STUDIES ON MULTIFUNCTIONAL TEXTILE MATERIALS. IMAGE BASED ANALYSIS AND CLASSIC SPECTROSCOPY

T. BEICA1, L. FRUNZA1, L.C. NISTOR1, I. ZGURA1, A. DOROGAN2, E. CARPUS2 1National Institute of Materials Physics, 077125 Magurele, Romania

2Research-Development National Institute for Textile and Leather, 030508 Bucharest, Romania

Received July 28, 2008

Measurements by optical microscopy and spectroscopy were performed on different textile materials (yarn, woven, knitted materials) in order to get their characterization. Thus, using non-specialized classical equipment, the value of the yarn diameter can be estimated. The yarn behavior during the stretching can be directly observed. The observation of the water imbibition by following the shape and stability of a water droplet placed onto the textile material was also developed; in this way the wetting kinetics of different textile materials was obtained. In addition, the spectral properties of woven materials allowed for the study of the modifications induced by different treatments of the woven materials.

Key words: textile materials, optical microscopy, woven, non-woven fabrics, UV-vis spectroscopy.

INTRODUCTION

Textile materials functionalization is very important for its application in different life domains, for example in sport activities or free time. Thus, in order to obtain the functionalization, we have deposited hydroxyapatite and indium-tin oxide (ITO) onto model textile by plasma magnetron sputtering [1]. To demonstrate the gain of new properties, different methods were applied, which were particularly developed using laboratory equipment at hand.

This contribution presents some results obtained applying classical methods such as optical microscopy and spectroscopy in order to characterize the microstructure of some textile materials including non woven yarns, knitted and woven fabrics especially to put in evidence how water imbues such materials. The textile literature contains few data about these common methods [2], which are widespread for many other types of materials. Moreover, water sorption is an important feature often investigated [3–5], by using less accessible and highly specialized equipment.

Rom. Journ. Phys., Vol. 54, Nos. 3–4, P. 391–400, Bucharest, 2009

T. Beica et al. 2

392

EXPERIMENTAL

METHODS

The direct inspection of textile materials by polarizing microscopy was performed at normal incidence in a home made experimental set-up based on a polarizing microscope Zeiss-Laboval [6, 7], between crossed or parallel polarizers. The images were registered with a Panasonic DMC-FZ8 digital camera.

The direct inspection of textile materials by optical microscopy in diffuse light. The homemade experimental set-up has a bulb as light source, the illuminating beam makes an angle of ~45º with the observing direction. The inspection of the specimens were performed by the optical microscope. The images were registered with the Panasonic DMC-FZ8 digital camera.

The wetting of the textile materials was investigated by following the behavior of a droplet placed onto the textile surface. The experimental set-up ensures natural illumination and observation at an angle of ~45º through the optical microscope and a camera. The woven samples were mounted onto a frame in order to avoid their direct contact with the water penetrating through the meshes.

The water droplet was placed using a syringe needle ensuring a constant size of the droplets. The rate of the droplet spreading and passing through the woven meshes is a measure of the hydrophobic properties of the material. The wetting kinetics curves were then fitted with an exponential-type function and the kinetic parameters were extracted.

Panasonic DMC-FZ8 camera (with 30 images/s) allowed the observation of the rapid evolution of the drop size over a period of 200 s.

UV-Vis spectroscopy was performed in a classical arrangement of diffuse reflectance using a Lambda 45 (Perkin Elmer) spectrometer in the range 190-1100 nm. The diffuse reflectance attachment allowed collecting also the diffuse transmitted beam. The spectra were decomposed into Gaussian curves as previously described [8].

Fluorescence spectroscopy measurements were performed using an LS55 (Perkin Elmer) spectrometer.

SAMPLES

The studied textile samples are described in Table 1. They are yarn, woven and knitted materials.

3 Image based analysis and spectroscopy of fabrics

393

Table 1

Description of the studied textile samples

Sample Composition/ look Color/spectral properties in visible range PT1 PES+Teflon/

Yarn in skein Beige/some absorptions

PT2 PES+Teflon/ Material knitted from PT1 yarn

Beige/some absorptions

WT1 Woven White-light beige WT2 Woven White/ Emissions at 268, 366, 450, 655 nm WT3 Woven Dark red/ absorption at 629 nm WT4 Woven Red/ absorption at 625 nm WT5 Woven Dark yellow/ absorption at 376, 507, 608 nm WT6 Woven Dark grey/ absorption at ~700 nm T01 Teflon yarn White-light beige T13 Teflon yarn White-light beige T18 Teflon yarn White-light beige

RESULTS AND DISCUSSION

The color of the samples appearing in the following images is not identical to that observed by eye under the day light. This is due to the spectral components of the illuminating light and to the absorption properties of the specimens. However, in many aspects described below, these factors do not have importance, i.e., they do not influence the wetting phenomena. Consequently, they were disregarded.

A) ANALYSIS OF THE TEXTILE MATERIAL IMAGES

Thickness of some Teflon yarns

Different Teflon yarns were studied under polarized light, at the same magnification, for an easier comparison (see Fig. 1 a–c). Taking into consideration the scale factor, the yarn diameter can be evaluated and compared with the nominal value. For instance, in the images as those in Fig. 1, one can count the pixels covered by each of the yarns. The evaluation result leads to the following thickness of the investigated yarns: 138, 248 and 207 pixels, corresponding to 21, 39 and 32 µm respectively, close to their declared value.

A program might be further developed for thickness evaluation, as it was already done in the literature [5].

Our studies are in line with the fact that the general appearance of a yarn is one of the primary qualities affecting its commercial value. The method of grading spun yarns by subjective visual examination has long been recognized as a

T. Beica et al. 4

394

practical quality assessment tool in yarn manufacturing and fabric industries [9]. Some studies found that quantitative yarn characteristics derived from the optical yarn diameter measurement are determining factors for a human vision system to differentiate a good yarn from a bed one in terms of appearance (e.g., [9] and references herein).

a) b) c)

Fig. 1. – Photographs between crossed polarizers of some Teflon yarns. The scale factor is ~6.55 pixels/µm. a) T01/138 pixels/21 µm; b) T13/248 pixels/39 µm; c T18/207 pixels/32 µm.

Yarn of several components

A PT1 yarn can be observed in Figure 2a. One can easily see that there are two components. One component is twisted over the other. A knitted material realized from these yarns is shown in Figure 2b.

The yarn behavior during the stretching can also be directly observed. Figure 3 presents the image (at the same magnification) of a bi-component yarn as such or stretched.

a) b)

Fig. 2. – Micrograph of a) a PT1 yarn; b) a knitted material from this yarn.

5 Image based analysis and spectroscopy of fabrics

395

a) b)

Fig. 3. – Image of a yarn a) as such; b) slightly stretched.

B) OPTICAL CHARACTERIZATION OF WATER IMBIBITION PROPERTIES

Such a characterization is based on direct observation of the shape and stability of a water droplet placed onto the textile material. To understand the droplet-on-woven behavior, one mention that the water stain, which remained on the woven after the water droplet penetration, can be approximated with the following gray image overlapped over the grid:

These images were further processed by estimation of the stain size for each

image registered at different times from dropping, using the woven warp and weft directions as a helping grid for evaluation.

Water sorption is a topic which was developed in several papers [10, 11].

Water sorption properties of the knitted matter

A water droplet placed onto the knitted material from the above-mentioned PT1 yarn is shown in Figure 4. The water sorption properties depend on the place where water has been dropped. Thus, two droplets were placed in the same time. While the droplet from the right side remains practically unchanged after 20 s, the droplet from the left side disappears in 10 s. This shows that even at close positions on the knitted material, some places are hydrophobic, while others are hydrophilic.

T. Beica et al. 6

396

a) b)

c) d)

Fig. 4. – Time dependence of the sorption properties of the two close places of a knitted material (PT1 yarn): a) initially; after b) 1s; c) 2 s; d) 20 s.

Water sorption properties of woven materials

Figure 5 shows that a water drop can imbue the woven in 60 s. Initially the droplet placed on to the woven acts as a lens, giving the deformed images of the woven directions. Step by step, the drop is spread, the image is less deformed and water imbues the woven. After 60 s the stain due to the water imbued in the woven is 4 times larger than the initial size of the drop.

a) b)

c) d)

7 Image based analysis and spectroscopy of fabrics

397

e) f)

g)

Fig. 5. – Sorption properties of a woven (WT1): a) initial; after b) 10 s; c) 15 s; d) 20 s; e) 25 s; f) 50 s; g) 60 s. The images are obtained at the same magnification.

The sorption properties of the water might be different on the two sides of a woven, as it is shown in Fig. 6. Thus, the sample (WT6) is hydrophobic on the front side but hydrophilic on its backside. After 20 s the hydrophilic side is wet.

a)

b) c) d)

Fig. 6. – Sorption properties of WT6 sample: a) front side; b-to-d) backside of the textile. Images b-c-d are taken after 0, 15 and 20 s respectively.

T. Beica et al. 8

398

Wetting kinetics

On the basis of the registered images, one can measure (in arbitrary units) the size of the stain made by the water droplet as function of time elapsed from the droplet application. Kinetic sorption curves can be then drawn, as the estimated size values in function of the time. Such curves are shown in Fig. 7a.

Generally, the liquid absorption processes in fibrous structures can be described with the Lucas-Washburn formula [12]. However, for a rough estimation, our experimental curves were fitted with an exponential function as it can be seen in Figure 7b or with a quadratic function. The kinetic parameters resulted from data fitting with exponential function are given in Table 2.

It is obvious from Table 2 and Fig. 7 that the wetting kinetics is very fast in the case of samples WT3 and WT4.

Table 2

Kinetic parameters as resulted from the data fitting with y = A*exp(t/B) + y0

Sample Y0 A B WT1 0.4 6.5 39.5 WT3 1.5 2.2 3.8 WT4 2.2 1.7 1.8 WT6 3 0.004 3.1

a) b)

Fig. 7. – Kinetic water sorption curves: a) for the samples mentioned in the legend; b) for the sample WT1 but fitted with an exponential function.

C) SPECTRAL PROPERTIES OF THE TEXTILE MATERIALS

The spectral properties in the visible range are related to the textile color but the extended range in UV region might indicate the whole absorption properties of the chromophore. Any chemical modification of the woven materials should affect their spectrum. Since this is a topic beyond our work, here we will not insist further.

0 10 20 30 40 50 60

5

10

15

20

25

30

WT1 exponential fit

Dro

p si

ze [a

.u.]

Time [ s]

0 5 10 15 20 25

5

10

Dro

p si

ze [a

.u.]

T ime [s]

W T4 W T6 W T3

9 Image based analysis and spectroscopy of fabrics

399

Representative spectra for some woven materials are given in Fig. 8. Some of the characteristic absorption peaks resulted by calculation of the Kubelka-Munk function [13, 14] are given in Table 1.

Because the reflectivity of some investigated woven materials exceeded 100%, we looked for fluorescence properties. Figure 9 shows that indeed, the woven sample with reflectivity higher than 100% has emission maxima corresponding to excitation in this high reflectivity region.

CONCLUSIONS

The measurements by optical microscopy and classical spectroscopy performed under these studies pay attention on the usefulness of these widespread methods in characterization of textile materials.

The studies under polarized light, at the same magnification can be used to obtain the value of the thread diameter. The images are processed by taking into consideration their scale factor.

The image of the complex yarn can give details of the spun mode or of the knitted material made of these yarns. The yarn behavior during the stretching can be also directly observed.

Direct observation by optical microscopy of the shape and stability of a water droplet placed onto the textile material can allow the observations of the water imbibition in the textile material.

The sorption properties of water might be different on the two sides of a woven: this might be important for choosing the side to be in contact with the skin.

400 600 800 10000

20

40

60

80

VT5 VT3 VT4 VT6 VT1

R [

%]

Wavelength [nm]

350 400 450 500 550 6000

50

100

150

200 400 600 800 10000

50

100

150

200

250

Inte

nsity

Wavelength [ nm]

250 nm 270 nm 390 nm

Excitation at:

R [%

]

Wavelength [nm]

Fig. 8. – Diffuse reflectance spectra of different woven.

Fig. 9. – Diffuse reflectance spectrum of a woven WT2. The inset shows the emission spectra at different excitation wavelengths.

T. Beica et al. 10

400

Kinetic wetting curves were obtained by representing the size of the stain made by the water droplet as function of time elapsed from the droplet application onto the textile material. The experimental data were fitted with analytical functions giving the opportunity of a quantitative comparison of the kinetics.

The spectral properties in the UV-visible range are related to the textile color and the absorption properties of the chromophore. Any chemical modification of the woven material affects its spectrum. The fluorescence of a particular woven material can explain its enhanced diffuse reflection properties.

Acknowledgements. The authors are indebted to Romanian Ministry for Research for the financial support either under the Project CEEx S2 09 of the Program MATNANTECH (L.C.N., A.D., E.C.) or under the Project PN06-410102 of the Core Program (T.B. and L.F.). We acknowledge Mrs. Nicoleta Gheorghe for technical assistance.

REFERENCES

1. T. Beica, L.C. Nistor, C. Morosanu, L. Frunza, G. Stan, I. Zgura, D. Marcov, A. Dorogan, E. Carpus, J. Optoeletr. Adv. Mater., 10, 2811–2817 (2008).

2. a) M. Ding, J.L. Hu, X.M. Tao, C.P. Hu, Textile Res. J. 76, 406–413 (2006); b) A. Masuda, T. Murakami, K. Honda, S. Yamaguchi, J. Text. Engn., 52, 93–97 (2006).

3. D. Fakin, V. Golob, K. Stana Kleinschek, A. Majcen Le Marechal, Textile Res. J., 76, 448–454 (2006).

4. S.-J. Park, H. Tokura, M. Sobajima, Textile Res. J., 76, 383–387 (2006). 5. Z. Gombos, V. Nagy, L.M. Vas, J. Gaal, Per. Polytechnica Ser. Mech. Engn., 49, 131–148 (2005). 6. R. Moldovan, M. Tintaru, S. Frunza, T. Beica, S. Polosan, Cryst. Res. Technol., 31, 951–955,

(1996). 7. T. Beica, R. Moldovan, M. Tintaru, I. Enache, S. Frunza, Cryst. Res. Technol., 39, 151–156

(2004). 8. L. Frunza, J. Pelgrims, P.Van Der Voort, E.F. Vansant, R.A. Schoonheydt, B.M. Weckhuysen,

J. Phys. Chem. B, 105, 2677–2686 (2001). 9. Y.K. Kim, K.D. Langley, F. Avsar, J. Textile Engn., 52, 13–18 (2006). 10. J. Jopp, H. Gruell, R. Yerushalmi-Rozen, Langmuir 2004, 20, 10015–10019. 11. P. Stahel, V. Bursikova, J. Bursik, J. Čech, J. Janca, M. Černak, J. Optoelecton. Adv. Mater., 10,

213–218 (2008). 12. E.W. Washburn, Phys. Rev., 17, 27–283 (1921). 13. G. Kortum, Reflectance spectroscopy: principles, methods, applications, Springer, 1969. 14. W.W. Wendlandt, H.G. Hecht, Reflectance spectroscopy, Wiley, 1966.