linen-pile hand-knotted rug
Cellulosic browning on wall-to-wall carpet is, for all practical purposes, a thing of the past. That’s because most broadloom carpet today is made with all-synthetic materials: synthetic pile yarns, synthetic backing materials, even synthetic latex. The point is that, without any cellulose present, there is no chance of browning forming.
prespraying half w/reducer-shampoo
However, with area rugs, that’s a totally different story.
A tan-to-brown generalized staining on rugs – particularly hand-tufted rugs – can be caused by cellulosic browning. Cellulose is the basic building block of plant life. In rugs, cellulose can be found in pile yarns (e.g., jute, cotton, linen, sisal, coir, abaca), in foundation yarns (typically cotton or jute), in fringe (typically cotton), or in secondary backing fabrics (typically cotton).
In the case of hand-tufted rugs, cotton is used as the base fabric into which pile yarns are hand tufted, and the secondary backing is made of 100% cotton yarns. Even machine-woven 100% olefin pile rugs can exhibit browning if they have cotton warp or jute weft yarns in the foundation.
hot water extraction (acid rinse)
Factors that contribute to cellulosic browning include:
- a cellulosic material – e.g. cotton, jute, etc.
- old or degraded cellulose
- water or overwetting
- alkaline cleaning solutions, especially if hot, and
- prolonged drying
soil and browning removed
Browning arises when a rug’s cellulosic materials become wet during cleaning, or are made wet during unexpected releases of excess water (i.e., water damage). In cellulosic materials, the cells of cellulose are bound by a red-brown sugar-like substance called beta-glucose, or more simply, lignin. Lignin is soluble in water, especially hot alkaline water.
When lignin is dissolved in water, during drying, the water migrates or “wicks” to the surface of pile yarns. There the water changes from a liquid to a vapor during evaporation; however, the lignin, which does not evaporate, remains on yarn tips, eventually causing a tan or brown stain.
Cellulosic browning is corrected by cleaning using a reducing or a mild oxidizing bleach (i.e., hydrogen peroxide but never chlorine bleach, since that removes color and dissolves protein fiber). Reducers are preferred, since they are less apt to remove color and they have no long-term deleterious effect on natural fibers such as wool or cotton (see photos 1-6).
Once removed, browning is prevented from returning by leaving fibers in an acid state (i.e., pH 3-5) during rinsing, which is the normal pH range for processed wool fiber.
When browning occurs on machine-woven rugs with olefin pile, it’s simply a matter of giving the rug a light rinse, followed by forced drying.
Browning correction on cotton fringe (photo 7), which was covered in a previous ICS article, is removed by applying a reducing solution, followed by hot water rinsing using an approved acid rinse (photo 8).
browning corrected w/reducer
To prevent cellulosic browning during future cleaning of any rug, especially hand-tufted rugs, they should be cleaned by an IICRC-Certified and experienced technician. Certified technicians who have achieved the Carpet Cleaning Technician (CCT) and Rug Cleaning Technician (RCT) designations can be located at www.certifiedcleaners.org.