A few weeks ago, I described carbon fibre and this article is about Kevlar – another material discovered via chemistry. It was back in 1965 that a chemist at Du Pont, Stephanie Kwolek, discovered the forerunner of Kevlar. She had mixed a batch of polymers and it was cloudy rather than clear and so she decided to test it further. The cloudy solution was spun into a very light and very strong para-aramid synthetic fibre which turned out to be 5 times stronger than steel. In fact Kevlar is the registered trade name and is owned by Du Pont.
What is a para-aramid fibre? Aramid is short for aromatic polymide and this is a very strong synthetic fibre that has the basic structure similar to wool or silk but is made from oil based chemicals. Para-aramids like Kevlar were developed after chemists had discovered materials like nylon and nomex.
Nylon was really the start of something big because from this base, chemists at companies like Du Pont and ICI in the UK started to experiment to see what other materials could be developed. Nomex from Du Pont was developed in the early 1960s and had flame resistant qualities, so garments such as racing suits were created because they could offer the driver a safety suit in case things got a little hot. When I started racing (34 years ago!) I used a single layer Nomex suit that gave me 9 seconds before it disintegrated. 9 seconds doesn’t sound much but in reality it could be enough time to deal with the impending problem! Many suits were 3 layers that gave significantly longer times before the suit gave way.
So, Kevlar came from this base too and has significant strength qualities like carbon fibre and as such was first used to replace steel in racing tyres – the manufacturers wanted the strength without the weight. Kwolek and her team at Du Pont were looking for a synthetic fibre for tyres because in the early 1960s there was a concern that oil would run out and they wanted to find a way to reduce consumption. An odd thought as oil was the basis of the original material!
There are three grades: Kevlar, Kevlar 29 and Kevlar 49. Base Kevlar is still used in tyres and similar products, Kevlar 29 is used in body armour and products where the manufacturer wants to replace asbestos. Brake pads are a good example. Early pads used asbestos that turned into a dangerous powder, but later pads use Kevlar instead that produces an aramid powder that is harmless. Kevlar 49 is the strongest version and is used in race cars, boats and other load bearing items.
Kevlar is affected by Ultra Violet (UV) rays and decomposes when subjected to high doses, so manufacturers paint or cover the Kevlar with a resin layer to protect it from the sun. Kevlar also loses its strength if it is subjected to high temperatures for a period of time. By high temperature, I mean well over 150C for many hours will reduce the strength of the fibre. Thankfully, most uses of Kevlar are in products that get used in a much lower temperature range.
For many years Du Pont owned Conoco, the oil company and this guaranteed a steady supply of oil for use in their chemical plants, however, in 1995 they sold their shares as Conoco was merged with the Philips Petroleum company and Du Pont started to look at how they could extract the raw materials needed from plants.
Like many products, there have been other companies developing similar fibres under different trade names and Du Pont has been clever in licensing the manufacture of Kevlar to other organisations so that their product has a wider reach in the market.