The earliest fabric softeners were developed during early 20th century and were based on a water emulsion of soap and olive oil, corn oil, or tallow oil.
Static build-up in clothing is caused by fiber-to-fiber, fiber-to person and even fiber-to-air friction, and depends on the type of fiber from which the garment is made.
The amount of static build-up is also highly dependent on the relative humidity, the higher the humidity the lower the charge.
Fibers such as rayon, silk, wool, cotton, and linen have high moisture “regain”, their fibers absorb a great deal of moisture at a given humidity from a bone dry condition, and are low in static.
Fibers such as polyester, acrylic, and polypropylene, having low moisture regain, are high in static.
Antistatic finishes or sprays come in two types.
The first are made of molecules that contain polar groups, in which charge is unevenly distributed, and these act as conductors to dissipate static charge. The second type are humectants, or water-absorbing materials, that also permit the textile to dissipate static electricity.
The increased moisture present on the surface or within the fiber itself increases electrical conductance, helping to drain away the charge.
Textile technologists can design fibers and fabrics to minimize static electricity.
In carpets, a small percentage of fibers (up to 3 percent) can have either a carbon core or a carbon strip to drain away static charge. Carpets and upholstery fabrics may also be made with carbon lampblack mixed into the latex or hot-melt backing material for the same purpose.
If the carpet is made of yarn spun from staple fibers, a small percentage of stainless steel fibers or fibers coated with aluminum or silver vapor may be incorporated into the blend to reduce static electricity. However, less than 5 percent of this type of fiber can be used because otherwise the fabric takes on a gray tinge.
Fabric softeners contain a type of compound called a surface active agent or surfactant. It’s a cationic surfactant, meaning it’s a long molecule (rather like an oil or a fat) with a positive charge at one end.
Often the surfactant used is an ammonium compound in which the nitrogen atom is surrounded by four organic groups.
During the washing process the negative charge that forms on the surface of the fabric draws the positive end of the surfactant molecules to itself. These long oily molecules then lubricate the fibers to prevent the friction that causes static cling. It makes ironing easier, and allows the weave to relax and supply that soft, fluffy feel.
Static electricity is an imbalance of electric charge: a lack or overabundance of electrons on the surface of the material.
This typically occurs by “tribocharging” when two materials are brought into contact then separated; electrons are exchanged by the materials, leaving one with a positive charge and the other with a negative charge. Friction between the two materials can enhance this charge-separation process.
Under normal atmospheric conditions, fibers such as cotton and wool have a relatively high moisture content, which makes them slightly conductive.
This prevents the charge separation from occurring by allowing static electricity to be conducted away. However, synthetic materials have a high surface electrical resistance particularly when humidity is low, and this prevents the charge dissipating.
A layer of fabric softener simply reduces the electrical resistance of the surface of fabrics.