Fabric softener

A Fabric softener (also called fabric conditioner) is a chemical compound that is typically applied to laundry during the rinse cycle in a washing machine. Fabric softeners are available as solutions and solids, and may also be impregnated in dryer sheets used in a clothes dryer.^[1]

Varieties

Many modern washing machines have a dispenser for adding liquid fabric softener to the load of laundry automatically on the final rinse; in launderette machines it may need to be added manually. Some brands of washing powder have fabric conditioning mixed in which is claimed to save money when compared to buying ordinary washing powder and fabric softener separately. Some manufacturers claim their products make ironing easier and/or make clothes dry faster. All liquid fabric softeners are designed to be added to water – either by adding the product directly to the final rinse water or by 2:1 (water:softener) dilution in an automatic dispenser. Even diluted fabric softener will cause spotting when poured directly onto clothes and can ruin them.

Dry fabric softeners are typically supplied in the form of dryer sheets, which are added to clothing in the clothes dryer to soften the fabric and prevent buildup of static electricity in susceptible fabrics. Many alternative uses of dryer sheets have been suggested by users^[2] such as dusting, and removing hair from clothes.

Mechanism of action

Fabric softeners coat the surface of a fabric with chemical compounds that are electrically charged, causing threads to "stand up" from the surface and thereby causing the fabric to feel softer. Cationic softeners bind by electrostatic attraction to the negatively charged groups on the surface of the fibers and neutralize their charge; the long aliphatic chains are then oriented towards the outside of the fiber, imparting lubricity.

The electrically conductive fabric softener chemicals may also prevent buildup of static charge that can occur in clothes dryers. Other functions claimed by manufacturers include improvements of iron glide during ironing, increased stain resistance, reduction of wrinkling and pilling, and reduced drying time. Many contain fragrances. Cationic fabric softeners are added during the rinse cycle rather than the wash cycle, as they can interfere with the cleaning action of detergents.

In addition to fabric softening chemicals, fabric softeners may include acids or bases for maintaining the optimal pH for absorption, silicone-based anti-foaming agents, emulsion stabilizers, fragrances, and colors.

Composition

Early cotton softeners were typically based on water emulsion of soap and olive oil, corn oil, or tallow oil. The softening compounds differ in affinity to different materials. Some are better for cellulose-based fibers (i.e., cotton), others have higher affinity to hydrophobic materials like nylon, polyethylene terephthalate, polyacrylonitrile, etc. Silicone-based compounds such as polydimethylsiloxane comprise the new softeners which work by lubricating the fibers. Derivatives with amine- or amide-containing functional groups are used as well. These groups help the softeners bind better to fabrics.

As the softeners themselves are often hydrophobic, they are commonly occurring in the form of an emulsion. In the early formulations, soaps were used as emulsifiers. The emulsions are usually opaque, milky fluids. However there are also microemulsions where the droplets of the hydrophobic phase are substantially smaller. The advantage of microemulsions is in the increased ability of the smaller particles to penetrate into the fibers. A mixture of cationic and non-ionic surfactants is often used as an emulsifier. Another approach is using a polymeric network, an emulsion polymer.

Cationic fabric softeners

In the 1950s, distearyldimethylammonium chloride (DHTDMAC), was introduced as a fabric softener initially to counteract the harsh feel that the machine washing imparted to nappies. This compound was discontinued because the cation biodegrades very slowly. Contemporary fabric softeners tend to be based on salts of quaternary ammonium cations. Characteristically, the cations contain one or two long alkyl chains derived from fatty acids.^[3] Other cationic compounds can be derived from imidazolium, substituted amine salts, or quaternary alkoxy ammonium salts.^[1]

• Cationic surfactants used as fabric softeners
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  "Monoesterquat" used as fabric softener.

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  "Diesterquat" used as a fabric softener.

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  Another diesterquat used as a fabric softener.

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  Distearyldimethylammonium chloride, a fabric softener with low biodegradability, has been phased out.

Anionic fabric softeners

Anionic softeners and antistatic agents can be, for example, salts of monoesters and diesters of phosphoric acid and the fatty alcohols. These are often used together with the conventional cationic softeners. Cationic softeners are incompatible with anionic surfactants used in detergents because they combine with them to form a solid precipitate. So, they must instead be added during the rinse cycle. Anionic softeners can be combined with anionic surfactants directly. Other anionic softeners can be based on smectite clays. Some compounds, such as ethoxylated phosphate esters, have softening, anti-static, and surfactant properties.^[4]

Risks

Together with soaps and detergents, fabric softeners are a common household product that may cause irritant dermatitis.^[5] Some fabric softeners are made without dyes and perfumes so as to reduce the possibility of skin irritation. Overuse of fabric softeners may make clothes more flammable, due to the fat-based nature of most softeners; several deaths have been attributed to this phenomenon,^[6] and fabric softener makers recommend not using them on clothes labeled as flame-resistant.

References