Stephanie Kwolek, the American chemist and inventor who has died aged 90, created the first in a family of synthetic polymers that would later be spun together into Kevlar - a lightweight fibre with myriad applications, most famously in the construction of bullet-proof vests.
In the early 1960s the chemical company DuPont was searching for a way to reinforce car tyres without the use of heavy steel belts. At the time there were predictions of an oil shortage, and researchers hoped that a new lightweight-yet-strong breed of tyre would result in more fuel-efficient cars. With a team of chemists called the Pioneering Research Laboratory, Stephanie Kwolek began experimenting on a group of long-chain molecules with a rigid rod-like structure, known as aromatic polyimides.
She discovered that under certain conditions, these polyimides would form liquid crystals in solution. Whereas most polymer solutions are thick, this one was fluid and turbid, almost as though it had been contaminated. The colleague in charge of the spinneret initially refused to operate it on the grounds that it might clog up his equipment. When they persevered, however, the resulting fibre was stiffer and stronger than anything the team had seen before. “That’s when I said ‘aha’”, Stephanie Kwolek later recalled. “I knew then and there it was an important discovery.”
Subsequent testing showed that the polymer, dubbed “Fibre B”, was flame-resistant, about half as dense as fibreglass yet up to five times stronger by weight than steel. In 1971 DuPont patented Kevlar and began to search for possible applications. They came up with more than 200 uses, from reinforcing bicycles and hiking boots to creating spacecraft, bridges, army helmets - and body armour. The DuPont Kevlar Survivors Club, founded in 1987 by police officers who owe their lives to the Kevlar bullet-proof vest, currently has more than 3,100 members.