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The bird’s nest soup of filter media research

Adrian Wilson

From volcanic rock formations to low temperature plasma-coated membranes for advanced filtration may seem like something of a leap, but geo- and bio-mimicry are now throwing up such connections regularly in the development of new technical textiles and advanced materials in general. As the keynote speaker at this year’s Filtech conference – held last week in Wiesbaden, Germany – Professor Kuo-Lun Tung, of the Centre for Membrane Technology at the National Taiwan University, went right back to Leonardo Da Vinci in citing examples.

30th October 2013

Adrian Wilson
 |  UK

Construction, Industrial, Civil Engineering, Transport/​Aerospace

From volcanic rock formations to low temperature plasma-coated membranes for advanced filtration may seem like something of a leap, but geo- and bio-mimicry are now throwing up such connections regularly in the development of new technical textiles  and advanced materials in general.

As the keynote speaker at this year’s Filtech conference – held last week in Wiesbaden, Germany – Professor Kuo-Lun Tung, Department of Chemical Engineering at National Taiwan University and the R&D Centre for Membrane Technology at the Chung Yuan University, went right back to Leonardo Da Vinci in citing examples.

Da Vinci may have been unsuccessful in his time at appropriating the methods of birds to achieve a flying machine, but others following in his footsteps eventually succeeded in providing us with today’s miracle of manned flight.

An ideal filter media, Professor Tung explained, must have a high hydraulic permeability towards solvents, semi-permeability, mechanical strength and durability, chemical and thermal stability and reproducible properties in manufacturing. © Adrian Wilson

The very latest military development in this respect, however, is to mount micro-cameras on tiny machines adopted from the dragonfly’s structure.

“In the near future, it won’t be just fixed objects that are watching you constantly, but the insects too,” Professor Tung said, ominously.

He went on to identify the termite mound as the most successful air conditioning system – and show how this has been taken as the template for revolutionary new buildings.

The Eastgate Centre in Harare, Zimbabwe, for example, is the country’s largest office and shopping complex. It has no conventional air-conditioning or heating, yet stays regulated all year round, and with dramatically reduced energy consumption too.

Professor Tung’s own recent work has centred on the development of atmospheric plasma spraying onto advanced filtration materials. © Adrian Wilson

The phenomena of the Gecko lizard’s feet as a highly effective adhesives and the ‘lotus leaf effect’ in providing water-repellent textiles are now well known, but the bird’s nest as the template for nanofibre-coated needlepunched nonwovens is something I for one, had not really considered before – although it seemed obvious once mentioned by Professor Tung. The spaces in the structure of the nonwoven are simply plugged with layers of finer materials to provide infinitely more effective filtration and/or insulation properties, that can be tuned as appropriate.

In Japan and elsewhere, much work is also being done on approximating the properties of biological membrane proteins and the hydrophobic lipid cushioning layers within them that make them such effective filtration layers at the nanoscale.

As far as geo-mimicry is concerned, one need look no further than graphene, as a diamond-like nanosheet, along with other materials in the same ball-park such as ceramic composites based on the structure of ice and the collagen scaffolds developed in Japan that are based on similar micro-patterned structures.

The spaces in the structure of the nonwoven are simply plugged with layers of finer materials to provide infinitely more effective filtration and/or insulation properties, that can be tuned as appropriate. © Adrian Wilson

Professor Tung’s own recent work has centred on the development of atmospheric plasma spraying onto advanced filtration materials, and the lesson from nature taken has been in the formation of natural zeolites which form where volcanic rocks and ash layers react with alkaline ground water. This results in highly-effective filtering structures of both macro and micro pores.

An ideal filter media, Professor Tung explained, must have a high hydraulic permeability towards solvents, semi-permeability, mechanical strength and durability, chemical and thermal stability and reproducible properties in manufacturing.

But at the same time, it must also be cheap and easy to manufacture.

Professor Tung and his team at the National Taiwan University – along with industrial and academic partners around the world – believe they are now coming close to achieving all of these goals with their new and patented process for manufacturing such complex – if originally at least, entirely ‘natural’ – filter media.

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