All My Colours
June 2012
Scientists in Singapore are producing coloured silk by feeding dyes to silkworms.
Researchers from the Institute of Materials Research and Engineering Department of Bioengineering at the National University of Singapore have been conducting experiments on the uptake of pigments within silk worms’ fibroin glands to find ways of producing coloured fibres, and avoid costly and lengthy fabric dying. Dr. Natalia C. Tansil and Dr. Ming-Yong Han released their preliminary findings in a progress report published in the Journal of Advanced Materials in February this year. This primarily technical article has captured the imagination of fashion and textile designers with the colouring and luminescent possibilities hinted at by the report.
Silk holds exciting potential to be one of the first fibres to be produced in vibrant colour. Currently inherently coloured fibres are limited to black, brown, orange and grey wools, and a small range of natural tones from speciality cotton breeds.
One of the oldest textiles continuously farmed by humans, silk is produced by a variety of arthropods, most commonly the silk worm. Over the long history of silk farming, or sericulture, domestic worms have been bred to produce white cocoons for aesthetic purposes. White silk is traditionally coloured once the silk has been harvested by applying dyes. More recently science has been experimenting with different ways of inducing worms to produce coloured fibre, including genetic modification, and changing silkworms’ diet.
Colouration achieved by alteration of diet is attractive for a number of reasons. Genetically modified silk, while providing an alternative colouration, still faces anti-GMO consumer sentiment and market resistance. Conventional industrial silk dyeing involves harsh processing conditions, including high temperature and pH. These processes change the attractive characteristics of silk, weakening it and making it more brittle, and can require further chemical treatments to remove excess dye molecules, add lustre and handle, and to restore the original properties of silk. These processes are complicated and require additional time, money and transportation. Furthermore these processes are implicated in degrading the natural environment; efforts to address the negative impacts of textile dyeing are currently directed towards developing methods to remove toxic dyes from effluents, and this is a costly undertaking involving combinations of biological treatment, chemical coagulation and activated carbon adsorption. Inherent colouration would remove the need for these complicated and expensive procedures.
Towards developing a replicable and wide scale production of inherently coloured silks, Tansil and Han demonstrated that domesticated silkworms could absorb some colourants through their digestive systems into their silk-producing glands. This was achieved by feeding silkworm larvae carotenoid-rich leaves of mulberry mixed with different coloured and fluorescent molecules including Rhodamine B and Acridine Orange. They claim that this biological incorporation of dyes into silk is not only an environmentally but also commercially attractive way of producing the functional silk. They suggest that it eliminates external dyeing, along with the need for resources like time, water, energy and chemicals.
Additionally, where externally dyed silks show degradation of quality, inherently dyed silks show similar strength, handle and other performance indicators when Tansil and Han tested them against untreated white silk. They also suggested that the colours last longer due to the direct integration of pigment in the fibre structure.
Producing intrinsically coloured silk directly from silkworms gives hope for high quality, long lasting coloured silks, and promises to negate the need for wasteful processes associated with conventional dying. But what are some of the questions this process raises?
Firstly, how to achieve uniformity of colour saturation in silk farming conditions. To collect the silk for one shirt requires the silk from up to one thousand worms, so how is it possible to ensure that all of those worms eat the same proportion of pigment? How could standard colouration for an entire fashion collection be achieved?
A further consideration – how do silk moths with pigment in their systems interact with the wider ecosystem? If silk is farmed in industrial conditions and larvae killed to harvest the silk (a common practice unless silk is labelled ‘peace’ or ‘tussah’), how can the larvae be disposed of without the colourants leaching into the surrounding environment? It appears that the dyes used to feed the worms would not be toxic to avoid poisoning the worms, but what are the effects of colourants on other life forms, including humans, and how do these colourants persist as silk biodegrades?
Lastly, is the energy required to make the dyes, administer silk worm diets and farming less than the savings in time, energy, water and chemicals needed to dye silk? Intuitively this seems to be the case, but it would be interesting to view a comparative study.
Meeting those concerns, inherently dyed silk promises to be an exciting development in the textile industry. Luminescent textiles have multiple applications in fashion and performance wear. Clothes could be brighter and last for longer. Bike riders could be seen at night, mountaineers find their tents and luxury labels make life difficult for would-be imitators.
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