Carpet yellowing may occur under a given set of circumstances. The causes for this problem are many and it is therefore a very complex and confusing problem for the professional carpet cleaner confronted with it. Determining the cause of this problem can prove to be extremely difficult.
Carpet yellowing may have the following causes:
1. BHT (butylated hydroxytoluene) - a non-toxic, odourless preservative which is used in foods such as cereal, bread, and candies, and in articles such as plastics, shoe soles, and some carpets and carpet cushioning (latex foam, eg.). 2. Nitrogen dioxide - some heating fuels that are used in heaters at home or in the office set nitrogen dioxide free during combustion. In areas where the air flow or circulation is restricted or not present, this may lead to a build-up of this substance which may result in a chemical reaction with coatings (stain protector, for example) or preservatives, that are contained in the carpet. This reaction causes the carpet yellowing.
3. Heaters - in some homes heating is also achieved using fireplaces or ovens. If these are not ventilated well enough, this can also lead to a buildup of nitrogen dioxide which may result, as described in 2., in carpet yellowing.
4. Incorrect cleaning - if the carpet has been cleaned with strongly alkaline cleaner, it should be neutralized with water or a mildly acidic rinse in order to adjust the pH back to neutral. An alkaline residual pH in the carpet makes the carpet more susceptible to yellowing.
Other possible causes for carpet yellowing are: bleaching through light, incorrectly applied stain protectors, too much optical brightener (CEBE does not use these in any of their products), oily dirt, cellulose-caused browning, powder cleaners, pesticides and harsh, abrasive soil.
On the basis of the above mentioned causes, answers to the following questions may help find the actual cause of the carpet yellowing:
1. How good is the air circulation in the rooms or areas affected? Insufficient air circulation may lead to a buildup of nitrogen dioxide (see above).
2. Is there suffcient sunlight in the affected areas? Even though sunlight can have a bleaching effect on natural fibres, sunlight has the advantage that it results in a warming up of the air, leading to convective currents (from warm to cold), that is air movement, which prevents nitrogen dioxide buildup. In addition the UV light contained in sunlight prevents yellowing.
3. Are areas under furniture affected? If this is the case, the cause is insufficient air circulation or sunlight or both.
4. Is the yellowing restricted to traffic lanes? If so, this hints at oily dirt, caused by the soil carried in from garages, parking lots or similar sites, that build up with time. Similarly the yellowing may be caused by disinfectant or chlorine-based products, which are carried onto the carpet should the carpet be near toilets, changing rooms, swimming pools etc.
5. Have pesticides been used lately? Pesticides may also be carried in through traffic. The colouring may be affected over time which may result in a yellowish tint in the carpet.
6. Has the carpet been cleaned recently? If so, who cleaned the carpet (concerning the qualifications of the cleaner) and with which products did the cleaner clean the carpet ? If the products were alkaline, was the carpet neutralized afterwards ? If this was not the case, the alkalinity may have caused the yellowing.
7. Are there recognizable patterns in the yellowed areas? If the yellowing is restricted to traffic areas, search for causes that are not related to the carpet. If the entire surface is affected, it may have to do with the cleaning method.
The question that arises after the search for a cause has been completed is: can this yellowing be removed?
The answer is: not always.
How can one determine whether or not they can be removed?
For this purpose you need the CEBE product Acidic Prespray. This product is applied onto a clean white cloth and applied onto an affected area. Should the yellowing be reduced or removed entirely, the following possibilities, which should be explored in their order, exist:
1. Increase the amount of light or sunlight.
2. Increase the air circulation and exchange.
3. Apply the Acidic Prespray undiluted using the extraction method. Afterwards rinse the carpet with a 1:20 solution of Tapi Soft in order to minimize resoiling.