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 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: Stephani 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!
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)
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.
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 was working on making tougher, more durable polymer material for things like tires. In the early 1960s, there was a fear of a gasoline shortage coming, so more gas-efficient tires were deemed necessary.
DuPont's Pioneering Research Laboratory, 1940s
She was then put in the laboratory of Paul Morgan where she was assigned to work on a polymer called a para-aromatic polyamide. It broke apart at the molecular level when it was melted, it didn't dissolve easily in comment solvents, and was too stiff to be spun into threads. Nobody else in the lab wanted to work on the project, and Morgan was busy writing a book, so he didn't pay attention to her work.
Despite Morgan's absence, Kwolek credits all men who worked with and over her, saying that she felt fortunate they were very interested in making discoveries and inventions. In those days, you couldn't learn polymer science in school. Men and women alike "started on an equal basis ... I had to study up just as the men did. We helped each other and learned from each other. Somehow, I never set myself apart, or thought lesser of myself, because we all seemed to start on an equal footing." (quote from invention.si.edu) What's more, to her delight, they left her alone to do her own experiments even though she had only a bachelor's degree.
She worked on a specific polymer abbreviated 1,4-B (for poly-1,4-benzamide). But she couldn't just buy it off the shelf to do experiments. She had to make it on her own, including making all the necessary ingredients!
I had a technician who helped, but because it was such an early stage, I had to work with him to observe just what was going on. I had to devise new ways of doing things as we went along. I couldn’t just give him a recipe and say, “Do this.” (From March 21, 1998 interview, Chemical Heritage Foundation)
Image from YouTube
The next step was to dissolve 1,4-B and then run it through a machine to make thread. After testing many solvents unsuccessfully, Kwolek chose to dissolve her polymers in tetramethyl urea. Polymer solutions are usually transparent and syrupy. Stephanie's, however, was cloudy as buttermilk and opalescent (showing many small points of shifting color). She thought, "There’s something different about this. This may be very useful." Her technician in charge of the spinning machine (spinnaret) refused to use it because he thought the cloudiness meant it had particles floating in it and therefore would plug up the small holes (0.025 mm, or 0.001 inch in diameter) in the spinneret. Normally, such a solution would be thrown away.
But, Stephanie filtered the solution and observed no particles. So, she put some in a syringe and forced it out the needle to make a thread herself. When she heat-treated the strange thread, she measured a strong ability to resist a change in shape (deformation). So, she thought she was on to something and pestered the technician again until he ran the polymer solution through the spinning machine.
When she ran the strength (deformation) test on this material, it showed an amazing result.
- Soft rubber's value is 0.01-10 megaPascals
- nylon was 1,000-3,000 megaPascals
- her new material was 130,000 megaPascals
- in comparison, steel is 200,000 megaPascals
Further testing and refinements showed that the material matched the requirements of her project, that of being lightweight and heat resistant, but it was also five times stronger than steel. 1,4-B was then passed on to another section of the lab for further development. Stephanie donated some of the thread she'd made, and another scientist wove it into a vest and conducted early tests as a bulletproof vest material which later became Kevlar in 1971. Stephanie signed off her patent royalty rights to the polymer, and DuPont invested $500 million into it. It has since been used in over 200 applications.
Fibers used to make Kevlar (Wikipedia)
Kwolek continued to work at DuPont until she retired in 1986. During that time, she consulted on lab research into three other products: Nomex, the flame-resistant material for firefighters, Lycra spandex, and Kapton (a film for printed circuits and space blankets). She is the first female recipient of DuPont's Lavoisier Medal for technical achievement. (Only one other woman has received that, but it was in 2022 and in collaboration with another scientist.)
After retirement, she not only continued to consult with DuPont, but she tutored high school students (especially girls) in chemistry. She was the recipient of several other awards and honors including 17 patents. In 2001, her alma mater Carnegie Mellon University awarded her an honorary degree.
Stephanie L. Kwolek passed away on June 18, 2014 at age 90. On that day, DuPont announced that they has just sold the millionth vest made from Kevlar.
