Nanofibres spun out in bulk

The stands of materials are between 80 and 500nm and they are being used for numerous commercial applications, but are showing enormous potential for a host of industrial applications including fuel cells, solar cells, and fibre reinforcement to produce super strong composites. The technique has been given the name 'Nanospider', and it allows the production of very fine fibres at significantly lower cost over previous manufacturing methods. The technique uses electrostatic energy to produce streams of polymer from a rotating electrode partially immersed in a polymer dissolved in water. Fibres used to be produced by pumping solutions through single needles or a spinnerette with an electrostatic force being used to help to draw out the fibres. Although the Nanospider technique does require a higher voltage, 30 to 140kV versus 5 to 20kV, it can produce many more fibres at a time from solutions that often contain 15% polymer. And there is never a problem with small holes becoming clogged or blocked during the process. The process can be adapted to a wide range of solutions such as poly vinyl alcohol, polyethylene oxide and various biopolymers. It is already used to spin chitosan – a biodegradable polymer used in various medical device products – but it has also been suggested as a means of spinning synthetic spider silk which has long been a desirable material to artificially reproduce. Key account manager for Elmarco, Peter Sedo, says: "Its use of fibres in filters is now fairly common. You only need a very thin layer of fibres, typically around a micron thick supported by existing media." Elmarco has carried out some work with Clark Filter based in the US for the inclusion of fibres on its filters for environmental dust collection and various automotive air intake filters. It has also carried out work with HemCon Medical Technologies for its wound dressings. The nano fibres can also be very effective for thermal and noise insulation. In addition, there are a number of applications that are being investigated which could benefit from using the technology. Field tests of fibres in dye sensitised solar photovoltaic cells are under way. Sedo says: "Titanium dioxide is mixed into the polymer solution and fragments of fibres which are then incorporated into the cells. Burning off the polymer leaves an exceptionally fine and open matrix of oxide particles." Similar thinking is also being applied to making better fuel cell membranes and advanced composite materials. Because there can be up to three spinning heads with independent chemical distribution systems in the current generation of pilot machines, it is possible to produce threads of up to three different polymers at the same time.