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.
Many modern washing machines have a dispenser that adds liquid fabric softener automatically on the final rinse. Users of launderette machines may need to add it manually. Some washing powder brands have fabric conditioning mixed in, which manufactures claim saves money compared to buying separate washing powder and fabric softener. Some manufacturers claim their products make ironing easier or make clothes dry faster. All liquid fabric softeners are 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 can cause spotting when poured directly onto clothes, and can ruin them.
Dry fabric softeners are typically supplied in the form of dryer sheets added in the clothes dryer to soften the fabric and prevent buildup of static electricity in susceptible fabrics. Many users advocate alternative uses of dryer sheets, 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 so the fabric feels softer and makes it fluffier. 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 then line up towards the outside of the fiber, imparting lubricity.
Electrically conductive fabric softener chemicals may also prevent static charge buildup in clothes dryers. Other functions manufacturers claim include less friction during ironing, increased stain resistance, reduced wrinkling and pilling, and lower drying time. Most contain fragrances. Cationic fabric softeners are added during the rinse cycle rather than the wash cycle because they can interfere with detergent cleaning action. In addition to fabric softening chemicals, fabric softeners may include acids or bases to maintain optimal pH for absorption, silicone-based anti-foaming agents, emulsion stabilizers, fragrances, and colors.
Early cotton softeners were typically based on a water emulsion of soap and olive oil, corn oil, or tallow oil. Softening compounds differ in affinity to various fabrics. Some work better on cellulose-based fibers (i.e., cotton), others have higher affinity to hydrophobic materials like nylon, polyethylene terephthalate, polyacrylonitrile, etc. New silicone-based compounds, such as polydimethylsiloxane, work by lubricating the fibers. Manufacturers use derivatives with amine- or amide-containing functional groups as well. These groups improve the softener's binding to fabrics.
As softeners are often hydrophobic, they commonly occur in the form of an emulsion. In the early formulations, manufactures used soaps as emulsifiers. The emulsions are usually opaque, milky fluids. However, there are also microemulsions, where the droplets of the hydrophobic phase are substantially smaller[not specific enough to verify]. Microemulsions provide the advantage of increased ability of smaller particles to penetrate into the fibers. Manufactures often use a mixture of cationic and non-ionic surfactants as an emulsifier. Another approach is a polymeric network, an emulsion polymer.
Cationic fabric softeners
In the 1950s, manufactures introduced distearyldimethylammonium chloride (DHTDMAC) as a fabric softener, initially to counteract the harsh feel that the machine washing imparted to nappies (cloth diapers). They had to discontinue using this compound because the cation biodegrades very slowly. Contemporary fabric softeners are most often based on salts of quaternary ammonium cations. Characteristically, the cations contain one or two long alkyl chains derived from fatty acids. Other cationic compounds can be derived from imidazolium, substituted amine salts, or quaternary alkoxy ammonium salts.
A diesterquat derivative of trimethylamine used as a fabric softener, chloride salt.
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 in detergents because they combine with them to form a solid precipitate. This requires that they be added in the rinse cycle. Anionic softeners can combine 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.
As with soaps and detergents, fabric softeners may cause irritant dermatitis. Manufactures produce some fabric softeners without dyes and perfumes to reduce the risk of skin irritation. Fabric softener overuse may make clothes more flammable, due to the fat-based nature of most softeners. Several deaths have been attributed to this phenomenon, and fabric softener makers recommend not using them on clothes labeled as flame-resistant.
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