US researchers develop plastics that can be reshaped at low temperatures.

Imagine being able to squeeze plastic toys into drink bottles and vice versa. Impossible with any plastic available today, but materials scientists in the US have come up with 'baroplastics' that, under pressures of around 345 bar, melt at just 30°C.

The trick is that they contain one rubbery and one glassy component, says Ann Mayes, professor of materials science and engineering at the Massachusetts Institute of Technology (MIT). She and her team combine these components either as block-copolymers of the form polystyrene-block-poly( n -butyl acrylate), or PS-b-PBA, or as core-shell nanoparticles, with a rubbery polystyrene (PS) core and a glassy shell of about 70 nm diameter.

'We are now studying the mechanical properties of these materials and also of baroplastics-based composites including inorganic fillers,' says Mayes. 'These studies should give us a better idea of which applications are most promising for the first generation of materials.'

The MIT team has already moulded such binary materials into various shapes at low temperatures. They have also shredded objects into 3 mm pieces, and then re-moulded new forms, again and again. Preliminary results suggest that baroplastics remain completely unchanged after more than 10 cycles of cold remoulding.

Such resilience compares well with recyclable polyethylene terephthalate (PET), concedes JÖrg Jansen, a spokesman for the Deutsche Gesellschaft für Kunststoff-Recycling (DKR), which has been recycling plastic domestic waste since the early 1990s. 'Pure PET can run through a bottle-to-bottle cycle about six times before the decay of the carbon chains becomes noticeable', says Jansen. But he would not be drawn on the prospects of baroplastics: 'That is brand-new, we have not been able to test it yet.'

Mayes acknowledges the challenge: 'Introducing a new commodity plastic into the market is a difficult proposition'. She hopes the economic advantages of baroplastics will help to secure backing: 'The potential energy savings from low-temperature manufacturing are an important selling point.'

Should that fail, Mayes will fall back on plan B. 'It may be that the first commercial applications would be niche markets created by their unique low temperature processing capability,' she says. 'For example, as a matrix material for thermally sensitive components like biologically based therapeutics.'

Michael Gross