Camouflage made from biodegradable foams of algae and cellulose derived from wood pulp or tree bark could make objects in forests difficult to spot with visible and infrared light.
Full spectrum cameras can detect a wide range of wavelengths of light, so it is no longer good enough for camouflage to conceal objects in the visible part of the spectrum alone.
at the H盲me University of Applied Sciences, Finland, and her colleagues combined the insulating properties of a cellulose-based foam with the visual properties of microalgae and wood pulp or tree bark to make a green-and-brown camouflage. Not only do its 听colours blend in with forest hues, it releases little heat and so is also hidden from infrared light, which can be picked up using a thermal detector.
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鈥淭he idea was to make something like polar bear hair,鈥� says Laaksonen. 鈥淲e would have this very porous material that would have great thermal insulation properties, but then we added鈥� natural dyes and pigments from a biological origin.鈥�
To make the foam, Laaksonen and her team passed birch pulp through a series of high-pressure chambers to extract cellulose nanofibres. They then mixed these fibres with water and a dye and used a high-pressure pump to produce a foam.
It is difficult to camouflage objects using the greens found in nature because they are based on chlorophyll, which is unstable once it has been harvested from plants. 鈥淚f you just tried to extract the green chlorophyll out of some fresh leaves or something, you lose the colour very, very quickly,鈥� says Laaksonen.
The team instead used chlorophyll in a living microalga called Chlorella vulgaris, which gave the foam a stable green colour that matched some forest shades.
Even so, the alga on its own blended in relatively poorly, possibly because of the over-representation of one shade of green. Laaksonen and her team compensated for this by using a second foam containing pulp or bark-derived material, which offers a brown forest shade.听
The microalgae also appeared to make the foam more stable over a 2-hour period, although the full lifetime of the foam wasn鈥檛 measured. Laaksonen says the foam might need to last longer for real-world scenarios.
The material was originally developed as part of a report for the Finnish Ministry of Defence, but Laaksonen thinks the foam could have other uses for people who spend time in forests, such as hunters needing to hide from their prey.
Soft Matter
