Development of core-spun based conductive helical auxetic yarn for enhanced protective textiles

Abstract

Protective workwear calls for improved energy absorption that auxetic structures can answer. However, generating static charges through frictional contact remained a significant hurdle as textiles had high electrical resistance. This study produced conductive auxetic yarn (CAY) using core spun-based technology with commercially available staple fibers. It evaluated the impact of blends and Elastane (Lycra) count on the strength, auxeticity, electrical resistance, and air permeability characteristics of auxetic yarn and fabrics. Results demonstrated that CAY with 280D Lycra developed enhancement of yarn properties in comparison to 120D Lyra. For instance, yarn sample 2 better tensile strength (17.8 N), elongation (7.4%), electrical resistance (65 Ω) and auxeticity (PR of -3.97) than sample 1 yarn. Elevating the content of staple steel to 40% gave rise to a maximum of 42% less electrical resistance in yarn from sample 1 (80 Ω) to sample 3 (47 Ω). Like yarn, fabrics knitted with 280D Lycra containing CAY developed 13% better auxeticity as demonstrated by Poisson’s ratio of sample 6 (-2.02) and sample 5 (-1.746). However, coarser Lycra and higher staple steel content dropped air permeability. The highest air permeability of fabric sample 5 (521 mm/s) was lowered in sample 6 (441 mm/s) and sample 7 (388 mm/s) owing to coarser Lycra and higher content of steel fibers respectively. Electrical resistance of auxetic fabrics reduced utilizing 40% staple steel content yarns. The effect was more prominent in coarser Lycra, as sample 2 (1500 Ω) and sample 4 (800 Ω) drops by 46% in comparison to 30% reduction between sample 1 (970 Ω) and sample 3 (670 Ω). This verified the core spun-based CAYs and their resultant auxetic fabrics inherited substantial auxeticity with an electrically conductive nature for improved potential protective clothing.

1. Introduction

Personal protective clothing like workwear ensures safety with desirable operational function. These workwear garments demands improved energy absorption for a higher level of protection and antistatic character to mitigate static electricity problems. Static charges spawn through frictional contact not only hinder performance but also cause hazards to the wearer. ¹ An inferior level of energy dissipation in workwear can also be fatal. ² In search of a superior structure for workwear, auxetic fabrics gained significant attention owing to negative Poisson’s ratio (NPR). It allowed enhanced energy dissipation that became advantageous in applications like protective wear.^3,4 Poisson’s ratio is the ratio of lateral to longitudinal strain upon application of force. Generally, structures contract laterally by longitudinal strain, thus demonstrating a positive Poisson ratio. In contrast, auxetic structures show lateral extension upon longitudinal extension to exhibit NPR. This strange phenomenon occurs through the synergetic relation of structural components, e.g. honeycomb, lattices, and cellular structures.^5,6 NPR benefits the toughness, damping, and energy characteristics thus it enhances performance of protective textiles. ⁷ Protective textiles like helmets, seat belts, blast curtains, and impact absorbers were fabricated with auxetic structure. ⁸ Auxetic character is promoted in materials by introducing auxetic geometries, for instance, helical structures in auxetic yarn. Fabrics made from auxetic yarns have inherent auxetic character to display NPR. Auxetic yarns were manufactured through the conjunction of components with variations of elastic modulus. ⁹ A high-modulus component is wrapped helically around low-modulus components. Application of longitudinal force straightened the wrapped, dissipating the core into a helical shape. ¹⁰ This occurrence magnifies the diameter of yarn to insert auxeticity, as illustrated in Figure 1.

Figure 1.

Mechanism of auxeticity in CAY

A novel Helical auxetic yarn (HAY) was developed with polyamide wrap and polyurethane core with a NPR of -2.7. It was revealed that wrapping angle was the dominant factor in governing auxetic behaviour. ¹¹ Elastane cores of varied diameters were employed with PET and nylon filament wraps at different wrapping angles. Lower wrap angle showed triggered auxeticity at low strains, while ¹² polyethylene (ultra-high-molecular-weight; UHMWPE) wrapped over straight spandex core was also utilized for HAY spinning. ¹³ Its dynamic and mechanical behaviours showed that core/wrap ratio, and twist per inch (TPI) of wrap simulate variation in thermal character. ¹⁴ A moisture-sensitive HAY was developed with diverse wrapping angles to inspect the influence of TPI on wrap. Application of moisture transforms high modulus components in helical state, developing a straightened low modulus core. Upon application of force, moisture sensitive wraps straighten to transform core into a helix form, developing auxeticity. ¹⁵ Enhanced auxetic behaviour was achieved by a low-stiffness coarse core with high-stiffness fine wrap yarn. ¹⁶ The influence of plying on auxetic yarns was studied with two stiffer and two core yarns, for enhancement of NPR. Reduction of NPR was observed in plied yarns of coarser diameters. ¹⁷

Owing to boosted energy absorption, protective textiles were constructed from auxetic structures. Mostly auxeticity was imparted in fabrics through weave or knitting design for protective applications. Only a few researchers employed auxetic yarn based protective textiles. ¹⁸ Polyester and polyurethane based HAY were also utilized in knitting of auxetic fabrics for sports applications. ¹⁹ A core spun yarn of cotton and Elastane (Lycra) was wrapped with Dyneema filaments for manufacturing HAY for protective wear. It displayed NPR of nearly -4 with a tensile strength of 27 cN/tex. ²⁰ Impact resistant woven auxetic fabrics were constructed with auxetic yarn of polyurethane and nylon 6,6 that demonstrated an extraordinary NPR of -5.6. ²¹ Various commercial fibers were employed in HAY manufacturing for fabrication of abrasion-resistant socks with different knitting designs. The improved socks exhibit 40% to 60% additional abrasion resistance while retaining sufficient comfort. ²² Apart from enhanced protection, antistatic character for protective wear is an essential trait to mitigate threat of static electricity. Frictional contact of workwear generates static charges that can lead to spark, igniting flammable material.

Generally, polymers are doped with conductive components during melt spinning, to synthesize conductive fibers for antistatic applications. For instance, carbon black was enclosed in bicomponent fibers to reduce electrical resistance without compromising color. Synthesized fibers developed lowest resistivity of 0.1 Ωm. ²³ Carbon black was also incorporated in PET fibers in core sheath and segmented pie layout. It was revealed that core sheath layout was superior for less electrical resistance and strength. ²⁴ Protective textiles were manufactured with ceramic doping for oil and gas sector. Results verified ZnO-Antimony Tin Oxide blended ceramic embedded PET fabrics developed lower rub voltage owing to augmented conductivity. ²⁵ Another study manufactured multifunction PET fabrics with variable concentrations of Antimony Tin Oxide, Aluminium oxide and Titanium oxides. It was concluded that higher content of Antimony Tin Oxide exhibited the highest antistatic efficacy in contrast to Aluminium oxide and Titanium oxide specimens. ²⁶ Apart from conductive polymeric fibers, staple steel fibers were also employed with conventional fibers to lower electrical resistance. Addition of 10% staple steel blend with cotton and polyester respectively. Best result of 105 times enhancement in electrical conductivity was noted from in comparison to conventional yarn. ²⁷ Moreover addition of steel fibers also amplified the comfort and mechanical protection. ²⁸

Previous fabrication of auxetic yarn was mostly based on filament for high and low modulus components. It limits the scalability of auxetic yarn manufacturing with the state of the art in textile sector, as most industries consume staple fibers. Furthermore, addition of conductive components in auxetic yarns was rarely studied for antistatic applications. This research aims to develop auxetic fabric from conductive auxetic yarn (CAY) with a core of core spun yarn for improved energy absorption with antistatic character.

2. Methodology

2.1. Materials

Pakistani cotton (Bt variety: MNH 1050, Staple: 22.4 mm, and strength: 31.8 g/tex) and PET (polyester, Staple: 38 mm, and strength: 36.4 g/tex) fibers were provided by Qalandri cotton and Ibrahim fibers Pakistan. Staple steel sliver (Bekinox VS 08, diameter: 8 µm staple:60 mm, strength 6 cN) and UHMWPE (Dyneema) filament of 50 denier was procured from Bekaert and Dyneema. Elastane (lycra) multifilament of 120 and 240 denier was purchased from Sultan Elasto Products Pvt Ltd.

2.2. Methods

The manufacturing of conductive auxetic yarn (CAY) has two stages. In the first stage, conductive core yarn (CCY) was developed, and in the second stage, it was wrapped with Dyneema as shown in Figure 2.

Figure 2.

Schematic illustration of glove manufacturing with conductive auxetic yarn.

CCY manufacturing: Cotton and polyester fibers were blended and opened in a blow room and carding machine (C-70). Four polyester cotton (PC: containing more polyester fibers then cotton) and four chief value cotton (CVC: containing more cotton fibers then polyester) slivers of 65 grains/yard were produced. These carded slivers were mixed with Staple steel slivers over draw frame (DYH -500 C) to make a roving of 0.65 HR over simplex frame (FL-16). These roving were spun on ring frame (RY-5) with Lycra attachment to produce 8/1 Ne CCY with blended fibers sheath and Lycra core. Table 1 shows the composition of core spun yarn having different percentage of sheath fibers (cotton, polyester, Staple steel), and count of Lycra.

Table 1.

Composition of (CCY) sheath and core’s count.

Sample name	Cotton %	Polyester %	Staple steel %	Lycra denier (D)
1	32	48	20	120
2	32	48	20	280
3	24	36	40	120
4	24	36	40	280
5	48	32	20	120
6	48	32	20	280
7	36	24	40	120
8	36	24	40	280

Auxetic yarn manufacturing: Core spun yarn of Lycra core and blended sheath was used as low modulus components of CAY. The 8/1 Ne CCY was wrapped with Dyneema (50 denier) with 10 wraps per inch (WPI) on a doubling and twisting machine (AGTEKS) to produce 7 Ne CAY.

Fabric manufacturing: CAY of 7 Ne was used for conductive gloves manufacturing over Shima Seiki Glove knitting machine with 360 GSM single jersey fabric with 14 WPI, 60 CPI, and 4 mm stitch length. ²⁹ The resulting knitted fabrics were designated using the same nomenclature as their corresponding yarns.

2.3. Characterization

The influence of blend ratios and Lycra count on the properties of yarns and conductive gloves was analysed. A single yarn tester (Lloyd LRX Plus) was used to check strength (N) and elongation (%) CAY by ASTM D2256. The electrical resistance of helical core spun yarn was measures with digital multimeter (UT139) at length of 5 cm with a constant load on both ends under guidance of AATCC-84. ³⁰ The two probe method was selected due to the non-planar geometry of the helical auxetic yarn. Standard four-point probe techniques require a flat surface for accurate measurement. The uneven surface of the core-spun yarn prevents consistent contact with four separate probes. Consequently, the two-probe method provides more reproducible data for longitudinal resistance in fibrous structures.

Lateral strain (diameter for yarn and width for fabric) was measured by a high-resolution microscope (Optika) and setup was arranged using literature. ¹¹ Images were taken at an interval of 3 mm while applying longitudinal strain (lengthwise) to determine Poisson ratio by Equations (1), (2), and (3) for evaluation of auxeticity. Here Longitudinal strain and Lateral strain are the deformation produced in the length and cross-sectional direction respectively.

$\text{Longitudinal}\hspace{0.17em}\text{strain}\hspace{0.17em}{\mathrm{e}}_{\mathrm{x}}=\frac{\mathrm{L}-\mathrm{L}0}{\mathrm{L}0}\hspace{0.17em}\dots \dots \dots \dots \dots \dots \dots \dots \dots .\dots$

(1)

L = changed lengthLo = original length

$\text{Lateral}\hspace{0.17em}\text{strain}\hspace{0.17em}\text{by}\hspace{0.17em}\text{change}\hspace{0.17em}\text{of}\hspace{0.17em}\text{length}\hspace{0.17em}{\mathrm{e}}_{\mathrm{y}}=\frac{\mathrm{W}-\mathrm{W}0}{\mathrm{W}0}\hspace{0.17em}\dots \dots$

(2)

For yarns; W = change of diameter for yarn and Wo = original diameter for yarn. For fabrics; W = change of width of fabric and Wo = original width of fabric

The Poisson ratio is the negative ratio of lateral strain (ey) to longitudinal strain (e_x)

$\text{Poisson}\hspace{0.17em}\text{Ratio}\hspace{0.17em}\mathrm{v}=-\frac{\text{ey}}{\text{ex}}\hspace{0.17em}......$

(3)

The air permeability (mm/s) was measured using an Air Permeability Tester (M021A) by ISO 9237. The bending length and flexural rigidity of fabrics were measured by cantilever method following the ASTM D1388 for stiffness analysis. A digital multimeter was employed to measure the electrical resistance (Ω) of fabric by two probe method over 5 cm by AATCC-76. ²⁷ Three measurements of electrical resistance were performed with 60-second resting interval between consecutive readings to mitigate the influence of Joule heating. Also, the standard deviation was placed as error bars in Figure 6 and Figure 9 for yarn and fabric electrical performance respectively. Each physical characterization was of yarn and fabrics was performed five and three times respectively to ensure reproducibility. While the mean of these readings was used while the standard deviation was illustrated as error bars in figures.

3. Results and discussion

3.1. Yarn testing

3.1.1. Tensile strength

The tensile strength of a yarn is the maximum force it can endure under uniaxial tensile loading. It is reflected in properties of fabrics especially in protective wear, where it has utmost importance. The prime factor contributing to strength of auxetic yarn is the strength of high modulus wrap while low modulus components complement it under strain. Another factor that influences the strength of auxetic yarn includes core to wrap diameter ratio, fiber type, and wrapping angle. ³¹ Figure 3 illustrates the influence of fiber blends and Lycra counts of CAY core over tensile strength. Yarn with a sheath of PC blends shows higher tensile strength than CVC blends. Such as PC sheath containing yarns sample 1 and sample 3 showed 16.3 and 17.8 N tensile strength respectively. While CVC sheath yarns of sample 5 and sample 7 showed 15.1 and 15.6 N tensile strength respectively. This effect occurs for both 120D and 280D core containing yarns, as the higher content of polyester fibers that had comparatively higher strength than cotton, induce better tensile properties. The core yarn with 280D Lycra shows higher the strength than 120D, for instance sample 1 yarn’s 16.3 N strength increased to 17.8 N for sample 2 in 20% staple steel blended fibers. Likewise, the strength of yarns with 40% staple steel also increased by coarser Lycra, for example sample 3 17.8 N strength enhanced to 18 N for sample 4. Coarser Lycra imparts relatively higher modulus in the 8/1 core of CAY than 120D Lycra. It results in a higher modulus between wrap and core to maximize strength. ³² Raising the content of steel fiber to 40% increases the strength of yarn owing to intrinsically higher strength fiber. ³³ Such as 16.3 N of sample 1 to sample 3 17.8 N, similarly sample 5 strength of 15.1 N was elevated to 15.6 N in sample 7. For 280 den yarns the augmentation of strength was noticed with less intensity. As seen from sample 6 yarns strength (15.8N) to sample 8 (16N) and sample 2 (17.8N) to sample 4 (18N).

Figure 3.

Influence of staple steel content and lycra count on tensile strength of CAY.

The strength enhancement was also observed in 120D core yarns, from 15.2 N for sample 5 to 15.6 N for sample 7. While raising the content of cotton fibers in PC and CVC blends decreases the strength that relates to least strength of cotton fiber as the 17.8 N strength of sample 3 lowered 15.5N in sample 7.

3.1.2. Elongation

Elongation is the percentage increase in length of yarn before breakage. Its prime factors were fiber types and blend ratios in yarn that impact fiber slippage and extension. Fiber types influence that cross section and staple length, which play an influential role in altering fiber slippage before complete failure. ³⁴ Fibers with low intrinsic elasticity reflect low elongation in yarn such as cotton. Also, stiffer fibers show lower elongation in yarn. In knitted structures such as gloves, the impact of yarn elongation becomes synergetic with knitted structures, which impact superior elongation properties to affect drape and wearability. ³⁵ Figure 4 illustrates the influence of blend and Lycra count of core over elongation of CAY. Cores CAY with coarser Lycra shows higher elongation, as content of low modulus component increases in yarn. ³⁶ CAY showed reduced elongation with advancing content of polyester fiber and vice versa for cotton fibers. The higher content of Staple steel fibers decreases elongation owing to its stiffer fiber character that translates in yarn. The C48P32B20L2 showed superior elongation owing to coarser count of Lycra with a lower content of Staple steel and better synergy of cotton/polyester blend content.

Figure 4.

Influence of staple steel content and lycra count on elongation (%) of CAY.

3.1.3. Poisson’s ratio

Auxeticity is the peculiar behaviour of increased lateral strain by application of longitudinal strain. This enhances the force absorption capability allowing employment in protective textiles. Factor affecting auxetic behaviour include a ratio of core/wrap modulus and diameter, wrapping angle, and fiber type. As difference of modulus between core and wrap of yarns increase it enhances the NPR till it reach an optimum difference, after that wrap became embedded inside core, lowering the NPR. ³⁷ Similarly higher difference core/wrap diameter ratios also elevate NPR to a maximum point. ³⁸ Figure 5 shows the influence of blends and Lycra count over auxetic nature of yarn. All CAY shows pure negative Poisson ratio (NPR) during entire deformation, and it became maximum around 12 mm strain except for sample 7. Initial application of strain pushes warp into straight core of CAY causing a rise in diameter. As strain progresses, both core and wrap elements become crimped, achieving highest diameter highest NPR Further advance of strain replaces the core with wrap, resulting in reduced NPR. At 14 mm extension core of auxetic yarn (CCY) was replaced by high modulus wrap (Dyneema), showing highest auxetic nature. Further progress of strain, elongates Dyneema core and CCY wrap, resulting lower diameter that lower auxeticity. CAY cores having coarser Lycra demonstrated superior auxeticity, as its introduction amplified the ratio of core/wrap elastic modulus to raise NPR. For instance, the -2.60 Poisson’s ratio of sample 3 enhanced to -3.11 in sample 4 by changing Lycra count from 120D to 280D in core of yarn. CAY core with higher Staple steel content induces stiffness and lowers the ratio modulus of core/wrap of blended core spun yarn and Dyneema wrap to reduce NPR. Also, elevating the content of steel fiber induces denser fibers in yarn core (blended core spun yarn), thus reducing its diameter as all core spun yarns were of same count of 8/1 Ne. This reduced the diameter ratio of core to wrap. Therefore, yarns with 120 D Lycra, sample 3 (-2.60) and sample 7 yarns (-2.09) demonstrated relatively lesser negative Poisson’s ratio than sample 1 (-3.66) and sample 5 (-3.57). Likewise yarns with 280D Lycra core, the sample 4 (-3.11) and sample 8 yarns (-2.93) demonstrated relatively lesser negative Poisson’s ratio than sample 2 (-3.97) and sample 6 (-3.85). The best performance was demonstrated by auxetic yarn with C28P32B20L2 core having coarser Lycra and lower Staple steel content that showed Poisson’s ratio of -3.97 at 12 mm strain.

Figure 5.

Influence of staple steel content and lycra count on auxeticity of CAY.

3.1.4. Electrical resistance

Electrical resistance of materials is a hindrance to flow of electric charges. Mostly textiles are intrinsic insulators, that are transformed into conductive state by embedding conductive components for instance conductive fibers. ³⁹ The electrical resistance of conductive textiles significantly alters the sensitivity to decide the scope of application. ⁴⁰ CAY has Staple steel fiber as conductive content while remaining fibers in structure of CAY are insulators. Figure 6 shows the influence of blend and Lycra count of core over electrical resistance of CAY. Lesser electrical resistance is demonstrated by augmenting staple steel content from 20% to 40%, as it amplifies the conductive component. For instance, sample 1 yarn showed 80 Ω resistance while sample 3 showed 47 Ω resistance, similarly sample 5 69 Ω resistance became 33 Ω in sample 7. Yarn with 20% staple steel reveals reduction of electrical resistance by extending Lycra count from 120D to 280D, for example sample 1 yarn’s 80 Ω resistance became 65 Ω in sample 2. Similarly, sample 5 electrical resistance (69 Ω) was also lowered in sample 6 (58 Ω). Conversely, yarn with 40% staple steel exhibits an elevating electrical resistance by extending Lycra count to 280D such as sample 3 yarn’s resistance increased from 62 Ω to 69 Ω in sample 4. Similarly, the sample 7 showed a 33 Ω resistance that increased to 40 Ω for sample 8 yarn. It is attributed to uniformity of association in conductive staple steel fibers that incline with coarser Lycra at 20% and decline with coarser Lycra at 40%. ⁴¹ CVC blends showed lesser resistance than PC blends owing to hydrophilic nature and higher moisture content of cotton fibers polyester, that develop less electrical resistance in cotton fibers.^27,42

Figure 6.

Influence of core blends and lycra count on electrical resistance of CAY.

3.2. Fabric testing

3.2.1. Poisson’s ratio

Fabrics manufactured from auxetic yarns have inherent auxetic character. Application of tensile load on fabrics increases the width of fabrics, introducing auxeticity. ⁴³ For protective applications auxeticity imparts better energy absorption in fabrics, thus enhancing the performance of textiles. ⁴⁴ All fabric samples showed complete NPR in the entire duration of strain application as shown in Figure 7. Yarn with superior auxeticity revealed better auxetic fabrics. Max NPR was observed at 6 mm strain of all auxetic fabrics, exhibiting the spiralling of both core and wrap to show radial expansion of fabric. Further strain replaces the position of wrap and core, offering a slight decrease in NPR.

Figure 7.

Influence of core blends and lycra count of CAY on tensile strength of auxetic fabrics.

Yarns with 280D Lycra augmented the fabric’s Poisson ratio as it develops amplifies the modulus mismatch in elastic core and Dyneema wraps. For instance, the -0.85 NPR of sample 3 enhanced to -1.22 in sample 4 owing to Lycra count of 280D that enhanced the NPR of yarn and eventually its resultant fabric. While yarns with higher contents of Staple steel lower the difference of core/wrap modulus owing to stiff nature of sheath fibers, thus resulting fabrics also revealed less negative Poisson’s ratio. ⁴⁵ Thus, the fabrics of sample 3 and sample 7 have NPR of -0.84 and -1.02 owing to 40% staple steel content. In contrast the fabrics with 20% staple steel fibers like sample 1 and sample 5 developed better NPR of -1.06 and -1.75 respectively. Similarly, the fabrics with 280D Lycra showed same trend, as sample 4 (-1.22) and sample 8 (-1.42) fabrics NPR were less than that of sample 2 (-1.90) and sample 6 (-2.02).

The integration of conductive helical auxetic yarn modifies the physical response of the plain jersey fabric. During longitudinal extension, the yarn diameter increases due to the negative Poisson’s ratio of the core-spun structure. ⁴⁶ This radial expansion fills the interstitial spaces between the knitted loops. ⁴⁷ Consequently, the fabric maintains a more consistent thickness. In contrast, knitted fabric with standard yarns usually becomes thinner and the holes (pores) open up when stretched as yarns lack longitudinal thinning phenomenon. Thus, auxetic yarn effectively counteracts the typical structural thinning observed in conventional protective gloves.

This structural behaviour enhances potential for energy absorption and impact mitigation during mechanical deformation. The localized increase in fiber density at the point of contact distributes impact force across a wider area in fabric structure through known as structural densification. ⁴⁸ In conventional textiles, longitudinal strain leads to a reduced thickness of fabric. This weakens the protective barrier at the impact zone. Conversely, helical auxetic yarns (HAY) exhibit a negative Poisson’s ratio that triggers radial expansion of the wrap component when the core is under tension.^49,50 This expansion fills the knitted loops voids at the contact point. Thus, it transforms the kinetic energy into elastic strain energy across the fabrics. ⁵¹ This mechanism is critical for the protective performance of safety apparel. The structural “inward” flow of material prevents the opening of pores, ensuring a continuous shield against mechanical threats. Consequently, the auxetic structure provides a superior energy absorption as compared to conventional structures exhibiting a positive Poisson's ratio.

3.2.2. Air permeability

Comfort characteristics of fabrics are influenced by air permeability that is the flow of air volume per second through the fabric. Enhanced air permeability leads to elevated air passage from body to environment necessary for evaporation of sweat. It determines the utility of fabrics in various environments. Porosity of fabrics establishes the flow of air through the structure of the fabric that is altered by characteristics of yarn.^52,53 Figure 8 shows the influence of sheath fiber blends and Lycra diameter on air permeability of fabrics. Coarser Lycra diameter tends to lower the air permeability of fabrics. It is attributed to a reduction in stiffness of yarns, that enhanced cover in fabric structure to lower porosity. ⁵⁴ Gloves made from PC blend exhibit lower air permeability values than CVC blended samples. Higher content of polyester fiber slightly swells the yarns, lessening the inter-yarn spaces of auxetic fabric. This results in a decline in voids in fabric structure, hindering the air passage and lowering air permeability.^55,56

Figure 8.

Influence of staple steel content and lycra count on air permeability of auxetic fabrics.

3.2.3. Flexural rigidity

Bending stiffness of fabrics is influenced by flexural rigidity, which is the resistance of the material to deformation under its own weight. Flexural rigidity of fabrics reveals the resistance to movement through the structure of the fabric that is altered by characteristics of yarn and knitted structure. ⁵⁷ It directly impacts the dexterity of protective gloves and utility of gloves in various industrial environments where manual precision is required. A lower bending length indicates lower flexural rigidity, thus higher mobility for finger and hand.

Figure 9 shows the influence of sheath fiber blends and Lycra diameter on the bending length and rigidity of fabrics. It was revealed that the most significant factor was content of staple steel fibers, the most rigid component of entire structure. Consequently all fabrics with 40% steel content showed more stiffness than fabrics with 20% steel fiber content. ⁵⁸ The highest bending length and flexural rigidity was shown by sample 4 at 3.84 cm and 199 µNm respectively. It was closely followed by sample 8 with bending length and flexural rigidity of 3.82 cm and 196 µNm respectively, that also had lesser content of PET. It suggested that higher PET content slightly elevates the rigidity of fabrics due to its higher inherent stiffness as compared to cotton in their blends. These were followed by sample 3 and 7, having a finer Lycra core in yarns with same sheath than sample 4 and 8 respectively. It suggests that yarns with coarser Lycra (280D) produces fabrics of larger rigidity possibly by higher core to sheath ratio and stiffer Lycra count. ⁵⁹ Similarly, all fabrics with 20% steel fibers showed same trend, as 280DLycra based sample 2 and 6 had rigid characteristics than 120D Lycra based sample 1 and 5. Here, the higher content of PET (16%) in sample 2 and 1 also showed minor increase in rigidity than sample 6 and 5 respectively. Concludingly, the presence of higher content of steel fibers with coarser Lycra count, yields more rigid fabrics, while PET fiber also yields marginal enhancement of rigidity.

Figure 9.

Influence of staple steel content and lycra count on bending length and flexural rigidity of auxetic fabrics.

3.2.4. Electrical resistance

The analysis of fabric resistance is done by two probe method. Properties like anti-microbial, and anti-static particularly depends upon electrical resistance of conductive textiles. ⁶⁰ Figure 10 shows the influence of Staple steel fiber content on electrical resistance of auxetic fabrics. The results show that the electrical resistance has a direct relation with the Staple steel fiber content which is highest conductive fiber. With the increase in Staple steel fiber percentage from 20% to 40% the conductive fiber portion was increased in the resultant fabric lowering the electrical resistance. ⁶¹ For instance, electrical resistance of sample 1 (970 Ω) and sample 5 (200 Ω) fabrics was higher than that of sample 3 (670 Ω) and sample 7 (178 Ω) fabrics. In contrast to yarn, the fabrics with both 20% and 40% staple steel also showed incline of electrical resistance by extending Lycra count to 280D. For example, fabric with 20% staple steel, sample 5 fabric’s 200 Ω resistance increased to 435 Ω in sample 2. Similarly, sample 5 970 Ω resistance increased to 1500 Ω in sample 6 fabric. Likewise, the fabrics with 40% staple steel also showed increasing trend of electrical resistance with coarser Lycra. Such as sample 3 fabric’s resistance increased from 670 Ω to 800 Ω in sample 4. Similarly, the sample 7 fabric showed a 178 Ω resistance that increased to 240 Ω for sample 8 fabric. Here the structure of fabrics became a dominant factor that develop 2D links in fabrics different from 1D conductive links present in yarn structure. Thus, the reduction of content sheath content to coarser core of 280D develop lesser conductive links to increase the electrical resistance. PC blended samples have a more electrical resistance in comparison with CVC blended samples. Polyester fibers have higher electrical resistance as compared to cotton fibers, thus increasing its content in yarn and fabrics elevate the electrical resistance. ⁴¹ Consequently, the produced fabrics have electrical resistance in range of 10² to 10³ Ω. In literature, research apply 3D printed coating of graphene and PLA for heating applications. The resultant cotton fabrics showed resistance in range of 10³ Ω. ⁶²

The conductive auxetic yarn demonstrates significant potential for capacitive touchscreen interaction in industrial environments. Most capacitive screens require a resistance threshold below 10⁶ Ω. for reliable signal detection. These samples exhibit resistance in the 10² to 10³ Ω. range, ensuring rapid and accurate touch response. Also, the radial expansion of the helical auxetic yarn increases the contact area during finger bending at the screen interface. This geometric behaviour minimizes signal dropouts often observed with conventional conductive gloves. Consequently, the developed textile is suitable for smart protective workwear requiring interaction with digital control systems. Also, this core-spun yarns integrate conductive steel filaments within the yarn body. Surface-coated textiles suffer delamination from mechanical deformation while laundering removes conductive particles from coated surfaces. ⁶³ Wrapping layers protect steel filaments from abrasion. Internal placement prevents oxidation during handling tasks. The structure maintains resistance levels over the glove lifecycle. This design suits smart workwear in industrial settings.

Figure 10.

Influence of staple steel content and lycra count on electrical resistance of auxetic fabrics.

4. Conclusion and future aspect

Advanced auxetic workwear was developed with antistatic character through conductive HAY. Blends of commercially used fibers comprising on cotton, polyester, and stainless steel staple fibers were used with varied counts of Lycra to develop CCY. CCY was wrapped with Dyneema filament for manufacturing of HAY to knit conductive auxetic fabric. Yarns containing 280D Lycra demonstrated up to 9% and 17% enhancement in tensile strength and elongation respectively than yarns containing 120D Lycra. Auxeticity was augmented by 40% and 43% respectively for yarns and fabrics by insertion of 280D Lycra instead of 120D. All samples of yarn and fabrics displayed a pure auxetic nature throughout the loading, while best NPR of -3.97 and -2.02 was revealed for auxetic yarns and fabrics respectively. Elevating staple steel fiber content from 20% to 40% reduce electrical resistance by 60% and 40% for 120 and 280D Lycra respectively, substantially improving antistatic character. Changing Lycra to 280D showed a reduction of 19% in electrical resistance, only with 20% in steel fibres. In contrast, electrical resistance was increased by 21% at 40% in staple steel content in yarn. However, all auxetic fabrics showed an upward trend electrical resistance with 280D Lycra. Auxetic fabrics manufactured with 40% staple steel yarns revealed lowered electrical resistance up to 81% and 84% for 120D and 280D Lycra respectively. In comfort characterization, 120D Lycra and 20% staple steel content showed better performance than 280D Lycra with best results of 521 (mm/sec). The developed conductive auxetic textile demonstrated the commercial feasibility to produce improved workwear with current textile manufacturing. The resultant product developed augmented mechanical, electrical and comfort characteristics for application in Protech. In conclusion conductive auxetic structure not only improved the current level of safety, also mitigate hazard of static charge that can be fatal in sector working with flammable materials.

Future studies can conduct a comprehensive trial analysis of these durability factors and structural resilience to check effect of fatigue on electrical behaviour and Poisson’s ratio of developed textiles for improve practicality. Also, the stability of these functional characteristics under real-world contamination environment is critical for utilization of full potential of these structures. Future work can investigate the synergy between auxetic geometry with self-cleaning characteristics. Additionally, in work wear, the human perception of textile also plays a significant role in performance of wearer. Therefore, objective evaluation of comfort using approach like Kawabata Evaluation System (KES) or Fabric Touch tester is also significant. These research trajectories will facilitate the development of advanced, multifunctional protective equipment with optimized ergonomic and safety profiles.