Nylon Fibers and Stains
Nylon accounts for more than 60 percent of total carpet fiber consumption.
Ninety percent of the nylon carpet consumed by the residential sector and nine percent by the commercial sector is treated with a stain resistant finish, according to Sharon Mohney Smith of AlliedSignal business planning and market research.
In a number of marketing studies completed in the early 1980s, the major carpet problems from the point of view of the consumer were durability, soiling, spots and stains.
Durability in nylon carpet is a function of the construction. The soiling was largely overcome by fourth generation carpet fibers and application with fluorochemical treatments. Fluorochemical coating reduces wetting of the carpet surface, minimizing contact between carpet surface and substances that can spot and stain the carpet.
Though many of the stains and spots could be removed by employing appropriate spot and stain removal techniques, the food and drink dye stains were more difficult to solve. Studies showed that the stains which did not respond to these appropriate spot removal techniques consisted mainly of acid type dyes used in foods, cosmetics and drinks.
Nylon fibers offer a combination of desirable properties such as comfort, warmth, ease of manufacture and a broad range of colors, patterns and texture. However, nylon and other similar polyamide fibers and fabrics are stained by certain natural and artificial food colorants; these include coffee, mustard, wine and soft drinks.
While fluorochemical coatings are effective in protecting carpet from substances such as soil, they offer little protection from the types of stains mentioned in the previous paragraph. Acid dyes are bases which bond to the amino sites in the polyamide fiber. A number of methods were developed to make polyamide fibers more resistant to staining by acid dyes.
Acid dyes are called such because the original members of the class were applied in a bath containing mineral or organic acids; also, because they were nearly all sodium salts of organic acids and the colored component was the acid part. These acid dyes have a direct affinity towards protein fibers like wool or silk. Many of these acid dyes will not exhaust on wool or silk unless the dye bath is acidified. Acid-dyeable nylon behaves similar to wool.
When nylon 6 and 6,6 were first produced, both were difficult fibers to dye. Nylon is made dyeable by adding different amounts of additive chemicals called amines (to make it acid dyeable) or carboxyl groups (to make it dyeable with basic dyes).
The level of these additive chemicals in nylon determine if the fiber is light, medium, or deep dyeable. Acid dyes (anionic), with their superior fastness properties, produce the maximum overall quality available. Most of nylon carpet produced is acid dyeable and stains on nylon are due to acid type dyes.
Whereas the addition of amines makes the fiber acid dyeable, it also has the disadvantage of allowing to retain acid dye stains. Nylon 6 has a greater substantivity (affinity) towards dyes than nylon 6,6 and the two should never be mixed together in goods which are destined to be dyed.
Cationic dyeable nylons generally exhibit inherent stain resistant properties, especially to acid-type stains, as compared to other nylon types used for carpet. Cationic dyeable nylons are dyeable with selected cationic dyes, but suffer from poorer lightfastness, especially in light shades, than do comparable shades dyed on acid dyeable nylon.
How effective are these methods to providing stain resistance? All you have to do is read the exclusions in the warranties of stain resistant carpet.
Aziz Ullah, Ph.D., MBA, is president of Fabpro Manufacturing, a leading formulator of carpet and upholstery cleaning products. He is a member of the American Chemical Society, senior member of the American Association of Textile Chemists and Colorists and a member of The Textile Institute (UK). He can be reached at www.Fabpro.com.