Indigo is a vat dye and it needs to be reduced to its water-soluble leuco-form before dyeing. This allows the actual dye to pass on to textile fibres. Glucose is known to be a good reducing agent, and Vuorema’s work demonstrates that it also works with indigo.

Glucose dyeing seems to suit plant-derived fibres, such as cotton and flax, which withstand a high pH (11–12). However, at this stage it cannot be recommended for animal fibres, such as wool and silk (which can only withstand a pH of up to 9).

Anne Vuorema’s field of study is not widely known, and there are perhaps only 20 researchers worldwide whose work focuses on plant-derived indigo. Vuorema and MTT launched the indigo research as part of the EU Spindigo project in 2001–2004. The project prompted questions which Vuorema attempted to answer in her dissertation.

Vuorema works as an external researcher for MTT Plant Production Research. The Finnish Cultural Foundation granted a scholarship for her doctoral dissertation in three years. In 2007, the Academy of Finland funded her research at the University of Bath in England. This is where she has conducted most of her electrochemical research.

Vuorema conducted her research at the University of Bath and the University of Reading in 2004–2006. Professor Philip John at the University of Reading was the leader of the Spindigo project and he also supervised Vuorema’s research in Reading.

Anne Vuorema’s research provides answers that enable researchers to improve the extraction of indigo from the leaves of dyer’s woad (Isatis tinctoria L.). Her work enhances the energy efficiency of dyeing and can potentially promote the profitable use of plant-derived indigo.

Dyer’s woad is the best known of all indigo-producing plants in Europe. Plant-derived indigo was commonly produced until the early 20th century when synthetic indigo replaced it. The blue dye used in jeans, for instance, is nowadays synthetically produced from oil, in a process which wastes non-renewable natural resources and burdens the environment with synthetic chemicals.

Electrochemical reduction enables a clean process

In her dissertation research, Anne Vuorema developed a new electrochemical method for determining the purity of indigo. She reduced plant-derived indigo using glucose and measured the indigo concentration in the mixture using a new method. This is a great improvement in determining the purity of plant-derived indigo.

The method can also be applied to assess the purity of other similar chemicals.

“The degree of purity of plant-derived indigo is fairly low. Crude indigo has a dye content of less than 50%, while synthetic indigo has a dye content of over 95%. The impurities and means to reduce them are not yet well known,” Vuorema explains.

Businesses look for guaranteed standard quality of dye. At the same time, ecologically geared companies are looking for increasingly natural methods for dyeing fabrics, among other things.

“Plant-derived indigo is a marginal, alternative product, and it does not currently compete with synthetic indigo,” Vuorema says.

Vuorema also investigated indirect electrochemical reduction. She discovered that 1.8-dihydroxyanthraquinone was an efficient catalyst for glucose-induced reduction. Electrochemical reduction can only be introduced by major companies as it requires investment in special equipment.

“We still need to achieve a lower pH in glucose reduction and solve the matter of impurities,” Vuorema muses.

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