- Email: [email protected]
Effects of corona discharge treatment on the surface properties of wool fabrics
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 7 ( 2 0 0 8 ) 125–129
journal homepage: www.elsevier.com/locate/jmatprotec
Effects of corona discharge treatment on the surface properties of wool fabrics Guizhen Ke a,b,∗ , Weidong Yu b,a , Weilin Xu a , Weigang Cui a , Xiaolin Shen a a b
Wuhan University of Science and Engineering, Wuhan 430073, PR China Textile Materials and Technology Lab., Donghua University, Shanghai 200051, PR China
a r t i c l e
i n f o
a b s t r a c t
Article history:
Wool fabric was treated by corona discharge and treating conditions were optimized. The
Received 20 September 2006
surface properties of the treated wool fabrics, such as hydrophilicity and dyeability with nat-
Received in revised form
ural dyes, have been investigated. After the corona discharge treatment, the hydrophilicity
26 November 2007
of the wool fabric was improved and the dyeability with Rhizoma coptidis was increased.
Accepted 15 December 2007
Scanning electron microscope (SEM) images indicated that some epicuticle scales on the wool surface became loose. The X-ray photoelectron spectroscopic (XPS) analyses show the oxygen contents of the wool surface were increased and sulphur contents decreased after
Keywords:
treatment. © 2007 Elsevier B.V. All rights reserved.
Corona discharge Wool fabric Surface properties XPS analysis
1.
Introduction
Wool fiber is one natural fiber with the most complicated structure. It is known that the presence of scale on wool fiber surface introduces many problems such as felting and surface barrier to dyestuffs in wool industry process. It was reported that in the past the additive methods and the subtractive methods were most popular in the surface modification of wool fiber (Kan et al., 1998a,b). However, it was considered that during the treatments various chemicals were produced from the incomplete reactions, which polluted the effluent to some degree (Kan et al., 1998a,b). With the increase of ecological and economical restrictions imposed on textile industry, it is required to find environmentally favourable alternatives in wool treatment processes. The appearance of plasma treatment has offered an alternative method. Plasma treatment, as an effective technique for modifying the surface properties, can be used to modify different types of textile products (Zhu
∗
et al., 2002; Sun and Stylios, 2006; Wakida et al., 1993; De Puydt et al., 1989; Lehocky and Mracek, 2006). Corona discharge, as one kind of plasma treatment, has also gained considerable applications in the treatment of metal and polymer materials (Wang et al., 2003; Zhu et al., 2006). The purpose of this paper is to investigate the effects of corona discharge treatment on the surface properties of wool fabrics. The surface chemical and physical composition and serviceability have been thoroughly investigated.
2.
Experimental
2.1.
Materials
The wool twill fabrics (serge, 270 g m−2 ) were selected for the samples. The linear densities of the end yarn and weft yarn were 11.1 × 2 tex, and 18.5 tex, respectively. The sample size
Corresponding author at: Wuhan University of Science and Engineering, Wuhan 430073, PR China. E-mail address: [email protected] (G. Ke). 0924-0136/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2007.12.068
126
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 7 ( 2 0 0 8 ) 125–129
Table 1 – Factors and levels of orthogonal experiment Level 1 2 3
Wet content (%)
Treating time (s)
11 14 8
20 40 60
Treating voltage (kV) 8 10 12
was 35 cm × 15 cm. All of the specimens were washed with deionized water, then dried, finally conditioned at atmosphere (20 ◦ C, relative humidity 60%) before use.
2.2.
Optimum condition for corona treatment
Corona discharge treatment was conducted using a glow discharge generator (SDCD16-2-10 manufactured by Dalian no. 9 Electronic Incorporation, China) in the presence of air. Corona discharge experiment was carried out according to L9 (34 ) orthogonal table (Table 1). The three factors were wet content, treating time and treating voltage and each factor had three levels. To control wet content of fabrics, the fabrics were wetted, and then placed in constant temperature and humidity room. The fabrics were in the state of liberating moisture. According to the previously established curve of time versus moisture regain in the state of liberating moisture (Shen et al., 2004), wool fabrics with different wet content were obtained and treated with corona immediately. After the treatment, the wool fabric samples were laid down on a table, 0.2 mL distilled water was dropped using an injector from 2 cm above the sample. The time period of water absorption was recorded when there was no obvious mirror reflection on the fabric surface. Two replications were conducted for each fabric. The mean value of two replications was taken as the final result, which was used to evaluate the effects of corona discharge on the wettability of wool fabric. Based on the orthogonal experiment, optimum conditions (including moisture regain of wool fabric, treating time and voltage) were selected and applied in following experiments. The surface properties of the wool fabrics treated under optimum conditions were investigated by using SEM, XPS contact angle test and dyeing rate measurement.
2.3.
SEM morphological study
The morphology of the treated and untreated wool fabrics was observed using a scanning electron microscope (SEM Hitachi S-530). The samples were coated with gold before SEM testing.
2.4.
2.5.
Contact angle measurement
A contact angle/surface tension meter (JC2000A, Shanghai Zhongchen Digital Technic Apparatus Co.) was used to measure the contact angle of the fabrics. Liquid drop was dispersed on each fabric sample. The image of each drop projected to screen was quickly photographed, and then the intersectant angle between the tangent and the phase interface was measured.
2.6.
Dyeing rate
The famous Chinese medicine Rhizoma coptidis was used as dyestuff. R. coptidis was boiled in distilled water for 40 min, and then extraction was filtrated and used as dyeing solution. The pH value of the extract was 6.5. Wool fabric was dyed with R. coptidis extraction at 80 ◦ C with a liquor ratio of 1:150 and the dyeing rate was tested. Spectrophotometer was used to measure the absorbance of the dye solutions before and after exhaustion. The relative concentration of dyes was calculated based on a previously established absorbance–concentration relationship at max (345 nm) of the dyes. The dye adsorption (%) of the fabric was estimated using the following equation: dye uptake% = 100% − c%
(1)
where 100% and c% are the relative concentration of dye in the initial and the final bath, respectively. Wool fabrics of the treated and untreated were dyed under the same conditions mentioned above. The K/S values of the dyed fabrics at durations of 0, 5, 10, 15, 20, 30, and 40 min, respectively, were determined using Shimadzu 2550 UV/Vis spectrophotometer plus an integrating sphere attachment (ISR-240A, diameter 60 mm) and color-measuring software. Measurements were taken with illuminant D65 and CIE 10◦ observer. During measurements, fabric samples were held flat and securely using a spring-loaded sample clamp. Three measurements were repeated on each dyed fabric. Relative color strength (K/S value) is a function of color depth and is represented by the equation of Kubelka–Munk (Eq. (2)) (Warren, 1996). K (1 − R) = S 2R
2
(2)
where R is the reflectance of the dyed fabric, K the sorption coefficient, and S is the scattering coefficient.
3.
Results and discussion
3.1.
Results of orthogonal experiment and analysis
XPS surface chemical analysis
The chemical composition of the samples’ surface has been investigated using X-ray photoelectron spectroscopy (XPS, XSAM800, Krcotos, England). Mg K␣ X-ray was used for spectral resolution. All binding energy was calibrated with C1s (285.0 eV) as inner standard. The analysis area was about 100 m in diameter, which indicated many fibers were measured.
Previous research showed that treating voltage, treating time and wet content of fabric had important effects on corona discharge treatment of wool fabric (Zhang and Guo, 2003). In this study orthogonal experiment was used to find the optimum treatment condition. The results of orthogonal experiment and simple analysis are shown in Table 2.
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 7 ( 2 0 0 8 ) 125–129
127
Table 2 – Results of orthogonal experiment Number 1 2 3 4 5 6 7 8 9 Ki1 Ki2 Ki3 R
Wet content (%) 1 1 1 2 2 2 3 3 3 607.7 1210.0 245.0 965.0
Treating time (s) 1 2 3 1 2 3 1 2 3 930.0 806.7 326.0 604.0
Blank 1 2 3 2 3 1 3 1 2 785.0 371.7 906.0 534.3
Treating voltage (kV) 1 2 3 3 1 2 2 3 1 1540.0 291.7 231.0 1309.0
The results indicate treating voltage was the most important factor in corona discharge irradiation, then follows wet content and treating time in sequence. The higher the discharge voltage, the more neutral atmosphere can be ionised for collision of high-energy electron. Accordingly ionisation degree and electron density are increased. Thus, with the increase of treating voltage, wool surface was etched more intensively by the plasma, which loosed scales and improved hydrophilicity of wool fiber (Zhu et al., 2002). With wet content of wool fabric increasing, water molecule absorbed much energy of plasma produced from the corona discharge, which may decrease sputtering effects on wool surface and block the introduction of hydrophilic group. As a result, the time of water absorption was prolonged, namely the wettability decreased. Treating time had the least effect on the improvement of hydrophilicity. Though the increase of treating time can make plasma treatment more effectively, treating time should not be too long in case of the appearance of burnt spot on the fabric. Finally, optimum treating conditions were selected as follows: treating voltage 12 kV, wet content 8%, treating time 40 s. To verify the conclusion, wool fabric was treated under the selected optimum conditions and tested according to the terms in orthogonal experiments. The time of water absorption of the treated wool fabric was turned out to be about 5 s.
3.2.
Fig. 1 – SEM photographs of wool fabric (A) untreated wool fabric and (B) corona discharge treated.
SEM observation
SEM images of wool fabrics, which were treated and untreated with corona, are shown in Fig. 1. It is obvious that the surface scale was more relaxed for the treated wool fabrics as compared with the untreated. In addition, cracks and holes were visible on the wool fabric surface treated with corona. This is attributed to the etching effect caused by the bombardment of the air plasma species on the fabric surface. As a result, the specimen surface became rougher.
3.3.
XPS surface chemical characterization
The chemical composition of untreated and corona treated wool fabric surface has been investigated by X-ray photoelectron spectroscopy, as shown in Fig. 2.
Fig. 2 – XPS images: overall scan of untreated (A) and treated wool surfaces (B).
128
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 7 ( 2 0 0 8 ) 125–129
Table 3 – Quantitative data of the XPS curves Element
Binding energy (eV)
XPS chemical composition (%) Untreated
C1s O1s N1s S2p
285.0 532.5 399.8 164.1
84.6 10.1 3.9 1.4
Treated 79.1 16.8 3.2 0.9
It is obvious that the intensity of the oxygen peaks from the corona discharge treated surface was much stronger than the untreated surface. The O/C ratio of the treated samples increased as shown in Table 3. It is expected that rich oxygen containing groups in the surface were produced after corona treatment. On the contrary, the intensity of the S2p peaks from the corona discharge treated surface was weaker than the untreated surface (see Fig. 3). It means the decrease of –S–S for the removal of cuticular material from wool fiber. However, the shoulder peak at 167 eV increased slightly, which may be an indicator of the increase in the oxidation state of the sulphur atoms at the fiber surface (Kan and Yuen, 2006). In addition, N1s content decreased slightly after discharge treatment due to the etching of plasma on wool surface.
3.4.
Fig. 4 – Dyeing rate curves of wool fabrics with Rhizoma coptidis.
carboxyl and hydroxyl groups formed in the fiber surface, which increased the wetting properties of wool fabric (Wang et al., 2003).
3.5.
Effect on dyeing properties with natural plant dye
Effect on contact angle
The effect of corona treatment on contact angle of wool fabric was shown in Table 4. To compare the effect of treating voltage, the wool fabric with 8% wet content was treated under 8 and 12 kV for 40 s, respectively. The results indicate the corona treatment improved the hydrophilicity of wool fabric, and with the increase of treated voltage, high energy leads to an obvious increase in wetting properties. It was mainly ascribed to the breakage of macromolecule bond resulting from the bombardment of high-energy particle. Thus, the free polar component of the fiber surface was increased. These free radicals contacted with air and more hydrophilic constituents such as
Dyeing rate curves of R. coptidis are presented in Fig. 4. It is notable that the dyeing rate and dye exhaustion increased after corona treatment. As is evident from XPS analysis, corona treated wool fabric incorporated some oxygen groups such as OH and COOH in the wool surface and increased electro-negativity. At the same time, some disulphide bonds in wool epicuticle were broken, which made the wool more prone to wetting and swelling. As a result, corona discharge treatment increased dyeing rate for R. coptidis. R. coptidis has a cationic structure and is thus considered to integrate wool by electrovalent bond. Therefore, saturation dye exhaustion depends on the amount of hydroxyl group in the fiber. The K/S values of dyed fabric are shown in Fig. 5 and indicate that the relative color strength of the fabric increased as dyeing time prolonged. For the same type of fabric, the K/S value can be taken as the apparent dyeing rate and has a positive correlation to dye amount in fabric surface, therefore the change of K/S value further confirmed the trend of dyeing rate. However, corona treatment was restricted to the substrate wool surface and did not appear to affect bulk properties of wool fabric (Zhang and Guo, 2003), thus final dye exhaustion and color depth
Table 4 – Contact angle values for wool fabric samples Samples
Fig. 3 – XPS images: S2p of untreated and treated wool surfaces.
Contact angle (◦ )
Untreated
130
Corona discharge treated 0.8 × 103 V 1.2 × 103 V
125 79.5
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 7 ( 2 0 0 8 ) 125–129
129
Acknowledgements We would like to thank Peiwu Zhang, Yong Wang, Xin Wang and Jianhua Huang for their assistance in this work.
references
Fig. 5 – Relative color strength of dyed wool fabric.
of the treated fabric did not increase too much to some extent.
4.
Conclusions
Wool fabric was modified by corona discharge irradiation. Orthogonal experiment indicated that treating voltage was the most important factor, followed by wet content. The optimum treating conditions were selected: treating voltage 12 kV, wet content 8%, treating time 40 s. After corona discharge treatment, the surface properties of the wool fabric were changed. Scanning electron microscope images showed the epicuticle scale was more rough and relaxed. XPS analysis indicated corona discharge treatment changed chemical composition of the wool fiber surface. Carbon, sulphur and nitrogen contents were decreased after treatment, while oxygen contents were increased in the surface layer. The contact angle test indicated the treatment increased the wettability of wool fabric toward water. Corona discharge treatment also improved dyeing rate and exhaustion of wool fabric with natural dye R. coptidis to some extent. However, a more detailed study on the influence of corona discharge treatment on the dyeing properties of the wool fabric would be thoroughly conducted in the future research.
De Puydt, Y., Bertrand, P., Novis, Y., 1989. Surface analyses of corona-treated poly(ethylene terephthalate). Br. Polym. J. 2, 141–146. Kan, C.W., Yuen, C.W.M., 2006. Surface characterisation of low temperature plasma-treated wool fibre. J. Mater. Process. Technol. 178, 52–60. Kan, C.W., Chan, K., Yuen, C.W.M., Miao, M.H., 1998a. The effect of low-temperature plasma on the chrome dyeing of wool fibre. J. Mater. Process. Technol. 82, 122–126. Kan, C.W., Chan, K., Yuen, C.W.M., Miao, M.H., 1998b. Surface properties of low-temperature plasma treated wool fabrics. J. Mater. Process. Technol. 83, 180–184. Lehocky, M., Mracek, A., 2006. Improvement of dye adsorption on synthetic polyester fibers by low temperature plasma pre-treatment. Czech. J. Phys. 56, 1277–1282. Shen, X.L., Zhang, M.L., Cui, W.G., Xu, W.L., 2004. Study on influence of regain on shrink-proof properties of wool fabric treated with corona discharge. Wool Technol. 9, 35–38. Sun, D., Stylios, G.K., 2006. Fabric surface properties affected by low temperature plasma treatment. J. Mater. Process. Technol. 173, 172–177. Wakida, T., Niu, S., Lee, M., Uchiyama, H., Kaneko, M., 1993. Dyeing properties of wool treated with low-temperature plasma under atmospheric pressure. Text. Res. J. 63 (8), 438–442. Wang, B., Jin, Z.H., Qiu, Z.M., Liu, A.H., 2003. Effect of corona treatment on the surface and interfacial adhesion properties of high performance poly(p-phenylene benzobisoxazole) (PBO) fibre. Acta Mater. Compos. Sin. 20 (4), 101–106. Warren, S.P., 1996. Textile Coloration and Finishing. Carolina Academic Press. Zhang, J.Ch., Guo, Y.H., 2003. Technology of Corona Discharge Irradiation. China Textile Press, Beijing. Zhu, R.Y., Hua, J.K., Huang, G., Ji, H.Z., 2002. Research on dyeing properties of low temperature plasma treated wool fiber. J. Tianjin Polytech. Univ. 21 (4), 22–27. Zhu, Y., Otsubo, M., Honda, C., 2006. Degradation of polymeric materials exposed to corona discharges. Polym. Test. 25, 313–317.
journal homepage: www.elsevier.com/locate/jmatprotec
Effects of corona discharge treatment on the surface properties of wool fabrics Guizhen Ke a,b,∗ , Weidong Yu b,a , Weilin Xu a , Weigang Cui a , Xiaolin Shen a a b
Wuhan University of Science and Engineering, Wuhan 430073, PR China Textile Materials and Technology Lab., Donghua University, Shanghai 200051, PR China
a r t i c l e
i n f o
a b s t r a c t
Article history:
Wool fabric was treated by corona discharge and treating conditions were optimized. The
Received 20 September 2006
surface properties of the treated wool fabrics, such as hydrophilicity and dyeability with nat-
Received in revised form
ural dyes, have been investigated. After the corona discharge treatment, the hydrophilicity
26 November 2007
of the wool fabric was improved and the dyeability with Rhizoma coptidis was increased.
Accepted 15 December 2007
Scanning electron microscope (SEM) images indicated that some epicuticle scales on the wool surface became loose. The X-ray photoelectron spectroscopic (XPS) analyses show the oxygen contents of the wool surface were increased and sulphur contents decreased after
Keywords:
treatment. © 2007 Elsevier B.V. All rights reserved.
Corona discharge Wool fabric Surface properties XPS analysis
1.
Introduction
Wool fiber is one natural fiber with the most complicated structure. It is known that the presence of scale on wool fiber surface introduces many problems such as felting and surface barrier to dyestuffs in wool industry process. It was reported that in the past the additive methods and the subtractive methods were most popular in the surface modification of wool fiber (Kan et al., 1998a,b). However, it was considered that during the treatments various chemicals were produced from the incomplete reactions, which polluted the effluent to some degree (Kan et al., 1998a,b). With the increase of ecological and economical restrictions imposed on textile industry, it is required to find environmentally favourable alternatives in wool treatment processes. The appearance of plasma treatment has offered an alternative method. Plasma treatment, as an effective technique for modifying the surface properties, can be used to modify different types of textile products (Zhu
∗
et al., 2002; Sun and Stylios, 2006; Wakida et al., 1993; De Puydt et al., 1989; Lehocky and Mracek, 2006). Corona discharge, as one kind of plasma treatment, has also gained considerable applications in the treatment of metal and polymer materials (Wang et al., 2003; Zhu et al., 2006). The purpose of this paper is to investigate the effects of corona discharge treatment on the surface properties of wool fabrics. The surface chemical and physical composition and serviceability have been thoroughly investigated.
2.
Experimental
2.1.
Materials
The wool twill fabrics (serge, 270 g m−2 ) were selected for the samples. The linear densities of the end yarn and weft yarn were 11.1 × 2 tex, and 18.5 tex, respectively. The sample size
Corresponding author at: Wuhan University of Science and Engineering, Wuhan 430073, PR China. E-mail address: [email protected] (G. Ke). 0924-0136/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2007.12.068
126
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 7 ( 2 0 0 8 ) 125–129
Table 1 – Factors and levels of orthogonal experiment Level 1 2 3
Wet content (%)
Treating time (s)
11 14 8
20 40 60
Treating voltage (kV) 8 10 12
was 35 cm × 15 cm. All of the specimens were washed with deionized water, then dried, finally conditioned at atmosphere (20 ◦ C, relative humidity 60%) before use.
2.2.
Optimum condition for corona treatment
Corona discharge treatment was conducted using a glow discharge generator (SDCD16-2-10 manufactured by Dalian no. 9 Electronic Incorporation, China) in the presence of air. Corona discharge experiment was carried out according to L9 (34 ) orthogonal table (Table 1). The three factors were wet content, treating time and treating voltage and each factor had three levels. To control wet content of fabrics, the fabrics were wetted, and then placed in constant temperature and humidity room. The fabrics were in the state of liberating moisture. According to the previously established curve of time versus moisture regain in the state of liberating moisture (Shen et al., 2004), wool fabrics with different wet content were obtained and treated with corona immediately. After the treatment, the wool fabric samples were laid down on a table, 0.2 mL distilled water was dropped using an injector from 2 cm above the sample. The time period of water absorption was recorded when there was no obvious mirror reflection on the fabric surface. Two replications were conducted for each fabric. The mean value of two replications was taken as the final result, which was used to evaluate the effects of corona discharge on the wettability of wool fabric. Based on the orthogonal experiment, optimum conditions (including moisture regain of wool fabric, treating time and voltage) were selected and applied in following experiments. The surface properties of the wool fabrics treated under optimum conditions were investigated by using SEM, XPS contact angle test and dyeing rate measurement.
2.3.
SEM morphological study
The morphology of the treated and untreated wool fabrics was observed using a scanning electron microscope (SEM Hitachi S-530). The samples were coated with gold before SEM testing.
2.4.
2.5.
Contact angle measurement
A contact angle/surface tension meter (JC2000A, Shanghai Zhongchen Digital Technic Apparatus Co.) was used to measure the contact angle of the fabrics. Liquid drop was dispersed on each fabric sample. The image of each drop projected to screen was quickly photographed, and then the intersectant angle between the tangent and the phase interface was measured.
2.6.
Dyeing rate
The famous Chinese medicine Rhizoma coptidis was used as dyestuff. R. coptidis was boiled in distilled water for 40 min, and then extraction was filtrated and used as dyeing solution. The pH value of the extract was 6.5. Wool fabric was dyed with R. coptidis extraction at 80 ◦ C with a liquor ratio of 1:150 and the dyeing rate was tested. Spectrophotometer was used to measure the absorbance of the dye solutions before and after exhaustion. The relative concentration of dyes was calculated based on a previously established absorbance–concentration relationship at max (345 nm) of the dyes. The dye adsorption (%) of the fabric was estimated using the following equation: dye uptake% = 100% − c%
(1)
where 100% and c% are the relative concentration of dye in the initial and the final bath, respectively. Wool fabrics of the treated and untreated were dyed under the same conditions mentioned above. The K/S values of the dyed fabrics at durations of 0, 5, 10, 15, 20, 30, and 40 min, respectively, were determined using Shimadzu 2550 UV/Vis spectrophotometer plus an integrating sphere attachment (ISR-240A, diameter 60 mm) and color-measuring software. Measurements were taken with illuminant D65 and CIE 10◦ observer. During measurements, fabric samples were held flat and securely using a spring-loaded sample clamp. Three measurements were repeated on each dyed fabric. Relative color strength (K/S value) is a function of color depth and is represented by the equation of Kubelka–Munk (Eq. (2)) (Warren, 1996). K (1 − R) = S 2R
2
(2)
where R is the reflectance of the dyed fabric, K the sorption coefficient, and S is the scattering coefficient.
3.
Results and discussion
3.1.
Results of orthogonal experiment and analysis
XPS surface chemical analysis
The chemical composition of the samples’ surface has been investigated using X-ray photoelectron spectroscopy (XPS, XSAM800, Krcotos, England). Mg K␣ X-ray was used for spectral resolution. All binding energy was calibrated with C1s (285.0 eV) as inner standard. The analysis area was about 100 m in diameter, which indicated many fibers were measured.
Previous research showed that treating voltage, treating time and wet content of fabric had important effects on corona discharge treatment of wool fabric (Zhang and Guo, 2003). In this study orthogonal experiment was used to find the optimum treatment condition. The results of orthogonal experiment and simple analysis are shown in Table 2.
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 7 ( 2 0 0 8 ) 125–129
127
Table 2 – Results of orthogonal experiment Number 1 2 3 4 5 6 7 8 9 Ki1 Ki2 Ki3 R
Wet content (%) 1 1 1 2 2 2 3 3 3 607.7 1210.0 245.0 965.0
Treating time (s) 1 2 3 1 2 3 1 2 3 930.0 806.7 326.0 604.0
Blank 1 2 3 2 3 1 3 1 2 785.0 371.7 906.0 534.3
Treating voltage (kV) 1 2 3 3 1 2 2 3 1 1540.0 291.7 231.0 1309.0
The results indicate treating voltage was the most important factor in corona discharge irradiation, then follows wet content and treating time in sequence. The higher the discharge voltage, the more neutral atmosphere can be ionised for collision of high-energy electron. Accordingly ionisation degree and electron density are increased. Thus, with the increase of treating voltage, wool surface was etched more intensively by the plasma, which loosed scales and improved hydrophilicity of wool fiber (Zhu et al., 2002). With wet content of wool fabric increasing, water molecule absorbed much energy of plasma produced from the corona discharge, which may decrease sputtering effects on wool surface and block the introduction of hydrophilic group. As a result, the time of water absorption was prolonged, namely the wettability decreased. Treating time had the least effect on the improvement of hydrophilicity. Though the increase of treating time can make plasma treatment more effectively, treating time should not be too long in case of the appearance of burnt spot on the fabric. Finally, optimum treating conditions were selected as follows: treating voltage 12 kV, wet content 8%, treating time 40 s. To verify the conclusion, wool fabric was treated under the selected optimum conditions and tested according to the terms in orthogonal experiments. The time of water absorption of the treated wool fabric was turned out to be about 5 s.
3.2.
Fig. 1 – SEM photographs of wool fabric (A) untreated wool fabric and (B) corona discharge treated.
SEM observation
SEM images of wool fabrics, which were treated and untreated with corona, are shown in Fig. 1. It is obvious that the surface scale was more relaxed for the treated wool fabrics as compared with the untreated. In addition, cracks and holes were visible on the wool fabric surface treated with corona. This is attributed to the etching effect caused by the bombardment of the air plasma species on the fabric surface. As a result, the specimen surface became rougher.
3.3.
XPS surface chemical characterization
The chemical composition of untreated and corona treated wool fabric surface has been investigated by X-ray photoelectron spectroscopy, as shown in Fig. 2.
Fig. 2 – XPS images: overall scan of untreated (A) and treated wool surfaces (B).
128
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 7 ( 2 0 0 8 ) 125–129
Table 3 – Quantitative data of the XPS curves Element
Binding energy (eV)
XPS chemical composition (%) Untreated
C1s O1s N1s S2p
285.0 532.5 399.8 164.1
84.6 10.1 3.9 1.4
Treated 79.1 16.8 3.2 0.9
It is obvious that the intensity of the oxygen peaks from the corona discharge treated surface was much stronger than the untreated surface. The O/C ratio of the treated samples increased as shown in Table 3. It is expected that rich oxygen containing groups in the surface were produced after corona treatment. On the contrary, the intensity of the S2p peaks from the corona discharge treated surface was weaker than the untreated surface (see Fig. 3). It means the decrease of –S–S for the removal of cuticular material from wool fiber. However, the shoulder peak at 167 eV increased slightly, which may be an indicator of the increase in the oxidation state of the sulphur atoms at the fiber surface (Kan and Yuen, 2006). In addition, N1s content decreased slightly after discharge treatment due to the etching of plasma on wool surface.
3.4.
Fig. 4 – Dyeing rate curves of wool fabrics with Rhizoma coptidis.
carboxyl and hydroxyl groups formed in the fiber surface, which increased the wetting properties of wool fabric (Wang et al., 2003).
3.5.
Effect on dyeing properties with natural plant dye
Effect on contact angle
The effect of corona treatment on contact angle of wool fabric was shown in Table 4. To compare the effect of treating voltage, the wool fabric with 8% wet content was treated under 8 and 12 kV for 40 s, respectively. The results indicate the corona treatment improved the hydrophilicity of wool fabric, and with the increase of treated voltage, high energy leads to an obvious increase in wetting properties. It was mainly ascribed to the breakage of macromolecule bond resulting from the bombardment of high-energy particle. Thus, the free polar component of the fiber surface was increased. These free radicals contacted with air and more hydrophilic constituents such as
Dyeing rate curves of R. coptidis are presented in Fig. 4. It is notable that the dyeing rate and dye exhaustion increased after corona treatment. As is evident from XPS analysis, corona treated wool fabric incorporated some oxygen groups such as OH and COOH in the wool surface and increased electro-negativity. At the same time, some disulphide bonds in wool epicuticle were broken, which made the wool more prone to wetting and swelling. As a result, corona discharge treatment increased dyeing rate for R. coptidis. R. coptidis has a cationic structure and is thus considered to integrate wool by electrovalent bond. Therefore, saturation dye exhaustion depends on the amount of hydroxyl group in the fiber. The K/S values of dyed fabric are shown in Fig. 5 and indicate that the relative color strength of the fabric increased as dyeing time prolonged. For the same type of fabric, the K/S value can be taken as the apparent dyeing rate and has a positive correlation to dye amount in fabric surface, therefore the change of K/S value further confirmed the trend of dyeing rate. However, corona treatment was restricted to the substrate wool surface and did not appear to affect bulk properties of wool fabric (Zhang and Guo, 2003), thus final dye exhaustion and color depth
Table 4 – Contact angle values for wool fabric samples Samples
Fig. 3 – XPS images: S2p of untreated and treated wool surfaces.
Contact angle (◦ )
Untreated
130
Corona discharge treated 0.8 × 103 V 1.2 × 103 V
125 79.5
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 7 ( 2 0 0 8 ) 125–129
129
Acknowledgements We would like to thank Peiwu Zhang, Yong Wang, Xin Wang and Jianhua Huang for their assistance in this work.
references
Fig. 5 – Relative color strength of dyed wool fabric.
of the treated fabric did not increase too much to some extent.
4.
Conclusions
Wool fabric was modified by corona discharge irradiation. Orthogonal experiment indicated that treating voltage was the most important factor, followed by wet content. The optimum treating conditions were selected: treating voltage 12 kV, wet content 8%, treating time 40 s. After corona discharge treatment, the surface properties of the wool fabric were changed. Scanning electron microscope images showed the epicuticle scale was more rough and relaxed. XPS analysis indicated corona discharge treatment changed chemical composition of the wool fiber surface. Carbon, sulphur and nitrogen contents were decreased after treatment, while oxygen contents were increased in the surface layer. The contact angle test indicated the treatment increased the wettability of wool fabric toward water. Corona discharge treatment also improved dyeing rate and exhaustion of wool fabric with natural dye R. coptidis to some extent. However, a more detailed study on the influence of corona discharge treatment on the dyeing properties of the wool fabric would be thoroughly conducted in the future research.
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