Thermophysiological comfort and objective hand properties of modal, Naia™, cashmere and cotton included denim fabrics

In this study, the thermophysiological comfort and objective hand properties of modal, Naia™, cashmere, and cotton containing denim fabrics were investigated. Therefore, the air permeability, thermal conductivity, thermal absorptivity, thermal resistance, water vapor permeability, overall flexural rigidity, and compressibility of the fabrics were examined. It was concluded that using Naia™ sustainable fiber improved the thermal comfort and objective hand properties of denim fabrics. The elastane containing fabrics (T5 and T6) were uncomfortable because of their lower air permeability, lower water vapor permeability and higher overall flexural rigidity properties. Sulfur dyeing only affects the thermal resistance of fabrics, and the thermal resistance of sulfur dyed fabrics is higher than that of indigo dyed fabrics with the same compositions.


Introduction
Denim is a durable cotton fabric traditionally woven with indigo dyed warp yarns and white fills.Studies have been conducted on the use of regenerated cellulose and animal fibers in denim structures, together with cotton and polyester.The cellulosic fiber modal developed by Lenzing is mostly preferred in underwear and daily wear because it prevents sweating.The natural modal produced from beech wood is a completely natural fiber type with high wet and dry strengths.The manufacturer claims that it is quite resistant to wear, has good moisture transfer properties, and has a soft touch. 1 Modal fiber can also be used in denim fabric structures owing to its silky appearance and soft handling properties.
Cashmere fiber was obtained from goats living in high and dry plateaus from northern China to Mongolia, including the Gobi Desert.Cashmere fibers have a soft, light, warm, and matte appearance. 2 Cashmere is commonly referred to as "soft gold" or "fiber diamond" and is one of the softest and warmest animal fibers used mainly for clothing. 3Cashmere is not the best material for making jeans, because it requires dry cleaning and is prone to pilling. 4 However, it can be used in certain proportions in denim construction owing to its thermal properties.Recently, there has been increasing interest in the use of recycled materials as alternatives to clothing and denim fabric.
The Naia™ cellulosic acetate fiber allows safe solvents to be recycled and reused owing to its closed-loop manufacturing process, resulting in fiber with a low environmental impact.It is obtained by acidifying the cellulose raw material obtained from wood and cotton fibers, dissolving the acetyl cellulose, and spraying the solution.This raw material, also known as rayon, has become the favorite fiber of fashion and designers in the textile industry today.It can be used as a raw material in the manufacture of high value-added products when its properties, such as sustainability, silky softness, fast drying, unique touch, and antipilling, are considered. 5Consisting of 40% confirmed recycled waste plastics and 60% wood pulp from sustainably managed forests, Naia™ Renew adds worth to waste and materials. 6egenerated cellulose fibers are used in the production of denim fabrics for the development of comfort.For this purpose, regenerated cellulose, modal, Tencel, and bamboo yarns were used in the weft direction.It was found that cellulosic content determines the moisture content within the fiber, resulting in a cool sensation. 7Sabir and Doba Kadem investigated the comfort properties of raised and laminated denim fabrics and measured their air and water vapor permeabilities.Raising and laminating processes were found to increase thermal resistance and air permeability 8 In another study, the effects of different finishing treatments on the thermal and moisture management properties of 100% cotton denim fabrics were investigated.The thermal comfort features of denim fabrics were affected by the weight of the fabric, as the weight increased, water vapor and air permeability decreased. 9The impacts of different softeners on the thermal comfort of 98% cotton and 2% elastane including denim fabrics were examined.It was found that non-ionic and anionic softeners applied fabrics had low thermal conductivity values. 10Şen et al. investigated the fastness and dimensional stability of regenerated cellulose fibers such as Naia™, Tencel, and Ecocell knitted fabrics.It was found that regenerated cellulose fibers could be an alternative to cotton and could be used in clothing because of their comfort properties 6 The effects of using elastane, T400 elastane, and wool elastane yarns in denim structures have been investigated in a previous study.For this purpose, the elasticity, fabric growth, thermal resistance, air permeability, and water vapor permeability were measured.It was observed that dual-core weft yarn containing wool yarn/elastane improved the comfort properties without negatively affecting the elasticity and fabric growth. 11In another study, the thermal comfort of chenille weft yarn included denim fabrics was investigated to improve the potential of denim fabrics in cold climates.It was found that permeability of denim decreased with bulkier pile materials and acrylic pile had a smoother surface. 12Saricam investigated the comfort features of hemp and flax including denim.It was observed that the blended fabrics had good moisture management and thermal properties than cotton. 13In another study, the impact of different washings on mechanical and tactile properties of denim fabrics were investigated with Kawabata KES-FB device.It was found that the compressibility of fabrics increased after finishing operations, and finished cotton fabrics were stiffer than untreated ones. 14he shrinkage and tensile properties of denim fabrics were examined in another study.It was found that elastic yarns exhibited higher shrinkage and a new parameter was introduced to understand fabric comfort. 15ustainable generation in textiles is a significant topic, and new generation regenerated cellulose fibers significantly improve sustainability.One of the aims of this study was to examine the effect of Naia™ fibers obtained by acidifying cellulose raw materials obtained from wood and cotton fibers on the thermal and hand features of the denim fabric structure.The difference between this study and previous studies is that it investigates the use of new-generation fibers, such as modal, Naia™, and cashmere in denim structures.Studies have generally investigated the thermal comfort properties of denim fabrics containing cotton, polyester, elastane and the impacts of the different washing operations applied to them.In addition, the effects of new-generation fibers on thermal comfort, water vapor permeability, compressibility, and overall flexural rigidity were investigated in this study.

Material and method
The structural properties of the denim fabrics are listed in Table 1.The textile sector, especially the denim sector, is the largest end user of vat and sulfur dyes, and 80% of denim is dyed in classic blue, black-blue, or blue black shades using indigo and sulfur black dye. 16All fabric samples were produced with the same warp yarns (50% modal/ 50% Naia™) and by changing the weft yarns and two different dyeing methods (indigo and sulfur).The TS 391 EN ISO 9237 standard and SDL Atlas Air Permeability device were used for the air permeability measurements.For the air permeability measurements, the test area was 20 cm 2 , air pressure was 100 Pa and the unit of air permeability was l/m 2 /s. 17he thermal resistance (m 2 °K/W), thermal conductivity (W/m °K), and thermal absorptivity (Ws 1/2 m −2 °K−1 ) of the fabrics were tested using an Alambeta device according to the EN ISO 11092 (EN ISO 11092 standard).The relative water vapor permeability (%) of the samples was obtained using the Permetest instrument according to the EN ISO 11092 standard (EN ISO 11092 standard). 18In addition, a James Heal thickness test device was used to measure fabric compressibility.The fabrics were compressed under pressures of 5 and 50 g/cm², and the compression ratios were determined as a percentage by determining the difference between the fabric thicknesses.The James Heal Shirley Stiffness Tester was utilized for bending rigidity measurements of fabrics according to ASTM 1388-64 and TS 1409 standards. 19The Shirley Stiffness Tester and overhang length of the tested fabric are shown in Figure 1.
The following equations were used to calculate the overall flexural rigidity:

Air permeability
Air permeability is the volume of air in liters that is passed through 100 cm 2 of fabric in 1 min at a pressure difference  of 10 mm head of water. 17,21When the air permeability of the fabrics was examined, the highest air permeability result was measured for T1 coded 50% modal/50% Naia™ including indigo dyed fabric (Figure 2).It was declared that viscose/Tencel and viscose/modal blends have better mechanical and comfort features than 100% cotton and 100% viscose; therefore, such sustainable blends can replace 100% cotton in clothing. 22The lowest air permeability value was measured for T5, which was 37% cotton/ 31% modal/31% Naia™/1% elastane including indigo dyed fabric.When the effect of dyeing on the air permeability of fabrics was examined, it was found that the dyeing method was not a determining factor for the air permeability.Although the Naia™ fiber was used in the warp direction in all fabrics, it can be said that the air permeability value increased even more when the Naia™ fiber was used in the weft direction.It can be concluded that as the Naia™ fiber content increased in the fabric composition, the air permeability increased, except for the elastane containing fabrics.Although it is used in small amounts, the elastane content reduces the air permeability value by tightening the structure, as in previous studies. 23The ANOVA test showed that the fabric factor had a significant impact on air permeability (p = 0.00 < 0.05).

Thermal comfort properties
Thermal conductivity.The coefficient of thermal conductivity (λ) represents the amount of heat that passes from a 1 m 2 area of the material through a distance of 1 m within 1 s and causes a temperature difference.The thermal conductivity of the textiles varies between 0.033 and 0.01 W/m °K. 24The thermal conductivity results of the fabrics are shown in Figure 3.The fiber type, amount of entrapped air in the fabric structure, and any treatment applied to the fabric affect this feature.In this study, fabric weights were approximated and the effects of different fiber types, compositions and two dyeing processes were examined.The highest thermal conductivity was measured for T5, which contained 37% cotton/31% modal/ 31% Naia™/ 1% elastane.The lowest thermal conductivity was measured for the T1 coded 50% modal/ 50% Naia™ fabric.The thermal comfort of cotton and viscose rayon fabrics was compared in a previous study, and it was observed that the thermal conductivity of cotton was higher than that of viscose rayon. 25In this study, the thermal conductivity of fabrics containing Naia™ fiber was measured to be lower than that of fabrics with higher cotton content.As a result, it can be said that as the Naia™ fiber ratio increased in the mixture, the thermal conductivity decreased.When the T2 and T3 coded fabrics were compared, it was observed that there was no difference in the thermal conductivity between sulfur dyeing and indigo dyeing.When the T4, T5, and T6 coded fabrics were compared, the lowest thermal conductivity was measured for the T4 coded fabric sample containing 4% cashmere.It was observed that using elastane in the fabric composition increased the thermal conductivity of the fabrics, as in a previous study. 26he ANOVA test showed that the fabric factor had a significant impact on thermal conductivity (p = 0.00 < 0.05).
Thermal absorptivity.Thermal absorptivity is an objective measure of the warm-cool feeling of fabrics and can be expressed by the following equation: where λ is the thermal conductivity, ρ is density of fabric, and c is the specific heat of the fabric. 27The thermal absorptivity value of fabrics is affected by the surface roughness, and the heat flow increases if the contact area between the skin and fabric is increased. 9The value calculated can be used to explain the thermal handle of textile. 28he highest thermal absorptivity value was observed for T6, which was 37% cotton/ 31% modal 31% Naia™/ 1% elastane including sulfur dyed fabric (Figure 4).This means that the fabric felt colder than the other fabrics.When the T4, T5, and T6 coded fabrics were compared, the lowest thermal absorptivity was measured for the T4  coded fabric containing 4% cashmere.It can be said that this fabric felt warmer in contact than the others did.It was stated that the thermal absorptivity of fabrics containing 10% or more cashmere in the fabric structure is lower than that of the others. 29The lowest thermal absorptivity was observed in the T1 coded 50% modal 50% Naia™ fabric, which also had the lowest thermal conductivity value.In a previous study, the highest thermal absorptivity was measured in 100% modal fabric compared with viscose and cotton. 30Therefore, it can be said that the use of Naia™ fiber together with modal fiber reduced the thermal absorptivity value of the fabric.In addition, the thermal absorptivity value is related to the fabric density; as the fabric density decreases, the thermal absorptivity value also decreases.The lowest thermal absorptivity was observed for the fabric with the lowest bulk density of 50% Naia™/50% modal, which means that this fabric felt warmer than the others.The ANOVA showed that the fabric factor had not a significant effect on the thermal absorptivity of the fabrics (p = 0.159 > 0.05).
Thermal resistance.Thermal resistance is an indicator of how good thermal insulation properties of a material, and can be calculated using the following equation: where h is the thickness of the fabric (m) and λ is the thermal conductivity (W/m °K). 31The thermal resistances of the fabrics are shown in Figure 5.The highest thermal resistance was observed for the 50% modal/ 50% Naia™ fabric (T1), which exhibited the lowest thermal conductivity.When T1, T2, and T3 coded fabrics are compared, it can be said that the fiber type has an impact on the thermal resistance value, and the thermal resistance of the T1 coded fabric containing 50% Naia™ was higher.In addition, this can be explained by the fact that the density of the fabric is lower than that of the other fabrics.An inverse relationship exists between the thermal resistance and the density of the fabric.As the fabric density decreased, the air gaps between the fibers increased. 32Consequently, the heat transfer of the fabric decreased, increasing the thermal resistance of the fabric.It can be concluded that the T1 coded 50% Naia™ included fabric retained more entrapped air within its fabric structure than the other fabrics.Because the thermal resistance of the entrapped air is much higher than that of the fibers, the thermal resistance of this fabric (T1) was measured to be higher than that of the other fabrics.When the T2 and T3 coded fabrics are compared, it can be said that the thermal insulation of the fabric with the sulfur dyeing process is higher than that of the fabric with the same content of indigo dyeing.In previous studies, it has been stated that the thermal resistance properties of cotton/modal fabrics are better than those of 100% cotton fabric because of the high thermal conductivity of cotton. 33The lowest thermal resistance was observed in T5 coded 37% cotton/31% modal/ 31% Naia™/1% elastane fabric.When the T4, T5, and T6 coded fabrics were compared, it was observed that the thermal resistance of the sulfur dyed fabric was higher than that of the indigo dyed fabric.It can be concluded that the thermal resistance of sulfur dyeing is higher than that of indigo dyeing for fabrics of the same composition.The ANOVA test  showed that the fabric factor had a significant effect on the thermal resistance of the fabrics (p = 0.00 < 0.05).

Relative water vapor permeability
The relative water vapor permeability of textile samples is an important factor that determines the relative heat flux responsible for body cooling.The water vapor permeability of a garment fabric must be sufficiently high to allow water vapor to be continuously released from the skin, even when the person is in an inactive state. 34This can be calculated using the following equation: where q 0 [W/m 2 ] is the heat flow passing through the measuring head without the sample and q S [W/m 2 ] is the heat flow passing through the measuring head covered by the sample. 35The water vapor permeability of fabrics is a considerable comfort parameter because it facilitates the evacuation of excess sweat to the outside environment, especially in hot and humid environments.Additionally, in hot environments, fabrics should allow a greater amount of sweat to be thrown away from the skin surface to the outside by diffusion.A higher relative water vapor permeability indicates a lower water vapor resistance (R et ) and better thermal comfort of the garment. 36The highest RWVP was measured in T1 coded 50% modal/50% Naia™ fabric (Figure 6).It can be said that when clothes made of this fabric are worn, it will be easier to throw away sweat on the outer surface and the users feel more comfortable.The lowest RWVP values were observed for the elastane included T5 and T6 coded fabrics.In a previous study, cotton/spandex containing denim fabrics showed lower air and water vapor permeability values than those made from 100% cotton weft yarn. 37It can be said that the use of elastane in the weft direction reduced water vapor permeability.When a sufficient amount of water vapor is not removed from the body, the relative humidity on the skin surface increases, and the person feels uncomfortable.It can be said that when the T5 and T6 coded fabrics are worn, it is difficult to throw away sweat to the outer surface, and people feel uncomfortable.When we compared T1, T2, and T3 coded fabrics, the highest relative water vapor permeability was measured in the T1 coded fabric containing 50% modal/50% Naia™, which underwent indigo dyeing.Notably, the highest water vapor permeability among these fabrics was measured for the fabric containing the most Naia™ fibers (T1).The ANOVA test showed that the fabric factor had not a significant effect on water vapor permeability of the fabrics (p = 0.215 > 0.05).

Objective hand properties
Flexural rigidity.The overall flexural rigidity is affected by many factors, including the yarn-to-fabric construction and washing process applied.As the bending length increases, the stiffness of the fabric also increases.Fabrics with higher bending stiffness are difficult to sew and have poor handle values. 38,39Flexural rigidity is an important factor that affects tactile comfort.When we touch the fabric, we can feel tactile sensations such as smoothness, evenness, stiffness, and softness.Fabrics with higher overall flexural rigidity values are very stiff fabrics and feel uncomfortable.However, a lower overall flexural rigidity indicates that the fabric has good drape and better comfort.
The flexural rigidity of the fabrics in the warp direction was higher than that in the weft direction (Figure 7).The highest warp flexural rigidity values were observed for T5 and T6 elastane containing fabrics.In addition, these fabrics exhibited the highest flexural rigidity in the weft direction.This supports the previous study of fabrics including elastane, as single or double core yarns, having greater stiffness than fabrics that do not. 40The lowest warp flexural rigidity was observed in T1 coded 50% modal/ 50% Naia™ included fabric, and the lowest weft flexural rigidity value was observed in T4 coded 36% Naia™/35% modal/25% cotton/4% cashmere included fabric.The overall flexural rigidity results of the fabrics are shown in Figure 8.The highest overall flexural rigidity was observed for T5, which was 37% cotton/31% modal/31% Naia™/1% elastane containing fabric.It also exhibited the highest warp and weft flexural rigidities.It was found that the fabric handle was inversely proportional to the bending value, and if the bending rigidity increased the fabric handle value decreased. 41Which means T5 coded fabric had the worst handle value, and the sewability of the fabric was lower than that of the others.The lowest overall flexural rigidity was measured for T1 coded 50% modal/ 50% Naia™ fabric, which had the lowest warp flexural rigidity.It can be concluded that the more Naia™ fiber in the fabric composition, the fabric felt softly and its sewing properties easier.

Compressibility
Compression can affect various characteristics of fabrics such as fabric hand, drape, bulkiness, comfort, and thermal insulation properties. 42The compressibility features of fabrics are important in terms of final application, use, softness, handling, bending quality, tearing, drape, and overall quality.The higher the compressibility of woven and non-woven fabrics, the softer the fabric can be said. 43he highest compressibility value was observed for T1 coded 50% modal/50% Naia™ included indigo dyed fabric (Figure 9).This means that the fabric felt softer than other fabrics.Notably, this fabric also exhibited the highest thermal resistance, lowest thermal absorptivity, and lowest overall flexural rigidity.The lowest compressibility value was observed for T3, which was 42% cotton/ 29% modal/ 29% Naia™.This means that this fabric is a worse handle than other fabrics.It was also found in a previous study that the use of modal and Tencel yarns with cotton in the denim reduced compressibility. 44In this study, the compressibility feature of the fabric containing modal/Naia™ in the weft and warp directions was the highest, and the compressibility feature decreased when cotton and cotton/ elastane yarns were used instead of Naia™ fiber in the weft direction.The ANOVA test showed that the fabric factor had a significant impact on the compressibility of the fabrics (p = 0.00 < 0.05).

Conclusion
The thermophysiological comfort and objective hand properties of modal, Naia™, cotton, cashmere including, indigo and sulfur dyed denim fabrics were examined.The highest Naia™ composition T1 coded fabric showed the highest air permeability, thermal resistance, water vapor permeability and compressibility values.On the other hand, the lowest thermal conductivity, thermal absorptivity and overall flexural rigidity values were seen in this fabric.It was observed that T1 fabric felt warmer and softer than the other fabrics, and its sewability was easier than that of the other fabrics.The elastane including T5 and T6 coded fabrics showed the lowest air permeability, lowest water vapor permeability, and the highest thermal conductivity, absorptivity, and overall flexural rigidity.It can be concluded that the fabrics coded as T5 and T6 were uncomfortable because of their lower air and water permeabilities.Sweat could not easily pass through the outer side of the fabric, and the sewability of these fabrics was more difficult than that of the others.The results showed that using sustainable fibers, such as Naia™ improved the thermal comfort and objective hand properties of the denim fabrics.In addition, the advantage of using cashmere in the weft instead of elastane is that it increases air permeability, water vapor permeability, and compressibility.Sulfur dyeing only has an impact on the thermal resistance of fabrics, and the thermal resistance of sulfur dyed fabrics is higher than that of indigo dyed fabrics with the same composition.
c = bending length in cm, O = overhang length in cm, G = Flexural rigidity in mg.cm, W = weight per unit area in mg/ cm 2 , Go = Overall flexural rigidity, Gw = Warp flexural rigidity, and Gf = Weft flexural rigidity.20Statistical significance of variances was tested with an ANOVA single factor test with the SPSS 23 program.The p-values were taken to look at the significance of the factor, and if the p-value was higher than (p > 0.05), there was no significant change.

Figure 1 .
Figure 1.Shirley Stiffner tester and overhang length of denim fabric.

Figure 6 .
Figure 6.Relative water vapor permeability of denim fabrics.

Table 1 .
Properties of fabrics.