Discarded plastic bottles can be broken down to make ultra-strong carbon spheres that could be used in lubricants. 

Vilas Pol from Bar-Ilan University, Ramat-Gan, Israel, and colleagues produced strong carbon microspheres from waste polyethylene terephthalate (PET). They heated used cola bottles at 700 °C for three hours in a closed reactor. The plastic then decomposed under self-generated pressure to form the hard carbon spheres with diameters between two and ten micrometres. 'We broke one diamond knife and damaged a second while cutting a cross-section of the spheres,' says Pol.

'The strength of these materials is interesting,' says Neil Coville, coordinator of the Carbon Nanotubes and Strong Composites group at the University of the Witwatersrand, Johannesburg, South Africa. 'The results are impressive and suggest others should be measuring this property in the future.'   

'The process is particularly interesting,' says Philippe Serp, an expert in carbon nanostructures at the National Center for Scientific Research, Toulouse, France, 'as it does not use any catalyst.' Pol's scalable process also does not require solvents and improves on existing methods that can be limited by low yields and poor separation of the spheres from carbon soot. 

Carbon spheres are used in energy storage and nanodevices. Pol's microspheres can withstand significant pressure, so they could be used in lubricants. Lowering the reaction temperature to below 700 °C gives larger carbon particles that could be used in printers, toners and filtration technology.  

'The challenge facing today's scientific community to find an innovative solution to the degradation of waste polymers motivated us,' explains Pol's colleague Aharon Gedanken. 'Our process demonstrates a way to remediate waste PET polymer to fabricate value-added products.' 

Kathryn Wills