Dimensional, Physical and Thermal Properties of Plain ... - Springer Link

Fibers and Polymers 2011, Vol.12, No.8, 1083-1090

DOI 10.1007/s12221-011-1083-3

Dimensional, Physical and Thermal Properties of Plain Knitted Fabrics Made from 50/50 Blend of Modal Viscose Fiber in Microfiber Form with Cotton Fiber Ahu Demiroz Gun Textile Engineering Department, Engineering Faculty, Usak University, Usak, Turkey (Received April 11, 2011; Revised July 8, 2011; Accepted July 15, 2011) Abstract: In this study, the dimensional, physical and thermal comfort properties of the plain knitted fabrics made from 50/50 blend of modal viscose fiber in microfiber form with cotton fiber are compared with those of the similar fabrics made from 50/50 blend of conventional modal viscose fiber with cotton fiber and made from 100 % cotton fiber. All the fabric types are produced in three different stitch lengths. The slight differences among the fabric types are observed in terms of the stitch density results and the dimensional constants calculated in the fully relaxed state. In the fully relaxed state, the dimensional K values of the modal microfiber blended knitted fabrics are found to be more closely resemble those of the cotton fabrics rather than those of the conventional modal fiber blended fabrics. The lowest fabric thickness and bursting strength results are obtained for the modal microfiber blended fabrics. The modal microfiber blended fabrics reveal lower air permeability than the conventional modal fiber blended fabrics and higher air permeability than the cotton fabrics. It is also observed from the thermal comfort results that the modal microfiber blended fabrics have the lowest thermal resistance and the highest thermal absoptivity values. The thermal conductivity results of the modal microfiber blended fabrics are lower than those of the cotton fabrics and higher than those of the conventional modal fiber blended fabrics. Because of the highest thermal absorptivity values, the modal microfiber blended fabrics provide the coolest feeling when compared with the other two fabric types. Keywords: Microfiber, Micromodal air, Modal, Viscose, Cotton, Plain knitted fabric, Dimensional properties, Thermal comfort properties, Blended fabrics

recently. The dimensional, physical and thermal comfort properties of the plain knitted fabrics having modal viscose microfiber are investigated in comparison with those of the similar fabrics having conventional modal viscose fibers. The fabrics with microfiber reveal lower shrinkage, thickness, air permeability and, higher bursting strength and pilling tendency than those with conventional fiber. It is also observed from the thermal comfort results that the fabrics made from microfiber have higher thermal conductivity, thermal absorptivity and maximum heat flux values and, lower thermal resistance and thermal diffusivity values. As can be seen from the literature given above, in these very limited studies, the properties of knitted fabrics made from 100 % micromodal fiber [5,6] are dealt with. Modal fiber or its microfiber form is often blended with different fibers such as cotton, polyester, wool etc. as well as spun alone. The combination of modal fiber or its microfiber form with cotton fiber is one of the most preferable blends and allow the production of fine and super fine yarns without using high quality cotton fiber [2]. The combination of modal fiber in microfiber form with cotton fiber is frequently used in a wide range of knitwear applications including underwear, shirting, blouses, dresses etc. In this study, the dimensional, physical and thermal comfort properties of the plain knitted fabrics made from 50/50 blend of modal viscose fiber in microfiber form with cotton fiber are investigated. In order to see the differences and similarities, the results are then compared with those of

Introduction Modal viscose fiber is one of the regenerated cellulose fibers. It is obtained by process giving a high tenacity and a high wet modulus [1]. Compared with viscose fiber, modal fiber is characterized by some advantageous properties such as higher dry and wet tenacities, higher wet modulus, lower water retention capacity and lower level of swelling [1,2]. Fabrics made from modal fiber are claimed to have bright colors, and soft and silky handle [3]. Therefore, modal fiber is frequently used as an alternative to viscose fiber due to its better properties. Modal fiber is produced in different fineness values. Microfiber form, which is defined as a fiber in the 0.1-1.0 dtex range [4], is commonly used to provide fabrics with more functional and aesthetic fabric properties. A limited number of studies have been reported about knitted fabrics having micromodal fiber so far. Srinivasan and Ramakrishnan [5] investigated the properties of knitted fabric made from high performance viscose microfiber in comparison with those of the fabrics made from conventional viscose fiber and cotton fiber. Knitted fabrics with high performance viscose microfiber reveal better drapeability, spirality, bursting strength, dimensional stability, and fabric cover properties than those with conventional viscose fiber and cotton fiber. Another comparative study has been carried out by Gun [6] *Corresponding author: [email protected] 1083

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similar fabrics made from 50/50 blend of conventional modal viscose fiber with cotton fiber and made from 100 % cotton fiber.

Experimental In order to produce the plain knitted fabrics, three different yarn types are used. One yarn type is made from 100 % cotton fiber. The other two yarn types are made from 50/50 blends of modal viscose fibers in different fiber fineness values with cotton fiber. The modal viscose blended yarns are composed of microfiber of 0.8 dtex, and conventional fiber of 1.3 dtex. The modal viscose fibers consisting of the fiber finenesses of 0.8 dtex and 1.3 dtex in the blended yarns are referred by using the commercial names of micromodal air and modal respectively. The properties of the 50/50 micromodal air/cotton, 50/50 modal/cotton and 100 % cotton yarns are presented in Table 1. The knitted fabrics were produced on E28 gauge Terrot knitting machine in 30 inch diameter and with 96 feeders. By using each yarn type, the fabrics in three different stitch lengths were knitted in order to cover the range of tight, medium and loose fabrics. The stitch length values for each fabric type are given in Table 2. Table 1. Yarn properties Yarn types Yarn properties Mean CV% Mean Twist (turns/m) CV% Mean Strength (RKM) CV% Mean Elongation (%) CV% U Evenness (%) CVm Thin places (-50 %) Thick places (+50 %) Neps (+200 %) Hairiness index Count (Ne)

50/50 50/50 micromodal modal/cotton air/cotton 28.71 30.05 4.09 3.71 828.40 798.40 0.28 0.33 19.50 16.7 5.46 5.70 6.35 5.35 5.80 5.82 9.25 8.75 11.73 11.07 0 0 17 11 58 35 5.41 5.45

100 % cotton 29.72 4.34 883.20 0.26 14.25 8.52 5.42 4.58 10.29 12.97 1 28 10 6.80

Table 2. Average stitch length values Yarn types 50/50 micromodal air/cotton 50/50 modal/cotton 100 % cotton

Short 0.258 0.251 0.253

Stitch length (cm) Medium Long 0.280 0.289 0.264 0.275 0.267 0.278

After knitting, some part of the raw fabrics was subjected to dry relaxation. The remainder of the other part was subjected to pretreatment and dyeing processes. After pretreatment and dyeing processes, the dyed fabrics were subjected to full relaxation process. For the dry relaxation, the fabrics were laid on a flat surface in the standard atmosphere of temperature 20±2 ºC and relative humidity 65±2 % for one week. For the full relaxation, the fabrics were washed with 0.05 g/l wetting agent in a fully automatic washing machine at 60 ºC for 1 h and then tumble dried at 70 ºC for 1 h. These washing and tumble drying processes were performed twice. For both the dry relaxed raw and fully relaxed dyed plain knitted fabrics, the stitch density parameters such as wales per cm (wales/cm) and courses per cm (courses/cm) and the stitch length were measured. Wales/cm and courses/cm values were determined by counting the numbers of wales and courses per 10 cm from the twenty different places of the fabrics. The stitches per square cm (stitches/cm2) were obtained by the product of wales/cm and courses/cm values. For the determination of the stitch length, the yarn length over 100 wales in the same course was measured by hanging 10 g weight on it and then, one stitch length was calculated. Thirty yarn lengths were taken from each fabric. The dimensional constants (K values) are calculated by using the following relationships, which were introduced by Doyle and Munden [7,8]. KW = wpc x l

(1)

KC = cpc x l

(2)

KS = S x l

2

(3)

K KR = ------CKW

(4)

where wpc is the wales/cm, cpc is the courses/cm, S is the stitches/cm2, and l is the stitch length in cm. Weight, bursting strength, and air permeability of the fabrics were evaluated according to the standards of TS 251, TS EN ISO 13938-2, and TS 391 EN ISO 9237 respectively. The bursting strength and air permeability tests were performed on Truburst 610 bursting strength and Textest 3300 FX air permeability testers, respectively. Thickness and thermal comfort properties (thermal conductivity, thermal resistance, and thermal absorptivity) of the fabrics were measured with the help of an ALAMBETA device constructed by HES. Before all the measurements, the fabrics were conditioned for 24 h in a standard atmosphere.

Results Dimensional Properties The relationships of the wales/cm and the courses/cm values of the dry relaxed raw and fully relaxed dyed fabrics

Fabrics from 50/50 Blend of Modal Viscose Fiber

Figure 1. Wales/cm values of fabrics with reciprocal of stitch length.

Figure 2. Courses/cm values of fabrics with reciprocal of stitch length.

with the reciprocal of the stitch length are given in Figures 1 and 2, respectively. Figure 1 shows that the fully relaxed dyed fabrics have higher wales/cm than the dry relaxed raw fabrics, which may result from the widthwise shrinkage after the pretreatment, dyeing and full relaxation processes. The wales/cm values of the dry relaxed fabrics do not seem to change with the reciprocal of the stitch length linearly. This observation, which is also consistent with the findings in the previous studies [6,9], indicates that the recovery of strains in the dry relaxed fabrics is slow, especially in the wale direction. However, after full relaxation process, the wales/ cm values linearly change with the reciprocal of the stitch length as expected. When the fiber types are considered, in the dry relaxation state, the micromodal air/cotton fabrics reveal slightly the


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Figure 3. Stitches/cm2 values of fabrics with reciprocal of square of stitch length.

highest wales/cm values. The highest elongation value of the micromodal air/cotton yarn as given in Table 1 may help the fabrics made from such yarn to recover from their strains much more easily. After the full relaxation process, the wales/cm values of the micromodal air/cotton and modal/ cotton fabrics are quite close to each other and lower than those of the cotton fabrics. The higher widthwise shrinkage potential of the cotton fabrics compared with the other fabric types can be explained by swelling tendency of cotton fiber as reported by Suh [10]. In the light of this result, it can be say that after full relaxation, modal fibers seem to reduce the shrinkage tendency of the knitted fabrics, especially in the widthwise direction. Figure 2 shows that the differences between the courses/ cm values of the dry relaxed raw and fully relaxed dyed fabrics are not very high as in the case of the differences between the wales/cm values of such fabrics. Thus, full relaxation process seems to cause widthwise shrinkage rather than lengthwise shrinkage. For both of the relaxation states, the courses/cm values of fabrics change with the reciprocal of the stitch length linearly. In terms of the fiber types, in the dry relaxed state, the modal/cotton and micromodal air/cotton fabrics reveal lower courses/cm values than the cotton fabrics. In the fully relaxed state, the micromodal air/cotton fabrics reveal slightly higher courses/cm values than the modal/cotton and cotton fabrics. For the dry and full relaxation states, the relationships of the stitches/cm2 values with the reciprocal of the square of the stitch length are given in Figure 3. The stitches/cm2 values of all the fabric types from the three yarn types in all stitch lengths seem to be very close. However, the stitches/ cm2 values of the micromodal air/cotton and cotton fabrics are slightly higher than the modal/cotton fabrics. The mean and CV% values of the dimensional constants

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Table 3. K dimensional parameters of the fully relaxed plain knitted fabrics Fibre type 50/50 micromodal air/cotton 50/50 modal/cotton 100 % cotton

KC

KW Mean 4.36 4.27 4.37

CV (%) 2.40 1.61 2.98

Mean 5.70 5.73 5.69

(K values) calculated by using equations (1)-(4) are given in Table 3 for the fully relaxed fabrics from three different yarn types. Since the KW, KC and KS values are positively relate with the stitch density values such as wales/cm, courses/cm and stitches/cm2, these dimensional K values reflect the stitch density values given in Figures 1-3. It can be observed from the K results that the fiber type slightly seems to affect the dimensional K values of the fabric types. The K values of the micromodal air/cotton and cotton fabrics are quite close to each other. The KW and KS values of the micromodal air/ cotton fabrics are higher than those of the modal/cotton fabrics and are slightly lower than those of the cotton fabrics. The KC value of the micromodal air/cotton fabrics is lower than that of the modal/cotton fabrics and is slightly higher than cotton fabrics. The KR value, which is called as loop shape factor, gives the ratio of courses/cm to wales/cm. The KR value of the micromodal air/cotton fabrics is lower than that of the modal/cotton fabrics and is higher than that of the cotton fabrics. From the average K values, it can be concluded that in the fully relaxed state, the dimensional behaviors of the micromodal air/cotton fabrics more closely resemble those of the cotton fabrics rather than those of the modal/cotton fabrics.

KS CV (%) 2.62 1.67 1.60

Mean 24.85 24.44 24.87

KR CV (%) 0.31 1.88 2.25

Mean 1.31 1.34 1.30

CV (%) 5.06 2.71 4.18

potential of the fabrics. The fabric weight values of both the dry and fully relaxed fabrics decrease with the increase of the stitch length. This is because the increase in the stitch length decreases the number of the stitches. The micromodal air/cotton fabrics tend to reveal the highest fabric weight results in both of the relaxation states due to having the slightly lowest yarn count (the thickest yarn) of the micromodal air/cotton yarn used for the production of these fabrics.

Fabric Weight From the weight results in Figure 4, it can be observed that the weight of the dry relaxed raw fabrics increases after the full relaxation treatment as expected, due to the shrinkage

Fabric Thickness The results in Figure 5 show that the fabric thickness results of the fully relaxed dyed fabrics are higher than those of the dry relaxed raw fabrics. This result may also be attributed to the shrinkage potential of the fabrics after dyeing and full relaxation processes. In the dry relaxation state, the fabric thickness does not seem to change with the stitch length. This behavior may result from that the fabrics have not reached the dimensionally stable state after the dry relaxation. However, in the full relaxation state, the fabric thickness increases with the increase of the stitch length. In both of the relaxation states, the micromodal air/cotton fabrics have the lowest fabric thickness values. The highest thickness results are obtained for the cotton fabrics. The fine fibers in the micromodal air/cotton yarn make the yarn structure more compact. The compactness in the yarn structure may decrease the yarn bulkiness, leading to decrease in the fabric thickness. The lowest hairiness index value of the

Figure 4. Fabric weight results.

Figure 5. Fabric thickness results.


micromodal air/cotton yarn as given in Table 1 may also be other possible reason for the lowest thickness results of the fabrics made from such yarn. Similarly, the highest thickness values of the cotton fabrics may be attributed to the highest hairiness index value of the cotton yarn. Bursting Strength The bursting strength results of the dry relaxed raw and fully relaxed dyed fabrics given in Figure 6 reveal that except for the cotton fabrics, the dry relaxed raw fabrics have higher bursting strength results than fully relaxed dyed fabrics. This can be attributed to the fact that the chemicals, mechanical agitations and heat during pretreatment, dyeing and full relaxation processes applied to the fabrics may reduce the bursting strength of the fabrics by damaging the fabric structure. The comparison of the bursting strength results of the micromodal air/cotton fabrics with those of the modal/cotton fabrics in the dry relaxed state indicates that the bursting strength values of the micromodal air/cotton fabrics are higher than those of the modal/cotton fabrics. This is because the micromodal air/cotton yarn has higher strength than the modal/cotton yarn as given in Table 1. However, in the fully relaxed state, the bursting strength behaviors are reversed for these two fabric types. The micromodal air/ cotton fabrics reveal lower bursting strength values than the modal/cotton fabrics. According to this result, yarn strength does not seem to influence the bursting strength of the fully relaxed such fabrics. The reason of this case may be explained by the thickness results of these fabric types. Thicker fabrics may increase the resistance towards the applied force. Consequently, the lower fabric thickness values of the micromodal air/cotton fabrics when compared with the modal/cotton fabrics as given in Figure 5 may lead to decrease in the bursting strength of these fabrics. The comparison of the micromodal air/cotton and modal/cotton fabrics with the cotton fabrics in terms of the bursting

Figure 6. Bursting strength results.


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strength indicates that the bursting strength values of these two fabric types are lower than those of the cotton fabrics in the both of the relaxation states. Therefore, the cotton fabrics reveal the highest bursting strength results although the cotton yarn used to produce these fabrics has the lowest yarn strength. This results can also be attributed the highest fabric thickness results of the cotton fabrics. The bursting strength results of the dry and fully relaxed fabrics tend to decrease with the increase of the stitch length. The reason of this can be explained by the stitch density values of the fabrics. As the stitch length increases, the stitch density values of the fabrics decrease. Therefore, the less number of stitches meet the applied bursting strength. Air Permeability Figure 7 shows that the air permeability results of the fully relaxed dyed fabrics are lower than those of the dry relaxed raw fabrics as might be expected from the shrinkage properties. For both of the relaxation states, the micromodal air/cotton fabrics slightly reveal lower air permeability than the modal/cotton fabrics. The finer fibers in the micromodal air/cotton fabrics may make the fabric structure more compact, leading to prevent the air passage through the fabric structure. When the micromodal air/cotton fabrics are compared with the cotton fabrics, it is observed that the micromodal air/cotton fabrics for both of the relaxation states have higher air permeability results. This result may be explained in the light of the fabric thickness and yarn hairiness index values. The highest hairiness index values of cotton yarns and the highest thickness values of the fabrics made from such yarns may increase the compactness of the fabric surface. The air permeability also tends to increase with the increase of the stitch length as expected. As the stitch length increases, the compactness of the fabrics decreases due to the decrease in the number of stitches.

Figure 7. Air permeability results.

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Figure 8. Thermal conductivity results of the fully relaxed dyed fabrics.

Figure 9. Thermal resistance results of the fully relaxed dyed fabrics.

Thermal Conductivity The thermal conductivity results of the fully relaxed fabrics are shown in Figure 8. The comparison of the fabric types in terms of the thermal conductivity indicates that the micromodal air/cotton fabrics have lower thermal conductivity than the cotton fabrics and have higher thermal conductivity than the modal/cotton fabrics. According to results, the highest thermal conductivity values belong to the cotton fabrics. Thermal conductivity of a fibrous material mainly depends on the combination of conductivities of fiber and of air entrapped within a fabric [11-13]. The conductivity of a fiber is higher than that of air [11]. The lowest air permeability of the cotton fabrics as given in Figure 7 indicates that the ratio of fibers to air is the highest for the cotton fabrics, which leads to have the highest thermal conductivity values of the cotton fabrics. The reason that the thermal conductivity values of the micromodal air/cotton fabrics are higher than those of the modal/cotton fabrics can be explained by the fact that the fiber fineness affects the number of fibers in the fabric structure. The thinner fibers in the micromodal air/cotton fabrics compared with the modal/ cotton fabrics increase the number of fibers in the yarn cross-section, while at the same time they decrease the availability of air spaces in the fabric structure. The lower air permeability results of the micromodal air/cotton fabrics also confirm that the fiber amount is higher in these fabrics than in the modal/cotton fabrics. Consequently, the micromodal air/cotton fabrics containing more fibers and less air may tend to have the higher thermal conductivity values than the modal/cotton fabrics. As can be seen from Figure 8, the thermal conductivity tends to decrease with increasing stitch length. As the stitch length increases, the compactness of the fabric structure decreases, resulting in decrease in the availability of fibers in the fabric structure.

Thermal Resistance The ratio of fabric thickness to thermal conductivity gives the thermal resistance [14]. The thermal resistance results in Figure 9 show that the micromodal air/cotton fabrics have the lowest thermal resistance values, whereas the modal/ cotton fabrics have the highest thermal resistance values. The thermal resistance values of the cotton fabrics are found to be between those of these two fabric types. The lowest thermal resistance values of the micromodal air/cotton fabrics may be attributed to the lowest fabric thickness values of these fabrics, because thermal resistance is positively proportional to fabric thickness. The highest thermal resistance of the modal/cotton fabrics probably results from the lowest thermal conductivity of these fabrics, since thermal conductivity is inversely proportional to thermal resistance. The reason that the thermal resistance values of the cotton fabrics are lower than those of the modal/cotton fabrics despite having the highest thickness values can be explained by the thermal conductive properties of these fabrics. The highest thermal conductivity values of the cotton fabrics as shown in Figure 8 may lead these fabrics to reveal lower thermal resistance than the modal/ cotton fabrics. As the stitch length increases, the thermal resistance increases, due to the increase in the fabric thickness and the decrease in the thermal conductivity. Thermal Absorptivity Thermal absorptivity describes the warm-cool feeling of fabric [15]. The lower the thermal absorptivity, the warmer the feeling during the short thermal contact of the skin with the fabric is obtained [15]. Opposite is true for the higher thermal absorptivity. Thermal absorptivity is determined by using thermal conductivity and thermal capacity [15]. Any increase in these parameters increases thermal absoptivity.


Figure 10. Thermal absorptivity results of the fully relaxed dyed fabrics.

The contact area between skin and fabric surface also affects the warm-cool feeling of fabric, and thus thermal absoptivity [13,16,17]. In this case, the surface properties of fabrics to great extent reflect thermal absorptivity. A smooth surface increases the area of contact with human skin and therefore, creates a cooler feeling. Conversely, a rough fabric surface reduces the area of contact and therefore, gives a warmer feeling [13,16,17]. From the thermal absorptivity results in Figure 10, it can be seen that the micromodal air/cotton fabrics have the highest thermal absorptivity followed by the modal/cotton and then the cotton fabrics. Due to having the highest value of the thermal absorptivity, the micromodal air/cotton fabrics give the coolest feeling. Oppositely, the cotton fabrics have the lowest value of this parameter, so they provide the warmest feeling. The highest thermal absorptivity values of the micromodal air/cotton fabrics may be attributed to the fact that the finest fibers in these fabrics may lead to smooth fabric surface. The lowest thermal absorptivity values of the cotton fabrics can be explained by the hairiness index property of the cotton yarn. Since the cotton yarns having the highest hairiness index value make the fabric surface made from such yarns rough, the lowest thermal absorptivity values may be acquired for these fabrics. The thermal absorptivity tends to decrease with the increased stitch length as consistent with the previous studies [6,17]. As the stitch length increases, the smoothness tendency of a fabric surface decreases, which leads to decrease in the thermal absorptivity values. The other possible reason for this is the decrease in the thermal conductivity values with the increase in the stitch length.

Conclusion In this study, the dimensional, physical and thermal


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comfort properties of the plain knitted fabrics made from 50/ 50 blend of modal viscose fiber in microfiber form with cotton fiber in three different stitch lengths are investigated in comparison with the fabrics made from 50/50 blend of the conventional modal fiber with cotton fiber and made from 100 % cotton fiber. Dimensional properties are investigated by using the dimensional parameters such as wales/cm, courses/cm, stitches/ cm2, courses/wales, and stitch length. The dimensional constants (K values) are also determined by using the dimensional parameters. The K values together with the stitch density values seem to indicate that slight differences exist among the fabric types. In the fully relaxed state, the K values of the modal microfiber blended fabrics are found to be very close to those of the 100 % cotton fabrics. Therefore, it can be concluded that in the fully relaxed state, the dimensional behaviors of the modal microfiber blended fabrics more closely resemble those of the cotton fabrics rather than those of the conventional modal fiber blended fabrics. From the experimental results, it is shown that the fiber type affects the some of the physical properties such as fabric thickness, bursting strength, air permeability and all of the thermal properties of the fabrics. The modal microfiber blended fabrics reveal lower thickness, bursting strength and air permeability results than the conventional modal fiber blended fabrics. Similarly, when compared with the cotton fabrics, the modal microfiber blended fabrics reveal lower thickness, lower bursting strength and higher air permeability. Considering the thermal comfort properties, the lowest thermal resistance and the highest thermal absorptivity values are obtained for the modal microfiber blended fabrics. The thermal conductivity values of the modal microfiber blended fabrics are found to be between those of the other two fabric types. The highest thermal absorptivity values of the modal microfiber blended fabrics indicate that these fabrics give the coolest feeling. As far as the stitch length is considered, it is observed that with the increase of the stitch length, the fabric weight and bursting strength values decrease, however, the fabric thickness and air permeability values increase. Regarding to the thermal comfort properties, the increase in the stitch length tends to decrease the thermal conductivity and thermal absorptivity values, whereas it tends to increase the thermal resistance values.

Acknowledgment I would like to thank the Research Center of the Usak University for financially supporting this research. I also would like to thank Dr. Kemal Sengül and Ozgurel Textile Company in Usak in Turkey for performing the dyeing of the fabrics.

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