Remembering plastics find new uses

A remarkable new material is prompting some innovative thinking about what to do with it. Tom Shelley investigates

Shape memory plastics – polymers that return to their original shapes when heated – are finding applications in textiles and medicine but have the potential to play much more important roles. Studies are now underway to incorporate them into shape changing storage containers, furniture and even cars, giving new meaning to the word 'convertible'.
These rather special materials were first discovered by researchers at the University of Hokkaido in 1995 and polyurethane composite test samples for development work are currently available from Mitsubishi Heavy Industries. They can be moulded to shape when heated, lock in that shape when cooled, and then recover the original shape if re-heated unrestrained. In this respect they behave differently to shape memory metal alloys, which may be deformed when cold and recover their original shape when heated.
The first commercial use for the Mitsubishi material is in outdoor wear fabrics produced under the Diaplex trademark. On being warmed, natural Brownian motion opens up pores, allowing moisture and body heat to escape. The pores close again on cooling.
According to entries on the World Wide Web, research is under way in Germany and the United States on the use of shape memory plastics for medical purposes. Reported uses under development include self-tightening thread for stitches, temporary implants which could be inserted in a compressed form, and artery opening stents, which could be inserted as linear fibres but then and turn into ‘corkscrews’.
Florian Ortkrass and Hannes Koch, with support from the Audi Design Foundation, have been investigating the possibility of making shape memory cars and furniture as part of their degree course studies at Brunel University. At the recent university Design Show they showed model shape changing cars capable of transforming from a saloon with minimal wind resistance to one with an expanded rear section. This, achieved with the aid of waste engine heat, would allow the transportation of bulky cargo items. They were also able to demonstrate shape changing furniture made from composite sheets with built-in heating elements. These took two minutes to heat up, could then be formed into any desired shape, and then took five to ten minutes to freeze. Re-heating restored the original shape.
The two designers say that Mitsubishi can make materials that transform at temperatures from 55 to 90degC and is working on one that transforms at 120 deg C. And they are now working together in a company they have set up in Berlin to develop their ideas further.
Another student, Dan Shepherd, had the bright idea of making initially flat containers that could be heated under a hot tap, expanded to hold food, and then frozen to shape under the cold tap.
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Design Pointers

D/T/A-Text: Shape memory plastics may be formed to shape above their transition temperature and then frozen to retain this shape

D/T/A-Text: They then recover their original shape if heated without restraint

Tom Shelley

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