Cleaning & Restoration Association News

Cellulosic Browning Causes & Solutions

All is not lost when browning occurs on newly cleaned carpet or upholstery. Along with additional dry passes, air movers, and of course prevention, tackle a common problem with uncomplicated solutions...

One of the main topics that I remember from my first carpet cleaning training course, from Ed York in May, 1973 Cellulosic Browning. This problem is caused by a naturally occurring gum called lignin, which is present in cellulosic fibers such as jute, linen, or cotton, being dissolved by an extended exposure to water and then making its way to the surface of the fiber/fabric. This results in a reddish-brownish discoloration of the fiber/fabric in these areas. The problem will be more severe if there are alkaline agents, such as pre-conditioners, present.

Three factors must be present for cellulosic browning to occur: 1) A cellulosic fiber must be present; 2) It must be overwet; 3) It must dry slowly. If the moisture that is present is alkaline in nature, then the resulting discolorations will be more severe. The best cure for cellulosic browning is prevention, followed by: removing as much of the moisture involved in your cleaning/restoration process as possible; Vacuum, vacuum and vacuum; and then get air flowing over the damp surface. If browning still occurs, it may be correctable with a formulated browning corrector product. Follow label directions carefully. A browning corrector need be nothing more than an acid solution; sometimes it may also have an oxidizing agent to correct brown discoloring. A browning corrector doesn’t need optical brighteners. These optical brighteners don’t remove color but will alter light reflection from the fibers so they appear to be bleached—a situation which cannot be corrected and may cause problems with the carpet owners. A browning prevention treatment, sometimes called a “soure,” may prevent the problem from occurring. However, using a preventer will also add more water to the problem and may make it worse. Keep in mind that the water/carpet does not have to be in alkaline condition for browning to occur; it only needs to be wet.

The physical action, which causes browning, is called wicking and occurs from capillary action within the yarn bundles/tufts. This wicking action is actually what causes the carpet to dry. Moisture wicking to the surface will evaporate, resulting in drying of the carpet. The wicking action will also carry to the surface any solid materials present in the carpet, such as soils or residues. A problem similar to cellulosic browning is soil wicking. Some refer to this problem as browning. But since considerably less than 1% of carpets made today have any jute or cotton content, usually there is no cellulosic fiber present and the problem is really soil wicking. These are both examples of problems caused by the wicking action of the drying process.

Many times, browning is exactly what the name implies. Loose, dark particle soil is present at the base of the fibers. This will be true to some extent of all carpets, worse in others where soil control is not practiced. The problem will be compounded if the fiber is non-absorbent, such as a polypropylene. You’ve heard this before. After the carpet dries the customer calls and says, “The carpet is dirtier now than it was before you cleaned it!” What happened? All that dirt down at the base of the fibers (where it’s invisible) has moved up the fiber as a result of the wicking action of drying. Now it’s all up on top of the carpet and quite visible. What to do? Go back with a bonnet system or do a quick rinse with an extractor.

How do you prevent this problem? Recommend that the carpet owner arrange to have the carpet thoroughly vacuumed on a daily basis. This may prevent the soil load from building to the point that it can’t be controlled during drying. In a commercial situation, pile lift the carpet every 30 days. This will help minimize the amount of particle soil that must be dealt with. Thorough vacuuming immediately before extraction cleaning will remove much of the built-up particle soil since the last cleaning, will open the pile and fluff the yarns so that they will be penetrated more effectively by the preconditioning agents. This will allow the detergents to work more quickly on the soils adhered to the fibers. It will also help if you ensure that the extraction process is performed properly and that the moisture used for soil removal is thoroughly removed. A couple of extra dry vacuuming passes will allow the carpet to dry quickly so wicking will be minimized. When necessary, utilize drying fans and auxiliary dehumidifiers to speed the drying process. In some extreme cases, the answer may be to use a “minimal moisture” process even though the carpet owner really wants or needs a wet extraction cleaning for the carpet. Use of an acid rinse may also help prevent the problem if it contains a weak bleaching material such as sodium bisulfite, which may lighten the color of the wicked materials.

If you’d like to see wicking take place, roll a table napkin into a cylinder and place it into a small amount of water or other liquid, such as coffee, and then watch the liquid move up into the napkin. It will move up until the napkin is saturated or until all of the liquid has moved into the napkin.

In a nutshell: to prevent browning or wicking, get the carpet clean and get it dry. Extra dry vacuum passes and airflow will help. Until next month, Seeya!

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