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Development of AOPs based novel Technology for water conservation and pollution reduction in textile dyeing

Shaikh, Irfan Ahmed (2010) Development of AOPs based novel Technology for water conservation and pollution reduction in textile dyeing. PhD thesis, University of the Punjab, Lahore.

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Abstract

This study discusses the application of a newly developed method capable to decolorize liquor by ozone and re-use it to rinse dyed materials for the removal of unfixed dyes simultaneously. After successful application of the new method on a laboratory scale, the method was upgraded using a pilot plant and more than 100 runs were carried out employing a variety of reactive, disperse and vat dyes.The quality of textile materials treated with new method was determined in terms of color evenness, fastness properties, color differences, and total color difference with respect to reference.The new method was also patented as “Method and device for dyeing a textile substrate” in various Intellectual Property Offices (IPOs) of the world. Initially, the effects of process parameters (pH, treatment time, type of dyestuff, dye contents and proprietary chemicals) on the color removal efficiency of ozonation process were studied for synthetic effluents of reactive, disperse and vat dyes on a bench-scale. In the case of reactive dyes, the color removal efficiency of the process was significantly increased in an alkaline environment. For effluents containing disperse and vat dyes, the efficiency of the process though enhanced with increasing pH of the effluent and ozone exposure time but that increase in the efficiency was negligible as compared to the increase observed in the effluents containing reactive dyes. The deceolorization performance of ozone was significantly dropped for effluents of higher dye contents. The addition of chemicals like salts and leveling agents showed no noticeable effect on the color removal efficiency of ozone. However, addition of sequestering agent (EDTA) slightly reduced (2-3%) the efficiency of the process. CI Reactive Black 5, CI Reactive Blue 19, and CI Reactive Orange 7 dyed fabrics were then treated with new method using a bench scale experimental set-up. It was observed that an increase in treatment time (40-50 minutes) improved the fastness properties of all three dyes due to the decolorization of surface deposited unfixed dyes by ozone. CI Reactive Blue 19 dyed fabric samples appeared to be resistant to ozone decolorization, and best wash fastness (4.5) was obtained after 50 minutes ozone treatment. The shade of ozone treated fabric was almost identical to reference, and the minor differences in terms of lightness (ΔL*= 0.03), hue (Δh*=0.01), and total color difference (ΔE*=0.10) between reference and fabric treated using new method were observed. In case of CI Reactive Black 5, 30 minutes washing-off by ozone assigned color properties (ΔL*= -0.07, Δh*= -0.18, ΔE*=0.32) similar to reference. On contrary, CI Reactive Orange 7 behaved differently and showed wash fastness rating half point less than that of reference. The shade was darker (ΔL*= -0.51), slightly brighter (Δc*= 0.34) and yellower (Δb*=0.31) than reference. Total color difference (ΔE*= 0.91) was, however, within permissible limit (ΔE*<1.0). This implies that unfixed dyes are still present on the fabric surface, which is required to be removed either by extending the ozonation time or by increasing the ozone dose. The application of ozone treatment also resulted into a gradual decline in the pH of the bath water, which owes to the formation of organic ions in the form of their corresponding acids. Since dyed materials are extremely sensitive to ozone dose, it was essential to determine an optimal dose before applying new method on a pilot scale. An ozone dose of 10 g/hr was found to be optimum for very dark shade (7% owf). The new method was then extensively tested using a pilot plant, and more than 100 trial runs were carried out using a wide range of dyes from various classes of dyestuff (predominantly reactive dyes) obtained from world renowned dye manufacturers (Dystar, Clariant, Ciba, and Sumitomo). Vinylsulfone dyes were prone to rapid degradation by ozone, and liquor was almost colorless after 20 minutes of ozone treatment. For all shades such as Black (16), Indigo (18), M.Blue (21) and Navy (24), wash fastness (4.5) was similar to reference after 20-30 minutes ozone treatment. Total color difference values (ΔE*= 0.83-1.0) were in the acceptable limit (ΔE*<1.0). However, the color differences (ΔL*, Δa*, Δb*, Δc*, and Δh*) between reference fabric and those washed-off using new method showed the occurrence of unfixed dyes on the surface of fabric. In case of monochlorotriazine (MCT) reactive dyes, the color removal of bath water was in the range of 85-99% after 30 minutes ozonation treatment. The wash fastness of ozone treated fabric was excellent (4.5) for all shades including Yellow (11), Orange (19), Dark Blue (32) and Light Blue (37). However, color differences in terms of ΔL*, Δa*, Δb*, Δc*, and Δh* between ozone treated fabric and reference showed that shades of ozone treated fabrics were darker, which implied that surface deposited loose dyes were still there. Total color difference values (ΔE* = 0.69 - 1.26) were in the acceptable limit (ΔE*<1.0). For bi-functional reactive dyes (Green (17), Burgandy (25) and Dark Grey (27)) bathwater was almost colorless after 30 minutes of ozone treatment. Wash fastness of all fabrics was similar to reference fabric. Total color difference values (ΔE*= 0.58-1.23) were also in the acceptable limit (ΔE*<1.0). Fabric samples of Blue (10) and Dark Pink (26) shades of monoflourotriazine reactive dyes showed excellent wash fastness (4.5) after 10-40 minutes ozone treatment. The color removal of bath water was in the range of 82-99% after 40 minutes of ozonation. For all shades, the total color difference values (ΔE*= 0.43- 1.50) were closer to the acceptable limit. However, color differences (ΔL*, Δa*, Δb*, Δc*, and Δh*) between ozone treated fabric and reference showed the presence of some surface deposited unfixed dyes. Similarly, the wash fastness properties of fabrics (Choco (31) and Slate (33)) treated with new method were excellent (4.5), and total color difference values (ΔE*= 1.10 - 1.14) were near to allowable limit. Overall, most of the shades of ozone treated fabrics were a bit darker with respect to reference indicating the presence of surface deposited unfixed dyes, however, these unfixed dyes can be removed by either extending ozone treatment time or by increasing ozone dose. The new method was proved to be very economical because it reduces the water consumption (50% water saving), is less energy intensive (applicable at ambient temperature), and is environmental-friendly (involves no chemicals).

Item Type:Thesis (PhD)
Uncontrolled Keywords:Acids, Based, Textile, Chemicals, Dyestuff, Dyeing, Reduction, Method, Experimental, Technology, Conservation, Ozon, Development, Aops, Reference, Environmental, Water, Pollution, Novel
Subjects:Physical Sciences (f)
ID Code:6112
Deposited By:Mr. Javed Memon
Deposited On:25 Apr 2011 12:50
Last Modified:20 Aug 2011 10:02

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