chemical heritage

Egbert van Heemskerck - An Alchemist in His Study

17th century

oil on canvas

Chemical Heritage Foundation, Philadelphia

Kevlar turns 50

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 and helmets.

Kwolek beneath a picture of Nylon inventor Wallace Carothers © Chemical Heritage Foundation 

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 it.’

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.’

By Simon Frost.

vimeo

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.