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Last Updated: Wednesday, 26 November, 2003, 18:25 GMT
Low-heat plastics aid recycling
By Paul Rincon
BBC News Online science staff

Plastic straws
The new process could benefit recyclers
Scientists have moved a step closer to the large-scale recycling of plastic, one of the great environmental problems of the 21st Century.

Researchers have worked out a way to mould plastics into shape without heating them.

At present, plastics are exposed to high temperatures until they are soft enough to be pressed into new shapes, something that weakens them.

The US researchers have published their study in the journal Nature.

The new method allows the plastics to be reprocessed without visibly damaging the molecular chains they consist of.

The team from Massachusetts Institute of Technology (MIT) in Cambridge, US, mixed powdered polystyrene - a "hard" plastic - with a powdered soft plastic, such as polybutyl acrylate.

When pressure was applied to these powdered plastics in a mould, the hard component dissolved into the soft component making it malleable and easy to remould.

Shredded plastic

The scientists shredded and remoulded these plastics up to 10 times and saw no change in their properties.

"It is quite similar to the processes we use that are already part of the plastics manufacturing process," said Dr Anne Mayes of MIT, who led the research.

The key difference, said Dr Mayes, was the use of hard and soft components in the plastics.

Pressure-moulded plastic, Mayes
The plastics were remoulded at room temperature
This removes the need to heat plastics to high temperatures and would reduce the high quantities of energy used to heat and then cool the moulds at manufacturing plants.

The technique may also require lower amounts of additives, such as flame-retardants and ultraviolet stabilisers to be applied to plastics.

The process could go a long way to making large-scale recycling of plastics more feasible.

Viable process

"It would be useful for recycling, provided it really does not [degrade the plastics]," said Dr Hazel Assender, a materials scientist at the University of Oxford.

"It also needs to be a viable industrial process."

Dr Assender said there were many other issues impeding large-scale plastics recycling. For example, plastics need to be sorted so that the same types are recycled together.

At the moment, there are few alternatives to doing this by hand. Plastic recycling is currently very costly, making it difficult for recycling firms to recover the costs.

"Right now we have to learn more about what [this technique] can do and what it can't do," said co-author Juan Gonzalez-Leon of MIT.

Mr Gonzalez-Leon said the technique could improve controlled drug delivery systems. This includes devices implanted under the skin to administer medicines inside a person's body.

These are made by implanting drugs in a polymer matrix and they work by releasing the drug slowly as the polymer erodes.

But many proteins lose their shape and function when exposed to temperatures above 37C and might be harmed if the polymer matrix part of the drug delivery device is heated.

Moulding the devices at room temperature could eliminate this problem.




SEE ALSO:
Call for levy on plastic bags
28 Oct 03  |  Scotland
Battling to recycle
11 Jul 03  |  UK


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