May 4, 2012
Image: Silkworm cocoons. Photo: Wikimedia/Colegota
A new examination of silkworm cocoons suggests how they could inspire lightweight armour and environmentally-friendly car panels.
Scientists from Oxford University’s Department of Zoology studied 25 types of cocoons for clues to how the structures manage to be very tough but also light and able to ‘breathe’.
Fujia Chen, David Porter, and Fritz Vollrath report in Journal of the Royal Society Interface on their research into the factors that enable cocoons to protect their occupants.
‘Cocoons protect silkworms in the wild as firstly a hard shell, secondly a microbe filter and thirdly as a climate chamber,’ Fritz tells me, adding that this order of importance will change depending on the threats and environmental conditions faced by each species.
The lightness of cocoons is down to both the material they are made of – silk – and the way that this is turned into a layered composite material with a clever arrangement of silk loops that are woven together with gum only at the intersections.‘By controlling the density of the 'weave' the animal controls the material properties of each layer, and by having different properties for different layers the animal can make tough yet light structures,’ Fritz explains.
‘In addition many wild silk worms integrate mineral crystals (which they obtain from their food plants) into the composite to give extra strength. Silk cocoons could bring inspiration to light-weight armour by showing ways that animals have solved some of the problems faced by human designers.’
At present most of the cocoons produced around the world are boiled and unravelled to be made into textiles, but the researcher suggest that they could be used to create composite materials that could satisfy the demand for car panels and other components in fast-growing economies such as India and China.
‘Silk cocoons are fully sustainable, non-perishable and climate-smart agricultural products,’ Fritz comments. ‘They are also very light, tough composites. Using cocoons as base materials, in combination with equally sustainable fillers should help us make sustainable composites with many layers of complexity.’
The next stage in the research will involve looking for natural glues and resins that interact well with mats of ‘raw’ (unwoven) cocoons.
Fritz adds: "This will require a good understanding not only of the cocoon materials but also of composite theory and the issues involved in turning that into practice."
Source: Oxford University
- In the paper "Structure and physical properties of silkworm cocoons" by Fujia Chen, David Porter and Fritz Vollrath in the Journal of the Royal Society Interface, published on May 2, 2012.