cut & pasted this info on acid dyes;
Acid dyes are negatively charged anionic dyes primarily used on nylon as well as wool and other animal fibers. Seldom used on cotton since this process requires a mordant.
These are also the dyes commonly used to artificially dye drinks, candies, etc., including Kool-Aid®
Acid dye blockers are negatively charged anionic naphthalated phenolic resins that act like colorless dyes and cause nylon fibers to resist most common household food and beverage stains containing acid dyes by occupying remaining dye sites.
Sometimes called stain blockers, acid dye blockers work by blocking the positively charged nylon dye sites, thus preventing (theoretically) staining by acid dyes.
Acid dye resistance is the additional property built into fifth generation nylon fiber.
Note: Nylon stain resist warranties are most often covered under installations in owner-occupied residences.
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Acid dyeable nylon is nylon polymer that has been modified chemically to make the fiber receive acid dyes. Acid dyes are negatively charged (anionic). Dye sites are charged areas on a fiber to which oppositely charged dyes are attracted. For example, cationic (positively charged) dye sites on nylon polymer attract acid dyes that are anionic (negatively charged). With today’s modern light colored carpets, very few of the dye sites are occupied by a dye, leaving plenty of dye sites available to react with Kool-Aid® (a registered trademark of Kraft Foods) and other foods and drinks containing acid dyes.
Acid dye blockers are negatively charged anionic naphthalated phenolic resins that act like colorless dyes and cause nylon fibers to resist most common household food and beverage stains containing acid dyes by occupying remaining dye sites. Sometimes called stain blockers, these work by blocking the positively charged nylon dye sites, thus preventing (theoretically) staining by acid dyes. This is how Stainmaster® works. These are added to the nylon by the fiber producer or by the carpet mill.
In the real world, with traffic, soiling, and cleaning, stain resistance gradually decreases. As a result, it is best to apply fluorochemical carpet protector on stain-resist nylon carpet after every cleaning.
