As DuPont’s year-long celebration of the 50th anniversary of Kevlar® came to close, CIMS’ Innovation Management Report marked the occasion by publishing a tribute to Stephanie Louise Kwolek, the inventor of the versatile, now-ubiquitous fiber, which is five times stronger than steel and has many lifesaving applications. In an article titled “Her Discovery Led to Kevlar®,” in the November-December 2015 issue, IMR Editor Mike Wolff reports on Kwolek’s honors, how she made the discovery that led to Kevlar®, and her early career experiences in a predominantly male world. Below is an excerpt:
“When I look back on my career, I am inspired most by the fact that I was fortunate enough to do something that would be of benefit to mankind. It’s been extremely satisfying discovery. I don’t think there’s anything like saving someone’s life to bring you satisfaction and happiness.”
Stephanie Louise Kwolek’s reflection concluded her 1996 video interview for the Chemical Heritage Foundation’s Catalyst series on women in chemistry. Among her many honors, Kwolek was the fourth woman inducted into the National Inventors Hall of Fame. Her bio on the Hall’s site (www.invent.org) attests to the widespread recognition and popularity she enjoyed during the last decades of her life, which ended at age 90 on June 18, 2014:
“Thousands of police can attest to the value of Stephanie Kwolek’s breakthrough research in para-aramid fibers,” her bio reads. “The fruits of her inventiveness can be found in mooring ropes, fiber-optic cables, aircraft parts, canoes, and lightweight bullet-resistant vests…”
Kwolek joined DuPont’s Buffalo, N.Y., Rayon Department in 1946 after receiving her bachelor’s degree in chemistry. Her monthly salary was $240. She transferred to the new Textile Fibers Pioneering Research Lab at the Wilmington Experimental Station four years later.
The 1950s was an exciting but also difficult time to be doing polymer chemistry, Kwolek told an interviewer in 1986: “I realized at the time that because I had only a bachelor’s degree, it would not be easy, that there would be prejudice, not only because of the fact that I had a bachelor’s degree, but especially because I was a woman. I decided that I would get my compensation from writing scientific papers, giving talks and doing quality research.”
David Tanner, technical director of DuPont’s Fibers Department, traced the events leading to Kwolek’s discovery in an address to the 1988 materials science conference celebrating nylon’s 50th anniversary.
“In Du Pont, in the early 1960’s, we were driven by two goals—a fiber with the heat-resistance of asbestos and the stiffness of glass. We visualized that a fiber of this type could fill many market needs. Experimental work indicated that the route to reach “new heights” lay with stiff chain aromatic polyamides. But these materials had evaded the scientist by nature of their extreme insolubility and intractability!
The breakthrough came in 1965. Assigned to work on the polymers with the rigid, rod-like molecular chains from which Kevlar was eventually made, Kwolek related how she was given “tremendous” independence.
“Devising” as she went along, “eventually, I was able to work out the whole procedure so that you were able to get high molecular weight polymer; but the problem, then, was that I couldn’t dissolve it. I spent quite a bit of time looking, because I had to have an organic solvent. … I went through a series of solvents and finally found that it was soluble in tetramethylurea with lithium chloride.
“By January of the next year, I had spun the polymer… I had noticed that once it was dissolved in tetramethylurea, this polymer made an extremely odd solution. It was unlike any of the polymer solutions that we had, which are generally rather viscous and transparent. Here I had this watery type of solution, even though it was somewhere about 10-15 percent in concentration. It was opalescent when I stirred it. It was cloudy and you thought, “Well, this is one of the no-no’s” as far as spinning is concerned because you would plug up those holes that were 1/1000th of an inch.
“I decided that I would filter this through a very fine filter and the solution was cloudy on both sides of that funnel. Then I put some on a spatula, and I saw that it flowed very readily, and it was a cohesive type of flow as compared to water, which usually drips after a while.”
Kwolek then told her interviewer the story she would repeat many times, of asking the man in charge of the spinning equipment to spin that solution. “He refused because he looked at that thing and he said, ‘It’s too thin. It’s cloudy. It’s going to plug up the holes’ and all this sort of stuff.”
She went back to the lab. Her account continues: “As I spun some from this hypodermic syringe, I saw that it was very crude. Generally when you spin, you also draw fibers, you stretch them. Of course, this was not drawn. But if I heat-treated it, I got this very high modulus. I tormented him for a while, and he finally conceded and said he would spin it. I think he probably thought, ‘Well, I’ll give it a try and if it fails, then that’s the end of that.’ We spun that 1,4-B solution and the fiber was very strong. It spun beautifully.”
Kwolek sounded more emotional in her 1996 interview: “It was very strong and very stiff unlike anything I had made before. I knew I had made a discovery. I was very excited as was the whole lab excited, and management was excited because we were looking for something new and something different, and this was it.”