| Author: | Tang, Yiu Lun |
| Title: | Development and analysis of solvent-assisted dyeing system for cotton fibre |
| Advisors: | Kan, C. W. (ITC) |
| Degree: | Ph.D. |
| Year: | 2020 |
| Subject: | Dyes and dyeing -- Cotton Cotton fabrics Hong Kong Polytechnic University -- Dissertations |
| Department: | Institute of Textiles and Clothing |
| Pages: | xxv, 281 pages : color illustrations |
| Language: | English |
| Abstract: | Cotton is a natural, cellulosic, plant fibre. It is soft and mainly in staple form. It has existed for more than 5000 years and was first cultivated by the inhabitants. Due to its outstanding and unique physical and chemical properties, it is still the most important and widely used natural fibre for textile production and garment making and of international importance in global trade. Colouration is one of the processes in textile wet processing. It has long been regarded as a significant consumer of water and producer of effluent. The effluents of reactive dyeing included (a) unfixed dye; (b) non-biodegradable inorganic salt; (c) inorganic alkali and (d) detergent. These chemicals may produce coloured effluent with high levels of dissolved solids and oxygen demand and require huge costs for effluent treatment. The present study focuses on developing a non-aqueous solvent-assisted dyeing system for cotton fibre based on the use of PEG-based non-ionic reverse micelles. Several dyeing parameters are initially optimised, including: (a) surfactant to water mole ratio (1:20 for octane and nonane, 1:25 for heptane, 1:30 for decamethyl cyclopentasiloxane); (b) surfactant to co-surfactant mole ratio (1:8); (c) solvent to cotton weight ratio (8:1); (d) dyeing and fixation temperature (70°C); (e) dyeing time (40 min); (f) fixation time (60 min); (g) water-pool volume for dye (0.5 mL); and (h) water-pool volume for soda ash (0.3 mL). Results reveal that the developed reverse micellar system (without electrolytes) can achieve better colour yield (K/Ssum value) than that of the conventional water-based system. SEM images show the surface morphology of the reverse micellar-dyed samples. Tough fibre surface was observed with loose microfibrils appeared in random directions. TEM images show the reactive dye molecules were well encapsulated in the interior core of the PEG-based reverse micelle. The effect of dye agglomeration was examined for the developed system by analysing the influence of surfactant to water mole ratio and surfactant to co-surfactant mole ratio in depth. The results validate that optimal surfactant to water ratio (1:25) and surfactant to co-surfactant ratio (1:8) were essential for stable formation of dye-encapsulated reverse micelles with spherical-like morphology. To further analyse the developed system, the influences of HLB value, reactive groups of reactive dyes, dyeing methods, and water pH and hardness are studied. The results reveal that the most appropriate range of HLB values for reverse micelle dyeing of cotton is from HLB values of 12 to 14. Too low HLB value (4.9) may lead to phase separation while too high HLB value (18) may lead to agglomeration of dye molecules. Hetero-bifunctional vinyl sulphone-based reactive dyes can achieve higher colour yield (K/S) than homo-bifunctional and monofunctional reactive dyes in non-aqueous heptane medium. Nevertheless, monofunctional reactive dyes generally gain better levelness than homo- and hetero-bifunctional reactive dyes. Concerning dyeing methods, both one-bath and two-bath (transfer dye liquor from one water bath to another water-bath) heptane-dyed samples can obtain higher colour yield (K/S) than that of conventional water-dyed samples. Even though one-bath method yields high K/Ssum value, unlevelness problem should be under consideration whereas two-bath method can strike a balance between levelness and K/Ssum value (in case of single jersey fabric). Regarding water pH and hardness, the results show that water-pool pH has more significant influence on colour yield and reflectance of the dyed samples than that of water-pool hardness while the hardness in water-pool has more significant influence on the unlevelness of the dyed samples than that of the pH value in water-pool. The reactive dye compatibility matrix (RCM) of the developed system is studied in comparison to the conventional water-based system. The calibration results reveal that red reactive dye can achieve higher absorbance value than that for yellow and blue dyes. Reverse micelle method can obtain higher dye absorption in both exhaustion and fixation processes, contributing to higher final dye exhaustion in fibre when compared with conventional water-based method. The applicability of computer colour matching (CCM) on the developed reverse micellar system for cotton fibre is examined under different solvent non-aqueous dyeing medium, such as heptane, octane, nonane and decamethyl cyclopentasiloxane (D5) and with the use of several colour difference formulae. The results validate that both solvents can be used as the dyeing medium for reactive cotton colouration and for CCM. The calibration curves were established with high linearity (R2 value close to 1) and the colour difference between predicted concentration and standard concentration was within ± 0.3 which is acceptable in CCM. Washing fastness test, according to AATCC-61 test method, is conducted. Excellent washing fastness, rating 4-5 and 5, is obtained for reverse micellar-dyed samples. This indicates that the unfixed and hydrolysed dyes are adequately removed after the washing process. In addition, the reflectance results attest that there is no chromatic change of the dyed specimens. No peak shifting of the reflectance curves is found, ensuring that the use of those solvents would not alter the colour properties of the dyed cotton samples. |
| Rights: | All rights reserved |
| Access: | open access |
Files in This Item:
| File | Description | Size | Format | |
|---|---|---|---|---|
| 991022385357903411.pdf | For All Users | 8.09 MB | Adobe PDF | View/Open |
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