Spray-On Fabric

CAREERS FABRICS tce Clothes in a can?

Paul Luckham explains what happens when the Arts meet chemeng

T

he chemical engineering department of Imperial College London has always been an excellent environment to work in, particularly because of the diversity of people that you meet by being here.

I met Manel Torres in around 2000, when he was just about to begin his PhD studies at the Royal College of Art, which is no more than 100 metres from my office. It was Torres who introduced me to the concept of sprayable fabrics.

lateral thinking This was not my first contact with a student from the Royal College of Art: a few years earlier I had met a masters student who had an idea about using the shear thickening properties of corn flour/water mixtures as a speed regulator for wheelchairs. He wanted to prevent them from going out of control going down hill. (See this YouTube video for an idea about corn flour/water properties if you are unsure: www.youtube.com/ watch?v=_SRl-SGTatM ). I was impressed by the lateral thinking here and this prepared me for being receptive to Manel’s ideas.

Manel phoned me just before Christmas 1999. He explained that he was a fashion designer and had been to a party where people had been playing with silly string and had thought wouldn’t it be good if you could actually spray a T-shirt from an aerosol can. To be honest it sounded a bit whacky to me but nevertheless I agreed to meet him. He impressed me with his vision and enthusiasm, though he had no idea how it might be achieved.

f l e s r u yo d e s s e r d Main picture: Activated Carbon Cloth (Carbon Filter Technology Ltd.) february 2011

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FABRICS

At that time I had no experience with aerosol technology. My research interests have been in an area perhaps best pigeonholed as particle technology, and specifically trying to understand how the bulk properties of particulate dispersions such as their rheology depends on the interactions between the particles at the individual particle level. I suggested that we concentrate on making a fabric which could be formed by spraying, and worry about the aerosol can later.

choices, choices The idea which occurred to me then, and which is still the basis of the technology, was that if you could make a formulation of fibres and polymer, the polymer could bind the fibres together to produce something like a fabric. A solvent would disperse the mixture and then evaporate. Our first effort with a plant water sprayer was not successful because there was not enough pressure to push the fairly viscous fluid out through the nozzles. Our thoughts then turned to using an

artist’s airbrush, which uses compressed air and which Manel was familiar with given his artistic background. This worked remarkably well and we were able to produce small volumes of fabric. However, spraying a whole garment in this way would take an hour or more, which was too long. So we invested in a spray gun, which is still the basis of the technology.

The original material was rather hard and brittle but the principle worked, so Manel and I started a company called Fabrican to further develop the technology.

Much of the intervening years were spent modifying the properties of the fabrics to strengthen and soften them. This was achieved principally by modifying the properties of the binding polymer.

The next stage was to put the materials into an aerosol can, so that it could be sold as a product rather than a technology which could be used in a factory. I had no prior experience in either aerosol can technology or propellants, so it was a steep learning curve.

Initially we tried simply pressurising the can

with compressed air, but we discovered that as the material is sprayed, the pressure in the can reduces and so the quality of the product changes with time. Most cans are pressurised with a propellant which transforms from a gas into a liquid on the application of a moderate amount of pressure. Some form of liquefied petroleum gas (often a mixture of propane and isobutene) is the most common; dimethyl ether, DME is also popular. Unfortunately the binders we were using up to this stage were incompatible with both of these propellants, forcing us to reformulate the product. This was disappointing to put it mildly and led to a lot of trial and error experiments.

It turns out that very few polymers are soluble in low molecular weight alkanes such as LPG, and most of those that are soluble are liquid-like anyway and so would be useless as a fabric binder, but a few are soluble in DME. It became clear to us that in addition to its main function, the propellant could act as a solvent to dissolve the polymers in. The first few attempts were disappointing as the nozzles kept blocking, but by experimenting with different valves and nozzles we progressed.

experimental dressing Clockwise from bottom left: Manel Torres sprays fabric on to a mannequin; close-up of the suede-like fabric; demonstrating its strength

Credit: All images Jody Kingzett

Figure 2 Spraying the fabric from a can (Images kindly supplied by Imperial College London photographer Jody Kingzett) Figure 3. A piece of fabric (Images kindly supplied by Imperial College London photographer Jody Kingzett)

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The types of fabrics which can be produced now are varied, ranging from suede and fleece-like fabrics to lint and cotton wool-like materials.

In addition, we can design fabrics to adhere strongly to surfaces or to peel away easily (as in the case of clothes). The difference is largely in the formulations of course, but also in the method of spraying, particularly the distance from the nozzle to the surface being sprayed.

Over the years the quality of the product has improved and become much stronger, though as a nonwoven fabric its strength will always be limited and dependent on how much material is applied. Still, a T-shirt can be sprayed, taken off over the head in a conventional way and put back on again without any problems (see right).

Others prefer to get a bit more creative in undressing. A T-shirt can be cut up the front with scissors and removed like a waistcoat, put back on again, and then the front can be re-sprayed to make a new garment.

In September 2010 we held a fashion show at Imperial College to showcase the technology. It was a very new type of occasion for Imperial College to host.

The main entrance was transformed into a catwalk, and while the girls were a few minutes late they looked stunning, especially when you consider that the

CAREERS FABRICS tce Credit: All images Jody Kingzett

Clockwise from above: Wear a sprayed-on T-shirt; take it off; admire the technology; put it back on again

Credit: Ian Gillett

entire show was created in around three hours. (Videos can be found at www.fabricanltd.com and www3. imperial.ac.uk/newsandeventspggrp/ imperialcollege/newssummary/news_219-2010-13-23-53 ) The fashion show achieved its goal, to showcase the technology, and it did it extremely well. The question is, what now?

While there will always be a use for the technology in fashion design, I do not envisage everyone getting dressed by spraying their clothes on (though the wedding dress pictured right might find a few fans), and people could create eyecatching and unusual clothes to wear to a night club.

Millinery is also another very likely application for the technology, already proved with a hat Manel Torres designed for my wife, Karen to wear at the fashion show.

However I believe that it is in the more mundane areas that this technology will have the greatest impact. I could imagine a shoeshine cloth or a cleaning wipe that comes in a can. Another application is in the field of medical treatment, with sprayable dressings and bandages.

The great advantage with spray-on fabrics is that, unlike a conventional bandage, a can of spray-on fabric stays sterile and can be used multiple times (provided the material was sterile when it was filled in the aerosol can). While hospital use may be limited, it could find use in the home, in first aid kits, on expeditions, and for military purposes including field hospitals. There are numerous other potential applications which we are pursuing currently, some of which, hopefully, you will soon be seeing in the shops. tce

The Wedding Dress from September Fashion show

Paul Luckham (p.luckham01@imperial. ac.uk) is professor of interface science at the department of chemical engineering, Imperial College London

 Related videos Corn flour/water properties: www.youtube.com/watch?v= _SRl-SGTatM Fashion show: www.fabricanltd.com www3.imperial.ac.uk/ newsandeventspggrp/imperialcollege/ newssummary/news_21-9-2010 -13-23-53

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