Fluoropolymer repellents differ from silicone- or hydrocarbon-based repellents in several aspects, of which oil repellency is the most important.

Fluoropolymers repel both water and oil, whereas repellents with silicone or hydrocarbons repel only water.

Soil repelling requires low surface-energy, as opposed to high surface-energy required for wetting.

The ability of fluoropolymers is related to their low cohesive force (non-stick) and low surface-energy barrier against wetting.

Fluoropolymers for carpet are designed more for soil resistance than for water or oil resistance.

However, products intended for upholstery are formulated for more oil and water repellency.

Chemistry of fluoropolymers
All fluoropolymer protector molecules consist of two parts, the fluorinated parts and the non-fluorinated parts.

The literature on fluoropolymer repellents is very extensive, but most of it deals with the non-fluorinated part.

The fluorinated part called the perfluoroalkyl group is common to all fluoropolymer protectors.

The fluorinated part consist of carbon atoms linked to other carbon atoms forming the core, and attached to and surrounding each carbon atom are fluorine atoms forming a sheath.

These fluorine atoms act like little umbrellas in a rain shower.

Research studies in fluorochemistry have shown, the more fluorine atoms attach to the carbon atoms and the more closely packed they are, the better the repellency.

It has been determined that the optimal number of the linking carbon atoms should be between 10 and 12; also, the linked carbon atoms should be linear rather than branched to get better performance.

There are very few practical methods to make the fluorinated part.

Among the two known methods, 3M employs an electrochemical fluorination method and DuPont uses what is called telomerization to make the fluoropolymer part.

The fluoropolymer part produced by either method is chemically attached with a non-fluorinated part which can be acrylic, vinyl or urethane.

The non-fluorinated part, in addition to being an extender by lowering the cost of the fluoropolymer, serves two other useful purposes: It forms a backbone to the fluoropolymer, making it more durable, and acts as the glue to bond the fluoropolymer part to the fiber.

How fluoropolymers work
Fluoropolymer protectors improve stain and soil resistance by lowering the surface energy of the fabric. They create a barrier.

The fabrics are more difficult to wet; hence, liquid stains will not spread or wick over large areas.

Dry soils will not adhere as strongly.

Keep in mind that fluoropolymers or any other non-film-forming material cannot make a typically porous fabric completely impervious to oily stains.

As long as capillary (wicking) action is the only driving force, the barriers resulting from the fluoropolymer prevent both penetration into the fabric and wicking over a large area.

Stains held on the surface of a fabric are readily removed by blotting.

If the spill or stain is being forced into the fabric and is water-based, it will usually be held out from significant penetration, but if the stain consists of certain oils, they may penetrate between yarns as their surface tension is too low and will overcome the fluoropolymer barrier.

However, even when oily stains are forced into fabrics, the fluoropolymer will help prevent wicking.

In addition, the fluoropolymer enhances stain release during spot cleaning and soil removal by diffusion of water and detergent into the soil-water interface, decreasing the adhesion of soils to the fibers, and reducing soil re-deposition during cleaning.

Affecting factors
First and probably most important to the factors essential to obtaining a satisfactory protection from a fluoropolymer is the concentration of the fluoropolymer applied to the fabric.

As a general rule, sufficient fluoropolymer should be applied to cover 50 to 70 percent of the surface.

Usually, 0.1 to 0.4 weight percent fluoropolymer solids (200 to 800 ppm fluorine based on the fiber weight) on the fabric will be enough to provide this coverage and give good repellencies and stain and soil resistance on the majority of carpet and upholstery fabrics.

Most fluoropolymers are sold as aqueous dispersions or emulsions and the percent active ingredient varies significantly between manufacturers.

It is important to follow the manufacturer’s recommended application levels.

Within these limits, the higher the product load, the better the end-use performance.

The water-based emulsions or dispersions can be cationic, non-ionic or anionic in nature.

Just prior to introduction of stain-resist-type nylon fibers, DuPont switched from a cationic water-based fluoropolymer dispersion to an anionic type, making it compatible with stain-resist-type fibers.

Use of cationic fluoropolymer protectors will void warranties on stain-resist-type carpet. For this reason and incompatibility among different protectors, they should not be mixed.

The geometry of the fabric surface is also an important consideration. Rough or smooth, flat or pile will have an influence on the ultimate uniformity of the fluoropolymer film.

Normally, the flatter and smoother a surface is, the easier it is to treat.

Treated level-loop carpet is expected to be somewhat more soil-repellent than cut pile carpet. Fabric preparation can be critical in obtaining good results from the fluorochemical polymer.

For optimum repellency and most efficient use of the fluoropolymer, the fabric should be as clean as possible.

Many auxiliaries used in carpet manufacture such as surface or yarn lubricants, dyeing assistants, softeners, or surface active agents can adversely affect repellency.

Application principles
Fluoropolymers can be applied three ways: By pad, spray or foam; most upholstery fabrics are treated by spray or foam.

Certain fabrics cannot be treated effectively, such as high-pile knit fabrics where application by pad, spray or foam gives significant fabric distortion and poor end- use performance.

Additives used with the fluoropolymer must also be chosen carefully for compatibility and effect on end results.

Softeners, lubricants and wax-type repellents can have a significant adverse effect on both repellency and dry soil resistance.

Literature on fluoropolymers points out that the fluoropolymers leave a hard durable film, so that it resists deformation when soil presses against it.

Most of the fluoropolymer treatments on the carpet are water-based and the fluoropolymer is water-insoluble to provide durability against cleaning.

To make it practical to apply, it is emulsified with various surfactants.

Fluoropolymers are also available in solvent bases, but are not the preferred method for treatments as the solvents can pose environmental and health hazards.

After-market fluoropolymer protectors sold as solvent-soluble will show better oil and water repellency compared to the water-dispersible type, but will not be as durable when used on carpet and will not have the same level of dry soil resistance.

It is also important that the fluoropolymer tails be properly oriented outward to produce a low surface-energy barrier.

In the mills, this is achieved by heating to 275 degrees Fahrenheit, which is the common cure temperature for latex backing.

Since the dry/cure temperatures are not feasible after application of market protectors, mill-applied protectors will show better soil protection than after market protectors.

Fluorochemical protectors applied at proper level and procedures to ensure adequate coverage can impart resistance to dry soiling and staining by water-based and oil-based substances to a wide range of textile materials, and these benefits are readily recognized by the consumer.

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Aziz Ullah, Ph.D., MBA, is president of Fabpro Manufacturing, and is a leading formulator of top-quality 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.