a new technique may solve one of the biggest snags for a plastic recycling company: the numerous variety of plastic waste, ranging from tough transparent cola bottles to soft, light polystyrene packaging.

When an assortment of different plastic polymer is melted, its various components don't mix well. They solidify into a material that contains different types of plastic, making it unstable and weak. "Different polymers just give rubbish,' says Alan Davey, general manager of Linpac, Britain's largest plastic recycling company.

But now Francesca Cavalieri and Franco Perella at the Italian National Agency for New Technology, Energy and the Environment (enea) in Rome have come up with a technique that produces a strong, high-value polymer from a mixture of waste plastics. It works by smashing up the molecules of the waste polymers, then allowing them to recombine to produce hybrid molecules that yield a homogenous melt.

enea's polymer recovery process uses a laboratory-scale version of an industrial machine called a ball mill. Its chamber is partially filled with tough tungsten carbide balls that are eight to 15 millimetres in diameter. When the chamber is vibrated vigorously, the balls smash anything in the chamber to a fine powder.

But this isn't enough to break apart the polymer molecules. Cavalieri and Parella's new twist is to add dry ice