Introduction

Emphasis on fault prevention and elimination of re-dyeing not only brings substantial water and energy savings but also results in higher quality, increased productivity, reduced labour costs and advantages in supplier-customer partnership. Ferrington¹ and Glover et al² have discussed and calculated the impact of re-dyeing cost. Considerable work has been carried out to optimize and ensure maximum reproducibility in dyeing. Reviews on this subject have been published³. The quality of water, grey preparation, dyeability of the substrate, weight of the substrate, weighing of dyes and chemicals, selection of dyes, standardization of dye strength (hue), moisture content of dyes and substrate, nature of dye bath, machine flow and sequence, time and temperature profile are the factors which are responsible for the complexity of dyeing processes. One of these factors, i.e. moisture content of the dye powder is recognized as being influential for depth of shade and reproducibility; however only a few quantitative results have been published on its effect and its consequences on dyeing. Adamiake⁴ reported the effect of variations in moisture content of wool dye powder on depth of the shade. One reason for variation in moisture content of dye powder is improper storage condition in dyeing factories. Many dyeing factories do not pay attention in storing dyes and chemicals. The stores personnel after issuing dyes and chemicals to production department do not bother to close the containers properly. Therefore these dyes and chemicals get exposed to varying temperatures and humidity depending upon the seasons. The change in humidity results in change in weight of the dye powder. The present work is an attempt to quantify the change in depth of shade due to change in humidity.

Even though reactive dyes have excellent wash fastness properties, often buyers complain of poor wash fastness. This is mainly due to adherence of hydrolysed dyes onto cotton. If they are not washed off after dyeing, they behave like direct dyes and bleed during the initial washings carried out by the customers. In order to avoid the complaints, some dyers take extra precautions by providing more than the required number of washings. Therefore the second objective of the present study is to develop a quick method to optimize the number of washings to be given after reactive dyeing to achieve good wash fastness properties, especially for dark and medium shades.

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About the Authors

The authors are associated with Northern India Textile Research Association, U.P, and Ginni Devi Modi Girls (P.G) College, Modinagar.