Color and electrical resistance evaluation of cotton fabrics composed of stainless steel yarns treated with direct and reactive dyes

Abstract

The aim of this work was to investigate the color change of cotton fabrics with stainless steel yarns incorporated. In order to establish the impact of conductive yarns’ composition properties in the fabric, concentrations and two different dyeing profiles based on direct and reactive dyes chemistry were applied. The success of this novel e-textile design was evaluated colorimetrically with two different dye concentrations as well through various linear electrical resistances to obtain solid statistical conclusions. The dyed samples were colorimetrically evaluated and the electrical resistances of conductive yarns inside the fabric structure were compared and discussed statistically before and after dyeing. The results provided evidence that dyeing has great influence on electrical resistances of conductive yarns used as transmission lines for electro-textile applications. The greatest changes in electrical resistances were observed with samples including thin conductive yarns and untwisted conductive yarn after dyeing processes. Additionally, it can be concluded that the presence of stainless steel conductive threads significantly retards the dyeing processes depending on the dyestuff concentration and weave type, resulting in major color differences, especially when plain weave type is used or the dyestuff concentration is less than 1% for twill and sateen weaves.

Keywords

conductive yarns color changes direct dyeing cotton e-textiles electrical resistances reactive dyeing stainless steel

The complexity of textile products, the diversity of textile constructions and the materials used for dyeing the textiles, result in variable dyeings in textile structures. The perception of color in textiles is dependent on several parameters such as illumination, spectral distribution of the color stimulus, as well as the surface state of the textile. In addition to the characteristics of the colorants, such as whether they include the metal ions (cadmium, lead, chromium or cobalt) or not, the dyeing procedures and dyeing agents' auxiliaries are crucial factor involved in textile dyeing processes. These diversities in textile materials used to produce textile compositions, the differences in constructions, dyes and dyeing processes lead to a color difference from one structure to another.^1,2

In recent years, there has been a progressive increase in the use of conductive threads in textiles, especially for wearable electronics and functional textile applications. Furthermore, the use of conductive threads or conductivity in fabrics is highly desired to create functional textile compositions through various conductive pathways that carry information or energy for diverse functional applications, such as conductive yarns for electro-textile applications. Many literature surveys and studies were performed on this particular topic; some focused on the conductive yarns for electro-textile applications. Some studies focused on the electro-mechanical performances of conductive yarns, whereas others related to simple fictionalization of e-textile compositions. The core of such investigation is focused on feasibility of interconnections for the purposes of conductive threads.^3–8

Conductive threads are generally embedded in a textile structure via weaving, knitting, embroidery or sewing technologies and they are becoming a part of e-fabric construction as a transmission line in a fabric structure to deliver data or energy transmission. For instance; by weaving of conductive and non-conductive yarns, Dhawan presented information about the formation of fabric-based circuit.⁴ This study observed signal crosstalk noise between transmission lines of a woven fabric owing to the distance. It was reported that as the distance between conducting transmission lines in a woven structure increases, the magnitude of crosstalk noise decreases.⁵ Additionally, Locher studied the electrical performance of fabric-based signal transmission lines. The conductive yarns (ground-G or signal lines-S) were woven and separated from each other by any number of non-conductive yarns. Configurations of signal and ground transmission lines were formed and electrical parameters (e.g., line impedance, insertion loss, far-end crosstalk, etc.) for different configurations of woven e-fabrics were investigated using time and frequency domain analysis.^6,7 In the work being carried out on communication systems, several fabric-based antennas operating at 2.45 GHz have been developed using conductive threads.^8–14 For instance, Gimpel et al. developed three-layer woven antenna of a textile Radio Frequency Identification (RFID) tag using silver polyamide (Ag/PA) threads.¹⁵ Nakad et al. designed an electronic acoustic array to detect the location of a passing vehicle according to a vehicle's acoustics emissions. This acoustic array e-fabric was developed firstly by weaving the conductive yarns and secondly by the integration of microphones in a certain location in the fabric.¹⁶ Moreover, other studies focus on the electromagnetic shielding effect of woven e-fabrics containing conductive yarns. In those studies, the effects of varying weft density, warp density, conductive yarn diameter/count, conductive yarn type such as copper, stainless steel, carbon etc. on electromagnetic shielding effectiveness were studied.^17–19

Apart from weaving techniques, there are other studies in which knitting techniques were used to produce e-fabrics with conductive threads. Kayacan et al. investigated heating behavior of knitted e-fabrics. Heated fabric panels including stainless steel yarns were produced by weft knitting techniques and the electrical and temperature characteristics of heated e-fabric panels were analyzed.^20,21 Scilingo et al. and Wijesiriwardana et al. developed conductive fabric electrodes using conductive threads with knitting technology to measure respiratory monitoring and electrocardiography (ECG).^22–24 Li et al. derived the analytical model of conductive knitted stitch network based on the common intarsia and jersey knitting techniques.²⁵ The pressure effects of different knitting stitches were also investigated. It was found that conductive knitted fabric including conductive yarns of specific stitches resulted in a different pressure effect on human skin.²⁶ In order to develop textile-based electronic circuits using conductive threads, researchers also used embroidery and sewing processes. For instance; Linz et al. developed a mechanism to embroider flexible electronic modules to textile structure using conductive yarns; thus interconnections of electronic modules with conductive yarns were accomplished by embroidery.^27,28

In spite of the realization of conductive threads as transmission lines in e-textile structures as mentioned in several studies, to satisfy reliable electrical transmission through conductive yarns among electronic components without any interruption is an extremely important issue.^29,30 During the insertion of conductive yarns in the weaving/knitting processes or through the embroidery or sewing methods, conductive yarns are subjected to mechanical stresses. These stresses sometimes lead to yarn breakages or discontinuities in sewn conductor lines and result in undesirable additional impedance in a fabric circuit or undesirable conductivity change in a transmission line. However, considering usage issues, e-textiles are also subjected to numerous mechanical stresses, moisture and perspiration impacts, washing etc., which can lead to failure of the line in terms of resistivity and signal transmission. Besides, in some applications e-textile structures containing conductive yarns may be totally immersed in water. In this case, even if the conductive yarns with exposed metallic layers are positioned between non-conductive yarns in a fabric structure, owing to the presence of water, short circuiting may still occur and leads to failure of the transmission line.³¹

Moreover, only a few studies have focused on problems encountered during the construction stages or the usage of transmission lines made of conductive yarns. For instance, the influence of washing on the electric charge of the coated conductive yarns,^32–34 the impact of ambient parameters on the electrical properties of transmission lines³⁰ and the electrical resistance of textile transmission lines under wet conditions³⁵ have recently been discussed. However, no discussion has been made on the impact of pre-production stages on the electrical resistance of textile transmission lines. In particular, although numerous works have been carried out to explain the use of conductive threads in textiles for electro-textile applications, no attempt has been made to predict the impact of dyeing processes on color change and electrical resistances of fabrics containing conductive threads. The influence of conductive threads on color remains a topic for future investigations. Indeed, as conductive threads are composed of metal ions, it is important to know their effect on the dyeability of fabrics containing them. Thus, in this paper, the color differences in cotton fabrics containing stainless steel yarns for electro-textile applications were evaluated statistically after the direct and reactive dyeing processes were completed. In addition, the electrical resistances of the conductive yarns used as transmission lines inside the fabric structure were also investigated after the dyeing processes.

Experimental procedure

Materials

As the applications of e-textiles are so popular for monitoring human health functions and cotton is friendly for human skin, to produce fabric samples including conductive yarns, 100% cotton with a yarn count of 20 Ne was considered for this study. They were used as warp and weft yarn in the woven fabric for the non-conductive area in the structure. Conductive yarns made of nickel-chromium steels (Type 316L: %Cr:16-18; %Ni:10-14; %C:0.03; %Mn:2; %Si:0.75; %P:0.045; %S:0.03; %N:0.10; %Mo:2.0-3.0) were inserted in the weft direction at a straight trajectory in order to achieve a defined interval, shown in Figure 1, during the manufacturing of woven samples. The fabric structures including conductive yarns were plain, twill (3/1S) and sateen (4/1) weave. In order to compare the weave types during the assessment of color change, the same fabric density was chosen to set up the threads in warp and weft directions. The plain fabrics had linear density in the warp direction 36 threads/cm and in the weft direction 38 threads/cm, whereas twill and sateen fabrics had linear density in the warp direction 36 threads/cm and in the weft direction 36 threads/cm. The fabric weights for plain, twill and sateen samples were 124 g/m², 119 g/m² and 115 g/m², respectively, the small difference between plain and twill or sateen mainly coming from both the construction and linear density of fabrics. Conductive yarns in the structure are positioned in such a way that the transmit signals for electro-textile applications at a straight trajectory without any undulation is achieved.

The measured characteristics of the conductive yarns used as transmission lines are presented in Table 1.

Table 1.

The conductive yarns used as transmission lines

Conductive yarn no	Material type	Grade	Diameter (µm)	Count (dtex)	Strength (cN)	Weight (g/m)	Elongation (%)	Linear resistance (Ω/m)
1	100% stainless steel	Type : 316L	12	1000f × 2	340	1.9	1.10	5
2	100% stainless steel	Type : 316L	12	275f × 3	125	0.78	1.10	10
3	100% stainless steel	Type : 316L	12	275f × 2	75	0.54	1.10	15
4	100% stainless steel	Type : 316L	8	1000f × 1	69	0.42	1.10	20
5	100% stainless steel	Type : 316L	12	100f × 3	69	0.28	1.10	25
6	100% stainless steel	Type : 316L	14	90f × 2	46	0.19	1.10	45
7	100% stainless steel	Type : 316L	14	90f × 1	25	0.11	1,10	60

Pretreatment procedure

All yarn samples were industrial sized with sizing agent prior to weaving, and woven fabrics are bleached before coloration. The conditions and formulations of the bleaching process applied to e-fabric samples are summarized in Table 2. Hydrogen peroxide was used as a bleaching agent throughout the process in the jet dyeing machine at a liquor ratio of 25:1. The formulation of hydrogen peroxide bleaching process consists of 3 g/L hydrogen peroxide (H₂O₂), 1g/L peroxide stabilizer, 1g/L wetting agent and 3g/L caustic soda at 90 ℃ for 90 min. The bleaching was performed according to industrial scale. All pre-treatment procedures were completed with neutralization and rinse with cold soft water-rinse.

Table 2.

Bleaching formulation

Treatment process	Recipe	Process temperature (℃)	Process duration (min)
Bleaching	Hydrogen peroxide (H₂O₂) 3 g/L Peroxide stabilizer 1g/L Wetting agent 1g/L Caustic soda (32.5%) 3g/L	90	90

Dyeing profile

The fabrics were dyed in an ATAC brand lab-type dyeing machine which works at high liquor ratio with, C.I. Reactive Blue 19 (Bezaktiv Blau V–RN 150, supplied by Bezema AG) and C.I. Direct Blue 71 (Tubantin Blau BRR h.c. supplied by Bezema AG). The chemical compositions of antraquinones C.I. Reactive Blue 19 dyestuff and trisazo C.I. Direct Blue 71 dyes are presented in Figures 2 and 3, respectively.

Reactive dyeing

The dyebath was based on 1g/L of Meropan DPE (Bezema) and 50 g/L sodium chloride dissolved in distilled water at room temperature. The dyeing process commenced as soon as the fabric was added to the dyebath using 60:1 liquor-to-fabric weight ratio. After 10 min, the temperature was raised to 60 ℃ at a rate of 1.5 ℃/min, and the 5 g/L sodium carbonate and 1 mL/L of Natronlauge (sodium hydroxide solution) (32.5%) were added. The dyeing process was held at this temperature for further 60 min. At the end of the process the fabrics were rinsed with warm and cold water and neutralized with 1g/L acetic acid (30%). In order to remove the residual of unfixed dyes and reactants the fabrics were soap-washed at 80 ℃ for 20 min in a bath (bath-to fabric weight ratio 60:1) using 2 g/L of non-ionic detergent Cotoblanc NSR (Bezema).The dyeing stage was completed by rinsing with tap water, followed by drying at room temperature.

Direct dyeing

The direct dyeing dyebath consists of 0.7 g/L leveling agent, Sarabid SBF-N (Bezema), 1g/L sodium carbonate and dyes. The dyeing procedure commenced at 50 ℃ using a 70:1 liquor-to-fabric weight ratio. Afterwards, the bath was heated-up to 100 ℃ (1.5 ℃/min), and 15 g/L sodium chloride added after 5 min. This temperature was held for 60 min before the dyebath was cooled down to 50 ℃. The rinsing with warm and cold tap water was followed by drying at room temperature.

Here, it should be noted that to distinguish between mechanical and chemical effects, preliminary researches were conducted, in which the fabrics were run in a mock dye cycle with water only. However, preliminary studies have shown that a mock dye cycle with water only does not cause any significant effect on the conductivity of transmission lines.

CIE Lab* color assessment

Dyed samples including different conductive yarns were colorimetrically evaluated with CIE L*a*b* color software in a two-ray SF600 + spectrophotometer (Datacolor, Switzerland) with an Ulbricht sphere and measuring geometry of d/8 °. The source of light was a halogen lamp with xenon lightning that gives standardized daylight D65. CIE L*a*b* color differences between various fabrics were determined from the coordinate differences in all three directions of color space (Figure 4.), i.e. lightness L*, red/green axis a*, yellow?blue axis b*, chroma C* and hue h*by the following equation:^36,37

d E^{*} = \sqrt{{(d L^{*})}^{2} + {(d a^{*})}^{2} + {(d b^{*})}^{2}}

(1)

where dE* is the total color differences, dL* is the brightness differences, da* is the differences at the red/green axis and db* is the differences at the yellow/blue axis.³⁸

Electrical resistance measurement

The linear electrical resistance of a conductive yarn is a measure of its opposition to the passage of electric current in a specified length. The electrical resistance of yarns was measured with Keithley® 2000 6½-Digit multimeter according to previously mentioned measurement procedure.⁴¹ The linear resistance of the conductive yarns is expressed in ohm per meter and measurements are taken along yarn sample length of 40 cm. Test were carried out in laboratory conditions of 20 ± 2 ℃ and 65 ± 2% relative humidity. All the measurements were repeated for three times and the average linear resistance values were calculated to prevent the diversity that can be comprised owing to experimental conditions.³⁹

Statistical verification

The analysis of variance (ANOVA) method was used to establishing the electrical effects on linear resistances between dyed and undyed fabric and also among used weaves. The verification of null hypothesis was $H_{0} : σ_{1}^{2} = σ_{0}^{2}$ , which assumes that there were no significant differences between the groups analyzed.⁴⁰

Result and discussion

Electrical resistance change in dyed fabrics containing stainless steel

Linear electrical resistance values after direct and reactive dyeing processes at 0.5% and 1%concentrations are presented in Tables 3 and 4, respectively. It should be noted here that the linear resistances of the all conductive yarns after weaving process were almost the same as the reference value. However, a detailed study has been also carried out to investigate the effect of bleaching and other selected pretreatment processes on the signal transferring capability of textile transmission lines and it has been discussed in detail.⁴¹ The results in the Tables 3 and 4 indicate that the significant changes in electrical resistance of conductive yarns after dyeing processes were observed compared to their original (reference) electrical resistance values and the values obtained after the bleaching process. The difference between the original (reference) electrical resistance values and the values obtained after bleaching process is relatively small; however, gradual increases were noticed after the dyeing process (Tables 3 and 4).

Table 3.

Average linear electrical resistance values after bleaching and direct dyeing at concentrations of 0.5 % and 1% (<ohm/m)

	Average linear electrical resistance values (<ohm/m)
		Plain			Twill			Sateen
Conductive yarn no	Ref. Value	Bleach.	Direc. 0.5%	Direc. 1%	Bleach.	Direc. 0.5%	Direc. 1%	Bleach.	Direc. 0.5%	Direc. 1%
1	5	9	11	13	9	12	28	9	19	18
2	10	17	28	29	18	26	52	27	30.5	28.5
3	15	18	34	27	22	44	52	20	27	27
4	20	30	123	74	33	298	292	25	67	71
5	25	25	31	25	30	24	33	31	46	46
6	45	45	214	191	48	328.5	243	46	123	120
7	60	70	148.5	171	84	540	650	80	136	151

Table 4.

Average linear electrical resistance values after bleaching and reactive dyeing at concentrations of 0.5% and 1% (<ohm/m)

	Average linear electrical resistance values (<ohm/m)
		Plain			Twill			Sateen
Conductive yarn no	Ref. Value	Bleach.	Reac. 0.5%	Reac. 1%	Bleach.	Reac. 0.5%	Reac. 1%	Bleach.	Reac. 0.5%	Reac. 1%
1	5	9	11	12.5	9	16	14	9	12	14
2	10	17	23.5	26.5	18	43.5	36	27	27	24.5
3	15	18	51	26	22	52.5	37.5	20	26	43
4	20	30	112	63	33	174	210	25	41	41
5	25	25	32.5	25.5	30	34.5	34.5	31	36	54
6	45	45	140	73	48	205	117.5	46	116	77
7	60	70	134	143	84	378	385	80	245	161

The gradual increase in electrical resistance values reveals that electrical resistance values generally increase, meaning that conductivity of the conductive yarns generally decreases after the dyeing processes. This may be attributed to the mechanical forces involved during the dyeing or chemical processes. Mechanical stresses during the dyeing procedure might lead to the deformation of the surface of the fabric as well as conductive yarns by removing the fibers protruding from the conductive yarns and possibly creating a combing affect. Furthermore, the dyeing processes may lead to deformation or surface cracks on the conductive yarns passing through fabric structure. From a chemical point of view, the high liquor ratio entails the use of high amounts of dyeing auxiliary chemicals, especially salt, which interact with the conductive yarns. Moreover, the use of tap water during dyeing and warm or cold rinsing is believed to cause additional adsorption by cotton of inorganic salt from the hard water and of chemical residues from auxiliaries.⁴² All those interactions influence absorption of dyestuff by cotton fabric, leading to probable change in total fixation and thus in shade differences. The place where deformation occurs is within the individual fibers and conductive yarns and both are capable of creating movement and damage throughout the woven fabric structures. Additionally, this could possibly leave an impact in surface cracks on the conductive yarns as well as deformation over the transmission lines (see Figure 5). The results of this phenomenon may consequently lead to a higher electrical resistance or discontinuities in conductor lines.

With reference to Figure 6, it was also found that direct dyeing exhibited a higher negative impact on electrical linear resistances of conductive yarns than reactive dyeing. A higher increase in the ratio of electrical resistance change was observed with direct dyeing compared to reference values and the values obtained after the bleaching process.⁴¹ This may be attributable to the chemical interactions in the direct dyeing process and the higher temperature (100 ℃) by dyeing with direct dyes. In other words, the ion exchange and easy deformation of conductive tracks, which is caused by frictional stresses or chemical interactions in direct dyeing, might be responsible for the observed phenomena. Owing to ion exchange, the electrolyte in the dyeing bath may be affected and this may cause an increase in electrical resistance. However, further studies will need to be executed in order to obtain solid conclusions about the chemical interactions upon the electrical properties.

In addition to the above findings, the statistical analysis also indicated that there were significant differences between dyed and untreated fabric samples (p-value = 0.013), and dyed and bleached fabric samples (p-value = 0.011) on electrical linear resistances (<0.05 ANOVA). This clearly indicates that the dyeing processes significantly influence the linear electrical resistance of the bleached e-fabric samples. However, no conclusion could be drawn regarding the electrical resistance of dyed e-fabric samples with respect to dye concentration, as the linear resistances of conductive yarns showed differences with increasing dye concentration. This may be attributed to the superior effect of the mechanical action in the resulting damage when compared to that of dye concentration. It is notable that, without depending on dye concentration, significant changes were observed on the linear resistance values of conductive yarns after dyeing with reactive and direct dyes (Tables 3 and 4).

The linear resistance values of direct and reactive dyed fabrics with increasing reference linear resistance values are shown in Figure 7. It is evident from the figure that the highest linear resistance changes compared to reference values and the values obtained after bleaching process were observed with conductive yarn nos 6 and 7. This could be attributed to the weight and yarn count of the samples. As conductive yarn nos 6 and 7 have lower weights and yarn counts, their structures are thinner than the others. Hence, their resistance to mechanical stresses is expected to be reduced. As indicated in Table 1, their strengths are also lower among other samples. Higher deformation or surface cracks on these thinner yarns and protruding of conductive fibers owing to the mechanical stresses during the dyeing process are more clearly evident in these samples than in others (see Figure 8). Therefore, a decrease in the number of conductive fibers holding each other, results in a decrease in conductivity level or, in other words, might cause a high linear resistance value.

Another result observed from the Figure 7 is that the conductive yarn no. 4 is also showing a gradual increase in linear resistance values after the dyeing processes. Indeed, the conductive yarn no. 4 is composed of 1000 filaments without any twist (Table 1: 1000F × 1). The untwisted structure with a high number of filaments may result in filament breakages inside the structure during dyeing processes, which leads to a decrease in conductivity level or in other words an increase in linear resistance. In addition, a high increase was observed with twill fabric structure.

It is also evident from Figure 9 that the twill weave type exhibited higher linear resistance values after the dyeing processes. The linear electrical resistance of direct and reactive dyed twill (3/1S) fabrics containing stainless steel is deteriorated as compared to plain and sateen (4/1) fabrics. The reason may be attributed to a change in the displacement of weft and warp yarns positioned in the fabric structure. As the weft and warp replacement passages during the weaving are higher in plain weave, the conductive fibers are better integrated in the body of the fabric. Hence, this may led to reduced deformation or surface cracks on the conductive yarns passing through plain fabric structure during the dyeing processes. However, as the sateen fabric weave type is considered as “open weave” compared to plain weave, during the dyeing process, dyes can easily move throughout the fabric itself and may coat the surface of the conductive threads inside the fabric structure conveniently. Possibly for this reason, the linear resistance values of sateen fabrics compared to twill ones showed similar behavior as plain ones. However, to clarify this phenomenon, a more intensive study is essential.

Moreover, according to ANOVA statistical analysis, it was found that there was a significant difference between weaving types on electrical linear resistance of conductive yarns after dyeing processes with a p-value of 0.005 (<0.05).

Colorimetric evaluation of fabrics containing stainless steel yarns

The colorimetric data of dyed cotton fabric samples without containing stainless steel are presented in Table 5.

Table 5.

Colorimetric data of dyed cotton fabric sample without containing stainless steel

Dyeing process	Weave type	L*	a*	b*
Direct dyeing (0.5%)	Plain	38.50	−1.74	−23.76
	Twill	39.10	−1.71	−23.99
	Sateen	38.05	−1.10	−23.81
Direct dyeing (1%)	Plain	31.05	1.61	−25.40
	Twill	31.72	1.46	−26.12
	Sateen	31.86	1.66	−26.25
Reactive dyeing (0.5%)	Plain	46.44	−6.37	−17.43
	Twill	47.13	−6.38	−17.94
	Sateen	48.78	−6.48	−18.31
Reactive dyeing (1%)	Plain	27.12	0.70	−30.14
	Twill	28.11	0.57	−30.91
	Sateen	28.92	0.38	−31.32

The lightness L* and chroma C* values of dyed plain samples containing stainless steel under direct and reactive dyeing with a concentration of 0.5% and 1% are presented in Figures 10 and 11, respectively.

A change of shade of the samples, including stainless steel conductive yarns, has been investigated and the results indicate that lightness was more pronounced at 0.5% dye concentration compared to 1% dye concentration. Additionally, the samples exposed to the reactive dyeing reflect higher lightness at lower concentration and lower lightness at higher dyestuffs concentration used, which is greatly dependent on the dye strength. Fabric sample containing stainless steel yarn no. 5 had the lowest lightness value at the concentration of 0.5% for direct dyeing among the fabric samples. however, it had the highest lightness value for direct and reactive dyeing at 1% concentration. The observed difference in color or lightness in that sample is probably attributable to the material characteristics influenced by both dyestuffs and dyeing processes.

Accordingly, statistical analysis also revealed that the L* values of samples including stainless steel yarns treated with direct and reactive dyeing at 0.5% and 1% dye concentrations were significantly different with the p-value of 0.000 (<0.05 ANOVA).

The characteristics of C* diagrams in Figure 11 showed a distinction between reactive and direct dyeing as shown on L* diagrams. Samples dyed with reactive dyes exhibited higher and lower chroma values compared to samples dyed with direct dyeing. Moreover, statistical analysis also indicated that there was a significant difference among dyed fabric samples on L* and C* values with the p-value of 0.000 (<0.05 ANOVA).

Furthermore, the conductivity levels of conductive yarns do not have a distinctive effect on color evaluation and color change assessment. As seen in Figure 12, the mean L* values of dyed samples containing conductive yarns showed similarity even with increasing electrical resistance. In addition to that, it is also evident from Figure 10 that the lightness values of samples containing stainless steel had also showed differences for each dyeing profile. With regard to electrical resistance change, when the statistical analysis was performed considering linear resistances of conductive yarns, it was also found that linear resistance has no significant influence on the L* values of samples with a p-value of 0.671 (<0.05 ANOVA). The general conclusion of this study may be that, depending on the conductivity level or electrical resistances of stainless steel yarns, no prediction can be made regarding the color values of dyed fabrics containing stainless steel yarns.

The L* values of dyed plain, twill and sateen fabrics including stainless steel relate to the dye concentration and weave fabric architecture are presented in Figure 13. It was observed that twill fabrics with incorporated conductive yarns had lower lightness values compared to plain and sateen fabrics.

Moreover, plain fabrics showed slightly higher L* values than sateen fabrics; however, their h* values were lower compared to sateen and twill fabrics (see Tables 6 –9 and Figure 13). Further evaluations revealed that there were minor color changes observed within plain fabrics compared to twill and sateen fabrics, which is also supported by the results of a* values (Table 6). No significant differences were observed for C* chroma values. These results were also supported by statistical tests. According to ANOVA statistical analysis, it was found that there was a significant difference between weave types on L* values of samples with a p-value of 0.001 (<0.05). From the presented results, it can be concluded that the fabric construction should be taken into account during the design processes of e-textile structures made of cotton fabrics with stainless steel in case they are subjected to a dyeing process.

Table 6.

Colorimetric data of dyed fabric samples containing stainless steel (direct dyeing at 0.5% dye concentrations)

Conductive yarn no.	Weave type	L*	a*	b*	DE*
1	Plain	42.02	−2.25	−23.67	3.56
2	Plain	42.07	−2.29	−23.63	3.62
3	Plain	42.73	−2.41	−23.61	4.29
4	Plain	41.83	−2.20	−23.65	3.36
5	Plain	41.71	−2.14	−23.66	3.24
6	Plain	42.85	−2.35	−23.59	4.40
7	Plain	42.33	−2.38	−23.53	3.89
1	Twill	38.22	−1.53	−23.97	0.90
2	Twill	38.24	−1.59	−24.06	0.87
3	Twill	38.69	−1.66	−23.82	0.45
4	Twill	38.72	−1.69	−24.11	0.40
5	Twill	38.54	−1.74	−23.76	0.61
6	Twill	39.14	−1.72	−23.97	0.04
7	Twill	38.34	−1.67	−23.79	0.79
1	Sateen	39.82	−1.88	−24.09	1.95
2	Sateen	40.41	−1.94	−24.18	2.53
3	Sateen	40.11	−1.79	−24.36	2.24
4	Sateen	39.81	−1.99	−23.44	2.01
5	Sateen	41.16	−1.95	−24.19	3.24
6	Sateen	40.19	−1.91	−24.13	2.31
7	Sateen	39.34	−1.92	−23.58	1.54

Table 7.

Colorimetric data of dyed fabric samples containing stainless steel (Direct dyeing at 1% dye concentrations)

Conductive yarn no.	Weave type	L*	a*	b*	DE*
1	Plain	33.71	1.09	−25.99	2.77
2	Plain	33.93	1.18	−26.13	3.00
3	Plain	33.78	1.25	−26.30	2.90
4	Plain	34.00	1.07	−26.06	3.07
5	Plain	34.61	0.90	−26.28	3.74
6	Plain	33.96	1.17	−26.12	3.03
7	Plain	34.23	0.99	−26.26	3.35
1	Twill	31.51	1.55	−26.12	0.23
2	Twill	31.66	1.61	−26.27	0.22
3	Twill	31.57	1.63	−26.05	0.24
4	Twill	31.26	1.62	−26.00	0.50
5	Twill	31.05	1.61	−25.40	1.00
6	Twill	31.03	1.74	−26.07	0.75
7	Twill	31.14	1.63	−25.71	0.73
1	Sateen	32.21	1.32	−25.95	0.57
2	Sateen	32.04	1.49	−26.20	0.25
3	Sateen	32.59	1.38	−26.31	0.78
4	Sateen	32.13	1.41	−26.16	0.38
5	Sateen	33.84	1.21	−26.33	2.04
6	Sateen	32.41	1.38	−26.26	0.62
7	Sateen	31.14	1.67	−25.43	1.09

Table 8.

Colorimetric data of dyed fabric samples containing stainless steel (Reactive dyeing at 0.5 % dye concentrations)

Conductive yarn no.	Weave type	L*	a*	b*	DE*
1	Plain	50.02	−6.52	−19.04	3.93
2	Plain	49.72	−6.60	−18.47	3.44
3	Plain	53.51	−6.40	−19.34	7.32
4	Plain	49.47	−6.52	−18.58	3.25
5	Plain	50.27	−6.55	−17.90	3.87
6	Plain	50.44	−6.63	−18.59	4.17
7	Plain	50.70	−6.51	−17.58	4.26
1	Twill	46.63	−6.42	−17.48	0.68
2	Twill	46.20	−6.36	−17.44	1.05
3	Twill	46.76	−6.36	−17.30	0.73
4	Twill	46.02	−6.37	−17.65	1.14
5	Twill	46.44	−6.37	−17.43	0.85
6	Twill	46.26	−6.18	−16.62	1.59
7	Twill	46.72	−6.44	−17.38	0.70
1	Sateen	49.90	−6.51	−15.99	2.58
2	Sateen	49.75	−6.73	−17.40	1.35
3	Sateen	49.32	−6.71	−17.97	0.68
4	Sateen	50.47	−6.72	−16.86	2.25
5	Sateen	49.09	−6.56	−17.43	0.93
6	Sateen	49.52	−6.70	−17.70	0.98
7	Sateen	49.62	−6.67	−17.62	1.11

Table 9.

Colorimetric data of dyed fabric samples containing stainless steel (Reactive dyeing at 1% dye concentrations)

Conductive yarn no.	Weave type	L*	a*	b*	DE*
1	Plain	30.66	0.19	−32.45	4.26
2	Plain	30.41	0.14	−32.07	3.85
3	Plain	30.34	0.10	−31.86	3.70
4	Plain	30.08	0.28	−32.22	3.64
5	Plain	31.00	−0.20	−31.90	4.35
6	Plain	30.54	0.03	−31.96	3.93
7	Plain	30.99	−0.28	−31.68	4.28
1	Twill	27.59	0.75	−30.73	0.58
2	Twill	27.17	0.62	−30.17	1.20
3	Twill	27.51	0.65	−30.17	0.96
4	Twill	27.40	0.77	−30.17	1.04
5	Twill	27.12	0.70	−30.14	1.26
6	Twill	27.45	0.64	−30.40	0.84
7	Twill	27.30	0.77	−30.26	1.05
1	Sateen	30.02	−0.23	−31.68	1.31
2	Sateen	29.46	−0.14	−31.31	0.75
3	Sateen	29.87	−0.39	−30.97	1.27
4	Sateen	29.82	−0.42	−31.18	1.21
5	Sateen	29.20	−0.30	−30.66	0.99
6	Sateen	29.39	−0.07	−31.60	0.71
7	Sateen	30.33	−0.24	−31.65	1.57

Another focus of the study was to investigate whether incorporation of stainless steel yarns would cause any major color difference in the fabric to be dyed. The results of such a study would answer the question of whether dyeing formulae will need to be changed when dyeing fabrics incorporating stainless steel yarns in order to reach same or similar colors. In order to answer this question, it would be wise to compare color values of fabrics incorporating stainless steel (see Tables 6 –9) with those of fabrics without containing stainless steel, which were reported in Table 5. ΔE values calculated accordingly are also given in Tables 6 to 9. Considering the ΔE values given in Table 6, it is apparent that for samples dyed with direct dyestuff at 0.5% concentration, plain fabrics had color differences ranging between 3.24 and 4.40, indicating that incorporation of stainless steel yarns retarded dyeing process significantly. Considering sateen fabrics, the color differences are limited, ranging between 1.54 and 3.24, still causing a major color difference. However, when color differences for twill fabrics are considered, it is observed that ΔE values range between as low as 0.04 and 0.90, all of which should be considered acceptable. When direct dyestuff concentration applied during dyeing is increased to 1%, the same trend is followed depending on effects of weave types on resulting color differences (see Table 7). However, the color differences for fabrics with plain weave were the only ones that were not acceptable, having color differences ranging between 2.77 and 3.74. The color differences for twill ranged between 0.22 and 1.00, whereas those for sateen ranged between 0.25 and 0.78, with the exception of yarn nos 7 and 5 having color differences of 1.09 and 2.04, respectively. It is apparent from the results of direct dyeing color differences, that increasing dyestuff concentration and thus increasing the amount of exhaustion of dyestuff into the fibers of the fabric to be dyed, limited the suppressing effect of stainless steel yarns on dyestuff penetration into fabrics, causing lower color difference values. However, it is obvious that having a more balanced weave, and thus offering a more level barrier, lead to fabrics with plain weave retarding the dyestuff regardless of its concentration. When reactive dyestuff is used in dyeing, the color differences are still unacceptable for samples having plain weave, ranging between 3.25 and 7.32 for 0.5% concentration (see Table 8), and between 3.64 and 4.35 for 1% concentration (see Table 9). Moreover, the color values are also acceptable to slightly unacceptable for samples having sateen and twill weaves, ranging between 0.70 and 2.58 for sateen dyed with 0.5% reactive dyestuff, and between 0.75 and 1.57 for sateen dyed with 1.0% reactive dyestuff, 0.68 and 1.59 for twill dyed with 0.5% reactive dyestuff, and between 0.58 and 1.26 for twill dyed with 1.0% reactive dyestuff, respectively. It is apparent from reactive dyeing color difference results that increasing dyestuff concentration can make limited contributions to reaching the desired shade, when compared to the effect of increase in concentration of direct dyestuff. This can be attributed to the dyeing mechanisms of the two dyestuffs selected for this study, as reactive dyestuffs are more prone to being affected by ionic changes in the dyebath during cotton dyeing having chemical dyeing mechanism, whereas cotton dyeing mechanism for direct dyestuff is rather by physical means.⁴³

It is apparent from the color difference results that complex weave structures will be more helpful in terms of reaching the desired color. On the other hand, it is obvious that even when fabrics with proper weaves are used, there will still remain color nuances, and some changes on dyeing recipes will be needed in order to reach the required shade. Moreover, when exhaust dyeing of fabrics incorporating stainless steel yarns with reactive dyes, use of cold brand reactive dyestuffs should be considered, as those offer better affinity to cotton fabric compared to hot brand ones.⁴³

Conclusions

This study was designed to assess the color and electrical resistances of cotton woven fabrics containing stainless steel for electro-textile applications. Conventional direct and reactive dyeing profiles under different concentrations and conditions were adopted to evaluate the color stability. Cotton fabrics, including different types of stainless steel were tested to determine dependence of their color values on the linear resistances of conductive yarns studied using CIE L*a*b* color space. The results obtained indicated that the dyeing process applied after the bleaching process has a considerable impact on electrical resistance of conductive yarns which were used as transmission lines for e-textile applications. It was found that direct dyeing has a greater negative impact on electrical resistances of conductive yarns than reactive dyeing. This might be attributed to the differences in the chemistry of direct and reactive dyes and different dyeing process. Additionally, greatest changes in electrical resistances were observed with samples including thinner conductive yarns and untwisted conductive yarn after the dyeing processes. Therefore, from the commercial point of view, this approach may need to be modified in terms of linear resistance to satisfy novel e-textile applications. The reactive dyeing results showed higher lightness in the presence of stainless steel fibers at lower concentrations and adverse effect with higher concentrations, compared to direct dyeing profiles. It was also observed that twill fabrics including conductive yarns had lower lightness values compared to plain and sateen fabrics. Nevertheless, no obvious effect of electrical resistances of conductive yarns on color values of fabrics may be observed. Additionally, it can be concluded that the presence of stainless steel conductive threads significantly retard the dyeing processes depending on the dyestuff concentration and weave type, resulting in major color differences, especially when plain weave type is used or the dyestuff concentration is less than 1% for twill and sateen weaves.

Footnotes

Acknowledgements

This project was supported by ITU-BAP Project no. 36120. Grateful appreciation is extended to Istanbul Technical University, Textile Clothing Control and the Research Laboratory; University of Maribor, Faculty of Mechanical Engineering, Department for Textile Materials and Design, OZGUMUS Tekstil A.S, YUREK Tekstil A.S and special thanks go to Mustafa YILDIRIM and Hamdi DEMIRLER for their support in the supply of materials and performing experimental work.

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This project was supported by ITU-BAP Project no. 36120.

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Color and electrical resistance evaluation of cotton fabrics composed of stainless steel yarns treated with direct and reactive dyes

Abstract

Keywords

Experimental procedure

Materials

Pretreatment procedure

Dyeing profile

Reactive dyeing

Direct dyeing

CIE L*a*b* color assessment

Electrical resistance measurement

Statistical verification

Result and discussion

Electrical resistance change in dyed fabrics containing stainless steel

Colorimetric evaluation of fabrics containing stainless steel yarns

Conclusions

Footnotes

Acknowledgements

Declaration of Conflicting Interests

Funding

References

CIE Lab* color assessment