While we may think of blue jeans as kind of earthy, basic clothing, the process by which they're dyed is definitely not eco-friendly. That may soon no longer be the case, however, thanks to the development of a new coloration technique.
Ordinarily in the dying of jeans, either natural or (more commonly) synthetic indigo pigment is mixed with water, in which the denim fabric is subsequently dipped. Because neither form of indigo is water-soluble in its initial state, though, toxic reducing agents such as sodium hydrosulfite have to be added in order to make it so.
After the dying process is complete, the wastewater is released back into the local waterways. And while government regulations do require that the bulk of the chemicals be removed from it first, the water invariably retains some pollutants.
Led by Prof. Sergiy Minko and doctoral candidate Smriti Rai, scientists at the University of Georgia have devised an alternative process in which indigo particles are mixed with wood-pulp-derived cellulose nanofibers, a natural sugar known as chitosan (which can be harvested from seafood waste), and water. Although natural indigo has been utilized so far, the researchers state that synthetic indigo could also be used.
When the resulting hydrogel is applied to untreated denim, the nanocellulose fibers form a mesh-like coating that encapsulates the indigo particles, adhering them to the denim fibers. The chitosan boosts the adhesion and fixation, ensuring that the indigo remains bonded to the denim once the material has dried and is subsequently worn and washed.
Not only does the technique not require the use of any toxic chemicals, but it's also more effective than existing processes at securing the dye into the denim. This means that much less water and dying time is required. According to the university, in order to get denim sufficiently blue, existing factories currently go through 50 to 100 liters (13 to 26 US gal) of water when performing multiple dips on just one pair of jeans.
Additionally, denim that's dyed via the new technique has approximately the same thickness, weight and flexibility as conventionally dyed denim.
"Denim and jeans manufacturing are a big market, so even small changes in the industry could have huge impacts," says Minko. "There are populations that are looking for products that are made in environmentally friendly ways. And as regulations become tougher, the industry will have to adapt."
A paper on the research was recently published in the journal Green Chemistry.
Source: University of Georgia
