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Yellowing by CR MITCHELL

Following is a lengthy article written by CR Mitchell, (Carrie?) on yellowing.

By C.R. Mitchell
Shaw Industries

(--Used with permission)

This article clarifies the issue of BHT yellowing of carpet, as the issue has mushroomed out of proportion in recent
months. Several years ago some carpet manufacturers sent out letters indicating that claims would not be paid where
BHT originating from the pad caused yellowing of the carpet.

In the early 1990's carpet manufacturers began seeing an increase in the number of complaints of carpets turning yellow.
While these new complaints occur in a wide variety of circumstances, some common factors have been identified. The
most common factor is that the carpets are usually installed over rebonded polyurethane cushion. This type cushion now
comprises about 75 percent of the market. A few instances have occurred where prime urethane cushions have been

Testing the urethane cushion under the carpet usually shows significant levels of a chemical called butylated
hydroxytoluene (BHT). This chemical is used as an antioxidant (preservative) in processed foods, the production of
polyurethane foam, many plastics, etc. It is capable of vaporizing and migrating up through the carpet and depositing on
the pile. Under some conditions, BHT reacts with atmospheric contaminants to form bright yellow derivatives which bond
to the fiber. Testing of the yellowed carpets shows the presence of two of the breakdown products of BHT.

The carpets involved are almost invariably light colors. Obviously, any discoloration is more visible on light colors.
Lighter colors have predominated in the marketplace during the past decade, hence the opportunity for occurrence is
greater. All synthetic fibers, polypropylene, polyester and nylon carpets are affected; Shaw has not seen the phenomenon
on wool carpet.

Several cushion manufacturers have published information suggesting that carpet mills' position and letters are not
accurate or are misleading. Most claim that the majority of yellowing complaints are due to causes other than BHT and
cite many other causes of discoloration. While many of the items mentioned do indeed discolor carpet, few cause
yellowing. None cause the distinctive lemon yellow that is peculiar to BHT yellowing. Most other materials that cause
yellowing result in dull or brownish yellows, very different from BHT. The characteristics of these other types of
discoloration are described at the end of this article. BHT and its two breakdown products can be positively identified in
the laboratory, although few carpet manufacturers have the capability for such chemical analysis.

Reviewing the chemistry, BHT is an antioxidant, or preservative, used in a wide variety of foods, plastics, etc. The
production of slab urethane foam generates high temperatures and BHT is added to prevent scorching and possible fires.
Even though BHT is a solid material, it slowly vaporizes form the cushion and can migrate up through the carpet and
deposit on the pile fiber. In rare cases, it reacts with atmospheric contaminants such as those created by the burning of
fossil fuels to form two breakdown products. Unfortunately these byproducts happen to be intensely lemon yellow even in
very small amounts - they are visible on white fiber at the single digit parts-per-million range.

BHT yellowing appears in several scenarios. First, is in the form of bright yellow splotches which may be more intense
near the backing and less intense near the surface of the pile. Second, is overall yellowing where large areas are
involved. Third is where yellowing occurs under furniture or area rugs in geometric shapes. Often, straight lines of
non-yellowed carpet are found along a wall over the tack strip or along seams where seaming tape prevents migration of
BHT through the carpet backing. While the intensity of the yellow color may vary from faint to very bright, the color is
always a pure lemon yellow - this is distinctive of BHTs breakdown products.

Most rebonded polyurethane cushion contains some BHT, as well as many prime cushions, and together these types
comprise about 90 percent of the market. Despite this fact, BHT yellowing is still very rare. Statistics indicate that less
than one claim in a thousand involved yellowing of any kind.

A very special combination of atmospheric contaminants, moisture, light and other conditions must come together for
this phenomenon to occur. Most complaints occur where the heating seasons are long and atmospheric contaminants
from fossil fuels are present. Carpet cleaners are often blamed for causing yellowing. In BHT yellowing cases the
cleaning process only triggers or accelerates the color change. The cleaning provides the moisture and raises the pH of
the fiber.

Determining conclusively whether BHT is involved requires sophisticated lab equipment and procedures. Historically,
analysis has usually been by a technique called gas chromatography/mass spectroscopy (GC/MS). While normally
considered reliable, in the case of analysis of BHT-related yellowing its results are often misinterpreted. BHT is
semi-volatile, meaning it vaporizes very, very slowly at room temperature. The GC/MS technique involves heating the
carpet or pad sample in a small closed chamber, collecting whatever vaporized material comes off, and passing it
through a separatory column. The separated chemicals are then identified by the mass spectrometer. GC/MS can identify
the colorless BHT easily and reliably.

Not generally recognized is the fact that the yellow material is not BHT, but the derivatives left when BHT oxidizes. Two
compounds, diphenquinone and bis-phenozyquinone are the most common. Both compounds are intensely yellow at
very low concentrations. They cannot be analyzed by GS/MS techniques because they are not readily volatile. They
must be extracted off the fiber using a suitable solvent and the solvent containing the derivatives analyzed. Analysis by
liquid chromatography, HPLC, which, as the name implies does the separation in the liquid state, is the preferred

When yellowed fibers are analyzed by CG/MS, a negative result for BHT is often misinterpreted to mean that BHT was not
involved. The fact is that there is no BHT present on the carpet fiber because it has all reacted into the quinone
derivatives, which cannot be found by this method. Since most labs do the analysis by GC/MS because it is fast and
usually accurate, much erroneous data has been developed. Unlike the GC/MS, the HPLC detects both BHT and the

Even more confusion has been caused by the belief that treatment with citric acid always reverses the yellowing, and is
therefore a conclusive test for BHT. This is not true.. While acid treatment does reverse the yellowing in many cases, it is
not universal and is absolutely unreliable as a test for BHT, as it may also reverse other types of yellowing. Further, it may
not reverse BHT yellowing that has existed for some time. Some say that the chemical reaction can only proceed at high
pH levels (highly alkaline). The fact is that it can occur at the neutral point, although more slowly. While treatment with a
mild acid often removes the yellowing by converting the yellow byproducts to colorless compounds - this may not be
permanent and the yellow color may return, especially if a volatile acid such as acetic (vinegar) is used.

Some of the information being circulated indicates that BHT yellowing can only be reproduced in the lab at
unrealistically high concentrations. The polyurethane foam industry tried without success for several years to cause
yellowing in the lab at concentrations commonly found in complaints. Shaw Industries has succeeded in reproducing it
at concentrations similar to those commonly found in complaints. That lab technique was shared with the Carpet Cushion
Council and the Polyurethane Foam Association at their Technical Conference in 1997.

The whole issue of BHT yellowing has mushroomed somewhat out of proportion for several reasons:

First, some carpet manufacturers issued disclaimers for this phenomenon several years ago. Others have taken a
case-by-case approach without issue of a disclaimer. Most mills have decided that BHT yellowing is not the fault of the
carpet and the focus has shifted to the cushion manufacturers, who are now faced with claims for carpet which are for
more costly per square yard than cushion. Despite claims that most yellowing complaints do not involve cushion, a recent
Floor Covering Weekly article quoted the Director of the Carpet Cushion Council "....combine the increased use of
bonded or prime urethane foam with the increasing consumer preference for light colored carpets and the result is more
complaints." Several cushion manufacturers have recently announced that they now offer BHT-free prime urethane

Second, much confusion exists in this situation. There have been allegations that carpet raw materials, particularly
polypropylene fibers and backings, contain BHT for various reasons, including to prevent yellowing! The truth is that BHT
is not used in the production of these materials. The use of acid treatment as a "test" for BHT has added to the confusion;
this is not a reliable test. It gives a "maybe" at best.

Third, some carpet manufacturers have tried to capitalize on the situation. One has offered to pay BHT yellowing claims -
in the gulf coast area. This is a very safe offer since very, very few complaints occur here; most occur in the snow belt
where heating seasons are long.

Although these claims have indeed increased in recent years with the increasing market share of rebonded urethane
cushions, the total number of complaints remains very small, but the issue has become highly visible. Carpet mills should
continue to address yellowing claims on a case by case basis, and those found to be the result of causes other than BHT
should be handled appropriately. Where BHT and/or its breakdown products are present, the complaints should be
referred to the cushion manufacturer.

Various types of discoloration

Information has been circulated suggesting that a number of conditions listed below cause yellowing similar to BHT.
Some clarification is in order. In considering yellow discoloration on site, the first step is to decide whether the yellowing
represents a gain in color or a loss of color.

Ozone fade - ozone fade is rare in moist areas of the country today, occurring typically where humidity is high for most of
the year; i.e., coastal areas and Hawaii. Ozone preferentially destroys blue dyes first. With most carpet colors, this leaves
the yellow and red components intact and the carpet turns a dull orange, not yellow. Further, this is a loss rather than a
gain of color.

Oxides of nitrogen yellowing - This rare phenomenon occurs in the manufacturing plant, when undyed nylon is stored
for long periods in areas where air circulation is poor. If oxides of nitrogen are present from gas-fired process equipment or
gas-powered lift trucks, yellowing may occur. Dye sites are blocked and the affected areas of the carpet cannot be dyed.
This yellowing occurs in the mill, not in the consumer's home, and carpet manufacturers took steps to eliminate stale air
years ago.

Formaldehyde - Some discoloration under furniture was traced to formaldehyde emissions from particle board subfloors
and furniture during the 1970s. This caused the yellow to turn dark green, not yellow. Since formaldehyde emissions were
brought under control by environmental regulations many years ago, this has not been seen in more than two decades.

Asphalt sealers - These contaminants are very dull brownish yellow in color and are found in areas where foot traffic
enters directly from newly paved or sealed asphalt parking lots. The discoloration is most visible in the traffic lanes near
the door and is less noticeable farther into the building. This occurs primarily in commercial situations while BHT
yellowing typically occurs in residential uses.

Calcium chloride - this material is used to melt snow and ice and is tracked onto carpet in the winter. It is a dirty white,
not yellow in color, and is removed with water. Over time this area will attract soil and the color can turn from white to
dingy yellow to brown to black.

Excessive stain blocker application - The phenolic stain blockers used in the early days of stain resist treatments (ca.
1987-89) did turn yellow under some circumstances. This was a very dull, brownish yellow, very different from the lemon
yellow caused by BHT. Today's stain blockers are chemically different and do not turn yellow.

"Optical brightner" carpet dyes - Optical brighteners are not carpet dyes as alleged, but are sometimes used in cleaning
agents. They sometimes turn yellow. Shaw Industries' maintenance literature has specifically recommended against their
use for years, not because of yellowing but because of their tendency to mask the carpet color resulting in a chalky

Oxidation of fiber spin finish - While some spin finishes used in years past have been demonstrated to turn a very faint,
dull or dingy yellow, carpet manufacturers routinely screen their finishes to insure that these are not used. This has
become even more important over the past decade due to the move toward light colors. This particular yellow color did
not resemble BHT yellowing at all and is easily distinguished; it does not respond to acid treatments.

Pesticides - In the early 1980s, two new dyestuffs were introduced to the carpet industry. It was soon learned that these
were susceptible to discoloration by organophosphate pesticides. In this case, the carpet turned green, not yellow. These
dyes were withdrawn from the market within a year of the discovery.

Silicone-based carpet protectors - some of these products were used in a base of crude mineral spirits in the early
1980s. The mineral spirits residues sometimes turned dull yellow. After a number of fires and instances of carpet
delaminating, the use of mineral spirits was discontinued. No carpet manufacturer recommends these products and most
warranties are voided if silicones are used.

Soil abrasion of fiber - In heavy commercial traffic areas with sandy soil, the surface of the fiber gets scratches, which
caused the fiber's luster to become dull, but no change in color occurs.

Urine - obviously, urine can result in yellow spots. Again, distinguishing from BHT yellowing is easy. Urine fluoresces a
yellow-green under UV light (black light) and the odor is a dead giveaway. The yellow is very dull, not lemon yellow as in
BHT spots.