20 years ago, Stephanie Kwolek became only the fourth
woman to enter the US National Inventors Hall of Fame, 30 years after she
first synthesised a material for the purpose of making strong but light tyres.
That material is now used in more than 200 different
applications. It protects undersea optical cables, suspends bridges with
ultra-strong ropes and creates super-taut drumheads. But Kevlar is perhaps best
known for saving countless lives as a protective material in bulletproof vests
Kwolek, a chemist at American company DuPont, created a
solution of para-phenylenediamine and terephthaloyl chloride in 1965 that was
‘cloudy, opalescent upon being stirred and of low viscosity’. Polymer solutions
are normally syrupy, but Kwolek’s was thin and watery.
DuPont technician Charles Smullen refused to run the
solution through a spinneret, the apparatus used to spin a polymer solution
into a fibre, saying it was too watery and interpreting the opalescence as
particles that would clog the machine. Thankfully, Kwolek was persistent, and
Smullen agreed to spin the fibre.
‘We spun it, and it span beautifully,’ Kwolek beamed in a
2012 interview. ‘It was very strong and stiff – unlike anything we had made
before. I knew that I had made a discovery. I didn’t shout “Eureka!” but I was
very excited, as was the whole laboratory excited, and management was excited,
because we were looking for something new. Something different. And this was
The high tensile strength-to-weight ratio of Kevlar is five
times that of steel. When layered together, it can absorb the velocity of
shrapnel or a bullet, distributing its force across the fibres instead of being
pierced. It is used in tennis rackets, skis, boats, ropes and cables and, as
first intended, in tyres.
Kwolek, who also developed the nylon rope trick classroom demonstration,
died in 2014 at the age of 90, having lived to see her invention take more
forms than she could have possibly anticipated. Kwolek’s was a rare discovery
with perhaps the most rewarding property a material can possess. As she put it,
‘I don’t think there’s anything like saving someone’s life to bring you
satisfaction and happiness.’
Here’s a fantastic documentary from the Chemical Heritage Foundation: Women in Chemistry: Lessons from Life and the Laboratory, featuring Nancy Chang, Uma Chowdhry, Mildred Cohn, Mary L. Good, Kitty Hach-Darrow, Paula Hammond, Stephanie Kwolek, and Kiran Mazumdar-Shaw. About an hour long, but worth it. By virtue of my education and the larger part of my career history, I am most familiar with Mildred Cohn. She was a goddess of biochemistry.