Nylon is the most popular yarn used in carpet and since its introduction in the 1950s, it has undergone improvements called "Generations." In 1988, the "Fifth Generation" was launched that contained a chemical coating called an "Acid Dye Blocker" which made the nylon stain resistant. Fifth Generation Nylon has had an ongoing problems with its Acid Dye Blockers reacting with certain types of chemicals and turning to a yellow darker than the surrounding carpet.
Among the chemicals that turned Fifth Generation nylon yellow are:
 | Alkalizes. A rule was developed in cooperation with the trade organizations and fiber producers that said that the pH of any cleaning product should not be over 10 when used on Fifth Generation Nylon. In some cases, yellowing can occur under a pH of ten making the carpet producer responsible. The pH rule is not clear as to whether its the pH of the concentrate or the ‘ready to use’, RTU, that is to be applicable. Most of the manufacturers of professional cleaning products take a ready to use interpretation of the rule. However, repeated use of diluted product will result in an accumulation of alkaline salts that will lead to yellow spots. The picture below is a classic example of this type of yellowing. |
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| BHT or Butyl Hydroxyl Toluene. This is a solvent used in some carpet cushions. Rebond contains materials that could contain BHT are mixed in with urethane. When this type of yellowing occurs, there are straight lines above the seaming tape that do not turn yellow, see picture below. Picture compliments of Tony Wheelwright of CLEAN & TIDY LTD - carpet-p.i@home.com |
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