How to identify which dye is used on the fabric (yarn)-Direct 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.Direct dye identification method

The sample is boiled with 5-10 mL of an aqueous solution containing 1 mL of concentrated ammonia water to fully extract the dye.

Take out the sample after extraction treatment, put 10-30mg of white cotton cloth and 5-50mg of sodium chloride into the extract, boil for 40-80s, place to cool and wash with water. If the white cotton cloth is dyed almost exactly the same hue as the sample, it can be concluded that the dye used for dyeing the sample is a direct dye.