Name: Amy

Thank you in advance for your help. Your response is very much appreciated.


What kind of tie-dye kit did she use? The dyes found in the Jacquard tie dye kit are all fiber reactive dyes of the Procion MX type: reactive yellow 86, reactive red 11 (fuchsia), and reactive blue 140 (turquoise). Most tie dye kits are the same. The Rit tie dye kit and the Magic Strings tie dye kit both use a completely different kind of dye, so it matters a great deal what brand of tie dye kit she used, as the explanation will be a little different.

Cotton is made of cellulose (the main structural material made by plants). This is a key point. You can find a picture showing the chemical structure of cellulose. Fiber reactive dyes can form a bond directly to the cellulose molecule, but they cannot react with polyester at all, because it does not have the right chemical structure. Polyester is made from petroleum products, but not in a way that mimics the structure of cellulose, except that they are both long polymers. (All textile fibers consist of very long chains molecules, which are twisted together to make yarns for weaving or knitting.)

Look at this page: "I'm wondering if you could explain the chemistry behind why cotton can't be dyed at an acidic pH". On it I show a picture of cellulose, and a picture of the chemical reaction between a typical fiber reactive dye and the cellulose. Your daughter may print out, cut out, and use the pictures from that page, as long as she gives credit as to where she found the pictures. Make sure she includes a bibliography at the end that lists where she found information. (There is a creation date at the bottom of each of my web pages.)

You can find a picture of the chemical structure of a polyester fiber by doing a web search. You can see that the polyester molecule does not contain the same chemical structure as the cellulose molecule. It lacks the -O-H group that is the site of the reaction of the fiber reactive dye with the fiber.

Also see "About Different Types of Dyes", and "About Fiber Reactive Dyes", and "Dyeing Polyester with Disperse Dyes". There are chemical structures of many Procion MX type fiber reactive dyes on this page: What is the chemical structure of Procion MX dye?

Polyester can be dyed only with disperse dyes, not with any other type of dye. It can't be dyed with fiber reactive dyes because it lacks the site that reacts with the dye. Polyester also can't be dyed with direct dyes, such as the cotton dyes in Rit dye, because the long molecules of direct dye do not fit inside the polyester fiber the way they do inside the cellulose fiber. That is harder to picture and harder to understand, though. Rit dye does not react with cellulose, it just associates with it loosely, which is why it fades so much more quickly than a good tie-dye kit does, and bleeds so badly in the laundry. If your daughter used Rit dye she should not talk about fiber reactive dye, but instead about all-purpose and direct dye.

(Please help support this web site. Thank you.)