Fabric softener (also called fabric conditioner) is a chemical compound that prevents static cling and confers many other desirable properties to laundry that has been machine-washed. They are available as solutions and solids, sometimes impregnated in "dryer sheets."
Many modern washing machines have a dispenser, which can add liquid fabric softener to the load of laundry automatically on the final rinse; in launderettes 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 tumble 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 such as dusting, and removing hair from clothes.
Mechanism of action
Fabric softeners work by coating the surface of the washed fabric with a thin layer of chemical compounds that are electrically conductive, thus preventing buildup of static charge and improving their feel. Other functions are improvements of iron glide during ironing, increased stain resistance, and reduction of wrinkling and pilling. They also reduce the drying time for clothes, saving energy. Many contain fragrances. Cationic fabric softeners are added to the final step of the wash cycle, lest they interact with the detergents used in the actual cleaning.
Other compounds may be included in the formulation of fabric softeners, e.g., to provide additional functions; acids or bases for maintaining the optimal pH for absorption to the fabric, electrolytes, carriers (usually water, sometimes water-alcohol mixture), and others, e.g. silicone-based anti-foaming agents, emulsion stabilizers, fragrances, and colors. A relatively recent form on the market are the ultra-concentrates, where the amount of carriers and some other chemical compounds is substantially lower and much smaller volumes are used.
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.
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[not specific enough to verify]. 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 diapers. 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. Other cationic compounds can be derived from imidazolium, substituted amine salts, or quaternary alkoxy ammonium salts.
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.
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