Reactive dyes stripping

The stripping of cellulosic materials dyed with reactive dyes is carried out by alkaline reduction followed by hypochlorite oxidation, preceded by a boiling treatment with EDTA if metal-containing dyes have been used. For example, a treatment with 5 gA sodium carbonate or sodium hydroxide and 5g/l sodium dithionite at the boil is followed by a treatment in 0.5-1 °Tw hypochlorite, an antichlor and thorough rinsing. 

It can be prepared either by using appropriate direct dyes or reactive dyes. In the latter case, pure linters (the raw material for high-quality paper) are suspended in water, and the solution of the reactive dye is added. For example, the dye 15 reacts via the sulfonic acid group in the side chain. The reaction mixture is then made alkaline and the dye reacts with the linters. After completion of the reaction, the fiber pulp is centrifuged, washed electrolyte-free, and processed on a paper machine to form the pH paper. Paper produced in this way is mostly bonded onto a plastic material and used as pH test strip. 

With regard to cellulosic fibres, the simplest test for the dyes which will probably be present, ignoring unlikely ones such as acid or basic dyes, is to boil for 1 to 2 minutes with a 5 per cent caustic soda solution. If a considerable quantity of colour is stripped a substantive dye is indicated, and it will probably be an azo dye if the colour of the fresh sample is destroyed by boiling for 2 minutes with Formosul G. If, on the other hand, very little or no dye is stripped, the inference is that the material has been dyed with a sulphur, vat, or reactive dye. When boiled for 1 to 2 minutes with Formosul G and a few drops of sodium hydroxide solution, azoic or reactive dyes are virtually stripped. They can, however, be distinguished because only reactive dyes and certain phthalocyanine derivatives, usually recognizable by their distinctive colour, will withstand the following treatment (Giles et. al., J.S.D.C., 1962, 78, 126) ... 

Guaratini CCI, Zanoni MVB, Fogg AG (2002) Cathodic stripping voltammetric detection and determination at a hanging mercury-drop electrode of dye contaminants in purified biomaterials study of the human serum albumin and reactive dye 120 system. Microchem J 71 65... 

The improved dyeability is postulated due to the presence of amide groups (-CONH2) available from the polyacrylamide, which also tends to improve the reactivity of cellulosic substrate. The attaehment of the dye molecules onto the partially modified eellulosie substrate is done by eovalent bonding, since no dyes strips out from the dyed sample. This is also indieative through the fastness properties wash fastness. 

Excellent stripping agent for vat, sulphur and direct dyes. Also used when washing off vat, reactive or acid dye prints to prevent staining of white or pale ground. 

Qualitative detection of excess protein in urine is largely based on use of dipstick tests. The reactive portion of the stick is coated with a buffered indicator that develops color in the presence of protein. A typical example is Albustix (Bayer Corporation, Diagnostics Division, Tarrytown, NY), in which bromphenoi blue, buffered to pH 3 with citrate, is present mostly in the protonated, yellow form. When protein is added, the affinity of the anionic form of the indicator dye for protein causes a shift of the equilibrium between anionic and protonated forms of the indicator toward formation of the blue anionic species. The intensity of the shade of blue produced is then proportional to the concentration of protein in the specimen. Combur 8 strips (Roche Diagnostics, Inc., Indianapolis, IN) are said to be less subject to drug interferences. Their detection hmit is 7mg/dL. 

Oxspring D A, Franklin Smyth W and Marchant R, Comparison of reversed-polarity capillary electrophoresis and adsorptive stripping voltammetry for the detection and determination of reactive textile dyes . The Analyst, 1995,120, 1995-2000. 

NFPA Health 1, Flammability 2, Reactivity 0 Uses Solvent for nitrocellulose, cellulose acetate, oils, resins, waxes, fats, dyes, tars, lacquers, dopes, coatings, printing inks, wood preservatives, rayon, artificial leather, metal cleaning, cosmetics laboratory reagent hydraulic fluids textile stripping agent in food-pkg. adhesives Regulatory FDA 21 CFR 175.105... 

Uses Dispersant, dye solubilizer, soaping off agent for reactive, direct, and disperse dyeing chelating agent for dyebath without demetalizing dyes Features Nonfoaming multifunctional increases the salt tolerance of carriers and disperse dyes increases the solubility of reactive and direct dyes does not strip metal from metal complex dyes... 

---