Dye basics: identification of dyes

Dye basics: identification of dyes
Introduction
It is difficult to identify the type of dyestuff on textiles with naked eyes, and it must be determined accurately by chemical methods, while our current general practice is to judge by the type of dyestuff provided by the factory or the person who reports for inspection, together with the experience of the inspectors and their understanding of the production factory. If we do not identify the type of dyestuff beforehand, it is very likely that the non-conforming products will be judged as conforming products, which undoubtedly has great disadvantages. There are many chemical methods for identifying dyes, and the general procedure is complicated and time-consuming. Therefore, this paper introduces a simple method for identifying the type of dyes on cellulose fibers in dyed textiles.

Principle
Determination of the principle of the simple identification method
According to the principle of dyeing textiles with dyes, the common textile fabric components and their generally applicable dye types are as follows:
Acrylic fibers – cationic dyes
Nylon and protein fibers – acid dyes
Polyester and other chemical fibers – disperse dyes
Cellulosic fibers – direct, vulcanized, reactive, reducing, naftal, paint and phthalocyanine dyes
For blended or interwoven textiles, the type of dyestuff is adopted according to its composition. For example, for polyester and cotton blended fabrics, the polyester component is made with disperse dyestuffs, while the cotton component is made with the corresponding type of dyestuffs mentioned above, such as dispersed/reactive, dispersed/reduced processes, etc. respectively.
For the identification of fabric composition, you can click: Collection | Common Fiber Identification Methods!
Methods

1. Sampling and pre-treatment
Identification of cellulosic fibers on the type of dye is the key step of sampling and sample pre-treatment. When taking samples, should take the same kind of dye parts, such as samples containing several shades, each shade should be taken. If fiber identification is required, the fiber type should be confirmed according to FZ/TO1057. If the specimen taken with impurities affecting the experiment, grease, paste, must be cleaned with detergent in 60-70 ℃ hot water treatment for 15min, washing, drying. If the specimen is known to be resin-finished, it is treated with the following methods respectively.
1)Urea-formaldehyde resin is treated with 1% hydrochloric acid at 70-80°C for 15min, washed and dried.
2)The acrylic resin can be treated with 50-100 times of dicuyu reflux treatment for 2-3h, removed and washed and dried.
3) silicone resin can be 5g / L soap and 5g / L sodium carbonate 90cI = 15min treatment, washing, drying.
2. Identification of direct dyes
The specimen with the addition of lmL of concentrated ammonia solution 5 ~ 10mL for boiling treatment, so that the dye is fully extracted.
After the extraction of the specimen is removed, 10-30mg of white cotton and 5-50mg of sodium chloride into the extraction solution, boiling 40-80s, placed in the cooling water washing. If the white cotton cloth is dyed with the sample almost exactly the same tone, then it can be concluded that the sample dyed with the dye is a direct dye.
3 Identification method of sulfide dyes
100-300mg sample in a 35mL test tube, add 2-3mL water, 1-2mL 10% sodium carbonate solution and 200-400mg sodium sulfide, heating and boiling 1-2min, remove the sample 25-50mg of white cotton and 10-20mg sodium chloride in the test tube. Boil for 1-2min, take out and put on the filter paper to let it re-oxidize. If the resulting color light is similar to the original sample, only different shades, it can be considered to be sulfide or sulfide reduction dyes.
4 Reduction of dyes identification method
100-300mg sample in a 35mL test tube, add 2-3mL water and 0.5-lmL 10% sodium hydroxide solution, heating and boiling, and then add 10-20mg of insurance powder, boiling 0.5-lmin, remove the sample into 25-50mg of white cotton and 0-20mg of sodium chloride, and continue to boil 40-80s, and then cooled to room temperature. Take out the cotton cloth and put it on the filter paper to oxidize. If the oxidized color is almost the same as the original sample, it means that the reduced dye exists.

5 Identification of Naftal dye
Boil the specimen in 100 times the amount of 1% hydrochloric acid solution for 3min, after sufficiently washing with water, boil with 1% ammonia 5-10mL for 2min, if the dye is not extracted or the extraction is very small, and then after treatment with sodium hydroxide a company of sodium bisulfite discoloration or decoloration, even if oxidized in the air can not be restored to the original color, and can not be determined to have the metal is present, at this time, can be carried out in the following 2 of the test, if the test in the If in the test of 1) the dye can be extracted, and in the test of 2) the white cotton cloth is dyed yellow and emits a glittering light, then it can be concluded that the dye used in the specimen is Naftal dye.
1) Place the specimen in a test tube, add 5mL of pyridine and boil to see if the dye is extracted.
2) Put the sample into a test tube, add 2mL of 10% sodium hydroxide solution and 5mL of ethanol, boil and then add 5mL of water and sodium dithionite, boil to reduce. To be cooled and filtered, the white cotton cloth and 20-30mg sodium chloride into the filtrate, and then boiled for 1-2min, placed to cool down and remove the cotton cloth, observe the cotton cloth with ultraviolet radiation whether to emit fluorescence.
6 Identification of reactive dyes
The characteristics of reactive dyes is that it has a relatively stable chemical bond with the fiber, difficult to dissolve in water and solvents. At present, there is no particularly clear test method. Can be first coloring test, respectively, with 1?1 dimethyl methylamine aqueous solution and 100% dimethylformamide on the specimen coloring test, not coloring the dye that is reactive dyes.
7 Methods of identification of paints
Paint, also known as pigment, has no affinity for fiber, through the adhesive (generally resin adhesive) fixed on the fiber. Available microscope method for testing, first remove the sample may exist on the starch or resin finishing agent, so as not to interfere with the identification of dyes. Then add 1 drop of ethyl salicylate in the above treatment on the fiber, cover the cover sheet in the microscope observation. If the surface of the fiber shows granularity, it can be confirmed as a resin-bonded pigment (paint).
8 Identification of phthalocyanine dyes
If a bright green color is produced by dropping concentrated nitric acid on a sample, it is a phthalocyanine dye. If the sample is burned in a flame and turns a bright green color, it can be identified as Phthalocyanine Dye.
Conclusion
The above quick identification method is mainly for the quick identification of the type of dyes on cellulose fibers. Through the above identification steps:
Firstly, it can avoid the blindness caused by the type of dyestuff provided by the person who reports for inspection only, and ensure the accuracy of the inspection and judgment;
Secondly, through this simple method of targeted verification, many unnecessary identification test procedures can be reduced.