Twist-related parametric optimization of Joule heating-triggered highly stretchable thermochromic wrapped yarns using technique for order preference by similarity to ideal solution

Yong Wang; Zihan Yuan; Mingkun Qi; Lizheng Zhang; Mingwei Li; Wei Wang; Changlong Li

doi:10.1515/epoly-2024-0009

Article Open Access

Twist-related parametric optimization of Joule heating-triggered highly stretchable thermochromic wrapped yarns using technique for order preference by similarity to ideal solution

Yong Wang , Zihan Yuan , Mingkun Qi , Lizheng Zhang , Mingwei Li , Wei Wang and Changlong Li

Published/Copyright: March 21, 2024

Published by

Become an author with De Gruyter Brill

Submit Manuscript Author Information

From the journal e-Polymers Volume 24 Issue 1

Abstract

A scalable approach for manufacturing highly stretchable thermochromic wrapped yarns has been reported previously. Herein, the effects of twist-related technological parameters, namely, wrapping density and outer-inner twist ratio are investigated and have been optimized by technique for order preference by similarity to ideal solution (TOPSIS). The results indicate that the preparatory twist-related parameters have a remarkable effect on the spiral geometrical configuration of yarn constituents, and thus in turn influencing the final tensile and elastic properties of wrapped yarns. The wrapping density of 800 T·m⁻¹ and outer-inner twist ratio of 1.25 were considered as the optimal alternative using TOPSIS. Moreover, a negative relation between voltage and color-changing time of yarn spun with optimal parameters was established. It was also found that the color of yarn above elevated triggered voltages always switched from purple to pink but followed different color-changing paths. More importantly, thermochromic response of yarn is insensitive to the applied strain.

Keywords: elastic thermochromic wrapped yarn; twist; metal wire; Joule heating; TOPSIS

1 Introduction

Smart/functional textiles have become a relevant and revolutionary material category in the textile industry and present a rapid increasing trend in recent years (1,2,3), and such textiles with tunable color conversion is an important branch (4,5,6,7,8). At present, commercial thermochromic textiles via surface coating involve complex fabrication procedure, weaker binding force of thermochromic inks onto textile surface, and they usually cannot be stretched, which limited their large-scale production. Hollow-spindle wrap spinning, a physical processing method, has distinct advantages in versatile and controllable structural reconstruction. However, little work has been completed on fabrication of stretchable thermochromic yarns using the above spinning method. Thus, it is considered obligatory to produce the above yarns from the viewpoint of materials exploration and fabrication strategy (9,10,11).

To spin elastic thermochromic yarns via spinning methods, apart from the inclusion of yarn constituents (e.g., thermochromic fibers, elastane filament; EF) and the process setting required to do this, the twist-related process parameters need to be taken into account because it specifies the configuration of constituents within the yarn and significantly, of the final physical behaviors, e.g., stretch and mechanics, of the resultant yarns. Prior to this study, Liao et al. pointed out that the wrapping structures and twist level are two significant parameters affecting the wicking property of yarns, and an optimal twist was obtained to modify yarns with greater moisture management capability (12). Konova et al. pointed out that the false-twister played a crucial role in deciding the morphology and behaviors of wrap yarns (13). Lou et al. revealed that an increase in the twist coefficient resulted in an increase in strength and a decrease in elongation of spandex-containing wrapped yarns (14). Hsiao et al. fabricated stainless steel/rayon/bamboo charcoal wrapped yarns with elevated twists, and it was found that an optimal twist is 4 turns per cm (15). Chen et al. prepared auxetic yarns with spandex and stainless steel wire (SSW) at a proper wrapping twist based on hollow-spindle spinning system (16). Yu et al. prepared antibacterial nylon/crisscross-section polyester/SSW commingled yarns with hollow spindle spinning method, and revealed that the wrapping density had an obvious influence on the tenacity and elongation of yarns (17). Some other researchers have worked on spinning methods other than hollow spindle spinning. Jiang et al. proposed a way for fabricating sheath core-wrap staple yarn on a modified ring-spinning frame, and pointed out that the twist multiplier and the core proportion were two key parameters affecting the final yarn properties (18). Effects of yarn count, twist multiplier, twist direction, and core/sheath proportion on mechanical behaviors of DREF-3 friction spun yarn made using twisted staple fibrous core were studied by Bhowmick et al. (19). Chandrasekaran et al. pointed out that the twist multiplier has a significant influence on the properties of viscose yarns (20). A facile and scalable method for preparing elastic-conductive composite yarns on a modified ring-spun frame was proposed (21), and the effect of applied twist on the structural and physical-mechanical properties of yarns was clarified by our group (22). Recently, a straightforward and scalable approach for manufacturing highly stretchable electro-thermochromic yarns was proposed by our group (23). Initial investigations of this yarn and the method for spinning it did not fully examine the twist-related effect on the mechanical behavior of such yarns. Thus, the aim of this study is to fill the gap.

Multi-criteria decision-making methods have received much attention from researchers and practitioners in assessing and ranking alternatives. Among numerous methods, the Technique for order preference by similarity to ideal solution (TOPSIS) turned out to be an appropriate choice (24). For example, the effect of repeated laundering on wicking and drying behaviors of seamless garments was studied, and the relative importance of liquid transfer parameters was evaluated by using the analytic hierarchy process (AHP) and TOPSIS (25). Akgul et al. evaluated the fastness of linen-based natural textile products via natural source using TOPSIS method (26). The effect of process parameters for lignin removal of coir was clarified using TOPIS by Verma et al. (27). Gocek studied synergistic effects of chemical finishing processes on comfort properties of knitted fabrics, and the hybrid AHP-TOPSIS approach was used to select the best fabric alternative for intimate wear (28). Moghassem used TOPSIS to analyze and optimize the quality parameters of yarns spun on a rotor spinning frame (29).

To address these above issues, the main goal of this study is to clarify the effects of twist-related technological parameters (i.e., wrapping density and outer-inner twist ratio) on mechanical response of the resultant stretchable electro-thermochromic wrapped yarns, and obtain the optimized parameters using TOPSIS. Moreover, the voltage-dependent electro-thermochromic response mechanism of such yarn was unraveled.

2 Experimental method

2.1 Raw materials and basic tensile behaviors

In this work, three raw materials of EF (1120 D), SSW (with diameter of 35 μm), and thermochromic polyester filament (TCPF, 75 D × 2, switches from purple to pink at temperature above 30°C) were employed to manufacture highly stretchable thermochromic wrapped yarns. The representative tensile curves of the above three materials are displayed in Figure 1. As can be visibly seen, the tensile characteristics of the three raw materials varies widely.

Figure 1

Typical tensile curves and the morphologies of (a) EF, (b) SSW, and (c) TCPF.

2.2 Manufacturing of elastic thermochromic wrapped yarns

A facile and scalable fabrication strategy was proposed to prepare highly stretchable thermochromic wrapped yarns as per the previous work by Wang et al. (23). Such yarns were fabricated based on a hollow-spindle spinning frame, which was retrofitted with positive feed rollers, as illustrated in Figure 2a. The fabrication procedure of yarns involves two main steps artificially: (i) First, combination of pre-stretch EF and SSW. The draw ratio of EF was controlled via the speed difference between the positive feed rollers and winding roller, and then the pre-stretch EF was located in the center of a lower hollow tube, the SSW wrapped on the surface of a lower hollow spindle was unwound and joined with pre-stretch EF, forming the preformed yarn; (ii) Compound formation of preformed yarn and TCPF. The second-layer TCPF wrapped on a higher hollow spindle was unwound and joined with the preformed yarn. Finally, an elastic thermochromic wrapped yarn was prepared. As graphically illustrated in Figure 2b, the main idea was to realize Joule heating-triggered thermochromism of wrapped yarns, irrespective of tensile strain considered. Specifically, the first-layer SSW can generate Joule heat, and the color of second-layer TCPF can be triggered when the heat reaches its threshold temperature (>30°C).

Figure 2

(a) Schematic diagram of fabrication procedure of elastic thermochromic wrapped yarns; (b) reversible Joule heating-triggered thermochromism of yarns; (c) stretchability characterization of yarn with optimized parameter; (d)–(f) the yarn can be wrapped around a finger or braided into any shape (e.g. butterfly, knot); (g) thermochromic photographs of yarn during stretch.

The spinning technological parameters play an essential role in influencing yarn structure and therefore, the final behaviors. Based on some preliminary trials, herein, the twist-related parameters, namely, wrapping density (400, 600, 800, 1,000, and 1,200 T·m⁻¹) and outer-inner twist ratio (0.5, 0.75, 1.0, 1.25, and 1.5) were controlled. Some other parameters were kept constant, that is, the draw ratio of EF of 2.5, and spindle speed of 5,000 rpm. All the yarn samples were fabricated on the same spinning head during the whole process. Taking a yarn with 800 T·m⁻¹ and outer-inner twist ratio of 1.25 for example, as shown in Figure 2c, a yarn with initial length of 4 cm was hung with one end attached to a weight of 500 g, but is upheld by a hand. It can be macroscopically extended to approximately 10 cm without holding, and the action is reversible, indicating its excellent stretchability of as-prepared yarn. Furthermore, as presented in Figure 2d–f, the yarn can be wrapped around a finger, and be braided into any shape (e.g., butterfly, knot), demonstrating the pliability and processability of the yarn. We also saw that the EF served as core and was tightly wrapped by SSW in one direction and TCP in opposite direction. Also, as presented in Figure 2f, the yarn-based knot could be triggered and the color switched from purple to pink when a voltage of 5 V was applied to the two ends of yarn.

Due to the intrinsic high stretchability of yarn in initial load-free state, thermochromic behavior under different amounts of stretch was observed. As presented in Figure 2g, when 5 V voltage was applied to the two ends of yarn, the color of yarn surface has an obvious change in a very short time, converting from purple to pink. The color remains pink with an increase in strain up to 150%. The color can be reversibly controlled by turning on and off the voltage without an observable loss of fidelity. The Joule heating originating from thermal resistance effect of SSW inside yarn in conducting electricity is responsible for triggering the thermochromism of our as-prepared wrapped yarn. Note that, such yarn can be integrated into elastic commercial textiles easily. Similarly, no obvious color change of integrated textiles can be seen whether stretch or not, indicating that the thermochromic behavior is not affected from yarn to integrated textiles.

2.3 Characterization

All the tests were performed in ambient temperature of 20 ± 2°C and relative humidity of 65 ± 3%.

2.3.1 Tensile behavior

The tensile behavior of yarns was measured using a YG(B)021DL tensile tester. Forty replicates, at a gauge length of 50 mm, testing speed of 500 mm·min⁻¹, and a preload of 0.5 cN·tex⁻¹ were measured per sample based on China standard GB/T 3916-2013 and FZ/T 12034-2012. Fracture modes, i.e., drastic fracture and non-simultaneous fracture for each group were summarized. Besides, box-whisker plots were used to characterize tensile force of yarns at varying parameters.

2.3.2 Elastic behavior

The testing procedure of elastic characterization of yarns is shown in Figure 3g. Yarn with an initial length of 25 cm was chosen with a preload (F _pre = [Tex_EF/D _EF + Tex_SSW + Tex_TCPF] × 0.88 cN·tex⁻¹, where D _EF refers to the draw ratio of EF), and the position was marked as OA. Then, 50% of average tensile strength of yarn was determined as applied load, and the load was applied to the yarn, held for 60 s, and this position was marked as OB. After that, the yarn with preload was unloaded for 120 s relaxation, and the position was marked as OC. Finally, elastic extension ratio (ε) and elastic recovery ratio (R) were obtained.

(1) ε = OB − OA OA × 100 %

(2) R = OB − OC OB − OA × 100 %

$Figure 3 (a) Schematic of structures of wrapped yarns with elevated wrapping densities; (b) effect of wrapping density on tensile response of yarns; (c) box-whisker plots; (d) representative tensile curves of yarns with elevated wrapping densities; (e) non-simultaneous fracture ratios of yarns with varying wrapping densities; (f) geometric structure of yarn with lower and higher wrapping density; (g) schematic of elastic testing of yarn; (h) effect of wrapping density on elastic behavior of yarns; (i) elastic recovery ratio of a wrapped yarn following cyclic tests.$

Figure 3

(a) Schematic of structures of wrapped yarns with elevated wrapping densities; (b) effect of wrapping density on tensile response of yarns; (c) box-whisker plots; (d) representative tensile curves of yarns with elevated wrapping densities; (e) non-simultaneous fracture ratios of yarns with varying wrapping densities; (f) geometric structure of yarn with lower and higher wrapping density; (g) schematic of elastic testing of yarn; (h) effect of wrapping density on elastic behavior of yarns; (i) elastic recovery ratio of a wrapped yarn following cyclic tests.

2.3.3 Electro-thermochromic behavior

The testing procedure of electro-thermochromic behavior of yarn is revealed as follows: first, the TCPF was peeled off from the yarn surface exposing the SSW component, and then the positive and negative poles of a power supply (MS-605D) were clamped to the yarn′s SSW ends. Finally, color variation of yarn with different voltages were recorded using a video microscope, and then the color-changing time can be obtained accordingly. The color and luminescence of the above yarn were accurately exhibited on CIE 1931 chromaticity coordinates. In addition, the thermal images of yarn with elevated voltages from 3 to 6 V were captured using a FLIR E5XT thermal imager.

3 Results and discussion

3.1 Effect of technological parameters on mechanical behaviors

3.1.1 Effect of wrapping density

The tensile behavior of wrapped yarns is determined by its constituent fiber properties, yarn structural geometry, and the technological parameters during the spinning process. Figure 3a graphically illustrates the schematic diagram of wrapped yarn structures with elevated wrapping densities. The effect of wrapping density on tensile response of yarns is shown in Figure 3b. The breaking force of yarns increased first to a maximum with an increase in wrapping density, and then decreased marginally with a further increase. The following possible reasons are responsible for the tensile variations trend of yarns. On the one hand, the denser packing effect of yarns happens with the increase in the wrapping density. The effective radial centrifugal pressure can be formed via the spiral winding of outer layers around yarn core. Upon stretching, the interlaced helical structure converts the tension in the longitudinal direction into a lateral compression in the radial direction (Figure 3f). The bias angle β and yarn diameter decrease, resulting in an enhanced cohesion force and friction between individual fibers. The more the wrapping density, the more the lateral pressure, which in turn, makes a positive contribution to the final yarn strength. On the other hand, with a further increase in twist, the parallel component of the force along yarn axis (F·sinθ, Figure 3f) decreases, making a passive contribution to the final strength. Changes in yarn strength with wrapping density are two respects of unity of opposites mentioned above. Interestingly, there is a positive relation between specific extension and given yarn twists. The term “specific extension” refers to the point where the maximum force happens. The denser packing effect with elevated twists is responsible for the increasing variation trend of specific extension. The results in Figure 3b were also reflected in Figure 3c, which presented the median and quartile breaking force values with twist. As yarn twist was increased to 1,000 T·m⁻¹, the median increased dramatically, after which it decreased marginally. With consideration of the shape of tensile distribution, the box-whisker plots for groups except for 600 T·m⁻¹ are obviously negatively/left skewed, whereas for 600 T·m⁻¹ it looks symmetric. Note that, as for wrapped yarns spun with different wrapping densities, the breaking force is not a simple sum of the three components within a yarn, and it is visibly less than the sum of breaking force of components. Apart from the above reasons, the interlaced helical structure of SSW and TCPF inside a yarn, and the remarkable difference of tensile modulus and extension at break among components (SSW, TCPF, and EF) are also responsible for the relatively lower “fiber to yarn” breaking force.

The representative tensile curves of yarns with elevated wrapping densities are shown in Figure 3d. As evident, the shapes of all these curves of yarns with elevated wrapping densities are mechanically differently and essentially nonlinear, indicating that the structural geometry of wrapped yarn is a key factor influencing the final yarn properties. Furthermore, due to the sophisticated structure of as-prepared yarns, the fracture modes were diverse with varying technological parameters. With an increase in wrapping density, the ratio of non-simultaneous fracture decreases on the whole, as shown in Figure 3e. As seen, 100% non-simultaneous breakage at 400 and 600 T·m⁻¹ was found, and the ratio decreases to 55%, 32.5%, and 0% at 800, 1,000, and 1,200 T·m⁻¹, respectively. The bigger constraints on the relative movement of three components (i.e., EF, SSW, and TCPF) within a yarn with higher wrapping density is mainly responsible for the decreased probability of non-simultaneous fracture of yarn. The results were also reflected in Figure 3d. For instance, two kind of breakages were found at 800 T·m⁻¹. One kind is where yarn breaks sharply (Case II). In this case, all the constituents inside break at the same time. Since the core EF is not sufficient to sustain the extra-large load applied to them at the breaking point of SSW and TCPF wrap components, they break and the wrapped yarn breaks. The other one is where the yarn depicts a small break tail (higher extension) with a sharp break (Case I). Since EF exists in a multifilament form, a small amount of EF, SSW, and TCPF break first and the remaining EF can sustain the extra-large load, and the tensile performances are accordingly affected presenting a “two-phase” fracture mode eventually.

Further, the testing procedure of elastic characterization of yarns is shown in Figure 3g, and the results of yarns with elevated wrapping densities are summarized in Figure 3h. The wrapping density has a remarkable effect on elastic properties of the resultant yarns. With an increase in wrapping density, the elastic extension ratio of yarns increased first to a maximum (e.g., 141.2% at 1,000 T·m⁻¹), and then decreased marginally with a further increase, while the elastic recovery ratio decreased gradually. The variation in elastic extension ratio is given: The length of wrap components (i.e., SSW and TCPF) of yarns at higher wrapping density is longer than the length at lower one, meaning that the wrap components have longer absolute length that can be straightened during stretch. Moreover, the value of OB in Eq. 1 is positively related to the absolute wrap length of yarns. Thus, the elastic extension ratio of yarns increased with an increase in wrapping density. However, too much densities had an adverse effect possibly due to the constraint action of relative movement of constituents inside the yarn, resulting in a marginal decrease. In short, a “first increase and then decrease” variation can be found for elastic extension ratio. In addition, as wrapping density increases, the wrap components (SSW and TCPF) are wrapped with EF firmly, resulting in enhanced constraints and reduced stretchability of the resultant yarns. Further, taking a yarn at 800 T·m⁻¹, e.g., no obvious change took place following ten cyclic tests (Figure 3i), indicating the structural and elastic robustness of as-prepared wrapped yarns.

In addition, keeping in view the different tensile data offered by yarns with varying wrapping densities, the breaking force data of yarns were statistically analyzed using one-way ANOVA (22). The results in Table 1 presented significant effect of tensile strength of yarns spun with different wrapping densities, (F _value > F _crit, P < α), indicating that the wrapping density parameter is essential.

Table 1

One-way ANOVA for breaking force of yarns with different wrapping densities (α = 0.05)

Source	Sum of squares	Degrees of freedom	Mean square	F _value	P
Between groups	2,480,742.84	4	620,185.71	106.72	0.000
Within groups	1,133,246.34	195	5,811.52
Total	3,613,989.18	199	F _value > F _crit = 2.42, P＜α = 0.05

3.1.2 Effect of outer-inner twist ratio

Figure 4a illustrates the schematic of wrapped yarn structures with elevated outer-inner twist ratios. Note that the wrapping density of SSW was kept constant, with controlling only the wrapping density of TCPF. Effect of outer-inner twist ratio on tensile response of yarns is shown in Figure 4b. The breaking force of yarns increased first to a maximum with an increase of outer-inner twist ratio, then decreased marginally with a further increase. The following reasons were given: On the one hand, as explained in Section “3.1.1”, the outer-inner twist ratio-enhanced lateral pressure results in a positive contribution to the yarn strength. On the other hand, the decreased effective parallel component of the force along yarn axis has an adverse effect on the final strength. The above aspects are finally responsible for the “first increase and then decrease” variation in the tensile force of yarns. Furthermore, as expected, there is a positive relation between the specific extension of yarns and given outer-inner twist ratios. The longer absolute wrap length of SSW and TCPF inside and the increased bias angle are responsible for the variation trend of yarns with elevated outer-inner twist ratios. Results in Figure 4b are also reflected in Figure 4c, presenting the median and quartile breaking force of yarns with elevated outer-inner twist ratios. As the twist ratio was increased to 1.0, the median gradually increased, after which it marginally decreased. With consideration of the shape of tensile distribution, the box-whisker plots for groups with lower ratios (0.5, 0.75, and 1.0) are negatively skewed, whereas for groups with higher ratios (1.25 and 1.5) are positively skewed.

$Figure 4 (a) Schematic diagram of structures of wrapped yarns with varying outer-inner twist ratios; (b) effect of outer-inner twist ratio on tensile response of wrapped yarns; (c) box-whisker plots of tensile strength; (d) representative tensile curves of yarns with elevated outer-inner twist ratio; (e) the non-simultaneous fracture ratios of components inside wrapped yarns with varying outer-inner twist ratios; (f) effect of outer-inner twist ratio on elastic behavior of wrapped yarns.$

Figure 4

(a) Schematic diagram of structures of wrapped yarns with varying outer-inner twist ratios; (b) effect of outer-inner twist ratio on tensile response of wrapped yarns; (c) box-whisker plots of tensile strength; (d) representative tensile curves of yarns with elevated outer-inner twist ratio; (e) the non-simultaneous fracture ratios of components inside wrapped yarns with varying outer-inner twist ratios; (f) effect of outer-inner twist ratio on elastic behavior of wrapped yarns.

The typical tensile curves of yarns with elevated outer-inner twist ratios were presented in Figure 4d. The essentially nonlinear tensile characteristics and “two-phase” fracture can be observed. Moreover, with an increase in outer-inner twist ratio, both the breaking point of the first breaking peak (for Case I, “two-phase” fracture) and the sharp breaking point (Case II, “one-phase” fracture) shifted gradually towards higher tensile extension within the scope of the given outer-inner twist ratio. In addition, the result in Figure 4e indicates certain fluctuations of non-simultaneous fracture of yarns, the variation increases with an increase in the outer-inner twist ratio on the whole.

Furthermore, Figure 4f highlights the upward trend of elastic characteristics (i.e., elastic extension ratio, elastic recovery ratio) of the resultant yarns as a function of outer-inner twist ratios, demonstrating that the outer-inner twist ratio is a key factor influencing the final elastic properties. Another interesting depiction is that the elastic performances increase sharply with an initial increase in outer-inner twist ratio up to 1.0, beyond which they increase only marginally. As expected, the larger wrap length of SSW and TCPF within a yarn (just as explained before) and the shorter length difference between SSW and TCPF (herein, twist ratio of 1.0 can be viewed as a critical point and it has the shortest length difference) account for the upward elastic trend of yarns. Similarly, taking a yarn with outer-inner twist ratio of 1.5 for example, no obvious change in elastic recovery ratio occurs following ten cyclic tests, revealing the structural and elastic robustness of as-prepared wrapped yarns.

Similarly, the breaking force data of yarns spun with different outer-inner twist ratios were statistically analyzed using one-way ANOVA. The results in Table 2 indicate that the outer-inner twist ratio parameter is fundamentally essential.

Table 2

One-way ANOVA for breaking force of yarns with different outer-inner twist ratios (α = 0.05)

Source	Sum of squares	Degrees of freedom	Mean square	F _value	P
Between Groups	460,661.88	4	115,165.47	27.91	0.000
Within Groups	804,585.14	195	4,126.08
Total	1,265,247.02	199	F _value > F _crit = 2.42, P＜α = 0.05

3.2 Entropy weight TOPSIS-based multi-objective optimization

3.2.1 Description of Entropy weight TOPSIS

Herein, the TOPSIS method was used to optimize the twist-related processing parameters of wrapped yarns. The method consists of the following several steps (23):

Step I: Construct the decision matrix

Based on objective/criteria, a decision matrix is constructed and expressed based on the response parameters, as shown in Eq. 3.

(3) x i j = A 1 x 11 x 12 x 13 … x 1 n A 2 x 21 x 22 x 23 … x 2 n A 3 x 31 x 32 x 33 … x 3 n … … … … … … A m x m 1 x m 2 x m 3 … x m n

where A ₁, A ₂, A ₃,…, A _m are the possible alternatives among which decision makers have to choose the best one. For i = 1–m and j = 1–n, x _ij represents the actual value of the ith experimental result for the jth process response.

Step II: Normalize the decision matrix

The decision matrix must be normalized and determined before quality characteristics can be compared. The output values can be expressed as per Eq. 4.

(4) T i j = x i j ∑ i = 1 m x i j 2

where i = 1–m and j = 1–n x _ij represents the actual value of the ith experimental result for the jth process response, and T _ij represents the corresponding normalized value.

Step III: Calculate objective weight and the weighted matrix

In this step, the entropy weight method is proposed to assign and determine different weights to different characteristics of the resultant yarns. Then, the weighted normalized decision matrix is calculated by multiplying the normalized matrix by its related entropy weights, as per Eq. 5.

(5) V i j = W j × T i j

where i = 1–m, j = 1–n, and W _j represents the entropy weight of the jth attribute.

Step IV: Estimate the positive and negative ideal solution

In this step, the positive (V ^＋) and negative (V ⁻) ideal solutions for the relative rankings of technological parameters need to be determined before the priority of wrapped yarns with m types of parameters and n types of evaluation criteria can be ranked, and they can be expressed as follows:

(6) V + = V 1 + , V 2 + , V 3 + … V n + , where V j + = { max ( V i j ) } V − = V 1 − , V 2 − , V 3 − … V n − , where V j − = { min ( V i j ) }

where i = 1–m, j = 1–n, and W _j represents the entropy weight of jth attribute.

As per the Euclidean distance equation, the relative degree of separation between each experimental data and its positive and negative ideal solutions can be calculated.

(7) S i + = ∑ i = 1 m ( V i j − V j + ) 2 S i − = ∑ i = 1 m ( V i j − V j − ) 2

where i = 1–m and j = 1–n.

Step V: Determination coefficient of closeness

In this step, the coefficient of closeness (CC) is calculated as per Eq. 8.

(8) CC = S i − S i + + S i − ( 0 < CC < 1 )

Step VI: Ranking order

Finally, the calculated results of CC are ranked and TOPSIS rankings were determined in accordance with ascending order of CC. A higher CC represents a preferred experimental run.

3.2.2 Parametric optimization based on entropy weight-based TOPSIS

TOPSIS is employed to determine the two technological parameters such as wrapping density, and outer-inner twist ratio, in terms of breaking force, specific extension, elastic extension ratio, and elastic recovery ratio of the resultant yarns. Taking yarns with different wrapping densities for an example, the results are summarized in Tables 3 and 4.

Table 3

Summary of relative entropy values of yarns with varying wrapping densities

Terms	Information entropy value (e)	Information utility value (d)	Entropy weight (%)
Breaking force	0.859	0.141	22.524
Specific extension	0.848	0.152	24.298
Elastic extension ratio	0.849	0.151	24.187
Elastic recovery ratio	0.819	0.181	28.991

Table 4

Ranking of the optimized solution of yarns with varying wrapping densities

Wrapping density (T·m⁻¹)	Positive separation matrix ( S i + )	Negative separation matrix ( S i ‒ )	CC	Rank
400	0.84266322	0.53843146	0.3899	5
600	0.31762048	0.75149610	0.7029	2
800	0.19071149	0.81419559	0.8102	1
1,000	0.36252329	0.83706166	0.6978	3
1,200	0.54300866	0.78813124	0.5921	4

Table 3 shows the relative entropy values. For yarns with different wrapping densities, the elastic recovery ratio has the highest entropy weight value of 28.991%, whereas the breaking force has the smallest value of 22.524%. The results reveal that the elastic recovery term is an essential factor in influencing the final properties. Moreover, with a decrease in information entropy value, the variation degree of surface index increases, and more information can be provided. Consequently, the bigger the role it plays in the comprehensive evaluation, results in higher weights. In other words, the information entropy value is negatively correlated with the entropy weight. In addition, there is a complement relationship between the information entropy value and information utility value (e + d = 1).

Table 4 displays the separation matrix ( S i + , S i − ) and CC for each experiment. A high CC means that the experimental value and the ideal value are similar. As shown, the third group holds rank one with wrapped yarn with the optimized wrapping density of 800 T·m⁻¹, whereas the first trial (400 T·m⁻¹) has the worst condition.

Similarly, the optimized outer-inner twist ratio of yarns was determined. Table 5 shows the separation matrix ( S i + , S i − ) and CC for each experiment with different outer-inner twist ratios. As seen, yarn spun with twist ratio of 1.25 holds rank one. Conversely, the first trial (0.5) has the worst condition.

Table 5

Ranking of the optimized solution of yarns with varying outer-inner twist ratios

Outer-inner twist ratio	Positive separation matrix ( S i + )	Negative separation matrix ( S i ‒ )	CC	Rank
0.5	0.99998684	0.00000000	0.0000	5
0.75	0.66873145	0.36066659	0.3504	4
1.0	0.36498839	0.76545137	0.6771	3
1.25	0.09337284	0.91762446	0.9076	1
1.5	0.13901341	0.94255061	0.8715	2

3.3 Voltage-dependent thermochromic response of wrapped yarn

In this section, if not otherwise specified, the wrapped yarn refers to yarn spun with the optimized technological parameters. As illustrated in Figure 5a, the yarn with an initial length of 5 cm was prepared, and both of the yarn ends were connected to the positive and negative poles of a power supply. A video microscope was used to observe the color variation of yarn with different voltages. Figure 5b shows the color-changing time of yarn from purple to pink with a voltage of 3.5 and 7 V, respectively. The color-changing time of yarn was negatively correlated to the given voltage. Higher voltage results in a shorter color-changing time. The results were also reflected in Figure 5d. Note that the same longitudinal section of yarn was observed in order to minimize the other potential variations. According to the CIE 1931 chromaticity diagram, it was found that the color of yarn always switched from purple to pink but followed different color-changing paths, considering the voltage applied. Moreover, since the points were obtained with the same interval time, the color-changing time at 3.5 V was obviously longer than that at 7 V, as shown in Figure 5c.

Figure 5

(a) The set-up system to observe the color change of wrapped yarn at different voltages; (b) color-changing time of yarn at voltage of 3.5 and 7 V, respectively; (c) CIE 1931 chromaticity diagram of yarn with different voltages during whole color-changing process; (d) the consecutive captured photographs of yarn with 3.5 and 7 V, respectively; (e) the captured thermal images as a function of voltage; (f) temperature profile of yarn with an increase in voltage.

In a thermochromic wrapped yarn, the heat originates from thermal resistance effect of SSW inside in conducting electricity. As shown in Figure 5f, voltages were varied from 3 to 6 V and the saturated surface temperature was noted to increase with voltage (see the consecutive captured thermal images in Figure 5e). The relationship between surface temperature of yarn and applied voltage is close to a parabola (i.e., T ∝ U ²). A minimum voltage required to trigger the thermochromism of such yarn is about 3.5 V. The color of yarn with 5 cm length switched from purple to pink when the voltage was beyond 3.5 V. The Joule heat-triggered thermochromic effect of such yarn is reversible with an on/off voltage without an observable color-changing fidelity.

4 Conclusion

A facile and scalable fabrication strategy to fabricate stretchable electro-thermochromic wrapped yarns has been previously reported. The EF in yarn core can offer the desirable stretchability, the first-layer SSW can generate Joule heat, and the color of second-layer TCPF can be changed when the heat reaches threshold temperature.

Controlling the twist is incredibly crucial in optimizing the properties of textile yarns. Herein, the effects of twist-related technological parameters, namely, wrapping density and outer-inner twist ratio were studied and optimized by TOPSIS. The results indicate that the preparatory twist-related parameters have a remarkable effect on spiral geometrical configuration of yarn constituents, and thus in turn affecting the final tensile and elastic behaviors of yarns. The optimized and feasible alternative using TOPSIS was wrapping density of 800 T·m⁻¹ and outer-inner twist ratio of 1.25. Moreover, the voltage-dependent electro-thermochromic response of yarn spun with the optimized parameters was clarified, and the color-changing time of yarn was negatively related to the voltage applied. The color of yarn was accurately exhibited on CIE 1931 chromaticity coordinates. It was found that the color of yarn with different voltages always switched from purple to pink but followed different color-changing paths. Importantly, no obvious color variation of yarn was observed during stretch.

As a promising smart wearable material, one of the next steps will be to systematically clarify the service stability of such yarns including immersing into organic solvents, acid, alkali, perspiration, etc., to simulate finishing treatments and daily practical uses, and unravel the respective underlying thermochromic mechanism. Such findings are expected to provide some insights to the further development of smart thermochromic textiles with excellent stretchability and color-changing robustness.

Funding information: This research work was financially supported by Science and Technology Project of Wuhu City (Grant number: 2022yf59); Open Project of National Local Joint Laboratory for Advanced Textile Processing and Clean Production; Open Project of Advanced Fiber Materials Engineering Research Center of Anhui Province (Grant number: 2023AFMC14); the Scientific Research Project of Anhui Polytechnic University (Grant numbers: Xjky2022074, FFBK202221, and FFBK202336).
Author contributions: Wang Yong: conceptualization, methodology, investigation, writing – original draft, data curation, and funding acquisition. Zihan Yuan: investigation and writing – original draft. Mingkun Qi: investigation. Lizheng Zhang: investigation. Mingwei Li: methodology and supervision. Wei Wang: supervision. Li Changlong: writing – review and editing and supervision. The authors applied the SDC approach for the sequence of authors.
Conflict of interest: Authors state no conflict of interest.
Data availability statement: The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

References

(1) Meng X, Jia XY, Qi YZ, Miao DG, Yan X. Fabrication of polylactic acid nanofibrous yarns for piezoelectric fabrics. e-Polymers. 2023;23(1):20230030. 10.1515/epoly-2023-0030.Search in Google Scholar

(2) Zhao HM, Dai Z, He T, Zhu SF, Yan X, Yang JJ. Fabrication of PANI-modified PVDF nanofibrous yarn for PH sensor. e-Polymers. 2022;22(1):69–74. 10.1515/epoly-2022-0013.Search in Google Scholar

(3) Wang Y, Qiao QF, Ding ZW, Sun FX. Strain-dependent wicking behavior of cotton/lycra elastic woven fabric for sportswear. e-Polymers. 2021;21(1):263–71. 10.1515/epoly-2021-0030.Search in Google Scholar

(4) Hakami A, Srinivasan SS, Biswas PK, Krishnegowda A, Wallen SL, Stefanakos EK. Review on thermochromic materials: Development, characterization, and applications. J Coat Technol Res. 2022;19(2):377–402. 10.1007/s11998-021-00558-x.Search in Google Scholar

(5) Nuroldayeva G, Balana MP. Flexing the spectrum: advancements and prospects of flexible electrochromic materials. Polymers. 2023;15(13):2924. 10.3390/polym15132924.Search in Google Scholar PubMed PubMed Central

(6) Ramlow H, Andrade KL, Immich APS. Smart textiles: an overview of recent progress on chromic textiles. J Text Inst. 2021;112(1):152–71. 10.1080/00405000.2020.1785071.Search in Google Scholar

(7) Civan L, Kurama S. A review: preparation of functionalized materials/smart fabrics that exhibit thermochromic behavior. Mater Sci Tech. 2021;37(18):1405–20. 10.1080/02670836.2021.2015844.Search in Google Scholar

(8) Kim SH, Ko HC. Double-sided printed circuit textiles based on stencil-type layer-by-layer coating with PEDOT:PSS:Ag nanowires and chitosan for electrothermo-chromic displays. J Mater Chem C. 2020;7(46):14525–34. 10.1039/c9tc04540f.Search in Google Scholar

(9) Tseghai GB, Malengier B, Fante KA, Nigusse AB, Van Langenhove L. Integration of conductive materials with textile structures, an overview. Sensors. 2020;20(23):6910. 10.3390/s20236910.Search in Google Scholar PubMed PubMed Central

(10) Grancaric AM, Jerkovic I, Koncar V, Cochrane C, Kelly FM, Soulat D, et al. Conductive polymers for smart textile applications. J Ind Text. 2018;48(3):612–42. 10.1177/1528083717699368.Search in Google Scholar

(11) Oliveira J, Correia V, Castro H, Martins P, Lanceros-Mendez S. Polymer-based smart materials by printing technologies: Improving application and integration. Addit Manuf. 2018;21:269–83. 10.1016/j.addma.2018.03.012.Search in Google Scholar

(12) Liao SY, Tao YF, Li L. Modification of yarn wrapping technology for natural-based textiles with highly efficient wicking and fast-drying performances. Text Res J. 2023;93(9-10):2257–72. 10.1177/00405175221142337.Search in Google Scholar

(13) Konova H, Angelova R. False-twister as a yarn formation factor in wrap spinning. Text Res J. 2013;83(18):1926–35. 10.1177/0040517513481865.Search in Google Scholar

(14) Lou CW, Hu JJ, Lu PC, Lin JH. Effect of twist coefficient and thermal treatment temperature on elasticity and tensile strength of wrapped yarns. Text Res J. 2016;86(1):24–33. 10.1177/0040517514557315.Search in Google Scholar

(15) Hsiao PC, Liu CM, Lu CT, Yin W, Huang YT, Lin JH. Manufacture and evaluations of stainless steel/rayon/bamboo charcoal functional composite knits. Text Res J. 2019;89(19–20):3893–9. 10.1177/0040517518821904.Search in Google Scholar

(16) Chen JL, Du ZQ. Structural design and performance characterization of stable helical Auxetic yarns based on the hollow-spindle covering system. Text Res J. 2020;90(3-4):271–81. 10.1177/0040517519862881.Search in Google Scholar

(17) Yu ZC, Zhang JF, Lou CW, Lin JH. Wicking behavior and antibacterial properties of multifunctional knitted fabrics made from metal commingled yarns. J Text Inst. 2015;106(8):862–71. 10.1080/00405000.2014.949504.Search in Google Scholar

(18) Jiang WJ, Guo MR, Gao WD. Research on a novel sheath-core wrap staple yarn based on the ring spinning frame with special-shaped roller. Text Res J. 2023. 10.1177/00405175231169291.Search in Google Scholar

(19) Bhowmick M, Rakshit AK, Chattopadhyay SK. Structure-property of DREF-3 friction spun yarn made using twisted staple fibrous core. J Nat Fibers. 2020;17(2):235–45. 10.1080/15440478.2018.1479995.Search in Google Scholar

(20) Chandrasekaran V, Senthilkumar P, Karthik T. Optimization of spinning parameters influencing the characteristics of structurally modified viscose yarn. J Text Inst. 2016;107(1):50–63. 10.1080/00405000.2014.1000017.Search in Google Scholar

(21) Wang Y, Yu WD, Wang FM. Structural design and physical characteristics of modified ring-spun yarns intended for e-textiles: A comparative study. Text Res J. 2019;89(2):121–32. 10.1177/0040517517741154.Search in Google Scholar

(22) Wang Y, Gordon S, Yu WD, Li CL. Twist-dependent behavior of helical-shaped elastic composite yarns containing metal wire produced on a modified ring spinning system. Polym Test. 2020;91:106822. 10.1016/j.polymertesting.2020.106822.Search in Google Scholar

(23) Wang Y, Zhang LZ, Qi MK, Yuan ZH, Li MW, Wang W, et al. Highly stretchable, durable, and reversibly thermochromic wrapped yarns induced by Joule heating: With emphasis on parametric study of elastane drafts. e-Polymers. 2024;24(1):20230189. 10.1515/epoly-2023-0189.Search in Google Scholar

(24) Behzadian M, Otaghsara SK, Yazdani M, Ignatius J. A state-of the-art survey of TOPSIS applications. Expert Syst Appl. 2012;39(17):13051–69. 10.1016/j.eswa.2012.05.056.Search in Google Scholar

(25) Duru SC, Candan C. Effect of repeated laundering on wicking and drying properties of fabrics of seamless garments. Text Res J. 2013;83(6):591–605. 10.1177/0040517512456754.Search in Google Scholar

(26) Akgul E, Bahtiyari MI, Aydogan EK, Benli H. Use of Topsis method for designing different textile products in coloration via natural source “Madder”. J Nat Fibers. 2022;19(14):8993–9008. 10.1080/15440478.2021.1982106.Search in Google Scholar

(27) Verma S, Midha VK, Choudhary AK. Multi-objective optimization of process parameters for lignin removal of coir using TOPSIS. J Nat Fibers. 2022;19(1):256–68. 10.1080/15440478.2020.1739589.Search in Google Scholar

(28) Gocek I. Synergistic effects of chemical finishing processes on comfort characteristics of micro-modal and lyocell knitted fabrics. Mater Test. 2019;61(3):243–54. 10.3139/120.111312.Search in Google Scholar

(29) Moghassem AR. Application of TOPSIS approach on parameters selection problem for rotor spinning machine. Fiber Polym. 2010;11(4):669–75. 10.1007/s12221-010-0669-7.Search in Google Scholar

Received: 2024-01-13

Revised: 2024-02-07

Accepted: 2024-02-11

Published Online: 2024-03-21

This work is licensed under the Creative Commons Attribution 4.0 International License.

Articles in the same Issue

https://doi.org/10.1515/epoly-2024-0009

Keywords for this article

elastic thermochromic wrapped yarn; twist; metal wire; Joule heating; TOPSIS

Creative Commons

BY 4.0