Yellowing in Carpet

Causes and Cures

One of the big problems that can happen with carpet is that it sometimes develops a yellow cast. The most common causes of this problem are:

Use of a detergent with a pH over 10 on stain-resist nylon carpet:
To cure the yellowing from an overly aggressive detergent, rinse with water to remove the excess detergent, apply Brown Out^® diluted 1 part Brown Out to 2 parts of water (43 ounces per gallon) to the affected areas, allow to work on the yellowing for 15-20 minutes, do a single wet pass with just plain water and 2 dry passes. Since the stain resistance has been destroyed, apply Scotchgard™ Carpet Protector or Teflon^® Advanced to the carpet. However, the stain resistance warranty has still been voided!
Application of silicone protector on stain-resist nylon carpet:
To cure the yellowing from an overly aggressive (pH above 10) detergent, rinse with water to remove the excess.
To cure the yellowing from the use of a silicone protector, remove the silicone by normal cleaning followed by the Brown Out treatment at 1:2 with water as above and apply Teflon. However, in both situations, the warranty has still been voided!

BHT yellowing:
BHT (Butylated Hydroxy Toluene) is a common slowly vaporizing preservative used in many plastics including rebond pad. It is even used as a preservative in bread, because it performs well against free radicals. Most of the problems have been on carpets in areas of low air circulation such as in closets, under low-lying furniture, or under throw rugs.

In this photo supplied to us by Beaulieu of America, you can see that the entire carpet has yellowed except where the tackless strip is - and where there there is no pad (cushion) under the carpet.
However, this problem can occur out in the middle of the room. Sometimes, most of the carpet will have yellowed except along the baseboard or directly above seaming tape.
This problem seems to occur more frequently in the winter in homes using fossil oil or gas heat. Most carpet manufacturers will not accept this as a claim since it is basically a cushion problem.

To cure this problem, most fiber producers recommend a 10% solution of citric acid to remove BHT yellowing, followed by vacuuming. The primary acid in Brown Out is citric. Using Brown Out at 1 part product to 2 parts water will cure this condition. Simply spray the affected area heavily with this solution, allow at least 15 minutes for the yellow to disappear, and do one single wet pass with water (no detergent) and two dry passes. This removes the excess Brown Out but leaves enough behind to reduce the likelihood of the yellow reappearing.

Mill oil (loom oil / yarn lubricant) on olefin or solution dyed nylon:
Mill oil, also called loom oil or yarn lubricant, is the lubricant used in the tufting machines and sometimes gets onto the carpet face during the tufting process. The yellowing is usually in straight lines. Mill oil residue is most common on solution dyed fibers because the step followed in rinsing out dyes is not needed and so the mill oil isn't removed either. To remove mill oil, simply apply TLS^® 2000 as the prespray and use normal cleaning. If this is a residence or other area where children may crawl around on the carpet, do a Brown Out flush by rinsing the carpet with a 2-4 ounce per gallon solution of Brown Out in water with no detergent through the base unit to remove all alkaline residue. Apply ARA to reduce resoiling by absorbing any remaining residue.For more details on mill oil, see "Mill oil" in the Glossary of Terms Section of the "Chemistry of Making and Maintaining Rugs and Carpets" Manual.
Calcium Chloride Ice melt:
Do a Brown Out flush as above. Use long walk-off floor mats to prevent track-in.

Asphalt chemical transfer:
Asphalt coating may be walked onto the carpet (and even onto vinyl tile) from driveways and parking lots and turn the carpet yellow. Since this is being tracked in from the outside, it is most noticeable near the entry areas. This is most common after repaving or sealing the asphalt, especially in the summer with elevated temperatures. Jennite^® J-16 driveway sealer causes less problem than other asphalt coatings.
This is most commonly a problem on blue and light gray carpet.
Yellowing from asphalt track-in is virtually impossible to remove. Asphalt coating and sealers are coal tar based materials, which are yellow when highly diluted in solvent. Unfortunately, the solvents required to totally remove these materials are also strong enough to delaminate the carpet. Whenever a customer asks for your advice on replacing carpet and has a parking lot, advise him or her to avoid blue and light gray
If the problem is fresh, apply TLS 2000 and do your normal cleaning followed with a Brown Out flush at about 2 ounces per gallon. If this fails, prespray Citrus APS™, scrub (if loop pile) and clean. Sometimes, adding Pro’s Choice Energy to your prespray will help. Use very long floor mats (at least 12 feet) to reduce the problem. The problem, however, will not permanently go away.

Optical brighteners:
Optical brighteners are highly specialized dyes which absorb invisible ultraviolet light and re-emit it as visible light, making the carpet appear brighter than it really is. They are used by some carpet cleaning chemical manufacturers who don't realize that their use will permanently cause the carpet to turn yellow. Since these are dyes, there is no cure for this problem. Optical brighteners are frequently found in carpet shampoos and bonnet cleaning compounds. Carpet manufacturers don't approve of carpet cleaning detergents and spotters containing optical brighteners.

Direct sunlight and ozone fading, especially on green carpet:
Yellow is typically the strongest dye in carpets. The loss of other primary colors, red and blue, can leave the carpet with a yellow tint. Yellowing due to direct sunlight fading and ozone fading cannot be reversed except by dyeing.
Pesticide treatment:
Discoloration around baseboards and sliding glass doors that have been treated with organophosphate or chlorinated carbamate for insects. This can also be a red discoloration. This condition is irreversible!
Soil Abrasion:
Heavy traffic coupled with gritty soil can quickly abrade the carpet giving it a yellowed appearance. This is, of course, irreversible, but can be prevented with proper (12-15 foot) entrance mats and proper maintenance.
Urine:
Must be treated for both stain and odor. The Bane-Clene Spotting Guide Manual for Professional Cleaners has complete details on how to handle urine stains. The Pro’s Choice Stain Removal Pet Odor/Stain Removal CD is extremely thorough in how to cure this problem. You will need Stain Magic, Stain Magic for Wool, or Urine Stain Remover.
Bleaching Agents:
Chlorine bleach and acne medicine may strip the blue and red dye from a carpet, leaving the yellow dye.

Nicotine (Tobacco):
Add Chemspec Heavy Duty Soil Lifter to your prespray and wall cleaner to help remove this. Treatment with 40 volume clear hydrogen peroxide is sometimes required.
Other causes of yellowing:
Tracked-in oils, cooking oils, burning of candles and floor finishes