Fifty-odd years ago, freezing conditions in the Korean War sparked a demand for woollen uniforms and a boom to remember for the Australian wool industry, but few could have then imagined that wool would be one day used to stop bullets, too.
Yet that is the unlikely role that wool can play when it is interwoven with the Kevlar fibre currently used in many bulletproof vests, RMIT in Melbourne has found through largely AWI-funded research.
Chief investigator Dr Rajiv Padhye of RMIT’s School of Fashion and Textiles, who worked on the project with Dr Lyndon Arnold and Mr Kanesalingam Sinnappoo, said that Kevlar’s legendary strength, which has revolutionised the practicality of body armour since its introduction in the 1980s, comes with some drawbacks.
One is that Kevlar is a low-friction material. Woven Kevlar vests are not designed to stop bullets outright, like ceramic or metal plate armour, but to dissipate a bullet’s energy and slow it up. Kevlar’s low friction makes it possible for a bullet to slip between fibres.
Kevlar’s other related failing is that it offers even less friction if it gets wet. It can become up to 20 per cent less effective in a ballistic vest as a result.
A typical bulletproof vest has 36 layers of fibre—enough to stop the bullet going through the vest, and at the same time absorb enough of the shock to prevent fatal “blunt trauma”.
As a bullet penetrates the first layers, the friction it creates as it breaks through fibres transforms kinetic energy into heat. The more layers, the more heat, and the more the bullet is deformed.
The ideal result is a bullet transformed into a mushroom shape, trapped in the fibres of the vest.
RMIT researchers found that weaving in 25-30 per cent wool fibre with the Kevlar helps the fibres to stay together, greatly decreased the chances of a bullet “shouldering through” Kevlar fibres without breaking them.
Importantly, this effect is enhanced when the Kevlar/wool vest gets wet.
Wool’s wet-weather performance, which has made it a favourite for outdoor wear for millennia, comes from the fact that it can absorb 36 per cent of its own weight in moisture before feeling wet, while at the same time expanding up to 16 per cent.
This expansion tightens the weave in the ballistic cloth, countering Kevlar’s loss of friction under wet conditions.
The research has mixed implications for the wool industry.
On the one hand, the market for bulletproof vests is large. Dr Padhye said that in the recent Indian elections, 1.4 million bulletproof vests were ordered for police and defence forces in anticipation of a lively contest.
Each vest weighs about 3.4-5 kilograms. If a quarter of that weight was wool, Dr Padhye observed, the election order alone would use up to 1.75 million kilograms.
On the other hand, the RMIT work is using coarse wool, straight from the scour, with no other treatment—not exactly the quality, value-added product that the industry has been pushing for years.
Dr Padhye acknowledges that wool mix ballistic vests aren’t going to hit the catwalks anytime soon.
“What’s important here is the profile that wool can get,” he said. “It’s a way of saying look, wool has lots and lots of properties that people aren’t aware of.”
RMIT has since completed enough work to commercialise the wool-mix ballistic cloth, and is now hunting for a commercialisation partner for the product.
Now, Dr Padhye said, the challenge is to find an Australian commercialisation partner who will use Australian wool.
As with so much Australian innovation, however, that is proving difficult. And the alternative is that Australia research will go overseas, to a company that chooses to buy cheaper wool from China or Russia.
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