|
|
| Issue date:01/02/2006 |
| ATA Journal for Asia on Textile & Apparel - Feb 2006 Issue |
| Source:Journal for Asia on Textile & Apparel |
| by Z.G. Hu, W.L. Chan, Y.S. Szeto |
|
| Researchers from the Hong Kong Polytechnic University have developed a new process to improve dyeability of silk with chitosan nanoparticles |
A kind of natural polysaccharide deriving from chitin, chitosan is cationic in acidic media, which makes it easily absorb anionic molecules such as direct, acid and reactive dyes.1 This property is useful in the dyeing of protein fibers such as wool and silk and much work has been done to improve the dyeability of silk with chitosan.2-4 The work proved the considerable value of chitosan in this area. Since the absorption of dyes by chitosan is mostly by electrostatic interactions, the larger surface area of chitosan nanoparticles is believed advantageous for better dyeability of silk. In this paper, silk fabrics were treated with chitosan nanoparticles, and then dyed with five acid dyes and five reactive dyes, to investigate the benefits of chitosan nanoparticles in silk dyeing.
Experiments
Materials
Bleached silk fabrics were from Yue Hwa, Hong Kong. Chitosan was from Haidebei Ltd, China. Lanaset dyes (acid dyes) and Lanasol dyes (reactive dyes) were from Ciba Specialty Chemicals Inc. Other chemicals were from Aldrich Chemical Co and used as received.
Instrumentation
Sonic 120 was used for the sonolysis. Laser scan was performed with a Zetasizer 3000HSA. JOEM JSM 6335F was used for SEM measurements. A Datacolor Elrepho 2000 spectrophotometer was used for color evaluation.
Preparation of chitosan nanoparticles
Typically, chitosan was dissolved in 0.5% (w/v) aqueous acetic acid solution. Aqueous ammonia was then dropped - wisely added into the chitosan solution under magnetic stirring. The precipitated chitosan was rinsed with deioned water to neutral, and was then transferred to a 250ml conical flask. The total volume of system was 100ml after adding deioned water. Ultrasonic treatments were conducted in an ice-water bath and a white nano-emulsion of chitosan was obtained. Some emulsions were converted to solutions by adding acetic acid.
Treatment of silk with chitosan nanoparticles
Silk fabrics were soaked in the chitosan nano-emulsion at four concentrations, 0.01%, 0.05%, 0.1% and 0.3% (w/v) for two hours, followed by padding at 80% pick-up. Then the silk fabrics were dried at 90°C for three minutes and cured at 150°C for three minutes. The experiment was repeated with a chitosan solution.
Table 1. The recipes of dye solutions |
Dyeing of the treated silk
A pad-dry-cure method was used. Silk was padded with a dye solution by a one-dip-one-nip method, then dried at 90°C for three minutes, followed by steaming at 110°C with 70% humidity for 15 minutes. The silk was finally washed with a nonionic detergent and tap water, and dried before any assessments. The recipes of the dye solutions are summarized in Table 1. The pH was adjusted to 6.5 with acetic acid for acid dyes and 8.5 for reactive dyes with sodium carbonate.
Evaluation of the dyed silk fabrics
The color yield (K/S value) and the color difference ΔE* (D65/10) were computed with the Kubelka and Munk equation and the CIELAB color difference equation respectively. The color fastness to rubbing was determined with the AATCC Test Method 8-2004.
Results and discussion
Figure 1. SEM photos - left: chitosan nanoparticles and right: surface of nanoparticle-treated silk
|
Morphology of treated silk
The chitosan nano-emulsion consisted of positive charged nanoparticles with average size of 350nm as determined by laser scan. The pH of the system was 7.0. In Figure 1, the left picture shows the profile of the spherical nanoparticles. These nanoparticles were believed to adhere onto the surface of silk by electrostatic interactions. The right picture shows a rough surface with tubular structures on the nanoparticle-treated silk.
Figure 2. SEM photos of silk surfaces - left: untreated silk and right: chitosan-solution-treated silk
Figure 3. SEM photos of fiber cross-sections - left: nano-emulsion-treated silk and right: chitosan-solution-treated silk
|
The tubular structure was not observed in the solution-treated silk as shown in Figure 2. Though both the chitosan solution and the nano-emulsion formed thin films on the silk, the film of nanoparticle-treated silk seemed thicker than that of the solution treated silk as shown in Figure 3. It is likely that the nanoparticles stacked together less closer than the chitosan molecules. More spaces were included in the structure as revealed in the SEM.
Evaluation of the dyed silk
Tables 2 and 3 summarize the K/S values of the dyeing of the untreated, chitosan-solution-treated, and the chitosan-nanoparticle-treated silk. The dyeability of the nanoparticle-treated silk was improved remarkably comparing with that of the untreated silk, which was also better than that of the solution-treated silk. At 0.1% and 0.5% chitosan concentrations, the K/S values of the former could be over 100% more than those of the latter.
Table 2. K/S values of silk dyed with 30g/L acid dyes
Table 3. K/S values of silk dyed with 30g/L reactive dyes |
This may be due to the larger surface area providing more dye sites. On the other hand, the dyeability of silk using acid dyes with the chitosan nanoparticles was better than that of reactive dyes. At 0.3% chitosan concentration, the K/S values of acid dye dyed silk were increased at almost 200% while those of reactive dyes were under 100%. Chitosan has high affinity to anionic dyes due to the electrostatic attractions because of its cationic property in acidic environments.1 The low pH of acid dyeing solution provides more protonated amino groups in chitosan which is difficult to happen in the alkali solution in the reactive dyeing.5-7 The changes of the ΔE* were similar to these of K/S values accordingly. Figures 4 and 5 show the minimal and maximal changes of acid and reactive dyed silk. The increase was no more than 40%. The results indicated that the chitosan nanoparticles did not cause any obvious change to the original property of dyes. The results show that the higher the dye concentrations, the greater the depth of dyeing. The effect is consistent in the chitosan-nanoparticle-treated silk.
Color fastness to rubbing and washing
Figure 4. Changes of ΔE* of silk dyed with acid dyes
Figure 5. Changes of ΔE* of silk dyed with reactive dyes |
Table 4. Washing fastness of chitosan-nanoparticle-treated silk dyed at 30g/L |
The dry rubbing fastness of the chitosan-treated silk was similar to that of the untreated silk. The grey scale assessments of the staining for all of the treated silks were at 4 to 4-5 in spite of the big difference in K/S values. The wet rubbing fastness was slightly inferior. Chitosan has good affinity to silk and dyes because of the amino groups and hydroxy groups. This property provides the treated silk with good fastness to dry rubbing. But water can destroy the interactions between treated silk and dye molecules and dissolve the dyes, and so the silk with high K/S values had inferior wet color fastness. Table 4 summarizes the washing fastness of chitosan-nanoparticle-treated silk. The fastness was the same or slightly less than that of the untreated one.
Conclusion
The dyeability of silk fabrics was remarkably improved with the chitosan treatments. It was found that chitosan nanoparticles were more effective than chitosan solution in dye-uptake enhancement. The SEM data indicates that the former had larger surface area on the treated silk than the latter. The dry rubbing fastness was not affected by the chitosan treatment but the wet rubbing fastness was slightly inferior.
References
[1] Lim, S.H.; Hudson, S.M. J. Macromol. Sci.-Polym. Rev 2003, 43, 223.
[2] Wu, Y.G.; Chan, W.L.; Szeto, Y.S. J. Appl. Polym. Sci. 2003, 90, 2500.
[3] Takeshi, K.; Akiko, N. Nippon Sanshigaku Zasshi 2002, 71, 147.
[4] Takeshi, K. Nippon Sanshigaku Zasshi 2001, 70, 117.
[5] Dragan, J.; Susana, V.; Tatjana, T. Carbohyd. Polym. 2004, 60, 51.
[6] Juang, R.S.; Tseng, R.L.; Wu, F.C. J. Chem. Tech. Biotechnol. 1997, 70, 391.
[7] Ravi Kumar, M.N.V. React. Funct. Polym. 2000, 46, 1.
From the Hong Kong Polytechnic University, Z.G. Hu and Y.S Szeto are researchers at the Institute of Textiles and Clothing, and W.L. Chan is researcher at the Department of Applied Biology and Chemical Technology.
|
| We are collecting readers' comment for improving our website. If you are willing to help, please CLICK HERE to complete a survey. Your comments matter. |
|
|
|
|
| Copyright © Adsale Publishing Limited. Any party needs to reprint any part of the content should get the written approval from Adsale Publishing Ltd and quote the source "ATA Journal for Asia on Textile & Apparel", Adsale Textile English Website - www.AdsaleATA.com. We reserve the right to take legal action against any party who reprints any part of this article without acknowledgement. For enquiry, please contact Editorial Department. |
|
| Copyright © Adsale Publishing Limited. Any party needs to reprint any part of the content should get the written approval from Adsale Publishing Ltd and quote the source "ATA Journal for Asia on Textile & Apparel", Adsale Textile English Website - www.AdsaleATA.com. We reserve the right to take legal action against any party who reprints any part of this article without acknowledgement. For enquiry, please contact Editorial Department. |
|
|
|
Close
|
|
|
Write a mail to the editor : 
