Shade Variation of Exhaust and CPB Dyed Cotton

Project Topic

The coloration of cellulosic cotton knit fabric in Cold Pad batch method and compares the difference with the Exhaust method in terms of shade variation.

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Abstract

Cellulosic cotton knit fabric is generally dyed with reactive dyes. These dyes have a distinctive reactive nature due to active groups which form covalent bonds with –OH groups of cotton through substitution and/or addition mechanism. Exhaust (discontinuous) and Cold Pad Batch (continuous) are two of the methods among the various application methods of cellulosic cotton knit fabric dyeing. In this project, we have followed these two processes profoundly from the floor. The steps and chemicals of both processes are different from each other. We have used single jersey cotton knit fabric in this project. We have dyed three of the samples (light, medium, and deep shades) of both Exhaust and Cold Pad Batch methods with the same ratios of dyes at the chemical lab of Impress Newtex Composite Textile Limited, following both procedures have been following there. Here, we have taken the Exhaust dyed samples as the standard samples and compared the spectrophotometric results with the CPB dyed samples. The CMC values, K/S with wavelength, and R% with wavelength values of Exhaust samples have been compared with the CPB samples of the same ratios of dyes.

Keywords

Reactive dyeing, Exhaust dyeing, Cold Pad Batch dyeing, Spectrophotometer, Padder, Batching, Winch machine, Continuous washing, Reflectance, Wavelength, and Shade.

Introduction

Dyeing is the process of transferring the dye molecules or pigments and chemicals from the dye bath to the textile materials such as fibers, yarns, and fabrics. A huge amount of water and energy are being consumed during the dyeing process. Profitability crisis and environmental issues are being a great concern for the industry now.

In recent years, the default reactive dye has become the first choice for dyeing the cellulosic cotton knit fabrics because of its good fastness to wet treatments, higher range of shades, and higher absorbency. The cellulosic cotton knit fabrics can be dyed in both discontinuous and continuous or semi-continuous processes. The discontinuous process includes more than one stage and the continuous process includes a higher fixation rate of the dye and the dyeing is done in a continuous or semi-continuous process.

Results and discussion

From the evaluation of three shades of Exhaust and CPB dyed fabrics it is clear that the CMC values of medium shades are lower than 1 which means the color difference is not more than the standard (Exhaust) samples. So the medium shade of the Exhaust method can be dyed easily by following CPB processes in bulk dyeing and that can save more water.

From the graphs of wavelengths, R%, and K/S it is found that with the increase of total shade% of dyes, in the same wavelength R% decreases and K/S increases but in the same shade with the increase of wavelengths R% increases and K/S decreases.