Denim 101: without chemistry, your favorite pair of jeans would be singing the blues.
* According to a survey by Cotton Inc., the average American owns 8.:3 pairs of jeans. The average American teen, however, owns 11 pairs. Americans between ages 16 and 24 wear denim jeans or shorts 4.6 times per week.
* Until the 1960s, jeans were called "waist overalls."
* It takes approximately 6,814 liters (1,800 gallons) of water to grow enough cotton to make one pair of blue jeans.
* What does it take to create a typical pair of Levi's[R][degrees] 501[R] jeans? Approximately 1.6 meters (1.75 yards) of denim, 195 meters (213 yards) of thread, 5 buttons, 6 rivets, and 37 separate sewing operations.
* Jeans are as popular as ever. Today, the price of jeans can range from a few dollars to several hundred dollars. Most jeans are made of the same fabric. So why are some jeans so expensive? Explain your reasoning.
SOCIAL STUDIES: Have students do research to write an essay about how the image of jeans has changed since their invention in the late 1800s.
* For more information about the science of jeans, read "The New Wrinkle," by Suzanne Wu, Wired, May 2005. The article is also available at: www.wired.com/wired/archive/ 13.05/start.html?pg=13
* To learn the answers to frequently asked questions, visit this Web site from Cotton Inc.: www.cottoninc.com/DidYouKnow/
* For more facts about jeans manufacturing, visit: http://ohioline.osu.ed u/hyg-fact/5000/5541.html
Suppose someone were to tell you that your favorite pair of boot-cuts held a chemistry lesson. You'd probably just laugh. But the joke would be on you. Read on to find out how science helps jeans go from drab to lab.
Whether they're light or dark, stiff or frayed, designer jeans all start out as run-of-the-mill, light-colored cotton yarn. So what sets apart your hippest pair of denims from preppy-looking khakis? The secret lies in a blue dye made of indigo molecules (particles of two or more atoms joined together).
Manufacturers dip the yarn, which comes from cotton plants, into a vat of indigo dye. Under the right conditions, atoms on the surface of the indigo molecules bond, or link, with atoms in the yam's cellulose (substance in a plant's cell walls). Indigo is such a large molecule that it can't penetrate the yarn. Instead, it forms a layer around the yarn's surface, says Mary Ankeny, manager of textile chemistry research at Cotton Inc. One dip creates a light-blue shade. To create darker shades, manufacturers dip the denim in the dye repeatedly, adding more and more layers of indigo to the layer that initially bonded to the yarn. One hitch: Indigo only bonds weakly to the surface of the yarn, so it is easy to bump off, says Ankeny.
Designers take advantage of indigo's short-lived bonding abilities to create stonewashed jeans. To give denim this worn-in appearance, manufacturers wash the denim with rough stones, which scrapes off layers of indigo.
An enzyme, or protein that starts or speeds up chemical reactions, called cellulase is also added to the wash. Cellulase further lightens the denim's color and softens the fabric by breaking down the cellulose in yarn. "Cellulase eats away at cellulose. And as it chews it away, the indigo comes off," explains Ankeny. Result: Jeans that look like you've lived in them for years.
How do some jeans get their permanent just-worn wrinkles? First, manufacturers crumple the jeans into the desired look. Next, they treat the denim fabric in a solution of resin. Then, they bake the treated fabric. During this drying process, the resin substance undergoes a chemical reaction and links molecules within the denim fibers, durably bonding them to one another. This holds the fabric structure in precisely the form it had at the time of baking. "Resin curing can give denim fabrics a memory of the appearance preferred by the designer," says Richard Aspland, a textile chemist at Clemson University in South Carolina. So jeans that were wrinkled before the baking process will still hold their wrinkles afterward.
MADE TO FIT
Like the form-fitting look of Raven Symone's jeans? They don't come easy. Along with every other pair of jeans, her denims were once as stiff as a piece of cardboard. That's because manufacturers coat the cotton yarns that make up a pair of jeans with starch, a molecule that plants use to store energy. Starch strengthens the yarn so it doesn't break in the machines that weave it into denim. It also makes the fabric easier to handle during cutting and stitching.
But you won't look great hobbling around in superstiff jeans that have been coated with this fabric strengthener. So before form-fitting jeans make it to the shelves at the mall, they have to be washed in a starch-dissolving enzyme called amylase--an enzyme that's also found in your saliva. Amylase removes the starch from jeans, softening them so they're ready to wear.
If you want distressed jeans but don't feel like spending all day working in the garage to get the look, you can relax. Many of today's jeans have the "dirt" and "grease" washed right into them.
How does it work? The greasy look comes from a slick-feeling polymer (chain of molecules) called urethane, says Cotton Inc.'s Ankeny. Fashion designers spray it on a pair of jeans mad then bake them, permanently bonding the urethane to the fabric. The result? Am oily look mad feel that won't wash out.
And to make jeans look like they've been dragged through the mud, designers spray on dyes in shades of brown, green, or purple. What will be the next hot denim look? It's anyone's guess, says Ankeny. "Anything you can possibly think of doing to jeans, I've seen people do."