(Image: CC BY-SA 3.0)
Combine the hard stuff in shrimp shells with a spider silk protein and you get shrilk, a tough, biodegradable replacement for world-choking plastics
At least the archaeologists will be pleased. If you were wrapped in disposable nappies any time after their widespread adoption in the 1960s, traces of your faeces will probably remain preserved deep in some landfill for a good few hundred years at least, awaiting analysis by scientists looking for insights into a peculiarly profligate era of human history.
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鈥�8.8% Of the 31.8 million tonnes of US plastic waste in 2012, the proportion recycled was only鈥�
That鈥檚 because those nappies, like a good deal of our worldly goods today, contain an unhealthy dose of non-biodegradable plastics: sodium polyacrylate, the polymer that traps urine in the nappy鈥檚 core; polyethylene plastic for the waterproof outer shell; and polymer-based adhesives to keep all the different bits together. Not to mention the polyethylene package they are sold in. Like them or loathe them, petroleum-derived synthetic polymers are the defining materials of our age.
They鈥檒l remain so for many years to come. Plastics have serious staying power, and few places on Earth have been spared: the remotest ocean gyres teem with our plastic castaways; deep oceans are choked by polymer particulates; and special expeditions are required to remove kilos of trash even from the 鈥渄eath zones鈥� of Mount Everest above 8000 metres.
Yet we can鈥檛 kick the habit. No material is as flexible, cheap and strong as plastic. Biodegradable plastics derived from the world鈥檚 most abundant organic polymer, plant cellulose, are one alternative, but their higher cost means that even after close to a century of research, .
Shelling out
For and Javier Fernandez of Harvard University鈥檚 Wyss Institute for Biologically Inspired Engineering, the answer lies with the world鈥檚 second-most abundant organic polymer: chitin, the stuff that makes insect exoskeletons so tough. Combine chitin from shrimp shells and fibroin, an insoluble protein in spider silk, and you get鈥� 鈥渟hrilk鈥�.
Shrilk is tougher even than chitin, and its flexibility can be dialled up or down by varying its water content. It is flame-retardant to boot. But its strength is the main draw. 鈥淚t鈥檚 stronger than either component by itself,鈥� says Ingber. Indeed, shrilk鈥檚 resilience rivals that of aluminium alloys. 鈥淲e still have moulded sheets we made out of the stuff more than a year ago,鈥� says Ingber. But as soon as you want it gone, just throw it on a damp composting heap and microbes will complete its transformation into fertiliser within weeks.
Ingber and Fernandez are now looking for commercial partners to help bring shrilk鈥檚 costs down. Its mouldability still leaves something to be desired, too, so the duo have moved on to chitosan, a derivative of chitin, which can be used to stamp-mould exactly the kinds of throwaway products that now clog landfills: cheap toys, bottles, cellphone parts. Last year they used injection moulding, the favoured plastic production method, to make a chitosan chess set as proof of principle.
But shrilk is the more flexible material in all senses of the word. 鈥淚t has the right properties to be used to replace many plastics,鈥� Ingber says, even plastic bags. The one thing shrilk cannot do is preserve centuries of our effluvia 鈥� but then, you can鈥檛 please everyone.
Read more: 鈥�Wonder stuff: Seven new materials to change the world鈥�
This article appeared in print under the headline 鈥淔uture stuff: Shrilk鈥�
