Stephanie L. Kwolek, Inventor of Kevlar (Bullet Proof Fibre), Dies at 90

Stephanie L. Kwolek, a DuPont chemist who invented the technology behind Kevlar, a virtually bulletproof fiber that has saved thousands of lives, died on Wednesday in Wilmington, Del. She was 90.

The chief executive of DuPont, Ellen Kullman, announced the death, calling Ms. Kwolek, who spent 15 years in the laboratory without a promotion before her breakthrough, “a true pioneer for women in science.”

Kevlar is probably best known for use in body armor, particularly bulletproof vests. A DuPont spokeswoman estimated that since the 1970s, 3,000 police officers have been saved from bullet wounds through the use of equipment reinforced with Kevlar, which is far stronger and lighter than steel.

The product has found its way into all corners of the modern world. It has been used in car tires, boots for firefighters, hockey sticks, cut-resistant gloves, fiber-optic cables, fire-resistant mattresses, armored limousines and even canoes. It is used in building materials, making them bomb-resistant. Safe rooms have been built with Kevlar to protect a building’s occupants during hurricanes. Kevlar has been used to reinforce overtaxed bridges.

Its popularity has proved a windfall for DuPont. Kevlar has generated several billion dollars in revenue for the company. Ms. Kwolek did not directly benefit from it financially, however; she signed over patent royalties to DuPont.

The research that led to Kevlar began in the early 1960s, when women were a rarity in industrial chemistry. Ms. Kwolek was part of a team at DuPont’s research laboratory in Wilmington that was trying to develop a lightweight fiber that would be strong enough to replace the steel used in radial tires.

The work involved manipulating strings of carbon-based molecules to produce larger molecules known as polymers. At one point, in 1964, Ms. Kwolek was struggling to convert a solid polymer into liquid form and finding the results to be a murky disappointment. Instead of the clear, syrupy mixture she expected, the liquid was thin and opaque.

Ms. Kwolek’s peers suggested that the polymer she had concocted would probably not work as a fiber. But Ms. Kwolek persisted. She persuaded another scientist to “spin” the liquid in the laboratory spinneret, a machine used to remove liquid solvent and leave behind fibers.

In “a case of serendipity,” as she put it, she discovered that polyamide molecules in the solution, a form of liquid crystal, lined up in parallel and that when the liquid was “cold spun,” it produced a fiber of unusual stiffness.

When the fibers were tested in 1965, they were found to be five times as strong as steel of equal weight and resistant to fire. Herbert Blades, Joseph Rivers and others at DuPont soon recognized the market potential for a tough, lightweight fabric and began to consider potential uses for the innovation. They have been credited with making it a mass market product.

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The New York Times