Cleaning grease and oil; suds vs. solvent … Why water and oil do not mix: ionic, polar, and nonpolar substances … Why soap and detergent work on oil and grease … Acids and alkalies, what pH means, list of pHs of common household substances … Green laundering
Readers who dislike anything technical should skip this chapter. But for those who can tolerate a short excursion into grade school science, it offers much traditional household lore. If you are the sort of housekeeping beginner who has always wondered why white vinegar and baking soda are supposed to be useful in the laundry, you can find here brief explanations of these and other snippets of household chemistry.
Laundering and stain removal make use of four basic types of chemical cleaning agents: soaps or detergents in water, solvents (such as drycleaning fluids), acids, and alkalies. (These categories can overlap.) A few simple chemical concepts explain why these are used for certain standard household purposes.
Cleaning Grease and Oil; Suds
You cannot clean anything greasy or oily with plain water. Grease and oil are not soluble in water. Most of the dirt on our bodies and clothes and much of the dirt in our homes—especially in kitchens—is combined with grease or oil. To clean grease and oil, you can use either soaps and detergents, mixed in water to make a sudsy solution, or a solvent-based cleaner. Because solvents are usually more toxic, more expensive, more odorous, less versatile, and flammable, soaps and detergents are what we try to use whenever possible on clothes, linens, draperies, carpets, and other fabrics in the home. We turn to solvents for cleaning fabrics that cannot withstand water, hot water, or soaps and detergents.
Why Water and Oil Do Not Mix: Ionic, Polar, and Nonpolar Substances. Dirt, foods, cleaners, and other substances in the home can be divided into three chemical categories: ionic, polar, and nonpolar. Ionic compounds are those whose smallest units are charged particles called “ions,” such as ordinary salt and hydrogen peroxide (H2O2). When salt (sodium chloride, NaCl) dissolves in water, its chemical units dissociate into one positively charged sodium ion (Na+) and one negatively charged chloride ion (Cl2). Polar substances are composed of molecules that have different charges at each end. For example, water molecules, which are polar, have different charges, negative and positive, at their sides or ends. Nonpolar molecules, such as those that make up olive oil, do not. Because they are polar, water molecules bond tightly to one another: the positively charged hydrogen atoms of one molecule are attracted to the negatively charged oxygen atoms of another. This is why water, unlike olive oil, beads on flat surfaces and has a high surface tension (as though a skin on its surface holds the drop of water together). Some other examples of familiar substances made of ionic, polar, and nonpolar molecules include:
Ionic: salt, baking soda (NaHCO3), hydrogen peroxide
Polar: water, alcohol (wine, spirits, rubbing alcohol), lemon juice, vinegar, chlorine bleach
Nonpolar: grease, oils such as cooking oils, fat from meats, furniture oils, drycleaning fluids, mineral spirits (paint thinners), floor waxes
As a rule, substances made of polar molecules do not mix with substances made of nonpolar molecules. And generally speaking, the more polar a substance is, the more soluble it is in water; the more nonpolar it is, the less soluble in water. When grease or oil is mixed with water (for example, when olive oil is mixed with vinegar, which is mostly water), the water bonds so tightly to itself that it forces the grease or oil molecules to form separate globules; they don’t mix. Nonpolar substances are also considerably less effective at dissolving ionic compounds such as salt, because they do not attract the charged Na+ and Cl—ions away from one another. Salt, for example, will not dissolve in olive oil—one more reason to put a little vinegar on the salad.
But nonpolar substances are effective solvents for one another. To put it in simple terms, nonpolar substances dissolve in other nonpolar substances. So drycleaning fluids are good for removing body oils and grease splatters from clothes, and you can remove wax with mineral spirits.
Why Soap and Detergents Work on Oil and Grease. Soap and detergents are surfactants. Surfactants reduce the surface tension of water. This causes the water to spread and to wet objects rather than bead up on them; when surfactants are mixed with water, oil and grease in the water are emulsified—they stay mixed or spread throughout the water in tiny droplets. The explanation for this is that surfactants’ molecules have long, complicated hydrocarbon chains, one end of which is polar and the other end of which is nonpolar. The polar end is attracted to water: it is water-loving or hydrophilic. The nonpolar end is soluble in oil and grease and repelled by water: it is water-hating or hydrophobic. The nonpolar ends of these surfactant molecules form a kind of circle-barrier around a droplet of oil in water, with their water-insoluble ends next to the oil and the water-soluble ends away from it. When the oil is emulsified, the polar ends of the surfactant molecules keep the droplet suspended in the water and keep it from joining other oil droplets and separating into large globules. Thus it can be rinsed out of fabrics or off countertops with water.
Both soaps and detergents are, or contain, surfactants. Chemically, soaps and detergents are similar, but detergents—also called “synthetic detergents”—are made from petrochemicals. Soaps are produced by mixing animal or vegetable fats and oils with some strong alkali such as sodium hydroxide (caustic soda, NaOH) or potassium hydroxide (caustic potash, KOH). Hard soaps, such as bar soaps, are generally made with sodium hydroxide, and liquid soaps are usually made with potassium hydroxide. Soaps often contain many other ingredients—from moisturizers, abrasives, deodorants, and bactericides to perfumes. Soaps are now rarely used for laundry in the United States, although cleaning soaps such as Murphy’s Oil Soap remain in use. Laundry soaps are still widely used in other parts of the world.
Soap has been supplanted as queen of the laundry by synthetic detergents because soap causes a scum to form when used in hard water. Hard water contains calcium or magnesium ions that combine with the soap to form insoluble salts, or scum, which then is deposited on clothes in the washing machine or on bathroom tiles and bathtubs. It looks ugly, and it can be hard to dislodge. Soap also is problematic when it is used in the presence of acids, for they will render the soap inactive and create a different kind of scum. Skin and clothing often contain acids from the decomposition of perspiration or food spills. Thus, the average load of laundry contains some acids, and these cause problems for laundry soap.
There are four types of detergents: anionic, nonionic, cationic, and amphoteric. Anionic detergents are the ordinary high-sudsing types generally used in laundry and all-purpose detergent products. Anionic detergents do essentially the same chemical job that soaps do, without causing hard-water scum to form. They are more powerful and less expensive than cationic or nonionic detergents. Unlike cationic and nonionic detergents, however, they can be partly deactivated by too-hard water. For this reason, alkaline substances such as phosphates or borax are sometimes added to anionic detergents (and to soaps, which are also anionic). The alkalies react with acids in the hard water and help the anionic detergents clean better, and, in the case of soap, also reduce scum formation. The first truly effective detergents contained phosphates, and it is still true, alas, that phosphate detergents clean better. But for good environmental reasons their use is widely restricted. See page 176.
Nonionic detergents are used for low-sudsing laundry detergents and dishwasher detergents. They are effective in hard water and work well on most types of dirt, especially oily dirt. Some cationic surfactants are used in fabric softeners and fabric-softening detergents. All soaps and detergents are antibacterial to some extent. But certain cationic detergents—quaternary ammonium compounds, or “quats”—have a stronger antibacterial effect and, therefore, are used as sanitizers or disinfectants. Amphoteric detergents are mild and are widely used in shampoos, personal-care products, and some household detergents.
Both soaps and detergents work better in warmer water and with the aid of mechanical action, whether muscle power applied in scrubbing or rubbing on a washboard or the agitation of a washing machine. Despite the advantages of detergents, some people prefer soaps because detergents are made from petroleum products, a nonrenewable resource, unlike the fats and alkalies from which soaps are made. But see “Green Laundering,” below. Others choose soaps when they want a mild product even though soaps are not necessarily “milder” than detergents. Some soaps are harsh, and some detergents quite mild. See “Detergents and soaps, mild,” on pages 78-80.
Laundry detergents marked “heavy-duty” or “all-purpose” are perfectly good all-purpose cleaners for the household. These are detergents that contain various “builders”—substances that enhance the detergent solution’s alkalinity and ability to emulsify grease and oil or inactivate water hardness. Phosphates are the builders that have most commonly been used, but they are now banned in many states—a decision the soap and detergent industry is still protesting.* See “Green Laundering,” page 176. Light-duty detergents, such as dishwashing liquids, are those that contain no builders. They are milder. Mild, generally, means neutral or near-neutral in pH. Strongly alkaline solutions burn the eyes and are harsh on the skin and on many household materials as well. Shampoos that do not burn the eyes have a pH between 6.0 and 7.0.
Acids and Alkalies
The efficacy of a household cleaner for any given purpose is in great part a function of its pH, the number that expresses how acidic or alkaline it is. Which substances clean which kinds of dirt and what cleaners are safe for what materials are strongly affected by pH. The pH scale runs from 0 to 14, with 7 being neutral. The higher the number over 7, the more alkaline the solution is. The lower the number under 7, the more acidic the solution is. Pure water is neutral, with a pH of about 7, but rainwater is slightly acidic, with a pH of about 6. (Pure water, by the way, should not be confused with potable water or plain tap water. Drinkable tap water and bottled water—unless the bottled water is distilled—contain many minerals and other substances in addition to H2O.)
A water-soluble substance is alkaline if a solution of the substance in water contains a greater concentration of hydroxyl ions (OH2) than of hydrogen ions (H+). It is acidic if, when mixed with water, the resulting solution contains more hydrogen ions than hydroxyl ions. Because most dirt and body soils are slightly acidic, most good cleaners are at least slightly alkaline. The term “base” is a synonym for “alkali,” and “basic” is a synonym for “alkaline.” (I use “alkali” and “alkaline,” however, to avoid confusion.)
Alkalies make it possible to clean without too much rubbing. Soap and soap-containing products and detergents are alkaline and perform well only in an alkaline solution. Automatic dishwashing detergents, all-purpose laundry soaps and detergents, and hard-surface cleaners (liquid or granules) are usually alkaline to one degree or another, but hand dishwashing detergents and “mild” detergents are neutral or close to neutral because more alkaline solutions are too harsh on the skin. (Some hand dishwashing liquids advertised as good for “sensitive skin” are actually slightly acidic.) These milder alkalies nonetheless work well sometimes because you add a little muscle power to the chemical power they provide. Because soaps and detergents form alkaline solutions, acids are sometimes added to shampoos to lower the pH to prevent them from burning your eyes. You sometimes see such products advertised as “pH balanced.”
Alkalies, such as ammonia, help in cleaning acidic, fatty, and oily dirt, which is why laundry products (and kitchen cleaners) tend to be alkaline. Baking soda (sodium bicarbonate or NaHCO3), a much weaker alkali than ammonia, has correspondingly gentle cleaning and deodorizing abilities. As a deodorizer, it works neither by perfuming nor masking odors, but by chemically neutralizing them. Pleasant odors are neutral in pH. Most unpleasant odors are caused by strong acids (e.g., sour milk) or strong alkalies (e.g., rotten fish). Baking soda reacts with the odor molecules to bring them to a more neutral pH. On the use of baking soda in the laundry as a deodorizer and mild detergent booster, see pages 69-70.
Acids can remove soap scum and hard-water deposits (calcium carbonate). Many bathroom cleaners, therefore, are mildly acidic. Acids—such as lemon juice or white vinegar—will also remove rust stains. Strong acids can damage clothing, leather, and other materials in the home. Although we enjoy eating many foods that are weakly acidic, such as tomato sauces and salad dressings containing vinegar, strong acids are extremely toxic if ingested.
Both alkalies and acids are found in the household in different degrees of weakness and strength. Strong alkalies and acids can cause serious injury to skin and eyes, and if swallowed can cause serious injury or death. Do not induce vomiting after accidental ingestion of such substances, as they can cause grave damage in the process of being ejected from the body. Instead, immediately call your local poison control center and follow the instructions you are given.
Here is a list of various foods and substances commonly found in the home, arranged according to pH, beginning with the strongest alkalies and ending with the strongest acids:
Very Strong Alkalies
13 Lye, caustic soda (sodium hydroxide—NaOH) (found in some oven cleaners and drain cleaners, e.g., Drano), caustic potash (potassium hydroxide—KOH)
11.8 Washing soda, sal soda, or sodium carbonate (Na2CO3) (added to detergents as a builder and to cleaners and presoaks to increase alkalinity; used in some drain cleaners)
Moderate Alkalies
11 Household ammonia (ammonia gas [NH3] in a 5 to 10 percent water solution) (a grease cutter, wax stripper, and general soil remover)
9-11 All-purpose detergents, soaps, window cleaners, mildew cleaners, most bathroom scouring powders, liquid cleaners, builders
9.28 Borax (a white crystalline powder)
Mild Alkalies
8.35 1percent solution of baking soda (sodium bicarbonate—NaHCO3) and water
8.3 Seawater
8.1 Soap
9 percent solution of baking soda and water
Gentle liquid detergent
7.8 Eggs
Neutrals
7+ Woolite
7 Pure water, milk, sugar water, saltwater
Fabuloso All-Purpose Cleaner
Orvus WA Paste
Ultra Palmolive for Pots and Pans
Ultra Palmolive Antibacterial
Dawn and Ultra Dawn
Very Mild Acids
6+ Some dishwashing liquids for “sensitive skin”
5-6 Rain in unpolluted environments
5.1 Seltzer water or carbonated water (contains carbonic acid [H2CO3], which breaks down and gives off carbon dioxide as fizz)
Cream of tartar in water
5 Boric acid solution (H3BO3) (used in eyewash)
4.2 Tomatoes
4 Rain in polluted environments (can be as low as 2)
4 Orange juice
Moderately Strong Acids
3.1 White vinegar (5 percent acetic acid)
3 Carbonated beverages, apples
2.3 Lemon juice, lime juice (contain citric acid)
2.1 Citric acid
Very Strong Acids
1.1 Sulfuric acid (NaHSO4) (found in many dry toilet-bowl cleaners)
0.8 Hydrochloric acid, or muriatic acid (HCI) (found in many liquid toilet-bowl cleaners)
Oxalic acid (H2C2O2) (effective as a rust remover, but toxic; contained in some scouring powders recommended for rust removal, such as Zud and Barkeeper’s Friend)
Green Laundering
Making Environmentally Sound Choices. There are many important ways to make environmentally favorable choices in laundering. One of the most valuable things you can do is to use as little detergent as necessary to get a good laundering result. This is true even if you use allegedly “natural” or “green” types. The same goes for all other laundry products. Tablets or other premeasured forms of delivery might help you to control quantities by preventing you from heaping the measure or throwing in a little more just for insurance. You can also use much less detergent simply by not overwashing your clothes and washing only with a full load. If you wash smaller loads, use less detergent.
Avoid detergents that contain phosphates. Phosphates that get into the waterways cause eutrophication. That is, they cause algae and other water plants to grow excessively, reducing and, finally, depleting the water of dissolved oxygen. Without oxygen, the water cannot support life. Eventually the pond, lake, or stream itself is destroyed.
Choose laundry products that come in biodegradable or recyclable packages, and choose those that omit unnecessary ingredients such as optical brighteners, dyes, and perfumes. Remember that “natural” dyes and perfumes are not necessarily harmless, and “synthetic” ones are not necessarily harmful; I am aware of no scientific evidence that environmentally condemns “artificial” scents and absolves “natural” or plant-derived scents. Avoid detergents that contain fabric softeners and bleaches (which may also have bleach stabilizers and bleach activators). Instead, buy bleach and softeners separately and use them sparingly. Fabric softener is much overused. See pages 81-82. Or try to use detergents with extra additives only occasionally instead of regularly. Choosing concentrated or “ultra” products is beneficial, as these contain fewer fillers and use less packaging. It is good to wash and rinse your clothes in water as cool as will work, but if you use water that is too cold, you are likely to end up using more chemicals to make up for the reduced cleaning and sanitizing power.
Questionable Advice? Some well-intentioned recommendations for environmentally aware laundering that you may encounter raise more questions than those just reviewed. Stores and websites offer dozens of laundry products advertised as “natural” and environmentally superior to common supermarket brands. It is often difficult to be sure their claims are warranted.
Do not assume that a product calling itself “natural” or “green” or “enviro-” anything is necessarily environmentally better. Look for specific claims about ingredients and choose the products of “green” companies with a good business reputation and a scientific orientation. Do not assume that the list of ingredients on the label includes all the ingredients in the box (unless the manufacturer is reputable and explicitly tells you that this is the case). In a frustrating trend, detergent manufacturers are listing fewer ingredients each year—many fewer than are actually used. This makes it impossible for people to make informed choices from any point of view, whether as to function, environmental favorability, or economy.
How Bad Is Household Chlorine Bleach for the Environment? Chlorine bleach is a powerful chemical. No one should store or use it in the home who does not understand how to do so safely. See page 73. Check manufacturers’ websites or the websites of the FDA, CDC, or USDA for information on the safe use of bleach as a general household disinfectant. But is it environmentally incorrect? Almost certainly, it is not nearly the profound environmental hazard that some people seem to think it is. The Internet is full of misinformation on this subject, much of it purveyed by vendors of allegedly “green” products who urge you not to pour dangerous chlorine into our streams and lakes. “Chlorine,” a gas in its pure form, is certainly dangerous to the environment, but household “chlorine” bleach (a 5.25 percent or 6 percent solution of sodium hypochlorite) neither contains chlorine gas nor releases chlorine gas into the environment as a result of laundering. (It contains chloride ions, just as table salt does.) Although certain uses of certain types of chlorine products in manufacturing and industry can result in the formation of dioxin, household bleaching does not.
In household use, sodium hypochlorite rapidly—before it leaves your home—breaks down, almost entirely, into table salt and water. Although no dioxins form, a small amount of other chemicals, including a very small amount of adsorbable organic halides (AOX) are formed. The term AOX is a measure of total halogens—fluorine, chlorine, bromine, and iodine—that encompasses naturally formed substances as well as pollutants. The amount of these created by domestic use of chlorine bleach is small not only in absolute terms but also relative to what is created by other human activities and relative to what comes from natural sources. Some say that the majority of the small fraction of AOX attributable to household bleach readily biodegrade, are water-soluble, and do not bioaccumulate. Moreover, chlorine bleach is remarkably cheap, effective, and versatile. Accordingly, they conclude that household bleach should be fairly low on the rational environmentalist’s list of household substances to worry about. Others say that because we do not really know what else might be included in these residues, we should either not use bleach or keep use to a minimum.
In deciding whether or not you will use household chlorine bleach, keep in mind this question: If you are going to use an alternative in place of chlorine bleach, are you sure that it is better for the environment than chlorine bleach?
Green Detergents? Many so-called green products contain surfactants made from plant oils and fats—oleochemicals, that is, rather than petrochemicals. (Most green products exclude animal fats on vegetarian or other principles.) Surfactants made from plant sources, including soaps, are chemically very similar to those made from petrochemicals, and in sewage plants and in the environment they act similarly to surfactants made from petrochemicals. Although surfactants differ in the rates at which they biodegrade, faster degradation is a function of the surfactants’ chemical structure; it is not a function of the type of raw materials from which they are made.
Nonetheless, many people argue that because plants are a sustainable resource and petrochemicals a finite one, we should use in our detergents only surfactants manufactured from oleochemicals. Of course, we need to husband our limited petrochemical resources. But it is not so obvious to what extent using oleochemical surfactants helps to do so when one takes into account the environmental effects and overall energy consumption (including energy derived from petrochemicals) involved in making oleochemical surfactants. This involves growing the plant (and, occasionally, animal) sources, which conceivably could involve pesticides, fertilizers, long transports, or other petrochemical uses, extracting the necessary substances from the plants, and engaging in the other complex chemical manufacturing processes required to create surfactants out of them.
Comparative studies of the environmental pros and cons of oleochemical versus petrochemical surfactants show that each type has certain environmental advantages over the other; oleochemical surfactants may, on balance, have more, but, if so, their advantages are not startlingly or conclusively better. Moreover, in evaluating such studies, we should keep this in mind: The amount of petrochemicals that it takes to supply the world with detergent is small compared with the amounts used for farming, airplanes, ships, trains, cars and other forms of transportation, industrial and manufacturing uses, heating, lighting, etc.