Renewable colours: Sustainable dyes

The petrochemical-based textile dyes that colour our wardrobes are responsible for nearly 20 percent of water pollution by industries.
The petrochemical-based textile dyes that colour our wardrobes are responsible for nearly 20 percent of water pollution by industries. © FRANCE 24

Fashionistas are spoiled for choice in tints, shades and hues, but our rainbow wardrobes come at an environmental cost: synthetic dyes, derived from petrol, are responsible for nearly 20 percent of water pollution by industries. For solutions, we look to the old and the new: rediscovering the woad plant, also known as pastel, whose blue pigment coloured the gowns and shawls of medieval Europe; and visiting PILI's laboratories to meet the team harnessing the power of bacteria in the hope of creating dye on an industrial scale without relying on fossil fuels.


Bringing back dyer's pastel  

Blue may be the most preferred colour in the world according to a global YouGov survey, but its occurrence in nature is quite rare. This is what makes the woad plant so unique, explains Sandrine Banessy from Terre de Pastel, a Toulouse-based company that is breathing new life into the plant-based dye.

The woad plant, Isatis tinctoria, also known as dyer's pastel, is "a very simple plant that grows like a big salad... but in fact it's a rare and very precious plant because it's one of the few plants in the world that produces blue," Banessy tells us.

At her workshop on the outskirts of Toulouse, Banessy, adorned in blue, demonstrates a dyeing process that hails from ancient times. Blue pigment is extracted from the woad plant's green leaves and then added to a vat with water. Once fabric is added to the mix, the material initially turns a yellowish green before transforming into blue after coming into contact with oxygen.

Today, Terre de Pastel cultivates 14 hectares of woad, making them one of the largest growers in Europe. The company has also partnered with the CRITT Agro-Ressources laboratory to research the most efficient way to grow and harvest woad with a high indigo content, the blue molecules which produce the colour.

Benessy says her passion stems from a desire to bring back this once treasured but now forgotten plant, as well as offering a cleaner solution to tomorrow's textile economy.

Green chemistry

One of the biggest problems with plant-based dyes is the amount of land required to produce it in sufficient quantities.

"Almost the entire surface of the globe would have to be covered with plants, which is not possible," laments Jérémie Blache, cofounder of the biotechnology start-up PILI.

Like Benessy, Blache and his team are also working to produce colours without fossil fuels. However, instead of plants, they are using microorganisms.

''Bacteria use sugar or agricultural waste for example to feed and as well as growing and reproducing, they produce other compounds such as dyes which we are able to extract and use either in paints or in textile dyeing,' explains Blache.

One of the advantages of this technique is that PILI can produce large quantities within a relatively small area. For example, the size of a swimming pool can produce hundreds of tonnes of pigment per year. One of the disadvantages is the cost, but PILI believes its colours will soon be competitive with synthetic alternatives.

Blue happens to be the first colour that PILI made through its fermentation process. But can they make others?

''We can produce many different compounds through fermentation and modify them into hundreds of colours using green chemistry, so there are few limitations,'' Blache assures us.

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