Author David Brown interviewed Stephanie Kwolek in November 2000.
David Brown: I've read that you were interested in science from a very young age. Did your parents support your interests?
Stephanie Kwolek: I had a father who was generally interested in science, probably more from a biological point of view than a chemical point of view. As a child I remember trudging through the woods near my house and looking for snakes and other animals that dwell in the woods. And I also, with him, studied the various wild plants and leaves and seeds. I remember as a child I had a number of scrapbooks which were devoted to leaves and seeds and flowers. . . . In addition, I was very much interested in designing fashions. I spent a lot of time with that, and I guess that interest came from my mother. I spent many hours creating clothes for my dolls, and drawings, of course. As I grew older I became interested in teaching. And I do remember teaching children in the neighborhood how to do math. I then went on to studying science in school and by the time I went to college, I thought of becoming either an M.D. or a chemist.
DB: When did you become interested in chemistry? Did you have a notable teacher?
SK: I didn't know any chemists as a child. My interest came primarily through school. I majored in chemistry while I was in college. When I got out, even before that, I realized I didn't really have enough money to go to medical school, so I decided to work in the field of chemistry and save my money with the intention of eventually going to medical school. DuPont was very well known for their research, and I very much wanted to work for DuPont. Fortunately at that time DuPont had representatives coming around the colleges and interviewing students. I was fortunate enough to be called for an interview in Buffalo, New York. DuPont had a research laboratory as well as a plant there. I was interviewed by Dr. Hale Charch, who is the inventor of moisture-proof cellophane.
I worked for four years in Buffalo and then the entire group of people who eventually become known as the Pioneering Research Laboratory moved down to Wilmington, Delaware, where a new building had been constructed for us. And this became the Textile Fibers Department, Pioneering Research Laboratory. That was in 1950. I started working for DuPont in 1946.
DB: So it was just a happy coincidence that you wound up working with textile fibers, considering your earlier interest in clothes?
SK: I wasn't aware that the group in Buffalo was even involved in making fibers. But it was just one of these things that happens. Fortunately for me.
DB: What kinds of opportunities were there for women chemists at the time?
SK: The field had opened up for technical people because it was right after the war ended. So there was a demand for women, particularly technical women, because so many of the men had been at war and were just not available. So at the lab in Buffalo there were a goodly number of women, all of whom had degrees in chemistry or physics. There were a number of analytical chemists, and then people like myself who were in the polymer field. I did not feel that there was a scarcity of women. Of course, that wasn't the case elsewhere. But for some reason, Dr. Charch employed a goodly number of women.
DB: What kind of lab work led to the discovery of Kevlar? What research had you done to lead you to that point, where you could be making that particular type of solution?
SK: I worked on new ways to make polymers and to make fibers. Prior to that time, all polymers had to be melt-spun. This required a polymer that could withstand high temperatures and was meltable without degrading. This is what got us into searching for new ways to make polymers, and particularly making polymers at low temperatures. By low temperatures I mean somewhere between 0 or 10 degrees and 100 degrees Centigrade [32 to 212 degrees Fahrenheit]. During that period, we made hundreds of thousands of polymers that could not be made by the old methods. We began making new fibers that were used in the textile field, like Orlon and Lycra, and so forth. We got into the field of polymers that did not melt, or degraded before they melted, because they melted at such high temperatures. It's then that we got into the field of industrial fibers. Of which Nomex is one, and this preceded Kevlar.
By 1964, we had decided it was time to search for a new high-performance fiber. At that time there was talk of a gasoline shortage. So we thought that if we could find a fiber that was lightweight like the textile fibers but which could withstand very high temperatures and was very strong and very stiff, it could be used for reinforcing radial tires, this would be our objective. The tires would be lighter weight, yet very strong and very stiff, the result of which was that they would use less gasoline.
So a number of people had been asked to take up this project and no one seemed to be particularly interested, so I was asked if I would do it. And I of course consented. I started out working with two polymers, which were aromatic, that means they had benzene rings in them. I knew from the work on Nomex they would be very resistant to high temperature, and I thought at the time that considering the structure with the polymers that they would also give me greater stiffness than Nomex did.
I started with two polymers, both of which were totally aromatic and they were what is called tara-oriented aramidic polyamids. . . . I started working with the two simplest ones in that field. And in the course of that work I made a discovery. I found that a certain class of these polymers, more specifically this group of polyamids, that had what are called rigid rod-like molecules, will form liquid crystals in solution, under very specific conditions. When these liquid crystalline solutions are forced through the hole of a spinneret, they form fibers in which the polymer molecules are arranged parallel to the long fiber axis, or along the length of the fiber. As a result of this arrangement of molecules, these fibers are very highly crystalline and oriented and have very high strength and very high stiffness and other desirable properties.
This is very important, because the standard polymers, like Nylon or Dacron, have fairly low softening points when they're heated up. What you can do is stretch these fibers of Nylon, and as you stretch the molecules in that fiber, which are generally scattered about in a haphazard fashion, they are straightened out along the long fiber axis. This improves the properties of that fiber. Yet here's this fiber like Kevlar which doesn't soften. This means you cannot stretch it. If you don't have a technology of having these molecules already arranged and stretched out, there's no way, up to this time, no way of improving the properties of this fiber.
But with [this new polymer], right in spinning, as a result of having liquid crystals, you immediately get a fiber with very high strength and high stiffness.
DB: When did you realize that it was an important thing?
SK: As soon as I had spun the first fibers. [These fibers weren't] the present Kevlar. Every time you spin a fiber you send it down to the physical test lab and they measure the strength and the stiffness and the elongation and break. And then they send these properties back to you. By the numbers you know what the quality of your fiber is. So the first fiber I obtained, I sent the fibers down and I remember especially because the strength, it was above the standard fiber, but what really shocked me was the stiffness. Nylon or Aspun or some of the other ones have a stiffness number of somewhere around 25 and 50 or so. This fiber came back with a value of 450. This at the time was stiffer than glass fiber, which was considered to be very stiff.
I was very hesitant about telling anyone, I didn't want to be embarrassed if someone had made a mistake, so I sent the fiber down several times. The numbers always came back in the same vicinity. And with that I told my supervisor and the lab director and everyone became very excited. We realized then that we had a fiber with great potential for commercialization, as a replacement for tire cord.
We then got together a fairly large group of people, the objective being to find the best fiber for commercialization from this group of polymers that have rigid rod-like molecules. So people worked on various fibers. We specifically dwelt on the other polymer that I had started out with and this eventually became the candidate. And of course during this time many people made significant contributions and other patents were issued. So this is the story of Kevlar, but there's more to it, because there were many problems that had to be resolved.
We thought the tire industry was going to be very interested in what we had. We discovered that they weren't, because they had steel wire for reinforcing tires and most people do not want to change the machinery in their plants. So we were stuck with no applications. So we got together a group of people whose function was to find new applications for the Kevlar fiber. They certainly found a lot of very interesting ones. Particularly, as you know, in protective vests and protective gloves, and actually used in tires for trucks and bicycles. I remember when I went to the White House, the men who protect the grounds use it in their bicycle tires. They came and told me that. We ended up with something over 200 applications.
DB: And the discovery was a bit of an accident?
SK: When I made that solution it was very different from the standard polymer solution. A standard polymer solution has the flexible molecules, so you end up with a rather viscous solution. This was a thin, cloudy solution. And when you stirred it, it was opalescent and it had a lot of strange features about it. I think someone who wasn't thinking very much or just wasn't aware or took less interest in it would have thrown it out. I looked at it and I put some on a spatula and I let it flow, and it wasn't dripping the way an ordinary thin solution like water drips when you put some on a spatula. It flowed beautifully, it was very cohesive. I filtered the solution through a very fine solution and it was still cloudy when it came through the filter. Yet when I submitted it for spinning the guy refused to spin it because he said it would plug up the holes of his spinneret. He assumed that these were particles, solid particles. So it was a while before he consented to spinning the solution. I spun with him. I think either I wore him down or else he felt sorry for me.
As I said, it spun beautifully. So for me it wasn't a surprise, but for everyone else it was a surprise. Especially because the lab had at no time had thought in terms of liquid crystals. But it was funny, when later on we went back to some textbooks, Paul Flory, the Nobel Prize winning chemist, had actually done a theoretical study of polymer liquid crystals. That was very exciting, particularly when someone who knew him got in touch with him and he came in. I remember how excited he was that someone had made this discovery, of something that he had said would happen theoretically.
DB: Is there something in your approach to research or chemistry that helped you see the potential in this batch of cloudy polymer?
SK: I'm very conscientious. And I discovered over the years that I seemed to see things that other people did not see. I don't know what you attribute that to. Also I love doing chemistry. And I love making discoveries. So I find it very exciting. Generally, if things don't work out I don't just throw them out, I struggle over them, to try and see if there's something there.
But you have to be prepared in chemistry. You have to have a certain background. You have to be inquisitive about things. You have to have an open mind.
DB: What is it like to be responsible for such a famous and lifesaving material?
I feel very humble. I feel very lucky. So many people work all their lives and they don't have a big break or make any big discovery that's of benefit to other people. I'm certainly very grateful and very pleased. I am [also] very happy for all the people who worked on the project.