Stephanie L. Kwolek, inventor of Kevlar

Sixty years ago, a Polish-American chemist named Stephanie Kwolek made a breakthrough in polymers that would have far-reaching applications. The fabric material Kevlar was born in 1965 and has since been used in racing tires, sails, tennis rackets, archery bow strings, brake pads, musical instruments, and much more. It is most famously known for the life-saving component in bulletproof vests. As with many discoveries, Kwolek created the material for Kevlar in an unexpected way.

Image from Science History Institute

She was born in New Kensington, Pennsylvania on July 31, 1923 to Polish immigrants. Her father, a foundry worker and naturalist, imparted in her a scientific curiosity of the world as they explored forests and fields near their home and filled scrapbooks with samples from those locations. Her mother was a seamstress, and for a while Stephanie considered being a fashion designer and practiced on paper dolls and then made cloth versions. The creativity in this practice gave her a lot of satisfaction.

Paper doll figures and fashions to attach to them ( Paperdoll Review )

However, that career ambition died early when her mother told her she probably couldn't make a living doing it because Stephanie was too much of a perfectionist.

In her public school, two grades of students were taught in the same room with separate lessons. But she got to hear what was going on in each, so essentially she learned two grades at the same time.

Kwolek's elementary school building ( YouTube, Women in Chemistry: Stephanie Kwolek )

Next, she attended Margaret Morrison Carnegie College (now Carnegie Mellon University) with a major in chemistry and hopes of becoming a doctor after graduating in 1946. Kwolek admits to being influenced by enthusiastic Professor Clara Miller in her chemistry class. She must have done something right, because she was invited to join a panel of male chemists to discuss their work at a gathering at the university in just her first year!

Image from video at sciencehistory.org

Carnegie Mellon photo, from YouTube "Stephanie Kwolek"

However, she couldn't afford medical school, and instead she thought about making enough money for that by getting short-term chemistry work. At this time, DuPont was the leading chemical company in America, so it seemed logical to her to apply there. DuPont had been founded in 1802 and played a significant role in supplying munitions to the Union side of the Civil War, plus 40% of smokeless gunpowder in World War II. It also built the nuclear facility in Hanford, Washington to make plutonium for the Manhattan Project. It also produced innovative materials like synthetic rubber neoprene (1930) and nylon (1935).

When she interviewed for a job there, DuPont's research director William Hale Charch said she could expect to hear back in two weeks. She pushed back, though:

With great boldness—I would never do it now—I said to him, “I wonder if you could possibly tell me sooner because there is another company that wants me to decide whether I should come and work for them.” So he called in his secretary, and he dictated the letter to me while I was sitting there, and offered me the job. (from March 21, 1998 interview, Chemical Heritage Foundation)

Image from PBS video

Work for women in science then was difficult because of the male-dominated culture. And, most female PhDs quit research after 2 years to transition into teaching. But, Stephanie admits to being stubborn and sticking it out because of her creative nature and desire to learn new things. Men and women were paid similar wages, too.

Stephanie Kwolek and her boss, Paul Morgan at DuPont (PBS NewsHour)

Her early work at DuPont was with polymers, which are long-chain molecules. A few years earlier, materials like nylon were produced with high temperatures, so her work was intended to save energy and improve safety by using low temperatures to make the same polymers. Those made at high temperatures were flexible and soft, but DuPont wanted a product that was more rigid for use in car tires and other tough uses. 

She was in the lab, mixing liquids for her polymer experiments one day when she noticed a cloudy, unusual polymer solution. It didn't look like it would work for what she was asked to make. Normally, polymer solutions are clear and syrupy, but this was cloudy and as runny as water. 

Kwolek and the cloudy polymer solution to be spun into pre-Kevlar fibers (A Mighty Girl)

The cloudiness bothered the technician that she asked to run it through in order to make fiber threads. He thought the cloudiness meant it had particles which would plug the spinneret machine's holes which were 0.001 inch in diameter.

Spinneret machine output (Textile Study Center)

and a diagram of the spinning process to change polymer solution into thread (Science Direct)

Stephanie filtered the solution and found no particles in it. The technician still refused. She ran it through a single syringe and found the threads to be very strong. So, the technician passed through the spinneret machine and generated far more material. Not only was the fiber incredibly strong and stiff, but it had a higher melting point than anything made before. 

Polymer fibers used to make Kevlar; Kwolek and DuPont team describing its properties (YouTube)

That liquid was made into the first fibers of Kevlar, with the strength about five times greater than steel by weight. Its other properties include being lighter than fiberglass and resistant to wear, corrosion, cuts, fatigue, and flame. All of this allowed Kevlar to be used in lightweight bulletproof vests and helmets, racing sails, aircraft, and even drums.

Kwolek and Kevlar thread and related materials (The Lemelson Center/Smithsonian)

She published her work in the journal Polymer in 1966 and her supervisor's name was Paul Morgan. Kwolek stated how proud she was to have discovered a product that saves lives. She credits her coworkers and supervisors, all male, for their encouragement and joint curiosity in doing research. To her own credit, it should be known that although she was instrumental in developing 16 patents with DuPont, she did not profit from any of the products, because she signed over the Kevlar patent to the company. DuPont saw the importance and invested $500 million to develop it further.

Kwolek with DuPont colleagues Herbert Blades, Paul W. Morgan, and Joseph L. Rivers Jr (sciencehistory.org)

Stephanie Kwolek worked at DuPont until she retired in 1986. Her discoveries led to such products as Lycra spandex (the elastic fiber for athletic clothing) and Nomex (a flame-resistant fabric for fire fighters). She continued working in chemistry as a consultant, but perhaps more meaningful was her volunteer work as a mentor for young women scientists in high school. 

Kwolek at a science event for children (YouTube)

Stephanie Kwolek was awarded many honors, including the Perkin Medal in 1995, and induction into the National Inventors Hall of Fame in 1996. Despite holding only a bachelor's degree, she received honorary degrees from Clarkson University and Worcester Polytechnic University. And, in 2007, her alma mater Carnegie Mellon issued her an honorary Doctor of Science degree, too. To this day, she is the first and only female recipient of DuPont's Lavoisier Medal for outstanding technical achievement.

Kwokek receiving her honorary degree from Carnegie Mellon (TIME for Kids)

Stephanie L. Kwolek passed away on June 18, 2014 at the age of 90. On that day, DuPont announced it had just sold its one millionth Kevlar vest.