Investigation of the electrical behavior of some textile materials

Investigation of the electrical behavior of some textile materials

ARTICLE IN PRESS Journal of Electrostatics 65 (2007) 162–167 www.elsevier.com/locate/elstat Investigation of the electrical behavior of some textile...

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ARTICLE IN PRESS

Journal of Electrostatics 65 (2007) 162–167 www.elsevier.com/locate/elstat

Investigation of the electrical behavior of some textile materials Koviljka A. Asanovica, Tatjana A. Mihajlidia, Svetlana V. Milosavljevica, Dragana D. Cerovicb,, Jablan R. Dojcilovicc a

Department of Textile Engineering, Faculty of Technology and Metallurgy, Karnegijeva 4, 11000 Belgrade, Serbia and Montenegro b Advanced Technical Textile School, Starine Novaka 24, 11000 Belgrade, Serbia and Montenegro c Faculty of Physics, Akademski trg 16, 11000 Belgrade, Serbia and Montenegro Received 23 July 2005; received in revised form 5 February 2006; accepted 12 July 2006 Available online 31 August 2006

Abstract Some electrophysical properties of textile samples having different forms and raw material compositions were studied. For determining the electric resistance, a measuring device, based on the measurement of direct current through textile samples, was developed. The dielectric loss tangents and relative dielectric permeabilities were measured for some of the textile samples tested. The dielectric properties were measured using specially designed capacitance cells. r 2006 Elsevier B.V. All rights reserved. Keywords: Measurement of electrophysical properties; Textile materials; Electric resistance; Dielectric properties

1. Introduction Textile materials are in continuous contact with other textile materials, as well as with parts of machine devices during the manufacturing process or, finally, with consumer bodies during use. The electric resistance of textile materials is usually very high. Also, unfavorable effects, caused by static electricity, occur during utilization. Some of these effects include increased dirt, cleaning problems, as well as sticking to textile fabrics and human bodies, which may cause an unpleasant feeling, an increase of pilling (the tendency of materials to form on their surface rolled-up ends of fibers). Some physiological disturbances, the mechanisms of which have not yet been definitely solved, may also occur, although pathological reactions of the nervous system, heart and blood vessels occurring in the presence of sufficiently high values of positive charges have been, suggested [1–4]. Therefore, the fight against electrostatic charge is an important task in the textile industry, especially when synthetic textile fabrics with extremely high electric resistances are considered.

Corresponding author.

E-mail address: [email protected] (D.D. Cerovic). 0304-3886/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.elstat.2006.07.008

Investigations concerning static electricity on textile materials have developed mainly in two different directions. One is the development of methods for decreasing static charge on textiles [1,5–8]; the other is the development of methods for the characterization and control of the tendency of textile materials to produce static electricity [9–30]. The connection between electric resistivity of textile materials (in the rest of this paper, this property is referred to as simply ‘‘resistance’’) and their tendency to produce static electricity embodies the problem of resistance measurement. This problem is especially important given the increasing use and production of synthetic fibers having very high resistances. Such fibers cause increased disturbances during production and use. By measuring the resistance, we have obtained a series of data that enable us to estimate and predict of the tendency of various textile materials to produce static electricity. These data thus contribute to the determination of how to minimize the detrimental influence of static electricity [15–24]. The very high values of resistance of textile materials cannot, in most cases, be measured using a common ohmmeter. A special device is required for this purpose. Due to the complexity of such measurements, an insufficient number of appropriate devices have been developed

ARTICLE IN PRESS K.A. Asanovic et al. / Journal of Electrostatics 65 (2007) 162–167

up to now in textile metrology practice. As indicated in the references to this paper, various methods for the direct determination of resistance have been proposed. Some of them are based on the measurement of the current intensity through the tested sample of textile material. These methods have proved to be the most precise and reliable. However, they involve the greatest difficulties in the correct performance of the experiments. Another group of simple, but less accurate alternative methods for indirect measurement of the resistance of textile materials is based on recording the charging and discharging dynamics of the samples [23]. The tendency of textile materials to produce static electricity can also be characterized by measuring their dielectric properties. It is well known that the dielectric behavior of a perfect dielectric can be expressed by its relative dielectric permeability, which is equal to the material’s absolute permittivity divided by the permittivity of vacuum. Since most textile materials are not perfect dielectrics, their behavior in an external electric field also needs to be expressed by the dielectric properties. One example is the tangent of the dielectric losses which indicates the imperfect nature of the dielectric and increases with a decrease in resistance. The paper considers the development of an experimental device for determining the resistance of textile materials and its application to various types of measurements of textile resistance and dielectric properties. These results are compared to actual resistance measurements. 2. Materials and methods The structural characteristics of the textile materials used in this study are presented in Tables 1 and 2. In Tables 1 and 2, the textile materials are made of following fibers:

 



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Viscose (fiber) generic name: A term used to describe fibers of regenerated cellulose obtained by the viscose process; PES-polyester (fiber) generic name: A term used to describe fibers composed of synthetic linear macromolecules having in the chain at least 85% (by mass) of an ester of a diol and bensene-1,4-dicarboxylicacid (terephthalic acid); PAN-polyacrylonitrile (fiber) generic name: A term used to describe fibers composed of synthetic linear macromolecules having in the chain at least 85% (by mass) of recurring cyanoethene (acrylonitrile groups).

A device for determining of the resistance of textile materials based on Ohm’s Law has been previously developed by our research group [4,19–25]. Such a device must meet strict metrological requirements. For example, it must contain precisely constructed electrodes for holding the sample. A tight and stable contact between the textile and the electrodes must be ensured by producing a defined tension within the sample. The effect of a resistance increase caused by axial strain of the sample, which commonly occurs in metallic wire conductors, is also observed in textile materials. For homogeneous conductors, this effect is ascribed to a decrease in the cross-sectional surface area of the conductor with increased mechanical load. A similar explanation may also be applied to non-homogeneous materials such as textiles. In this case, axial strain likewise causes a decrease in the cross sections of both the entire yarn and the component fibers. Due to the large value of the resistance of textile materials, the voltage drop between the electrodes should be high to enable the conduction of current through the sample. The electrodes should be mounted on supports having extremely high resistance in order to maximize the equivalent parallel resistance between the electrodes. To counteract the strong dependence of textile material resistance on the relative

Table 1 Structural characteristics of investigated textile yarns No.

Material composition

Yarn type

Fineness, tex

Twist, m1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Cotton (100%) Cotton (100%) Cotton (100%) Cotton (100%) Cotton (100%) Cotton (100%) Cotton/PES (50/50%) Viscose (100%) Viscose (100%) Pan (100%) Wool (100%) Hemp (100%) Hemp (100%) Hemp (100%) Hemp (100%) Hemp (100%) Flax (100%) Jute (100%)

Combed Combed Combed Rotor Rotor Rotor Rotor Carded Carded Combed Woolen Carded Carded Carded Carded, bleached Carded, bleached Carded Carded

12 20 25 30 72 20  2 25 30 30 25  2 75  2 286 400 800 139 270 333 351

1045 685 676 846 542 925 (K0); 541 (K1) 905 543 742 499 (K0); 456(K1) 292 (K0); 162 (K1) 165 194 107 268 205 192 130

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Table 2 Structural characteristics of investigated woven fabrics No.

19 20 21 22 23 24 25 26 27

Material composition

Cotton (100%) Viscose (100%) Silk (100%) Wool (100%) PES (100%) Hemp (100%) Flax (100%) Jute (100%) Wool/PES (60/40%) warp and weft-same composition Cotton/PES (22/78%) warp-PES; weftcotton+PES Cotton/hemp (13/ 87%) warp-cotton; weft-hemp

28

29

Type of weave

Fabric density, dm1

Fabric thickness, mm

Fabric weight, g m2

185 292 300 228 131 60 100 40 119

0.414 0.226 0.200 0.650 0.590 1.120 0.552 1.00 0.827

204 138 76.0 258 317 450 256 335 255

355

249

0.234

93

93

72

1.91

808

Yarn fineness, tex

Crimp, %

Warp

Weft

Warp

Weft

Warp

Weft

Plain Plain Plain Twill 2/1 Z Plain Plain Plain Plain Twill 6/6 Z

41 21 8 43 98 400 95 325 96

46 14 11 43 102 400 117 351 83

7.0 11.5 8.9 9.9 8.5 2.0 8.8 4.6 3.6

11.0 9.2 12.3 4.8 4.7 2.0 2.4 2.7 7.9

211 479 493 312 163 60 124 50 148

Plain

9

23

1.3

7.0

785

19.3

6.3

Twill 2/2 Z 45  2

Table 3 Resistance R of yarn samples at a humidity of j ¼ 35%

7 3

RP 1B

1A

4 5

1A,

2

EM

1B

6

+ C

-

Fig. 1. Scheme of the device for measuring the resistance of textile materials, 1A, 1A0 , 1B, 1B0 —electrodes; 2—sample with unknown electric resistance R; 3—screws for tightening the electrode plates; 4—sensors for measuring the humidity and temperature in the chamber; 5 and 6— Faraday-cage; 7—aperture providing a connection between the chamber and the external atmosphere; H—humidifier; RP—protective known resistor; C—capacitor for the elimination of parasitic high frequencies; HVS—high voltage source (400–2000 V); DM—digital multimeter; EM— electromotor with a compression circuit providing air circulation inside the chamber; DHM—digital humidity meter and thermometer measuring the temperature inside the chamber.

humidity of the environment (referred to here as simply ‘‘humidity’’), the device must be placed in a chamber that provides controlled measurement conditions, as well as Faraday shielding from extraneous, external electric fields.

Sample no.

R, TO

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

3.29 1.76 1.35 2.07 0.861 1.72 4.07 5.36 4.17 37.5 11.3 0.0676 0.0494 0.0175 1.02 0.476 0.389 0.189

The resistance of textile materials is strongly dependent on their absorbed moisture. The latter depends on the humidity of the environment. We therefore carefully controlled the latter by means of an air humidifier and a turbine circuit that produced uniform air circulation in the chamber. Fig. 1 shows the arrangement of the device developed for our experiments. The adjustable plate electrodes electrolytically silver-plated to achieve a stable electrode resistance. It is well known that silver oxide has a resistance similar to that of metallic silver. The resistance of textiles is usually extremely high, especially if they are produced from synthetic fibers. Hence

ARTICLE IN PRESS K.A. Asanovic et al. / Journal of Electrostatics 65 (2007) 162–167

the device was designed to enable the simultaneous connection in of a number of samples to the same voltage source. The detection limit of the resistance could thus be reduced by one or two orders of magnitude. This system also provided for some averaging of the values of the multiple samples. This is advantageous because exact measurements of textile Table 4 Resistance R of fabric samples at a humidity of j ¼ 35% R, TO

Sample no.

20 21 22 23 24 25 26 27 28 29

Warp

weft

0.362 24.0 23.0 43.5 0.00351 0.0187 0.0138 22.8 7.35 0.0445

0.693 30.0 30.5 65.1 0.00355 0.0211 0.0191 23.5 0.367 0.00204

resistance require long-term sample conditioning—on the order of several hours—for the sample to come to equilibrium with the surrounding atmosphere. The dielectric properties were measured using a previously developed device [26–30]. Relative permeability er was determinated from the ratio of the capacitance of parallel electrodes with (C) and without (C0) the textile sample material inserted between brass electrodes (diameter—25 mm). The latter consisted of two measuring electrodes and a guard ring. The spacing of the electrodes was controlled by a micrometer. The tangent of the dielectric loss (tand), which is a measure of the ratio of the electric energy lost to the energy stored per cycle in a material subject to periodic field, was determined using a cell in which the upper electrode (diameter—13 mm) was made of stainless steel and the lower electrode (diameter—13 mm) of silver alloy. The electrodes were isolated by a Teflon insulator and special low-temperature glue. The cell was evacuated by a turbomolecular pump to 105 Torr. Capacitance and tand values were measured using a Hewlett-Packard Model 4271B OPT101 1 MHz Digital LCR Meter.

0.07

Cotton yarn-sample No.2 Viscose yarn-sample No.8

5

R,T Ω

R,T Ω

0.05

3 2

0.03

0.01 0.00

0 35

40

45

50

55

35

60

ϕ,%

(a)

40

45

50

0.015

R,T Ω

0.2 0.1

60

Flax fabric-sample No.25 warp weft

0.020

0.3

55

ϕ,%

(b)

Flax yarn-sample No.17 Jute yarn-sample No.18

0.4

R,T Ω

0.04

0.02

1

0.010 0.005

0.0

0.000 35

40

45

50

55

60

ϕ,%

(c)

35

Jute fabric-sample No.26 warp weft

0.020

40

45

R,T Ω

0.015 0.010 0.005

50

55

60

ϕ,%

(d)

0.025

R,T Ω

Hemp yarn-sample No.12 Hemp yarn-sample No.13

0.06

4

0.05 0.04 0.03 0.02 0.01

Cotton/hemp fabric sample No.29 warp-cotton weft-hemp

0.002 0.001 0.000

0.000 35

(e)

165

40

45

50

ϕ,%

55

35

60

(f)

40

45

50

55

60

ϕ,%

Fig. 2. The dependence of the resistance R with humidity j for some yarn samples as well as some fabric samples in warp and weft direction.

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3. Results and discussion In order to demonstrate some of the measurments made possible by the developed device, the resistances of a number of yarns and woven fabrics were determined. The results of resistance measurements at a humidity of j ¼ 35% are shown in Table 3 (for some yarns) and Table 4 (for some woven fabrics in the directions of warp or weft).

Fig. 3. Dependence of viscose woven fabric (No. 20) resistance on sample tension.

The dependence of the resistance of some yarn samples as well as some woven fabric samples in warp and weft direction with humidity j are shown in Fig. 2. The results presented in Fig. 2 exhibit an extremely strong dependence of textile resistance on humidity. A 25% decrease in humidity causes a considerable increase of the resistance (approximately one order of magnitude). This fact suggests that caution be used when establishing equilibrium between a textile sample and the surrounding atmosphere. These results confirm the strong dependence of textile resistance on the composition of the raw material. Some differences in resistance may be observed between warp and weft direction measurements of woven fabrics of the same material composition. We suppose these differences to be caused by their differing construction, mechanical properties, and yarn properties. Smaller resistance in the warp direction, as compared to the weft direction, could be caused by a greater number of parallel threads able to conduct current. However, the results indicate that some other factors, for example yarn fineness (Fig. 2(b)) and yarn tension [19] may cause this difference. Both factors can be explained via an increase in resistance with decreasing yarn diameter. A increase in resistance with increasing sample tension F has also been observed in this investigation (Fig. 3).

0.08

0.08 0.06 tan δ

tan δ

0.06 0.04 0.02

0.02 0

10

20

50

0

60

7 6

5

5

4

4

3

3

(c)

20

30

40

50

0

60

6

6

5

5

εr

7

4

4

3

3 0.04 tan δ

0.06

0.08

0.02 (f)

6

8

10

4

6

8

10

R, TΩ

7

0.02

2

(d)

R, TΩ

4 R, TΩ

6

10

2

(b)

εr

εr

40

7

0

εr

30 R, TΩ

(a)

(e)

0.04

0.04

0.06

0.08

tan δ

Fig. 4. Relationship between the dielectric properties (er and tand), resistance (R) for samples No. 19, 22, 23 and 28 at humidities j ¼ 35% (a), (c) and (e) and j ¼ 60% (b), (d) and (f).

ARTICLE IN PRESS K.A. Asanovic et al. / Journal of Electrostatics 65 (2007) 162–167

In order to compare the different electrophysical properties of the textile samples, the relative dielectric permeability and the tangents of dielectric losses of some samples were also measured. A comparison of relative dielectric properties, i.e. relative dielectric permeability and dielectric loss tangent, for cotton (Sample No. 19), wool (Sample No. 22), polyester (Sample No. 23), and cotton/polyester (Sample No. 28) woven fabric is shown in Fig. 4, for humidities of j ¼ 35% and j ¼ 60%. The dielectric loss tangents are seen to decrease with increasing resistance (Figs. 4(a) and (b)). Interestingly, samples exhibiting higher permeability appear to have lower resistance (Figs. 4(c) and (d)). These dependencies illustrate an increase in the dielectric loss tangent with increasing permeability. 4. Conclusion The device reported in this paper can be used to test different textile yarns and textile fabrics for resistive properties. By changing the relative humidity in the measurement chamber, the influence of humidity on electric resistance was studied. The influence of relative humidity, specifically the change in dielectric properties, can be ascribed to an increase in the moisture content of the textile samples. As is well known, a decrease in resistance helps reduce the problem of static electricity during the processing of textile materials. On the basis of the proven regularity of dependencies between the electric resistance and dielectric properties of the samples tested, both parameters of the electrophysical properties could be recommended for indirect assessment of the tendency of textile materials to generate static electricity during processing or use. Acknowledgments This investigation was carried out within the Project TR6713B supported by the Ministry of science and Environmental Protection of the Serbian Republic Government. References [1] G. Nemoz, L’ Ind. Text. (1990) 56. [2] P.L. Gefter, Elektrostaticheskie yavleniya v protsesah pererabotki himicheskih volokon, Legprombytizdat, Moskva, 1989, p. 73.

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