permeability values of fabrics decreased. As the fabric weight increased, its ability to hold moisture increased.

Figure 4

Relative water vapor permeability results of denim fabrics.

Water vapor resistance is the ability of a fabric to allow moisture vapor to be transmitted through it. Water vapor resistance values of denim fabrics are shown in Figure 5. As it can be expected, the higher the fabric weight, the higher the water vapor resistance values obtained. The most important conclusion was that heavy fabric structures had higher water vapor resistance results that were not suitable for human comfort. Water vapor resistance values increased dramatically as the fabric weight increased for rigid and resin fabrics. Bleached and softened fabrics had lower resistance values because of greater thickness values creating more area for transmitting water vapor. As the fabric thicknesses increased, water vapor resistance values decreased because there was more space within the fabric structure for the passage of water vapor.

Figure 5

Water vapor resistance results of denim fabrics.

3.2 Transfer wicking and drying results

Transfer wicking results are shown in Figure 6. Transfer wicking is the transmission of liquid water through the thickness of a fabric. As stated by the researches, fiber type (hydrophobic, hydrophilic), fabric structure (mass, thickness), and finishing treatments had certain effects on the wetting and wicking properties of a fabric [29,30]. It can be seen from Figure 7 that as the fabric weight increased, transfer wicking values decreased because water holding capabilities of fabrics increased. Bleaching and softening treatments had significant influences on the transfer wetting values of fabrics. Softened fabrics had highest transfer wicking values because of the increase in fabric thickness. Wicking behavior of a fabric was strongly influenced by fabric weight and thickness values [30].

Figure 6

Transfer wicking results of denim fabrics.

Figure 7

Water evaporation rate values of fabrics.

The length of time required for a garment to dry while being worn is therefore important in maintaining a desired level of “comfort” and minimizing the additional weight from the liquid that the garment may have absorbed. Evaporation of water/sweat is a mechanism by which fabric and clothing dries during wear and also cools the human body by taking the required heat energy from the human body for the process [1].

Figure 7 shows the WERs of the samples. The WER values showed a decreasing trend when the fabric thicknesses increased. The drying is mainly related to the fabric density of the woven fabrics, so drying times are longer for heavy weight and thick fabrics for the same fabric construction. Heavy weight fabrics 4.3, 1.3, 2.3, and 3.3 had the highest drying time values. It may be due to the fact that the total contact area of fibers holding water is higher in heavy weight fabrics because of the higher fiber volume fraction in their structure. Denim fabrics with codes 3.1, 3.2, and 2.1 had the fastest drying times because of their lower weights. Moreover, finishing type was found to have a big influence on the drying behavior of fabrics. We had found parallel results with the previous studies stated in the literature, which concluded that drying time was mainly related to the spaces inside the fabric and fiber thickness [29,30,31].

3.3 Statistical analysis

Correlation coefficient results are shown in Table 3. We have obtained high correlation values between fabric weight and thermal absorptivity, RWVP, AWVP, air permeability, and transfer wicking. Fabric thickness values also had high correlation coefficient values especially with WER, thermal resistance, RWVP, air permeability, and transfer wicking.

The influence of fabric weight and finishing processes on the thermal comfort characteristics of denim fabrics was evaluated with one-way analysis of variance (ANOVA) statistical analysis. One-way ANOVA test results for factor weight are given in Table 4. As it is seen from the table, there is a significant effect of weight type (light, medium, heavy) on transfer wicking, WER, thermal absorptivity, air permeability, RWVP, and AWVP results (p<0.05). The finishing process had been found to be effective especially on thermal resistance values of denim fabrics (Table 5).