Compatibility Testing of Reactive Dyes

The present work deals with the ways of testing the compatibility of reactive dyes with cotton in different textile industries in Bangladesh. This report includes three laboratory trials that were carried out for three different reactive dyes to check the compatibility for use in a dye recipe on cotton knitted goods. In this study, Spectrophotometric analysis was conducted and the fixation of each dye was determined by using computer colour matching system. The results found from different industries were analysed and discussed. This testing can be used as a tool for selecting good quality dyes as well as to reduce dyeing cost and hazard. Finally few recommendations are highlighted to overcome the problem of selecting better quality dyes for cotton goods in textile industries in Bangladesh. INTRODUCTION Fabric dyeing usually requires three basic dyes in a mixture to achieve the desired hue and shade. Dyes with similar reactive groups and same exhaustion properties will be said to be compatible with each other and are ideal for use in such mixtures. Selecting compatible dyes is a part of ensuring an optimum dyeing recipe which will most efficiently utilize the dye, produce optimal dyeing results and will reduce the number of chemicals that enter the wastewater. So, checking the compatibility of dyes is a key way to minimize the amount of dyes used as well as ensuring the matching of the specific shade. Basic theory of testing of the compatibility of reactive dyes is available in different text books on textile dyeing. By testing the compatibility of dyes the costs of dyeing can be reduced and the level of productivity can be increased because of less time wasted in trying to get the correct shade. This work was carried out for three different reactive dyes to check their compatibility in a dyeing recipe. In this method, Spectrophotometric analysis was conducted and the fixation of each dye was determined by using computer colour matching system. EXPERIMENTAL PROCEDURE Three tests were carried out in two different industries. The list of materials used in these tests is given below: 1. Knitted Cotton Fabric ( at least 12 pieces: 5g of each) 2. Remazol Yellow RR 3. Remazol Red RR 4. Remazol Blue RR 5. Drimarine Yellow CL2R 6. Drimarine Red CL5B 7. Drimarine Blue CL2RL 8. Scanning absorbance spectrophotometer 9. Volumetric flasks (e.g. 50ml, 100ml, 250ml) 10.Pipettes (eg. 1ml, 5ml, 10ml, 25ml) 11.Beakers (eg. 100ml, 250ml) 12.Soda ash 13.Glauber salt 14.Washing agent 15.Acetic acid The spectrophotometric analysis puts emphasis on the exhaustion characteristics of any single dye for a particular shade. There were three steps as follows: a. Measuring the extinction coefficient of the three single dye for a particular shade b. Measuring the concentration at different stage of dyeing using the dyes of that specific shade c. Measuring the colour strength before and after washing and finding out the fixation. Measurement of extinction coefficient for a single reactive dye: Firstly, 0.1% stock solution of a single dye was prepared by dissolving out 1.000g of dye, diluted up to 1000 ml in a volumetric flask. A number of dye solutions of different concentrations were prepared by taking a certain quantity of the stock solution. These solutions were measured in a calibrated absorbance spectrophotometer (model: HACH DR 2500) to obtain an absorbance value for each, which were used to plot an absorbance curve and to calculate the extinction coefficient. A sample of a solution of known concentration was then placed in the spectrophotometer and absorbance values of a range of wavelength were produced. The absorbance value at the peak (λmax) was recorded. This was repeated for at least three other dilutions of the same dye keeping the wavelength same. For example, if λmax is 597 nm for the first sample then all readings were taken at 597 nm. Measurement of concentration and exhaustion of different reactive dyes: The measured extinction coefficients were used to calculate the concentration of those dyes used in the lab dyeing. To do this, twelve lab dyeing tubes were used. Four tubes were used for each dye of the proposed dye recipe (i.e. four tubes for dye 1; four tubes for dye 2; and four tubes for dye 3). The laboratory dyeing protocol normally used by the dye house was followed; the only exception being that the dyes were not mixed. 5ml sample was taken from tubes containing dye 1, dye 2 and dye 3. These three samples were diluted to a suitable concentration so that they can be analysed using the spectrophotometer to determine the absorbance. A suitable concentration is one where 5ml of sample is diluted to 250ml solution. Lab dyeing was conducted according to the dyeing profile shown in fig. 1. After 20 minutes another three samples of 5 ml were taken from each of the three dyes and analysed using the spectrophotometer to determine the absorbance. The same procedure is repeated after the addition of soda ash, 20 minutes after the addition of soda ash and at the end of the dyeing. Figure 1: Dyeing profile for testing the compatibility of reactive dyes 60C End of