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Plasma effects on anti-felting properties of wool fabrics
Surface & Coatings Technology 205 (2010) S349–S354
Contents lists available at ScienceDirect
Surface & Coatings Technology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / s u r f c o a t
Plasma effects on anti-felting properties of wool fabrics S. Shahidi a,⁎, A. Rashidi b, M. Ghoranneviss c, A. Anvari d, J. Wiener a a
Department of Textile Chemistry, Faculty of Textile, Technical University of Liberec, Liberec, Czech Republic Department of Textile, Faculty of Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran c Plasma Physics Research Center, Science and Research Branch, Islamic Azad University, P.O. Box 14665-678, Tehran, Iran d Department of Physics, Sharif University of Technology, Tehran, Iran b
a r t i c l e
i n f o
Available online 17 August 2010 Keywords: Wool Fabric Anti-felting Plasma
a b s t r a c t Low temperature plasma (LTP) is nowadays an intensively investigated superficial treatment of wool. In this work we have investigated the effect of LTP on wool fabric under different conditions. The effect of the position of samples inside the reactor and the kind of gases used as discharge medium has been also investigated. The results show that not only the topography of the surface is modified but also the chemical composition of the surface. It is shown that the hydrophilicity of the samples and also their shrink resistance and anti-felting behavior have improved significantly under LTP treatment. The results show that the shrinkage of 30.1% for untreated samples has reduced to about 1.5% or even less depending on the sample position and the kind of gases used. Many analytical skills such as XRD, FTIR, and SEM were used to characterize the different aspects of the treated fabric. The details of the experiment are discussed in the text. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Keratin fibers, like wool or human hair, can be considered as natural composite materials, where keratinous protein is the main basic constituent [1]. Wool is a high-quality protein fiber and is widely used as a high-quality textile material [2]. It is well known that the surface characteristic of fibers play an important role in the functional and aesthetic properties of their fabrics, and many surface modifications by chemical treatments are able to improve textile properties [3]. Felting is an undesirable feature of woolen clothes. It occurs as a result of the directionally dependent frictional coefficient of the wool fibers. To reduce felting, this directional dependency must be reduced. Nowadays, this is done by treating the wool in a chlorine-containing solution. During this treatment, the outer surface of the wool, which mainly consists of approximately three-quarters protein and onequarter lipid, is etched [4,5]. However, this procedure has to be replaced because of environmental care [4]. Plasma pretreatments are environmentally benign and energy-efficient processes for modifying the surface chemistry of materials [6–9]. This field of treatment, as a clean, dry and environmental friendly physical technique, opens up a new possibility in this field [10–19]. Plasma treatment can usually induce the following processes: dehydrogenation and consequent unsaturated bond formation trapped stable free radicals formation, generation of polar groups through post plasma
⁎ Corresponding author. E-mail address: [email protected] (S. Shahidi). 0257-8972/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2010.08.003
reaction, and generation of increased surface roughness through preferential amorphous structure ablation processes [20]. In this research work, we have shown that the surface of wool fabrics could be etched and oxidized by plasma treatment, a process which is necessary to improve the felting behavior of the wool. 2. Experimental 2.1. Preparation of wool fabrics Wool plain woven fabrics (Iran Merinus Co, Iran) used in this work were weaved by 20 denier warp and weft yarns composed of 36 filaments in each square inch. For sample preparation, size residue and contamination on the fabrics were removed by conventional scouring processes, and the fabrics were washed by 0.5 g l− 1 sodium carbonate and 0.5 g l− 1 nonionic detergent solution (dilution ratio to water=1:10) at 80 °C for 80 min. Washing was performed twice with distilled water at 80 °C for 20 min and once at ambient temperature for 10 min. 2.2. LTP treatment A DC magnetron sputtering reactor with non-polymerizing reactive gases, such as O2, N2 and Ar were used to treat the wool surface. In this reactor a sheet of wool fabric could be placed on the anode or cathode. Before each experiment the air and old gases were pumped out by a vacuum pump and then a proper gas such as O2, N2 or Ar was introduced into the chamber. Discharge voltage was 1000 V, discharge current was 200 mA and the inter-electrode distance was 35 mm. The
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S. Shahidi et al. / Surface & Coatings Technology 205 (2010) S349–S354
pressure remained at 0.02 Torr for the entire glow-discharge period. The discharge period was 7 min for each sample treatment. 2.3. Characterization tests The morphology of the LTP-treated wool was observed using a scanning electron microscope (SEM, LEO 440I). All the samples were coated with gold before SEM testing. Wettability was evaluated by measuring the absorption time of 4 distilled water dropped on the fabric. The functional groups on the surface of samples were examined using FTIR spectrometer (Bomem MB-100, made in Canada). Aqueous solutions, containing 3.0 wt.% of the Acid Blue dye were employed for dyeing wool fabrics. The bath ratio was 1:100 (1 g of fiber in 100 ml of dye solution). The following dyeing condition was adopted: an initial temperature of 40 °C, followed by a temperature increase of 3 °C min− 1 up to 80 °C, holding for 30 min at 80 °C. 5 g/l of acetic acid for pH adjustment, was added for anionic dyeing processes. After dyeing, the fabrics were rinsed with cold–hot–cold water and then dried at room temperature.
Color intensities of the dyed fabrics were measured by using a UV VIS–NIR reflective spectrophotometer, over the range of 350–500 nm and the reflection factor (R) was obtained. (The maximum wavelength of Blue dyes is 380–480 nm, so this area was chosen for investigation). The relative color strength (K/S value) was then established according to the following Kubelka–Munk Eq. (1), where K and S stand for the absorption and scattering coefficients, respectively [19,20]: n o 2 K = S : ð1−RÞ = 2R
ð1Þ
The dimensional changes of the LTP-treated wool fabric were tested according to AATCC Test Method 99–1993 [21]. Due to the limited size of the plasma reaction chamber, the dimension of the fabric sample used was 65 × 35 mm2, with a 60 × 30 mm2 marked inside the fabric. The fabric was conditioned before measurement. The measurement was then conducted to assess the shrinkage in length of both warp and weft direction, and finally the area shrinkage was
Fig. 1. SEM images of treated and untreated samples: untreated (a), Ar-cathode (b), O2-cathode (c), N2-cathode (d), O2-anode (e), N2-anode (f).
S. Shahidi et al. / Surface & Coatings Technology 205 (2010) S349–S354
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calculated. The degree of shrinkage in length and area change was calculated (expressed in %) according to Eqs. (2) and (3) respectively. Length change = ðlf −lo Þ = lo × 100
ð2Þ
Area change = fðA−OÞ = Og × 100
ð3Þ
where: lf lo A O
final length after treatment (mm), original length before treatment (mm), final area after treatment (mm2), original area before treatment (mm2).
3. Results and discussion
Fig. 3. Reflection spectroscopy of untreated and treated samples.
3.1. Morphological examination Fig. 1 shows the SEM images of untreated and treated wool fiber surfaces under different conditions. As we know the presence of a microporous hydrophobic layer called epicuticle makes the fiber surface difficult to get wet. However, it seems that after the plasma treatments, the scales on the fibers are broken and so for the epicuticle. This is due to the penetration of the active species from plasma through the pores in the wool fabric. The etching effects of plasma particles are also an important factor in roughening the surface of the fibers. These effects contribute to the wettability improvement of the wool fiber surfaces.
The figure also shows that, the scale change of samples is different when they are on the cathode or anode. The figure also reveals that the etching effect of Ar and oxygen plasma is more pronounced than nitrogen plasma under the same condition. The most important effect of LTP treatment on wool is that it changes its character from hydrophobic to hydrophilic and anti-felting. 3.2. FTIR The results of FTIR used to examine the functional groups of the samples are shown in Fig. 2. As shown, for both anode and cathode cases, a slight increase in absorbance at 1720 cm− 1, 1240 cm− 1 (C O, C–O bonds) after O2 plasma treatment, and 3400 cm− 1 corresponding to N–H group after N2 plasma treatment can be noticed [22–25]. However, Ar plasma treatment shows no significant difference in the FTIR spectra. 3.3. Dye ability of wool samples As it can be seen in Fig. 3, the reflection factor of dyed LTP-treated samples is less than dyed untreated sample. This shows that, LTP treatment causes more absorption of acid dye by wool fabrics. The results show that the O2 and Ar-cathode plasma treatments are more effective in increasing the dye exhaustion of wool with anionic dye. Furthermore, the colors achieved much more brilliant shades by LTP treatment. As it can be seen in Table 1, the K/S value of LTP-treated samples is more than that of original one, and the largest value belongs to Ar and O2-cathode LTP-treated samples. All these have contributed to
Table 1 The amount of K/S Value for the untreated and treated samples. Samples
Average of R
Average of K/S value
Untreated Ar-cathode O2-cathode N2-cathode O2-anode N2-anode
0.160 0.116 0.104 0.130 0.134 0.131
2.13 3.34 3.83 2.89 2.77 2.87
Table 2 Absorption time of treated and untreated samples.
Fig. 2. FTIR spectra of samples.
Sample
Absorption time
Untreated Ar-cathode O2-cathode N2-cathode O2-anode N2-anode
20 min 3s 1s 3s 2s 3s
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Table 3 Influence of the pretreatment on the area felting shrinkage of knitted fabrics after 30 simulated washing cycles. Samples
Dimensional change (%) in warp direction
Dimensional change (%) in weft direction
Area felting shrinkage (%)
Untreated Ar-cathode O2-cathode N2-cathode O2-anode N2-anode
18.4 0 0 0 1.5 0.7
14.2 0 0 0 0 0
30.1 0 0 0 1.50 0.70
wettability improvement of the wool fiber through penetration of active species from plasma and also by plasma etching effects. 3.4. Water drop test The quality of water repellency of the samples were evaluated by water drop test in which drops of controlled size were placed at a constant rate upon the fabric surface and the duration of the time required for them to penetrate to the fabrics was measured. The results are shown in Table 2 in which the absorption times have been
Fig. 4. X-Ray diffraction of untreated and LTP-treated samples.
S. Shahidi et al. / Surface & Coatings Technology 205 (2010) S349–S354
recorded for different treated samples. As can be seen after LTP treatment the water-absorption time has decreased. However this time is very low for O2-cathode LTP treatment. Here we should mention that the water-absorption time was reduced for both sides of the fabrics. The decrease of water-absorption time can be attributed to the destruction of the scale structure of the wool fiber surface due to plasma etching and the introduction of more polar groups such as hydroxyl groups due to plasma chemical modification. 3.5. Fabric shrinkage In shrinkage test of fabrics, we observed that the dimensional change in the warp direction is greater than that in the weft direction. The relaxation dimensional change occurred when the fabric was immersed in water without agitation, so that the strains and stresses imparted during fabric formation could be released. The fabric was then dried and reconditioned to the relative humidity of 65% at which it was originally measured. It was found that in all LTP treatments, the fabrics have got only a slight change in their dimensions after the relaxation process (up to 1.5% in the warp direction). The shrinkage of the samples when put on the cathode was even less and practically not measurable. However the shrinkage for the untreated wool fabric as shown in Table 3 was the greatest both in warp and weft directions. The felting dimensional change is an irreversible process which occurs in a wool fabric when it is subjected to agitation in laundering. The maximum value of the felting dimensional changes in the untreated wool fabric was 18.4%, which was only a moderate change for the untreated fabric. However, when this value is compared with that of LTP-treated fabric (1.5%), it demonstrates that the LTP treatment could impose significant shrink-resistant and anti-felting effects to the wool fabric. Table 3 shows that the area shrinkage has significantly decreased after the LTP treatment. As it can be seen, the type of gas used and the position of samples inside the plasma reactor have an important role in shrink-resist properties of the wool samples. For Ar, O2 and N2cathode plasma treated samples we had a marked improvement in shrink resistance, whereas, this improvement for the O2 and N2-anode plasma treated samples did not happen. For the fabric shrinkage study, generally speaking, the wool fabric shrinkage is correlated with the frictional coefficient of the constituent wool fibers, and it is common knowledge that LTP treatment increases the dry and wet frictional coefficients in the scale and antiscale directions [22]. However, the effect of the LTP process is attributed to several changes on the wool surface, such as the formation of new hydrophilic groups, the partial removal of covalently-bonded fatty acids belonging to the outermost surface of the fiber, and the etching effect. The first two changes contribute mainly to the increased wettability properties, while the last basically reduces the differential friction coefficients of the fibers, and thus decreases the natural shrinkage tendency. 3.6. X-ray diffraction X-ray diffraction (XRD) is a crystal structure analysis method using the atomic arrays within the crystals as a three dimensional grating to diffract a monochromatic beam of X-rays. The angles at which the beam is diffracted are used to calculate the inter-planer atomic spacing (d-spacing) giving information about how the atoms are arranged within the crystalline compounds. X-ray diffraction is also used to measure the nature of the polymer and extent of crystallinity present in the polymer sample. The results of XRD analysis are shown in Fig. 4. A study of the data of this analysis which are reported in Table 4 shows no noticeable changes in the value of dspacing, but instead some reduction in size of the crystals and slight decrease in the total crystallinity (Inet). It can be seen that, the
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Table 4 XRD data of untreated and LTP-treated samples. Samples
Peak no.
d
INet
FWHM
Untreated
1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3
6.55 3.05 2.22 6.28 3.05 2.29 6.40 3.00 2.35 6.32 2.99 2.30 6.66 3.55 2.45 6.45 3.25 2.25
26.45 34.10 12.16 26.05 20.25 6.34 26.8 21.03 6.00 26.30 20.05 6.20 26.4 24.35 6.30 26.75 23.83 6.52
3.88 0.47 0.74 5.8 0.46 0.54 5.70 0.56 0.75 5.76 0.53 0.49 5.68 0.55 0.50 5.85 0.55 0.56
Ar-Cathode
O2-Cathode
N2-Cathode
O2-Anode
N2-Anode
reduction of percentage of crystallinity for the samples put on the cathode is more as compared with that of those on the anode. This is attributed to the effect of plasma etching on the scale structure of wool fabric. 4. Conclusion In this work, we have shown that the surface of wool could be changed both physically and chemically by LTP treatment. The results show that not only the topography of the surface is modified but also the chemical composition of the surface. The effect of exposing the samples when they are on cathode or anode and their response to different gases such as Ar, O2 and N2 as the discharge medium, are also investigated. The corresponding results are reported in Tables 1–4. It is also shown that the wettability and dye ability of the wool could be increased under proper condition. The decrease of waterabsorption time and increase of dye ability of wool samples are attributed to the destruction of the scale structure due to plasma etching on a wool surface and the introduction of more polar groups such as carboxyl groups due to plasma chemical modification. Also it is demonstrated that, the LTP treatment could impose significant shrink-resistant and anti-felting effects to the wool fabrics. The results which are shown in Table 3 show that the shrinkage of 30.1% for untreated sample has reduced to 1.5% or even less depending on the sample position and the kind of gases used. Acknowledgment This work was supported by KAN101630651, Czech Republic. References [1] R. Molino, J.P. Espinos, F. Yubero, P. Erra, A.R. Gonzalez-Elipe, Applied Surface Science 252 (2005) 1417. [2] W. Xu, G. Ke, J. Wu, X. Wang, European Polymer Journal 42 (2006). [3] T. Wakida, S. Cho, S. Choi, S. Tokino, M. Lee, Textile Research Journal 68 (1998) 848. [4] F. Osenberg, D. Theirich, A. Decker, J. Engemann, Surface and Coatings Technology 116–119 (1999) 808. [5] G. Roberts, F. Wood, Journal of Biotechnology 89 (2001) 297. [6] R.A. Difelice, J.G. Dillard, D. Yang, International Journal of Adhesion and Adhesives 25 (2005) 342. [7] D. Sun, G.K. Stylios, Journal of Materials Processing Technology 173 (2006) 172. [8] T. Wakida, S. Tokino, S. Niu, M. Lee, H. Uchiyama, M. Kaneko, Textile Research Journal 63 (8) (1993) 438. [9] L. Kravets, S. Dmitriev, A. Gilman, A. Drachev, G. Dinescu, Journal of Membrane Science 263 (2005) 127. [10] H. Gulec, K. Sarioglu, M. Mutlu, Journal of Food Engineering 75 (2006) 187. [11] F. Huang, Q. Wei, X. Wang, W. Xu, Polymer Testing 25 (2006) 22.
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[12] P. Chaivan, N. Boonyawan, P. Suanpoot, T. Vilaithong, Surface and Coatings Technology 193 (2005) 356. [13] J. Yip, K. Chan, K. Sin, K. Lau, Journal of Materials Processing Technology 123 (2002) 5. [14] P. Chaivan, N. Pasaja, D. Boonyawan, P. Suanpoot, T. Vilaithong, Surface and Coatings Technology 193 (2005) 356. [15] M. Ghoranneviss, S. Shahidi, B. Moazzenchi, A. Anvari, A. Rashidi, H. Hosseini, Surface and Coatings Technology 201 (2007) 4926. [16] S. Shahidi, M. Ghoranneviss, B. Moazzenchi, A. Anvari, A. Rashidi, Surface and Coatings Technology 201 (2007) 5646. [17] S. Shahidi*, M. Ghoranneviss, B. Moazzenchi, A. Rashidi, D. Dorranian, Fibers and Polymers 8 (2007) 123. [18] Sheila Shahidi*, Mahmood Ghoranneviss, Bahareh Moazzenchi, Abosaeed Rashidi, Mohammad Mirjalili, Plasma Processes and Polymers 4 (2007) S1098.
[19] M. Ghoranneviss, B. Moazzenchi, S. Shahidi, A. Anvari, A. Rashidi, Plasma Processes and Polymers 3 (2006) 316. [20] Y. Chun Liu, Y. Xiong, D. Lu, Applied Surface Science 252 (2006) 2960. [21] Kan Chi-wai*, Chan Kwong, Marcus Yuen Chun-wah, AUTEX Research Journal 4 (2004). [22] C. Nastase, F. Nastase, A. Dumitru, M. Ionescu, I. Stamatin, Composites: Part A 36 (2005) 481. [23] M. Carmen, A. Almazan, J.I. Paredes, M. Perez-Mendoza, M. Domingo-Garcia, F.J. Lopez-Garzon, A. Martinez-Alonso, J.M.D. Tascon, Journal of Colloid and Interface Science 287 (2005) 57. [24] I. Errifai, C. Jama, M. Le Bras, R. Delobel, L. Gengember, A. Mazzah, R. De Jaeger, Surface and Coatings Technology 180–181 (2004) 297. [25] M.S. Kim, T.J. Kang, Fibers and Polymers 2 (2001) 30.
Contents lists available at ScienceDirect
Surface & Coatings Technology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / s u r f c o a t
Plasma effects on anti-felting properties of wool fabrics S. Shahidi a,⁎, A. Rashidi b, M. Ghoranneviss c, A. Anvari d, J. Wiener a a
Department of Textile Chemistry, Faculty of Textile, Technical University of Liberec, Liberec, Czech Republic Department of Textile, Faculty of Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran c Plasma Physics Research Center, Science and Research Branch, Islamic Azad University, P.O. Box 14665-678, Tehran, Iran d Department of Physics, Sharif University of Technology, Tehran, Iran b
a r t i c l e
i n f o
Available online 17 August 2010 Keywords: Wool Fabric Anti-felting Plasma
a b s t r a c t Low temperature plasma (LTP) is nowadays an intensively investigated superficial treatment of wool. In this work we have investigated the effect of LTP on wool fabric under different conditions. The effect of the position of samples inside the reactor and the kind of gases used as discharge medium has been also investigated. The results show that not only the topography of the surface is modified but also the chemical composition of the surface. It is shown that the hydrophilicity of the samples and also their shrink resistance and anti-felting behavior have improved significantly under LTP treatment. The results show that the shrinkage of 30.1% for untreated samples has reduced to about 1.5% or even less depending on the sample position and the kind of gases used. Many analytical skills such as XRD, FTIR, and SEM were used to characterize the different aspects of the treated fabric. The details of the experiment are discussed in the text. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Keratin fibers, like wool or human hair, can be considered as natural composite materials, where keratinous protein is the main basic constituent [1]. Wool is a high-quality protein fiber and is widely used as a high-quality textile material [2]. It is well known that the surface characteristic of fibers play an important role in the functional and aesthetic properties of their fabrics, and many surface modifications by chemical treatments are able to improve textile properties [3]. Felting is an undesirable feature of woolen clothes. It occurs as a result of the directionally dependent frictional coefficient of the wool fibers. To reduce felting, this directional dependency must be reduced. Nowadays, this is done by treating the wool in a chlorine-containing solution. During this treatment, the outer surface of the wool, which mainly consists of approximately three-quarters protein and onequarter lipid, is etched [4,5]. However, this procedure has to be replaced because of environmental care [4]. Plasma pretreatments are environmentally benign and energy-efficient processes for modifying the surface chemistry of materials [6–9]. This field of treatment, as a clean, dry and environmental friendly physical technique, opens up a new possibility in this field [10–19]. Plasma treatment can usually induce the following processes: dehydrogenation and consequent unsaturated bond formation trapped stable free radicals formation, generation of polar groups through post plasma
⁎ Corresponding author. E-mail address: [email protected] (S. Shahidi). 0257-8972/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2010.08.003
reaction, and generation of increased surface roughness through preferential amorphous structure ablation processes [20]. In this research work, we have shown that the surface of wool fabrics could be etched and oxidized by plasma treatment, a process which is necessary to improve the felting behavior of the wool. 2. Experimental 2.1. Preparation of wool fabrics Wool plain woven fabrics (Iran Merinus Co, Iran) used in this work were weaved by 20 denier warp and weft yarns composed of 36 filaments in each square inch. For sample preparation, size residue and contamination on the fabrics were removed by conventional scouring processes, and the fabrics were washed by 0.5 g l− 1 sodium carbonate and 0.5 g l− 1 nonionic detergent solution (dilution ratio to water=1:10) at 80 °C for 80 min. Washing was performed twice with distilled water at 80 °C for 20 min and once at ambient temperature for 10 min. 2.2. LTP treatment A DC magnetron sputtering reactor with non-polymerizing reactive gases, such as O2, N2 and Ar were used to treat the wool surface. In this reactor a sheet of wool fabric could be placed on the anode or cathode. Before each experiment the air and old gases were pumped out by a vacuum pump and then a proper gas such as O2, N2 or Ar was introduced into the chamber. Discharge voltage was 1000 V, discharge current was 200 mA and the inter-electrode distance was 35 mm. The
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S. Shahidi et al. / Surface & Coatings Technology 205 (2010) S349–S354
pressure remained at 0.02 Torr for the entire glow-discharge period. The discharge period was 7 min for each sample treatment. 2.3. Characterization tests The morphology of the LTP-treated wool was observed using a scanning electron microscope (SEM, LEO 440I). All the samples were coated with gold before SEM testing. Wettability was evaluated by measuring the absorption time of 4 distilled water dropped on the fabric. The functional groups on the surface of samples were examined using FTIR spectrometer (Bomem MB-100, made in Canada). Aqueous solutions, containing 3.0 wt.% of the Acid Blue dye were employed for dyeing wool fabrics. The bath ratio was 1:100 (1 g of fiber in 100 ml of dye solution). The following dyeing condition was adopted: an initial temperature of 40 °C, followed by a temperature increase of 3 °C min− 1 up to 80 °C, holding for 30 min at 80 °C. 5 g/l of acetic acid for pH adjustment, was added for anionic dyeing processes. After dyeing, the fabrics were rinsed with cold–hot–cold water and then dried at room temperature.
Color intensities of the dyed fabrics were measured by using a UV VIS–NIR reflective spectrophotometer, over the range of 350–500 nm and the reflection factor (R) was obtained. (The maximum wavelength of Blue dyes is 380–480 nm, so this area was chosen for investigation). The relative color strength (K/S value) was then established according to the following Kubelka–Munk Eq. (1), where K and S stand for the absorption and scattering coefficients, respectively [19,20]: n o 2 K = S : ð1−RÞ = 2R
ð1Þ
The dimensional changes of the LTP-treated wool fabric were tested according to AATCC Test Method 99–1993 [21]. Due to the limited size of the plasma reaction chamber, the dimension of the fabric sample used was 65 × 35 mm2, with a 60 × 30 mm2 marked inside the fabric. The fabric was conditioned before measurement. The measurement was then conducted to assess the shrinkage in length of both warp and weft direction, and finally the area shrinkage was
Fig. 1. SEM images of treated and untreated samples: untreated (a), Ar-cathode (b), O2-cathode (c), N2-cathode (d), O2-anode (e), N2-anode (f).
S. Shahidi et al. / Surface & Coatings Technology 205 (2010) S349–S354
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calculated. The degree of shrinkage in length and area change was calculated (expressed in %) according to Eqs. (2) and (3) respectively. Length change = ðlf −lo Þ = lo × 100
ð2Þ
Area change = fðA−OÞ = Og × 100
ð3Þ
where: lf lo A O
final length after treatment (mm), original length before treatment (mm), final area after treatment (mm2), original area before treatment (mm2).
3. Results and discussion
Fig. 3. Reflection spectroscopy of untreated and treated samples.
3.1. Morphological examination Fig. 1 shows the SEM images of untreated and treated wool fiber surfaces under different conditions. As we know the presence of a microporous hydrophobic layer called epicuticle makes the fiber surface difficult to get wet. However, it seems that after the plasma treatments, the scales on the fibers are broken and so for the epicuticle. This is due to the penetration of the active species from plasma through the pores in the wool fabric. The etching effects of plasma particles are also an important factor in roughening the surface of the fibers. These effects contribute to the wettability improvement of the wool fiber surfaces.
The figure also shows that, the scale change of samples is different when they are on the cathode or anode. The figure also reveals that the etching effect of Ar and oxygen plasma is more pronounced than nitrogen plasma under the same condition. The most important effect of LTP treatment on wool is that it changes its character from hydrophobic to hydrophilic and anti-felting. 3.2. FTIR The results of FTIR used to examine the functional groups of the samples are shown in Fig. 2. As shown, for both anode and cathode cases, a slight increase in absorbance at 1720 cm− 1, 1240 cm− 1 (C O, C–O bonds) after O2 plasma treatment, and 3400 cm− 1 corresponding to N–H group after N2 plasma treatment can be noticed [22–25]. However, Ar plasma treatment shows no significant difference in the FTIR spectra. 3.3. Dye ability of wool samples As it can be seen in Fig. 3, the reflection factor of dyed LTP-treated samples is less than dyed untreated sample. This shows that, LTP treatment causes more absorption of acid dye by wool fabrics. The results show that the O2 and Ar-cathode plasma treatments are more effective in increasing the dye exhaustion of wool with anionic dye. Furthermore, the colors achieved much more brilliant shades by LTP treatment. As it can be seen in Table 1, the K/S value of LTP-treated samples is more than that of original one, and the largest value belongs to Ar and O2-cathode LTP-treated samples. All these have contributed to
Table 1 The amount of K/S Value for the untreated and treated samples. Samples
Average of R
Average of K/S value
Untreated Ar-cathode O2-cathode N2-cathode O2-anode N2-anode
0.160 0.116 0.104 0.130 0.134 0.131
2.13 3.34 3.83 2.89 2.77 2.87
Table 2 Absorption time of treated and untreated samples.
Fig. 2. FTIR spectra of samples.
Sample
Absorption time
Untreated Ar-cathode O2-cathode N2-cathode O2-anode N2-anode
20 min 3s 1s 3s 2s 3s
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Table 3 Influence of the pretreatment on the area felting shrinkage of knitted fabrics after 30 simulated washing cycles. Samples
Dimensional change (%) in warp direction
Dimensional change (%) in weft direction
Area felting shrinkage (%)
Untreated Ar-cathode O2-cathode N2-cathode O2-anode N2-anode
18.4 0 0 0 1.5 0.7
14.2 0 0 0 0 0
30.1 0 0 0 1.50 0.70
wettability improvement of the wool fiber through penetration of active species from plasma and also by plasma etching effects. 3.4. Water drop test The quality of water repellency of the samples were evaluated by water drop test in which drops of controlled size were placed at a constant rate upon the fabric surface and the duration of the time required for them to penetrate to the fabrics was measured. The results are shown in Table 2 in which the absorption times have been
Fig. 4. X-Ray diffraction of untreated and LTP-treated samples.
S. Shahidi et al. / Surface & Coatings Technology 205 (2010) S349–S354
recorded for different treated samples. As can be seen after LTP treatment the water-absorption time has decreased. However this time is very low for O2-cathode LTP treatment. Here we should mention that the water-absorption time was reduced for both sides of the fabrics. The decrease of water-absorption time can be attributed to the destruction of the scale structure of the wool fiber surface due to plasma etching and the introduction of more polar groups such as hydroxyl groups due to plasma chemical modification. 3.5. Fabric shrinkage In shrinkage test of fabrics, we observed that the dimensional change in the warp direction is greater than that in the weft direction. The relaxation dimensional change occurred when the fabric was immersed in water without agitation, so that the strains and stresses imparted during fabric formation could be released. The fabric was then dried and reconditioned to the relative humidity of 65% at which it was originally measured. It was found that in all LTP treatments, the fabrics have got only a slight change in their dimensions after the relaxation process (up to 1.5% in the warp direction). The shrinkage of the samples when put on the cathode was even less and practically not measurable. However the shrinkage for the untreated wool fabric as shown in Table 3 was the greatest both in warp and weft directions. The felting dimensional change is an irreversible process which occurs in a wool fabric when it is subjected to agitation in laundering. The maximum value of the felting dimensional changes in the untreated wool fabric was 18.4%, which was only a moderate change for the untreated fabric. However, when this value is compared with that of LTP-treated fabric (1.5%), it demonstrates that the LTP treatment could impose significant shrink-resistant and anti-felting effects to the wool fabric. Table 3 shows that the area shrinkage has significantly decreased after the LTP treatment. As it can be seen, the type of gas used and the position of samples inside the plasma reactor have an important role in shrink-resist properties of the wool samples. For Ar, O2 and N2cathode plasma treated samples we had a marked improvement in shrink resistance, whereas, this improvement for the O2 and N2-anode plasma treated samples did not happen. For the fabric shrinkage study, generally speaking, the wool fabric shrinkage is correlated with the frictional coefficient of the constituent wool fibers, and it is common knowledge that LTP treatment increases the dry and wet frictional coefficients in the scale and antiscale directions [22]. However, the effect of the LTP process is attributed to several changes on the wool surface, such as the formation of new hydrophilic groups, the partial removal of covalently-bonded fatty acids belonging to the outermost surface of the fiber, and the etching effect. The first two changes contribute mainly to the increased wettability properties, while the last basically reduces the differential friction coefficients of the fibers, and thus decreases the natural shrinkage tendency. 3.6. X-ray diffraction X-ray diffraction (XRD) is a crystal structure analysis method using the atomic arrays within the crystals as a three dimensional grating to diffract a monochromatic beam of X-rays. The angles at which the beam is diffracted are used to calculate the inter-planer atomic spacing (d-spacing) giving information about how the atoms are arranged within the crystalline compounds. X-ray diffraction is also used to measure the nature of the polymer and extent of crystallinity present in the polymer sample. The results of XRD analysis are shown in Fig. 4. A study of the data of this analysis which are reported in Table 4 shows no noticeable changes in the value of dspacing, but instead some reduction in size of the crystals and slight decrease in the total crystallinity (Inet). It can be seen that, the
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Table 4 XRD data of untreated and LTP-treated samples. Samples
Peak no.
d
INet
FWHM
Untreated
1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3
6.55 3.05 2.22 6.28 3.05 2.29 6.40 3.00 2.35 6.32 2.99 2.30 6.66 3.55 2.45 6.45 3.25 2.25
26.45 34.10 12.16 26.05 20.25 6.34 26.8 21.03 6.00 26.30 20.05 6.20 26.4 24.35 6.30 26.75 23.83 6.52
3.88 0.47 0.74 5.8 0.46 0.54 5.70 0.56 0.75 5.76 0.53 0.49 5.68 0.55 0.50 5.85 0.55 0.56
Ar-Cathode
O2-Cathode
N2-Cathode
O2-Anode
N2-Anode
reduction of percentage of crystallinity for the samples put on the cathode is more as compared with that of those on the anode. This is attributed to the effect of plasma etching on the scale structure of wool fabric. 4. Conclusion In this work, we have shown that the surface of wool could be changed both physically and chemically by LTP treatment. The results show that not only the topography of the surface is modified but also the chemical composition of the surface. The effect of exposing the samples when they are on cathode or anode and their response to different gases such as Ar, O2 and N2 as the discharge medium, are also investigated. The corresponding results are reported in Tables 1–4. It is also shown that the wettability and dye ability of the wool could be increased under proper condition. The decrease of waterabsorption time and increase of dye ability of wool samples are attributed to the destruction of the scale structure due to plasma etching on a wool surface and the introduction of more polar groups such as carboxyl groups due to plasma chemical modification. Also it is demonstrated that, the LTP treatment could impose significant shrink-resistant and anti-felting effects to the wool fabrics. The results which are shown in Table 3 show that the shrinkage of 30.1% for untreated sample has reduced to 1.5% or even less depending on the sample position and the kind of gases used. Acknowledgment This work was supported by KAN101630651, Czech Republic. References [1] R. Molino, J.P. Espinos, F. Yubero, P. Erra, A.R. Gonzalez-Elipe, Applied Surface Science 252 (2005) 1417. [2] W. Xu, G. Ke, J. Wu, X. Wang, European Polymer Journal 42 (2006). [3] T. Wakida, S. Cho, S. Choi, S. Tokino, M. Lee, Textile Research Journal 68 (1998) 848. [4] F. Osenberg, D. Theirich, A. Decker, J. Engemann, Surface and Coatings Technology 116–119 (1999) 808. [5] G. Roberts, F. Wood, Journal of Biotechnology 89 (2001) 297. [6] R.A. Difelice, J.G. Dillard, D. Yang, International Journal of Adhesion and Adhesives 25 (2005) 342. [7] D. Sun, G.K. Stylios, Journal of Materials Processing Technology 173 (2006) 172. [8] T. Wakida, S. Tokino, S. Niu, M. Lee, H. Uchiyama, M. Kaneko, Textile Research Journal 63 (8) (1993) 438. [9] L. Kravets, S. Dmitriev, A. Gilman, A. Drachev, G. Dinescu, Journal of Membrane Science 263 (2005) 127. [10] H. Gulec, K. Sarioglu, M. Mutlu, Journal of Food Engineering 75 (2006) 187. [11] F. Huang, Q. Wei, X. Wang, W. Xu, Polymer Testing 25 (2006) 22.
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[12] P. Chaivan, N. Boonyawan, P. Suanpoot, T. Vilaithong, Surface and Coatings Technology 193 (2005) 356. [13] J. Yip, K. Chan, K. Sin, K. Lau, Journal of Materials Processing Technology 123 (2002) 5. [14] P. Chaivan, N. Pasaja, D. Boonyawan, P. Suanpoot, T. Vilaithong, Surface and Coatings Technology 193 (2005) 356. [15] M. Ghoranneviss, S. Shahidi, B. Moazzenchi, A. Anvari, A. Rashidi, H. Hosseini, Surface and Coatings Technology 201 (2007) 4926. [16] S. Shahidi, M. Ghoranneviss, B. Moazzenchi, A. Anvari, A. Rashidi, Surface and Coatings Technology 201 (2007) 5646. [17] S. Shahidi*, M. Ghoranneviss, B. Moazzenchi, A. Rashidi, D. Dorranian, Fibers and Polymers 8 (2007) 123. [18] Sheila Shahidi*, Mahmood Ghoranneviss, Bahareh Moazzenchi, Abosaeed Rashidi, Mohammad Mirjalili, Plasma Processes and Polymers 4 (2007) S1098.
[19] M. Ghoranneviss, B. Moazzenchi, S. Shahidi, A. Anvari, A. Rashidi, Plasma Processes and Polymers 3 (2006) 316. [20] Y. Chun Liu, Y. Xiong, D. Lu, Applied Surface Science 252 (2006) 2960. [21] Kan Chi-wai*, Chan Kwong, Marcus Yuen Chun-wah, AUTEX Research Journal 4 (2004). [22] C. Nastase, F. Nastase, A. Dumitru, M. Ionescu, I. Stamatin, Composites: Part A 36 (2005) 481. [23] M. Carmen, A. Almazan, J.I. Paredes, M. Perez-Mendoza, M. Domingo-Garcia, F.J. Lopez-Garzon, A. Martinez-Alonso, J.M.D. Tascon, Journal of Colloid and Interface Science 287 (2005) 57. [24] I. Errifai, C. Jama, M. Le Bras, R. Delobel, L. Gengember, A. Mazzah, R. De Jaeger, Surface and Coatings Technology 180–181 (2004) 297. [25] M.S. Kim, T.J. Kang, Fibers and Polymers 2 (2001) 30.