ANALYSIS OF DYES

ANALYSIS OF DYES

What are DYES?A dye can generally be described as a colored substance that has an affinity to the substrate to which it is being applied.Initially the dyes were obtained from animal, vegetable or of plant origin like roots, leaves, bark with no or very little processing.Soon after natural dyes were replaced by synthetic dyes. They cost less, they offered a vast range of new colors, and they imparted better properties to the dyed materials.

Classification Of DyesDyes are classified according to how they are used in the dyeing process.Commercially , the most widely used dyes are:-ACID DYES are water soluble anionic dyes that are applied to fibers such as silk, wool, nylon using neutral to acid dyebaths.BASIC DYES are water soluble cationic dyes that are mainly applied to acrylic fibers.DIRECT DYES are normally carried out in slightly alkaline dyebath, at or near boiling point, they are mainly used on cotton.VAT DYES are essentially insoluble in water and incapable of dyeing fibers directly. However, reduction inalkaline liquorproduces the water solublealkalimetalsaltof the dye, which, in this leuco form, has an affinity for the textile fibre. Subsequentoxidationreforms the original insoluble dye.REACTIVE DYES utilize a chromophore attached to a substituent that is capable of directly reacting with the fiber substrate. The covalent bonds that attach reactive dye to natural fibers make them among the most permanent of dyes. Reactive dyes are by far the best choice for dyeingcottonand othercellulosefibers.DISPERSE DYES were originally developed for the dyeing ofcellulose acetate, and are water insoluble. The dyes are finely ground in the presence of a dispersing agent and sold as a paste or powder. Their main use is to dyepolyesterbut they can also be used to dye nylon,cellulose triacetate, and acrylic fibres. In some cases, a dyeing temperatureof 130Cis required, and a pressurised dyebath is used. The very fine particle size gives a large surface area that aids dissolution to allow uptake by the fibre.

NEED OF ANALYSIS OF DYESAnalysis of dyes plays an important role in Quality and Process control.Accurate measurement of strength of dye leads to overcome the lab to bulk variation up to a certain limit.In Dyeing, RIGHT FIRST TIME can be easily achieved if the dyes content knowledge is up to the mark.Gives complete knowledge of dye behavior in the dyebath.LIST OF TEST METHODSMethod for Evaluating Strength of Reactive Dyes (Monochlorotriazinyl type) by Dyeing TestMethod for Estimation of Strength(Vat Content) of Vat dyes.Dispersibility of Disperse Dyes: Filter Test

TEST METHOD IS:7448-1974TITLE- Method for Evaluating Strength of Reactive Dyes (Monochloro triazinyl Type) By Dyeing Test.

STANDARD DYESTUFF- The standard sample of dyestuff , against which the strength of dyestuff under test is evaluated.

QUALITY OF REAGENTS- Pure chemicals shall be employed in test and distilled water shall be used.

EVALUATION OF STRENGTH OF DYESTUFF Prepare Dyeings of Standard sample of dyestuff by following the procedure. Prepare simultaneously additional dyeings of the standard sample with the percentage variation of dyeing strength by 0.1% of the recommended percentage.Compare the dyeing. Select the dyeing of the dyestuff under test which exactly matches with one of the dyeings of standard dyestuff . Note, the percentage of Dyeings which exactly matches.CALCULATIONS: Calculate the strength of the dyestuff under test by the following formula S=(A/B)*100S = Strength of dyestuff in percentageA = Percentage dyeing of the standard dyestuffB = Percentage dyeing of the dyestuff under test

REPORT: Strength of dyestuff in percentage

METHOD FOR DYEING

APPARTAUS- Dye Vessels, Graduated pipettes, Volumetric flasksDYEING ASSISTANTS- Water, Sodium Chloride Solution 20%, Sodium Carbonate Solution 10%, Soap Solution 0.3%PREPARATION OF FABRIC SAMPLE- Sample weight should be 10 0.1gm RFD sample should be used. Samples should be dipped in boiling water for 10 minutes, properly squeezed and then added in the dyebath.PROCEDUREWeigh accurately 1.0g of the dyestuff. Paste the dyestuff with cold water and dissolve by adding warm water ( 120 sExamine residue on filter paper versus the filter residue scale.

Also examine the paper for any visible coarse or granular particle, if present the test is automatically rated as Class 1. If none is present rate as follows:- Class 5- Excellent Class 4- Class 3- Intermediate values are interpolated Class 2- Class 1- Poor

REPORT- Dispersibility of disperse dyes is evaluated through filter test.