Kwolek learned how to make long molecules called polymers that can be made into fabric or plastics. In 1964, her supervisor asked Kwolek and her coworkers to search for high-performance fibers. "At that time, we were already thinking about strong and stiff fibers, and one of the reasons why we were thinking in that direction was we had already seen that there was the possibility of a gas shortage. Now, if you could reinforce tires with a textile-type of fiber, which is lightweight, rather than steel wire, which is very heavy, you could use much less gasoline to operate the cars or airplanes or whatever other vehicles." Research chemists were also looking for fibers that wouldn't melt at very high temperatures, so that they could be used safely for objects that might get very hot or be exposed to such conditions.
During a typical day, Kwolek would combine substances to make a polymer, melt the polymer into a liquid, and ask a coworker to spin the liquid in a machine called a spineret. The spineret turned the liquid into fibers. Then, other scientists would test the fibers to see how much they weighed, how strong they were, and whether they stretched or broke easily.
One day, Kwolek was experimenting with two polymers that just wouldn't melt. She had to find a solvent that would dissolve the polymers into a liquid, instead of melting them. But something unexpected happened when she mixed one of the polymers and the solvent. She tells the story: "And one day, after many, many tries, I dissolved the polymer. But the solution was unlike any other polymer solution we had seen in the laboratory. Ordinarily, when you have a polymer solution of a flexible polymer chain, it sort of reminds you of molasses. It may not be as thick but is generally of a transparent or transluscent nature. With the polymer solution that I had, it was almost like water, and it was cloudy." When she stirred the solution, it separated into two layers: one yellow and clear, and one opalescent and cloudy.
Curious, she took the solution to the man in charge of the spineret. As she remembers, "he said to me, 'this will never spin, it flows like water. And, furthermore, it has particles in it and these will plug up the holes of the spinneret.' Well, previous to talking to him, I had filtered the solution....and there was no separation—the whole thing went through. I was convinced this solution would spin, because it just had the right flow and cohesive properties." After several days arguing with the man, "I wore him down," Kwolek laughs. "He said he would spin it. So we spun it and it spun beautifully," she says with a big smile. "I pulled on the fibers and they didn't fall apart, so I took them down to the physical test lab. We had them measured for strength and stiffness. A few days later, the results came back and I was really amazed. It was a very strong fiber, but the thing that really amazed me was the stiffness." And, when she baked the fiber, it became even stiffer. Kwolek had discovered a new fiber, called an aramid fiber, and a new type of substance, called liquid crystalline solutions.
Stephanie Kwolek is still amazed at her discovery, saying, "I knew the direction in which to go, but I will tell you this: I never expected to get the properties I did the first time I spun it." Her discovery was, she says, "a case of serendipity."