Silkworms fed dyed mulberry leaves to produce coloured silk

Indian researchers have successfully developed an eco-friendly method to help silkworms spin naturally fluorescent, coloured silk - by feeding them dyed mulberry leaves.

For some 5,000 years, cultivated silkworms have been spinning luxurious white silk fibres destined for use in the finest clothing.

However, current dyeing practices produce wastewater that contains potentially harmful toxins, so scientists are now turning to a new, "greener" dyeing method in which they coax already-coloured fibres from the caterpillars by feeding them dyed leaves.

Anuya Nisal, Kanika Trivedy and colleagues from the National Chemical Laboratory in Pune point out that dyeing textile fabrics is one of today's most polluting industries.

The process requires huge quantities of water for bleaching, washing and rinsing, and it results in a stream of harmful wastewater that needs to be treated effectively before release into the environment, researchers wrote in the study published in the American Chemical Society (ACS)'s journal Sustainable Chemistry & Engineering.

To make the industry greener and more environmentally friendly, researchers have been developing less toxic methods, including feeding dyed leaves to silkworms so they spin coloured - rather than white - cocoons.

However, so far, this technique has only been tested with one type of dye, which is too pricey for large-scale production.

Thus, the team turned to azo dyes, which are inexpensive and account for more than half of the textile dyes used today.

They dipped or sprayed mulberry leaves, the silkworm's food of choice, with azo dyes to see which ones, when consumed, would transfer to the silk.

Of the seven dyes they tested, three were incorporated into the caterpillars' silk, and none seemed to affect the worms' growth.

Scientists noticed that certain dye traits, such as the ability to dissolve in water, affected how well the dye worked.

"These insights are extremely important in development of novel dye molecules that can be successfully used in this green method of producing coloured silk fabrics," scientists said.