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Soaps & Detergents: Chemistry

Soaps & Detergents: Chemistry

 

                Long ago medical science confirmed the important relationship between cleanliness and health. Wash your hands, wash your hands is the mantra of many health professionals and parents alike.      But what is needed for effective cleaning?   Water and soap and add some movement seems simple enough but it is also helpful to know more about soap and detergent chemistry.

                Water, the liquid most commonly used for cleaning, has a property called surface tension. In the body of the water, each molecule is surrounded and attracted by other water molecules. However, at the surface, those molecules are surrounded by other water molecules only on the water side. A tension is created as the water molecules at the surface are pulled into the body of the water. This tension causes water to bead up on surfaces (glass, fabric), which slows wetting of the surface and inhibits the cleaning process. You can see surface tension at work by placing a drop of water onto a counter top. The drop will hold its shape and will not spread.

                In the cleaning process, surface tension must be reduced so water can spread and wet surfaces. Chemicals that are able to do this effectively are called surface active agents, or surfactants. They are said to make water "wetter."  Surfactants also perform other important functions in cleaning, such as loosening, emulsifying (dispersing in water) and holding soil in suspension until it can be rinsed away. Surfactants can also provide alkalinity, which is useful in removing acidic soils.

                Soaps are water-soluble sodium or potassium salts of fatty acids. Soaps are made from fats and oils, or their fatty acids, by treating them chemically with a strong alkali – think the modern day version of lye.

                Although soap is a good cleaning agent, its effectiveness is reduced when used in hard water. Hardness in water is caused by the presence of mineral salts - mostly those of calcium (Ca) and magnesium (Mg), but sometimes also iron (Fe) and manganese (Mn). The mineral salts react with soap to form an insoluble precipitate known as soap film or scum.

                Soap film does not rinse away easily. It tends to remain behind and produces visible deposits on clothing and makes fabrics feel stiff. It also attaches to the insides of bathtubs, sinks and washing machines.

                Detergents are extremely effective cleaning products because they contains more than one surfactant.   Because of their chemical makeup, the surfactants used in detergents can be engineered to perform well under a variety of conditions. Such surfactants are less sensitive than soap to the hardness minerals in water and most will not form a film. Laundry detergents are either general purpose or light duty.  General purpose detergents are suitable for all washable fabrics. Liquids work best on oily soils and for pretreating soils and stains. Powders are especial effective in lifting out clay and ground-in dirt. Light duty detergents are used for hand or machine washing lightly soiled items and delicate fabrics.

                Laundry aids contribute to the effectiveness of laundry detergents and provide special functions.

Bleaches (chlorine and oxygen) whiten and brighten fabrics and help remove stubborn stains. They convert soils into colorless, soluble particles that can be removed by detergents and carried away in the wash water. Liquid chlorine bleach (usually in a sodium hypochlorite solution) can also disinfect and deodorize fabrics. Oxygen (color-safe) bleach is gentler and works safely on almost all washable fabrics.

                Bluings contain a blue dye or pigment taken up by fabrics in the wash or rinse. Bluing absorbs the yellow part of the light spectrum, counteracting the natural yellowing of many fabrics.

Boosters enhance the soil and stain removal, brightening, buffering and water softening performance of detergents. They are used in the wash in addition to the detergent.

                Enzyme presoaks are used for soaking items before washing to remove difficult stains and soils. When added to the wash water, they increase cleaning power.

                Fabric softeners, added to the final rinse or dryer, make fabrics softer and fluffier; decrease static cling, wrinkling and drying time; impart a pleasing fragrance and make ironing easier.

                Prewash soil and stain removers are used to pretreat heavily soiled and stained garments, especially those made from synthetic fibers.

                Starches, fabric finishes and sizings, used in the final rinse or after drying, give body to fabrics, make them more soil-resistant and make ironing easier.

                Water softeners, added to the wash or rinse, inactivate hard water minerals. Since detergents are more effective in soft water, these products increase cleaning power.

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