Indian Journal of Fibre & Textile Research Vol. 36, March 2011, pp. 58-62 Improvement in dyeability of wool fabric by microwave treatment Zhao Xue a College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, Shanghai 201620, China and He Jin-xin Key Lab of Textile Science &Technology, Donghua University, Shanghai 201620, China Received 16 March 2010, revised received and accepted 2 June 2010 Wool fabric has been treated with microwave irradiation at different conditions and then studied for its physical and chemical properties using a variety of techniques, such as Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron. It is found that the treated wool fabric significantly improves its dyeability. This may be due to the change in wool surface morphological structure under microwave irradiation which implies that the barrier effect in wool dyeing is diminished. The breaking strength of the treated wool fabrics also improves with microwave irradiation. The chemical structure and crystallinity do not show any significant change. Keywords: Dyeing, Microwave treatment, Wool fabric 1 Introduction The difficulty in dyeing of wool fibre is due to its scale like surface structure. This complex structure makes it difficult for the dye molecules to permeate into the fibre, resulting in low levels of dye exhaustion. A number of studies aimed at improving the dyeability of wool by modifying the wool fibre have been reported 1-6. The use of high efficient modification methods to improve the dyeability of wool fibres has been the subject of considerable importance. In recent years, modifications and dyeing of some materials have been conducted under microwave irradiation condition 7-9. Microwave irradiation is one of the powerful techniques of non-contact heating, and has been used for reacting, heating and drying wool materials. In the conventional processing of fabric, a large amount of energy is consumed. Some new techniques and methods for saving energy have also been studied 10-15. Microwave heating, as an alternative to conventional heating technique, has been proved to be more rapid, uniform and efficient. The microwave can easily penetrate the particle inside and all particles can be heated simultaneously, thus a To whom all the correspondence should be addressed. E-mail: jxhe@dhu.edu.cn reducing heat transfer problems. It has been assumed that the microwave irradiation modification could affect dyeability of wool fibres. However, the report on the effect of microwave irradiation on dyeability of wool is scanty. The present study is therefore aimed at developing a new modification technique using microwave irradiation for the improvement in dyeability of the wool fibres. The influence of the time and power of microwave treatment on the colour yield of dyeing, exhaustion, fixation, breaking strength, chemical structure, surface morphological structure and fine structure of wool fibres has been investigated. 2 Materials and Methods 2.1 Materials 100% wool woven fabric (from Qingfeng Textile Company, Beijing, China), having the specifications 15S/2 15S/2 74 64/inch, was used for the study. Lanasol Red 6G was supplied by Huntsman Co. Ltd, Shanghai, China; Palatin Red GRE by Dystar Co. Ltd, Shanghai, China; ammonium sulphate by Lingfeng NO.4 Reagent & H.V Chemical Co. Ltd, Shanghai, China; acetic acid by Boer Chemical Reagent Co. Ltd, Shanghai, China; sodium sulfate and sulphuric acid by Guoyao Chemical Reagent Co. Ltd,
XUE & JIN-XIN: IMPROVEMENT IN DYEABILITY OF WOOL FABRIC BY MICROWAVE TREATMENT 59 Shanghai, China; Peregal O by Saintyear Co. Ltd, Hangzhou, China; and ammonia by Zhenxing Chemical Reagent Co. Ltd, Shanghai, China. 2.2 Microwave Irradiation Treatment of Wool Fabric A microwave oven (Yk-01) having the continuous adjustable power of 250-1000W was used in this study. The microwave frequency of 2450MHz was chosen as it is widely used as ISM band (industrial, scientific and medical use). Wool fabric was kept under the conditions 25-30 C, 60-70% RH to achieve an equilibrium moisture content. Wool fabric (enclosed in polythene film) was placed in the microwave oven and then treated with microwave irradiation at various power settings (300, 400, 500, 600 and 700W) for various durations (0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 min) respectively. After irradiation, the fabric was removed from microwave oven and slowly cooled under vacuum for 24 h. 2.3 Dyeing Process Two different wool fabric samples (untreated and microwave-treated) were dyed at 100 C and 1:50 liquor ratio, using two different dyes with differ in chemical constitution. Dyeing was carried out using reactive dye (Lanasol Red 6G) and 1:1 metal-complex dye (Palatin Red GRE). The dyeing process was started at 50 C for 10min and the temperature of bath was then raised to the boiling point over 50min. The bath was kept at this temperature for a further 60min. The initial reactive dye-bath contained 2% Lanasol Red 6G, 4.0% ammonium sulphate, 5.0% sodium sulfate and acetic acid (80%), maintaining the ph at 4-4.5. Sodium sulphate was used to promote the dyeing of Lanasol reactive dye. The 1:1 metalcomplex dye-bath contained 2% Palatin Red GRE, 2.0% Peregal O and sulphuric acid (98%). Sulphuric acid (98%) was used to adjust the ph of dyeing solution at 3-3.5. The ph of the dyeing solution was evaluated using a PHSJ-4A ph meter (Sartorius Group, GER). The dyed fabrics were first rinsed with water at 40 C to remove dye portions not fixed to the substrate. Non-reactive dye portions formed by hydrolysis from the dye were washed off at 80 C by treatment with ammonia in an alkaline medium at ph 8.5 for 15 min. The dyed fabric was given one final rinse with water and then neutralized with acetic acid. 2.4 Fabric Performance Evaluation The breaking strength of the fabric was measured according to ASTM test method (ASTMD 5034). Colour yield (K/S values) was calculated using a Datacolor SF650 color measuring and matching instrument (Datacolor, USA) and was used to determine the depth of shade of dyed wool fabrics. Exhaustion (E%) was determined using a U-3310 UV-vis spectrophotometer (Hitachi Ltd, JPN) and can be expressed as the percentage of the decrease in the dye-bath concentration, as shown below: E%= (1-A/A 0 ) 100 (1) where A 0 is the optical density (initial dye concentration) of the dye bath at the very beginning of dyeing; and A, the optical density (dye concentration) of the dye bath at the end of dyeing. Fixation (F%) was determined using a Datacolor SF650 color measuring and matching instrument by measuring K/S ratio for wool fabrics, which were rinsed, washed, neutralized and then dried, along with those which were dried after fixation without washing. The surface morphological structures of untreated and microwave-treated wool fibres were measured by a JSM-5600LV scanning electron microscopy (JEOL Ltd, JPN). Crystallinity of untreated and treated wool fibres was measured by a D/Max-2550 PC X-ray Diffractometer (Rigaku Ltd, JPN), using Cu-K target at 40 kv, 300 ma and k = 1.54056. The chemical structures of untreated and treated wool fibres were measured by a 510P infrared spectrum (Nicolet Ltd, USA). 3 Results and Discussion 3.1 Effect on Colour Yield The colour yield of the wool fabrics treated under various conditions, i.e. the time of microwave treatment and the power of microwave, is given in Table 1. It is observed that the colour yield of wool fabric improves after microwave treatment. The treatment time and irradiation power have a greater impact on the colour yield of the dyed fabric. The colour yield of dyed fabric increases with increasing treatment time, but decreases with increasing power from 400W to 700W. The longer the treatment time, the greater is the colour yields of dyed fabric, as a result of the greater dyeability of the treated fabric. Higher treating power results in the serious damage of the scale structure. Some hydrophilic groups are lost and hence
60 INDIAN J. FIBRE TEXT. RES., MARCH 2011 Table 1 Influence of power of microwave and the length of treatment on colour yield of wool fabrics Dye Microwave K/S values power, W 0.5 a 1.0 a 1.5 a 2.0 a 2.5 a 3.0 a Lanasol Red 6G Palatin Red GRE a Treatment time in min. 300 20.809 20.930 21.042 21.569 21.874 22.033 400 20.911 21.205 21.553 21.732 21.905 22.149 500 20.299 20.514 20.560 20.698 21.052 21.724 600 20.317 20.394 20.412 20.587 20.871 21.093 700 20.290 20.497 20.612 20.819 20.374 20.369 Untreated 20.234 300 32.633 32.751 32.847 33.541 33.753 33.803 400 32.858 32.893 33.018 33.612 33.861 33.918 500 32.536 32.704 32.836 33.187 33.311 33.323 600 32.448 32.648 32.791 32.477 32.522 32.830 700 32.681 32.844 32.937 33.056 32.454 32.452 Untreated 32.447 Table 2 Exhaustion and fixation of untreated and microwave-treated wool fabrics [Optimum conditions: 400W irrediation power and 3.0 min treatment time] Dye Wool sample E, % F, % Lanasol Red 6G Untreated 73.6 94.8 Microwave-treated 75.0 96.7 Palatin Red GRE Untreated 90.7 93.7 Microwave-treated 92.6 95.8 the dyeability of the treated wool fabrics decreases with the increase in irradiation power. The optimum values of treatment time and irradiation power are found to be 3.0min and 400W respectively. 3.2 Effect on Exhaustion and Fixation The results of the dyeing exhaustion and fixation of the untreated and the treated wool fabrics are given in Table 2. It is observed that microwave-treated fabrics have improved exhaustion and fixation compared to the untreated fabric. This may be due to the change in wool surface morphological structure under microwave irradiation which implies that the barrier effect in wool dyeing is diminished. 3.3 Effect on Surface Morphological Structure In order to investigate the influence of the microwave treatment on the wool fibre surface morphological structure, wool fabric was subjected to microwave irradiation with 400W power for 3.0 min. The SEM photographs of surface morphological structure of untreated and treated wool fibres are shown in Fig. 1. Microwave pretreatment has a slightly damaging effect on the surface scale-like structure of wool as compared to the untreated wool fibre; the scale edges are slightly eroded. It is considered that the destruction of the surface improved the absorption of dye molecules by the wool fibres during dipping and the diffusion of dye molecules into the wool fibres. As a result, the probability of the reaction between the dye and the wool fibres is increased, resulting in improved colour yield of the dyed wool fabric. 3.4 Effect on Crystallinity In order to investigate the influence of the treatment with microwave on the wool fibre fine structure, the wool fabric was subjected to microwave irradiation with 400W power for 3.0 min. The X-ray diffraction analysis of the crystallinity of untreated and treated wool fibres is shown in Fig.2. The crystallinity of the modified wool fibre is found to be very similar to those of the untreated wool fibre. In other words, the microwave treatment does not significantly alter the crystallinity of the wool fibre. 3.5 Effect on Chemical Structure In order to investigate the influence of treatment with microwave on the wool fibre chemical structure, wool fabric was subjected to microwave irradiation with 400W power for 3.0 min. Figure 3 shows the FTIR curve of the untreated and treated wool fibres. It can be seen from Fig.3 that the FTIR curve of treated wool fibre is almost similar to that of untreated wool fibre. Hence, microwave irradiation does not significantly influence the chemical structure of wool fibres. 3.6 Effect on Breaking Strength Microwave power and treatment time under microwave irradiation condition also affect the
XUE & JIN-XIN: IMPROVEMENT IN DYEABILITY OF WOOL FABRIC BY MICROWAVE TREATMENT 61 breaking strength of wool fabric. The breaking strength values of the wool fabric untreated and treated with microwave at various power settings (300, 400, 500W, 600 and 700W) for various treatment time (0.5, 1.0, 1.5, 2.0, 2.5 and 3min) respectively are presented in Fig..4. It is observed that the breaking strength of the modified wool fabric increases with increasing the treating time and power. As compared to the untreated wool fabric, the breaking strength of treated fabric slightly increases after modification. This may be due to the existence of bound water molecules in wool (a) (b) Fig. 1 SEM micrographs of (a) untreated and (b) microwave-treated wool fibres Fig. 2 XRD plot of untreated and microwave-treated wool fibres Fig. 3 FTIR spectra of untreated and microwave-treated wool fibres
62 INDIAN J. FIBRE TEXT. RES., MARCH 2011 Fig. 4 Influence of power of microwave and the length of treatment on breaking strength fibre, which promotes adjustment of the fine structure of wool fibres and results in absorption of microwave energy, thereby eliminating the residual stress present in wool fibres. 4 Conclusion Microwave modification improves the dyeability of wool fabrics. The longer the treatment time the greater is the colour yield of dyed fabric. The dyeability of the treated wool fibres decreases with increasing irradiation power. The exhaustion and fixation of the treated wool fabrics improve with microwave irradiation. The microwave treatment also causes a slight damaging effect on the surface scale-like structure of the wool fibre, promoting the adsorption and permeation of the dye molecules into the wool fibres. This improves the extent of reaction between the reactive dye and wool fibres. Microwave irradiation does not significantly affect the crystallinity and the chemical structure of wool fibres. The breaking strength increases slightly after modification. Microwave modification technique has significant potential for industrial application as microwave is a clean and environment-friendly heating technology. References 1 Guizhen Ke, Weidong Yu, Weilin Xu, Weigang Cui & Xiaolin Shen, Effects of corona discharge treatment on the surface properties of wool fabrics, J Mater Process Technol, 207 (1-3) (2008) 125-129. 2 Chonyu Chen, Limei Fan & Hanchien Wang, Antibacterial evaluation of cotton fabric pretreated by microwave plasma and dyed with taiwan folkloric medicinal plants, Sen'i Gakkaishi, 63 (11) (2007) 252-255. 3 Fakin, Darinka, Ojstrsek, Alenka, Benkovic & Sonja Celan, The impact of corona modified fibres' chemical changes on wool dyeing, J Mater Process Technol, 209 (1) (2009) 584-589. 4 Kan, Chi-Wai, Yuen & Chun-Wah Marcus, Dyeing behaviour of low temperature plasma treated wool, Plasma Process Polym, 3 (8) (2006) 627-635. 5 Takayuki Okabe, Daisuke Kasai, Nayu Kobayashi, Toshihiko Shiina, Mami Takeda, Kunihiro Hamada & Kyohei Joko, Effects of auxiliaries on acid dyeing of shrinkproofed wool fibers, Sen'i Gakkaishi, 65 (5) (2007) 123-129. 6 Giri Dev V R,.Venugopal J, Sudha S, Deepika G & Ramakrishna S, Dyeing and antimicrobial characteristics of chitosan treated wool fabrics with henna dye, Carbohydr Polym, 75 (4) (2009) 646-650. 7 Masuhiro Tsukada, Shafiul Islam & Takayuki Arai,Microwave irradiation technique enhance protein fiber properties, Autex Res J, 5 (1) (2005) 40-48. 8 Yoshimura Yurika, Effect of microwave heating on dyeing, Seni Gakkaishi, 63 (6) (2007) 146-151. 9 Murugan R, Senthilkumar M & Ramachandran T, Study on the possibility of reduction in dyeing time using microwave oven dyeing technique, J Inst Eng India, [Part TX], Text Eng Div, 87 (2) (2007) 23-27. 10 Kan C W & Yuen C W M, Surface characterisation of low temperature plasma-treated wool fibre, J Mater Process Technol, 178 (1-3) (2006) 52-60. 11 Mori Masukuni, Matsudaira Mitsuo & Inagaki Norihiro, Mechanical property and anti-felting property of wool fabric treated with low-temperature plasma, Sen'i Gakkaishi, 52 (1) (2006) 19-27. 12 Sun D & G K Stylios, Fabric surface properties affected by low temperature plasma treatment, J Mater Process Technol, 173 (2) (2006) 172-177. 13 Schmidt A, Bach E & Schollmeyer E, The dyeing of natural fibres with reactive disperse dyes in supercritical carbon dioxide, Dyes Pigm, 56 (1) (2003) 27-35. 14 Lee M, Wakida T & Myung Sun Lee, Dyeing transition temperature of wools treated with low temperature plasma, liquid ammonia, and high-pressure steam in dyeing with acid and disperses dyes, J Appl Polym Sci, 80 (7) (2001) 1058-1062. 15 Nigar Merdan, Mehmet Akalin & Dilara Kocak, Effects of ultrasonic energy on dyeing of polyamide (microfibre)/lycra blends, Ultrason, 42 (1-9) (2004) 165-168.