New coating could make cars scratch-proof


12 March 2009

A futuristic new material that uses sunlight to repair any scratches on its surface has been developed by US researchers. The material has great potential for making self-repairing coatings for cars or electronic devices - keeping them looking brand new for longer.  

Biswajit Ghosh and Marek Urban at the University of Southern Mississippi in Hattiesburg modified polyurethane, a popular tough and durable polymer commonly used to make protective coatings, by adding a compound called  oxetane-substituted chitosan. This compound is derived from chitin, a natural polymer commonly found in nature that makes up the shells of crustaceans such as crabs. 

Cracks repair in 30 minutes

Hairline cracks are sewn up in 30 minutes

© Science

The approach works because any physical damage to the polymer, such as a deep scratch, results in damage at the molecular level - breaking open the polymer's oxetane rings. When incorporated into the polyurethane network, the chitosan strands break into two reactive free radical halves under UV light - these strands can react with the open oxetane rings, forming new polymer links across the gap and effectively 'sewing up' the scratch. 

The team demonstrated that a hairline crack - around 10 micrometres in thickness - could be completely knitted back together under bright UV light in around 30 minutes. However, they have not yet investigated more complex damage or deeper scratches.  

'This is the first time we have seen self-healing polyurethane coatings - which of course have a great deal of commercial importance,' says  Nancy Sottos at the University of Illinois at Urbana-Champaign, who works on developing self-repairing systems. 

The largest area of interest is in the automotive industry, where car paint is often designed with high scratch resistance to prevent damage from small objects like stones. Since this new material uses a cross-linking polymer reaction that is unaffected by humidity or moisture, there is a great deal of potential to make a protective "clear coat" for cars, Sottos says, but notes that it could be a while before it hits the market.  

'Like any new technology, this material will have to go through rigorous testing to show that it can withstand the same environment that a standard automotive paint would,' Sottos told Chemistry World. 'For example, one question would be how well the material performs in hot climates such as Arizona or Australia, where the cross-linking effect would be permanently activated by high UV levels.' 

Other industries could also be interested in the technology, and it will be up to engineers to develop the technology further, Sottos says. One huge market could be consumer electronics, as mobile phones and music players are notoriously prone to getting scratched. 

 Lewis Brindley 

 

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References

B Ghosh and M W Urban, Science, 2009. DOI: 10.1126/science.1167391

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