Various dye identification methods on fabrics

The types of dyes on textiles are difficult to identify with the naked eye and must be determined accurately by chemical methods. This article describes a simple method for identifying dye types on cellulose fibers in textiles.

The principle of determining a simple identification method

According to the dyeing principle of dyes on textiles, common types of dyes for common textile components are as follows:

Acrylic Fiber - Cationic Dyes; Nylon and Protein Fibers - Acid Dyes; Polyesters and Other Chemical Fibers - Disperse Dyes; Cellulose Fibers - Direct, Vulcanizing, Reactive, Reducing, Naftu, Coating Anthraquinone Dyes For blended or interwoven textiles, Dyes are used for their components. For example, for polyester and cotton blends, the disperse dye is used for the polyester component, and the cotton component is used for the corresponding dye type, such as dispersion/activity, dispersion/reduction process, and the like. According to the theory of dyeing, the main factor affecting the color fastness of textiles depends on the type of dye used in cellulose fibers. Therefore, how to determine the dye type of cellulose fibers is the key.

Identification of dye types on cellulose fibers

1. Sampling and pre-processing

The key steps in identifying the types of dyes on cellulose fibers are sampling and sample preparation. When taking a sample, the same dye site should be taken. If the sample contains several shades, each shade should be taken. If fiber identification is required, fiber type should be confirmed according to FZ/TO1057 standard. If the test sample contains impurities, grease, and slurry that affect the test, it must be treated with hot detergent in 60-70°C hot water for 15 minutes, washed, and dried. If the sample is known to be resin-finished, it is treated with the following methods, respectively.

1) Urine formaldehyde resin is treated with 1% hydrochloric acid at 70-80°C for 15 minutes, washed and dried.

2) Acrylic resin The sample can be treated with 50-100 times of the dioxins refluxed for 2-3h, taken out for washing and drying.

3) The silicone resin can be treated with 5g/L soap and 5g/L sodium carbonate 90cI= for 15 minutes, washed and dried.

Direct dye identification method

The sample was boiled with 5-10 ml of an aqueous solution containing 1 ml of concentrated aqueous ammonia to fully extract the dye. The extracted sample was taken out, and 10-30 mg of white cotton cloth and 5-50 mg of sodium chloride were placed in the extract, boiled for 40-80 seconds, and allowed to cool and wash. If the white cotton cloth is dyed to almost the same hue as the sample, it can be concluded that the dye used for dyeing the sample is a direct dye.

Sulfur dye identification method

Put 100-300mg sample in 35ml test tube, add 2-3ml water, 12ml 10% sodium carbonate solution and 200-400mg sodium sulfide, heat boil 1-2min, remove sample 25-50mg white cotton cloth and 10-20mg chlorinated Sodium in test tubes. Boil for 1-2min. Remove and place on filter paper to re-oxidize. If the resulting shades are similar to the original shades, only those with different shades may be considered as vulcanized or thiosulfur dyes.

Identification of vat dyes

Put 100-300mg sample in 35ml test tube, add 2-3ml water and 0.5-1ml 10% sodium hydroxide solution, heat and boil, then add 10-20mg of insurance powder, boil 0.5-1min, remove the sample and put it into 25- 50 mg white cotton cloth and 10-20 mg sodium chloride continue to boil for 40-80 s and then cooled to room temperature. Remove the cotton cloth and oxidize it on the filter paper. If the color after oxidation is the same as the original, it means that the vat dye exists.

Nafto dye identification method

In 100 times the amount of 1% hydrochloric acid solution, the sample was boiled for 3 min, fully washed, and boiled for 2 min with 1% ammonia water 5-10 ml. If the dye was not extracted or the extraction amount was small, then sodium hydroxide-sodium dithionite treatment was performed. After discoloration or decolorization, even if it is oxidized in air, it cannot be restored to its original color, and it cannot be determined that metal is present. In this case, the following tests of 2.5.1 and 2.5.2 can be performed. If the test is performed in 2.5.1, it can be extracted. Dyestuffs, and in the 2.5.2 test, the white cotton cloth dyed yellow, and emit fluorescent light, you can conclude that the dye used for the sample is nalford dye.

1) Put the sample in a test tube, add 5 ml pyridine and boil, and observe if the dye is extracted;

2) Put the sample in a test tube, add 2ml of 10% sodium hydroxide solution and 5ml of ethanol, boil it, add 5ml of water and sodium dithionite, and boil it to reduce it. After cooling, the white cotton cloth and 20-30 mg of sodium chloride were added to the filtrate, and the mixture was boiled for 1-2 min. After cooling, the cotton cloth was taken out to observe whether the cotton cloth emitted fluorescence when irradiated with ultraviolet rays.

Identification of reactive dyes

The characteristic of the reactive dye is that it has a relatively stable chemical bond with the fiber and is difficult to dissolve in water and solvents. At present, there is no specific test method. Coloring tests can be carried out first, respectively, with a 1:1 aqueous solution of dimethylformamide and 100% dimethylformamide to perform coloring tests on the samples. The non-staining dyes are reactive dyes.

Paint identification method

Coatings, also known as pigments, have no affinity for fibers and need to be anchored to the fibers by a binder, typically a resin binder. Microscopy can be used to test the removal of starch or resin finishes that may be present on the sample to avoid interference with dye identification. An additional drop of ethyl salicylate was added to the fibers treated above and the coverslipping was observed under a microscope. If the surface of the fiber is in the form of particles, it can be confirmed as a resin-bonded pigment (coating material).

Anthraquinone dye identification method

After the concentration of nitric acid drops on the sample, a bright green vat dye is produced. In addition, it can also prove to be an anthraquinone dye by burning the sample in the flame to be obviously green.

in conclusion

The above rapid identification method is mainly for the rapid identification of dye types on cellulose fibers. Through the above identification steps, one can avoid the blindness caused by the type of dye provided by the person who submits the inspection, and ensure the accuracy of the inspection and determination. Second, by using this simple method of targeted verification, many unnecessary identifications can be reduced. Test procedure.