The development of strong materials still continues, both for new fibres and for ways to use them.
Originally Kevlar was designed for use as a replacement for steel in radial tyres but now has seemingly unlimited uses, from chord on the airbags of the mars pathfinder; to shrapnel resistant shielding in jet aircraft to protect passengers in the event of an explosion; to lightweight, small diameter ropes used to moor large naval ship and supertankers; to lighter stronger sports equipment like tennis racquets and skis. And undoubtedly the range of uses will continue to expand as new pursuits and the need for lightweight materials increases.
However as strong and light Kevlar is it still has some disadvantages, in its most famous application as a bulletproof material Kevlar is not ideal as it is very stiff and so consequently the wearer suffers a great loss of movement, a great disadvantage when used by police who often need to react quickly. Kevlar also absorbs water and is consequently more susceptible to environmental influences than some other strong materials such as graphite base materials. Despite it incredible tensile strength Kevlar also has relatively poor compressive properties and so there are still improvements, which can be made.
Looking to nature
One of the most exciting developments in the search for super strong materials is the attempt to mass produce spider dragline filament (the thread used to suspend spiders from the ceiling), this substance is much stronger and lighter than steel and has a tensile strength of up to 300,000 pounds per square inch.
However spider silk has proved to be difficult to collect in large quantities as arachnids are extremely territorial and tend to eat other spiders in their vicinity and so producing large quantities has previously been uneconomic due to the very large spaces, which would be needed to collect enough thread.
In 1999 Nexia signed a research and development agreement with the US and Canadian Defense departments to look into the production of spider silk using goats. This is possible due to recombant gene technology and the fact that milk glands are very similar to the spider’s silk gland. The goats are genetically modified so their genome includes the DNA necessary to produce the silk, and once they start lactating the silk will be contained in the milk. Goat were chosen above cows for this process because of their much shorter gestation period, so the herd will expand more quickly and hence more silk can be produced.
The previous method of trying to gain spider thread for experimentation was using bacterial fermentation to produce the thread, but this method caused very short threads, unsuitable for making into fibres.
The goats milk is capable of producing 15g of spider thread per litre of milk and with production of milk being in the thousands of gallons, from 700 head at the two sites in Quebec and Plattsburgh NY, the amount of silk available will accumulate fairly rapidly.
The herd is now producing enough silk to be spun into fibres and an effective method of producing the thread, with the same pulling action that the spider employs to give the threads extra strength and the elasticity that are present in a spiders web.
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