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22/05/2008
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Low-cost, but super strong, nanocomposite plastics are not far off, says Tom Shelley
 Low-cost, but super strong, nanocomposite plastics are not far off, says Tom Shelley
The introduction of clay nano particles into low-cost polymers to greatly enhance their strength could be on the verge of wide adoption.
It has long been known that reinforcing with nanoparticles has the potential to make low-cost plastics very strong. Until now, however, introducing very finely divided materials into molten polymers – and ensuring they stay finely divided – has proved difficult, requiring the use of techniques such as building up fabrications in a succession of very thin layers.
AK Industries in Hereford and Pera in Melton Mowbray have been collaborating on a number of advanced plastics-based projects.
“There are certain ways you can introduce nanoclays into polymers,” says Alastair Green of AK Industries. “You can take a polystyrene or PBT and get these up to the properties of a nylon or glass-filled nylon. We are also working with Loughborough University, who are doing a lot of work on the clays. Pera is working on introducing it into the polymers. We are improving the clay at the outset and looking at better ways of introducing it into the polymer, so you get a better effect.”
Previously, the best that could be done was to build up fabrications in thin layers. For example, engineering professor Nicholas Kotov at the University of Michigan in the US has been leading a team in a project in which a piece of glass is dipped into a glue-like polyvinyl alcohol solution and then into a liquid containing a dispersion of clay nanosheets. After these layers have dried, the process is repeated. Using this method, it takes 300 layers of polymer and clay nanosheets to create a piece of material as thick as plastic wrapping. The layers form co-operative hydrogen bonds that, when broken, can easily re-form in a new place.
While this produces a structure similar to that employed very successfully in mussel and oyster shells, it is hardly a practicable method of manufacturing mass-produced products.
AK Industries and their colleagues have their sights set on using their new technologies to produce competitively-priced surgical instruments and other products. For example, concerns about cross infection mean there is a move to make surgical instruments that are disposable, rather than having to be sterilised before re-use. There is also disquiet that some infectious agents, particularly prions, are not destroyed at normal sterilising temperatures. Furthermore, there are a growing number of procedures that are not carried out in hospitals, but in GPs’ offices, where proper sterilising autoclaves are not to be found.
Part of the concern is price, but not entirely, since it was pointed out that steel instruments are now coming in at such a low prices that they can be disposed of. Alastair Green explains that instruments such as scalpels have a very small blade in a heavy handle.
“Plastic allows you to have a better distribution of weight,” he says. “We are looking mostly at forceps and scissors. These still have to be sterilised prior to use, in which case, nanoclays then help to reduce heat distortion.”
And there are other products to which nanoclay reinforcement might be applied. “Pera is focused on injection moulding,” he adds, “but we are also looking at passenger compartmentation on trains, where nanoclay-reinforced plastics could replace aluminium.”
Pointers
* Pera has developed technologies that allow nanoclays to be properly dispersed in polymers, in a way that renders them suitable for injection moulding
* They are working with a moulding company with commercial applications in mind and a UK university that is improving the preparation of the nanoclays
* The intention is to apply the technology to low-cost polymers and make products, particularly for the medical sector, with properties that would normally require the use of high-cost polymers
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Author
Tom Shelley
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