1. Topics
Static Electricity and how dryer sheets work
2. Purposes of the study
To determine how a dryer sheet works to reduce static electricity in clothing.
3. Research questions/hypotheses
How do dryer sheets reduce static electricity in clothing?
What is in a dryer sheet that helps reduce static?
The chemicals in a dryer sheet help to fight friction and static electrticity in clothing.
Do dryer sheets have a different effect on different materials?
4. Methods
Research what a dryer sheet is made of and how that reduces static.
Research how static electricity is built up in drying clothes.
See if dryer sheets have a different effect on different materials. ex. jeans, cotton, silk, etc...
5. Results and Findings
How did dryer sheets come about?
The wash cycle is complete. You toss your wet laundry into the dryer and chase it with a dryer sheet. Most people don't know how the thin sheets freshen and soften clothes or that they were developed by a chemist who wanted to help his wife out with the laundry.
In the late 1960s, Conrad J. Gaiser and his wife, Audrey, lived on the top two floors of a four-story duplex. Their laundry room was on the ground floor, and every time Audrey would wash a load, she had to run down the stairs to catch the final rinse cycle in order to add fabric softener. Liquid fabric softeners, which are commonly cationic, can't be mixed with detergents, which are anionic, because the mixture forms a precipitate.
Cindy Yamanaka/Orange County Register
Conrad, who had worked for a number of years in the soap and detergent industry, wanted to make his wife's life easier and got to work producing the first known dryer sheet. Laurel Gaiser, Conrad's daughter, tells C&EN how her father applied fabric softener to a piece of cotton flannel, likely from her mother's sewing room. He named his prototype Tumble Puffs, Laurel says.
In 1969, Conrad received a U.S. patent for this invention, and shortly thereafter he sold the rights to Procter & Gamble, which then marketed the product as Bounce dryer sheets.
The first version of the product had several problems, including getting trapped in the lint vent and distributing the softener unevenly onto clothes, says Gordon F. Brunner, who was P&G's associate director of research and development at the time. The company ironed out the wrinkles and launched the product nationally in 1975.
Today, many competing brands of dryer sheets are available. Each brand uses a slightly different formulation to achieve three primary goals: to soften clothes, to prevent static cling, and to deliver a fresh scent.
Most dryer sheets are made from a nonwoven polyester material coated with a softening agent that has a long hydrophobic chain. Fatty acids, fatty alcohols, and alcohol ethoxylates are all possible softening agents. P&G uses quaternary ammonium salts of fatty acids as its primary softening agents, whereas Unilever, which produces Snuggle dryer sheets, uses a stearic acid.
During tumble drying, the coating containing the softener melts and the compounds get transferred onto the fabrics being dried. The newly attached fatty chains give the fabric's surface a slippery feel, which people interpret as softness. The compounds also help dissipate static charge by lubricating and increasing the surface conductivity of the fabric fibers.
It's important that the softening agents have a relatively high melting point, notes Bien Santos, section head in products research at P&G. If the melting point is too low, "it will make your sheet very sticky inside the box, and you don't want that," Santos says. "What you want is something that's solid at room temperature and either softens or melts inside the dryer so you can effectively transfer it onto clothes."
Some dryer sheets also contain small amounts of inorganic compounds—such as montmorillonite, a naturally occurring calcium clay—that help control the viscosity of the fabric softener coating as it begins to melt in the dryer. "You don't want it to come off the nonwoven sheet too quickly, or you might have streaks of softener actives on some parts of the clothes and none on others," Santos says. "You want it as evenly distributed as possible."
Aside from providing softness and preventing static cling, dryer sheets also deliver a fresh scent to laundered clothes. This is done by adding fragrance molecules to the softener coating. Jack Linard, senior manager of scientific and regulatory affairs at Unilever, says that one challenge in developing dryer sheets is to minimize the amount of fragrance molecules that are lost through evaporation during the high-heat manufacturing process and in the dryer.
Linard says they choose fragrance molecules that can best survive the high temperatures inside the dryer. Moreover, they have patented a process in which the fragrance molecules are sprayed onto the substrate after the softening agents—which are heated until molten and pressed into the nonwoven fabric—has cooled. This minimizes loss of the fragrance molecule.
P&G staves off the degradation of fragrance molecules by encapsulating the molecules in cyclodextrins. In the dryer, water molecules evaporating from wet clothes help release the perfume molecules from the cyclodextrin carriers, according to Günter Wich, corporate R&D director of biotechnology at Wacker Chemie AG, the company that produces cyclodextrins for P&G.
What's In a Standard Dryer Sheet ?
Although you get the same basic effects from any dryer sheet, there are invisible differences in the chemicals that coat different brands of sheets. If you rub a dryer sheet between your fingers, you might notice a slightly tacky feeling. That's the surfactant, a compound that contains a positive charge and a fatty molecule such as a quaternary ammonium salt or a silicone oil [source: Kozen]. As the surfactant heats up during the drying cycle, the fatty substance coats your clothes, making them more pleasant to the touch, and the positive atoms prevent static.
But if you pick up a box of dryer sheets to find out which specific chemicals are in it, you might not see them. Cleaning product makers have to list only the ingredients that are active disinfectants or known to be hazardous [source: Gavigan].
Some safety advocates warn that this policy is a problem, because certain studies have shown that dryer sheet makers may use chemicals that are dangerous for people to ingest or inhale. One such study conducted by a University of Washington professor in 2007 showed that in a group of six scented laundry products and air fresheners, every one made use of chemicals typically considered toxic or hazardous but didn't include them on the label [source: Hickey]. Only one of those products was a dryer sheet, however, and the only two toxic chemicals it gave off were ethanol (also known as alcohol) and alpha-pinene, a fragrance known to be a moderate irritant [source: Steinemann].
How do Dryer sheets work?
Have you ever thought you lost a sock in the dryer, only to discover it stubbornly clinging to the arm of your sweater? Or maybe you've picked up a freshly cleaned shirt, only to feel a stiff texture instead of the warm softness you expected? Just running a load of clothes through wash and dry cycles isn't always enough to make them pleasant to wear.
The reason these problems arise isn't necessarily because your clothing is cheap or because something is going wrong in the laundry. Instead, they're usually side effects of wet washing and the automated dry cycle. When clothes are tumbling together in the dryer, they can become stuck together through static electricity. But fabric softeners -- dryer sheets, in particular -- can help prevent this.
When clothes tumble inside a dryer, friction causes an exchange of electrons on the surface of the materials. Items acquiring excess electrons become negatively charged while those losing electrons become positively charged. The items attract and cling together. The electric charge, which by some estimates can be as much as 12,000 volts, is commonly referred to as static cling. Dryer sheets are coated with positively charged substances that rub off on the clothes in the dryer in the presence of heat. With the clothes positively charged, there is no static cling.
Other chemicals in dryer sheets help to soften clothes and make them wrinkle resistant. Finally, dryer sheets include fragrances that make your clothes smell fresh.
Fabric softeners were invented in the mid-20th century to make clean clothes more pleasant to touch; and later, chemicals were added to help prevent static. But using softener wasn't convenient. They had to be added after the first wash cycle in an automatic washer, because softeners were cationic, with a positive electrical charge, and detergents were anionic, or negatively charged [source: Toedt et al]. Putting the two together caused them to counteract, reducing the effectiveness of both.
The static electricity caused by clothes tossing in the dryer is much like the one that causes a shock when you touch a doorknob.
For many people, the first thing that comes to mind when they think of dryer sheets is static electricity. Dryer sheets are supposed to keep clothes from creating static electricity; if you don't use one, you might have to peel your clothes apart as if they were glued together. What's going on is similar to the shock you get after you shuffle your feet across a carpet on a dry winter day and then reach for a doorknob.
In both cases, a static charge has built up as the result of two very different materials rubbing against each other. The rubbing can knock loose electrons -- the outer, orbiting, negatively charged parts of an atom -- from some fabrics onto others. So your sweater, for example, might end up with too many electrons and a negative charge while your sock might have too few electrons a positive charge. Opposites attract in electricity, which is why the sock might seem to have suddenly attached itself to the sweater.
Another problem is that once a material such as cotton or wool gets a static charge, it might take a while to wear off. So that shock you feel when your fingertip gets close to the doorknob comes from the very fast dispersal of the static charge your body has been holding onto. The doorknob is highly conductive, meaning it's able to move a lot of electrons very quickly. Your typical sweaters and socks aren't very conductive, so the static charges they pick up are slow to dissipate. This is also why a humid day or taking your clothes out while still damp can prevent static. Water is a great conductor, so it disperses a charge before it can build up [source: Krasicky].
If you'd rather wait until your clothes are completely dry, though, dryer sheets might be the way to go. Because static in the dryer is caused by too many loose electrons giving clothing atoms a negative charge, all dryer sheets have to do is balance the electrons with ions, particles with a positive charge. And as we learned in the previous section, fabric softeners are cationic, or positively charged, so they equalize the electrons to prevent static.
Dryer sheet makers solved the static problem early on, leaving them free to add other features such as long-lasting scents. Read on to learn what's in a typical dryer sheet, and whether the chemicals it uses could make you sick.
When clothes tumble inside a dryer, friction causes an exchange of electrons on the surface of the materials. Items acquiring excess electrons become negatively charged while those losing electrons become positively charged. The items attract and cling together. The electric charge, which by some estimates can be as much as 12,000 volts, is commonly referred to as static cling. Dryer sheets are coated with positively charged substances that rub off on the clothes in the dryer in the presence of heat. With the clothes positively charged, there is no static cling.
Other chemicals in dryer sheets help to soften clothes and make them wrinkle resistant. Finally, dryer sheets include fragrances that make your clothes smell fresh.
6. Discussion and Concluions
Making Sense of the Research
Static electricity doesn't just happen in the dryer. You can see it in many other situations, like when you walk across a dry carpet and then touch a metal doorknob, or when you rub two balloons together. In every case, though, some kind of friction is involved.
Although static electricity depends on friction, it isn't caused by friction itself. Rather, it's caused by adhesive forces between the molecules on the surface of the materials. To use laundry as an example: Your socks, like anything else on earth, are made up of atoms. Each of these atoms can be pictured as shells of electrons orbiting a nucleus.
As you might remember from chemistry class, there's a maximum number of electrons that can fit in each shell (usually eight). Atoms are more stable when their outer shell is full. Atoms crave this stability so much that if two atoms brush against each other, they'll try and share or exchange electrons in order to balance themselves out. That makes the atoms, and your socks, stick together—in other words, it creates static cling. When you pull your socks apart after a spin in the dryer, the crackling static electricity comes from the sticky surface electrons being yanked away from each other.
Dryer sheets pre-empt static electricity by releasing positively charged particles that satisfy the cravings of negatively charged surface atoms on your laundry. So now the negative surfaces are more positive, and therefore they're not so attracted to the other positive. The results? Less electron exchange, less adhesion, and less static cling.
7. Reference (information collected, e.g. websites, books, etc.) and Acknowledgement
http://home.howstuffworks.com/dryer-sheets.htm
http://www.wisegeek.com/what-are-dryer-sheets.htm
http://pubs.acs.org/cen/whatstuff/86/8615sci2.html
http://www.sciencenetlinks.com/sci_update.php?DocID=17
Putting the Research to the Test
Place jeans in the dryer with dryer sheet.
Result: The dryer sheet is found amongst the jeans when the clothes are finished drying.
Place cotton shirts in dryer with dryer sheet.
Result:The dryer sheet was found amongst the clothes.
Place delicates in the dryer with dryer sheet.
Result:The dryer sheet was clinging to a pair of silk underwear when the clothes finished drying.
