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True browning (sometimes confused with wicking or yellowing) only occurs when cellulosic fibers are present. Cellulosic fibers come from plant material and include cotton, jute, and rayon. Browning occurs on the tips of carpet tufts or on upholstery fabric. This will be more noticeable on light colored fabrics.
Browning is the oxidation of a sugar called lignin. This dissolves in water or cleaning solutions and wicks to the surface during drying. Alkalinity will greatly accelerate cellulosic browning. Over-wetting, slow drying and the age of the fabric also increase the likelihood and severity of browning.
Be aware of the fiber(s) you are dealing with. Jute backed carpets make up only a small percentage of the carpets you will clean. Woven carpet and area rugs are likely to have cotton foundation yarns. Cellulosic fibers are more common in upholstery fabrics.
If uncertain of the fiber content, do a burn test (this is covered in another Technical Bulletin).
Use a neutral or acid side cleaner if it will provide sufficient cleaning ability. For example, use Avenge Fabric Pre-spray, Haitian Powder, or Haitian Shampoo for upholstery. Rinse with Avenge Clean Rinse. If you use an alkaline cleaning agent, neutralize by rinsing with an acid side product such as Fab-Set.
This Quick Guide highlights preventing browning when cleaning natural upholstery fabrics. The detailed methods covered in this Technical Bulletin apply to both carpet and upholstery.
Spray a mist of Fab-Set over the entire area. Wet only the surface. Do not saturate. Allow a few minutes dwell time.
Go over the surface with a Micro Fiber or Cotton Bonnet dampened with Fab-Set. Use a rotary machine on carpet. There are powered tools for bonnet cleaning on upholstery or this step can be done by hand with white cotton terry cloth. The idea is to clean the browning off the surface without rewetting the entire fiber and allowing browning to recur.
In severe cases of browning it may be necessary to lightly re-clean the entire area in order to loosen the oxidized sugars. Then follow the correction steps listed above. Remember, moisture and alkalinity caused this problem. Use a neutral cleaner and be careful to control the moisture.
Using the prevention methods above for all of your cleaning situations will greatly reduce your callbacks. These methods help prevent browning, yellowing, soil wicking, bleeding, etc., in addition to preparing the carpet for Bridgepoint's Maxim Protector.
Older cellulosic fibers (cotton, jute) will pose the highest risk and correction will be the most time consuming. Be sure to identify cellulosic fibers before you start. It is always easier and less costly to prevent problems before they occur.
Recent advances in encapsulation chemistry are showing promise in helping to control and correct cellulosic browning.
Encapsulation cleaning using Encapuclean or Encapuclean with Maxim uses limited moisture and a neutral pH and thus is less likely to trigger browning. Try encapsulation on a carpet that has potential to brown.
If you decide to clean using hot water extraction, a post cleaning spray application of Encapuguard resists wicking of lignin to the surface.
Encapuguard can also be used as a corrective measure. Apply a light mist after Step 2 above (or in mild cases instead of Step 2) prevents additional wicking and browning.