Green denim

NO MATTER what season it is, denims are now a wardrobe staple. But the techniques used to process denim to suit the fashion, like rugged or faded, are highly polluting and hazardous.

Now a team of researchers from University of Innsbruck, Austria, have found a cheaper, more efficient and eco-friendly method for treating denim. The process called surface activation can be used to wash-down the denim. It can also be an alternative to the dangerous, and internationally banned sandblasting technique used to give jeans its worn-out look.

Denim is an indigo ring-dyed fabric. The central steps in its processing are the wash and bleach processes used to create a final wash-down effect. To remove the ring dyed indigo a combination of drum washing machines and chemicals like sodium hypochlorite are used. After bleaching pumice stones are used for washing and biopolishing (weakening of fibrils in a yarn to make the surface smooth). A large number of enzymes are also used for the processing.

The new technique—localised surface activation—involves applying concentrated alkali pastes onto the surface of denim followed by treatment with cellulase enzyme. Cellulases degrade the cellulose in the fibers of the yarn and weaken them, thus replacing biopolishing and defibrillation done by pumice stones. It also uses less number of enzymes. “The method replaces two hazardous processes. Sandblasting and hypochlorite-based denim bleaching. It makes the process chlorine-free,” says Thomas Bechtold, lead researcher of the study recently published in Biotechnology Journal.

But before it is used for commercial purposes, the technique needs optimisation to reduce costs and time for finishing process. “To the extent that enzymes are used you may say it is environment friendly, but you are still using strong alkali and other print ingredients,” says Kushal Sen, head of the textile department at IIT Delhi. They also need to be treated before being thrown out as effluents, he adds.

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