How to identify which dye is used on the fabric (yarn)-Vat dye？

1 Sampling and pretreatment

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

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

2) Acrylic resin can be treated with 50-100 times Erke reflow for 2-3h, and then taken out for washing and drying.

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

2.Vat dye identification method

Put 100-300mg sample in a 35mL test tube, add 2-3mL water and 0.5-1mL 10% sodium hydroxide solution, heat and boil, then add 10-20mg sodium hydroxide, boil for 0.5-1min, take out the sample and put it in 25- 50mg white cotton cloth and 0-20mg sodium chloride, continue to boil for 40-80s, and then cool to room temperature. Take out the cotton cloth and put it on the filter paper to oxidize. If the color is similar to the original after oxidation, it means that the vat dye is present.