Denim, one of the most iconic and popular clothing globally, is really costly for the environment. According to a report of National Geographic Magazine, 11000 liters of water is required from fiber to finishing process in washing to produce a single pair of blue jeans. Also, it takes almost a pound of chemicals and a substantial amount of energy.
For long – especially from when the sustainable fashion supply chain issue came forward – the brands, retailers and denim manufacturers alike sought eco-friendly denim processing from technology providers to reduce the consumption of water and chemical.
In the traditional dyeing process, indigo dyes are used to achieve the color. Indigo dyes are not water-soluble and its dye molecules are combined with each other thus it can’t be infiltrated into the core of the fiber.
Thus, the indigo molecules are needed to be reduced by strong reducing agent Hydrogen Sulfide (H2S) and it becomes negative charges. During this period the indigo dye molecules become yellow color changing from blue and the fiber absorbs the colors. Then the dyed yarns are passed openly for next dye vats and here the molecules are oxidized by the atmospheric oxygen and turn its original blue color.
Indigo dyes help to color the fiber very slowly thus it requires a greater number of dyeing vats. Due to this a huge amount of wastewater is generated with the contamination of Sulfide ions. Then it is passed through washing baths for cleaning and removing unfix dyes from the surface of the yarns.
Method of advanced denim technology
In advanced denim technology, only 3-5 dyeing vats are needed instead of 12-15 dyeing vats. In this method, denim is dyed with Sulfur dyes instead of indigo. Sulfur can give quick shades to the fiber with the various cast. It will give the same color as indigo gives but in different methods. Sulfur has no oxygen group but it has a functional group that is called thiol (-OH).
In the first step, the sulfur dye molecules are reduced and give negative charges, at that time it becomes yellow color instead of blue. At the second step, the dyed yarns are passed openly to the next dyeing vats and then it is oxidized by atmospheric oxygen and turned into original color. The molecules are then built a link with each other with strong ionic bondage; thus, the color fastness criteria improve and the jeans keep the same color longer.
This advance denim can cut the amount of water used to produce a pair of jeans by up to 92% while requiring up to 30% less energy than conventional denim manufacturing methods.
Additionally, the process is claimed to generate up to 87% less cotton waste, which is often burned to send CO2 and other greenhouse gases into the atmosphere and produces virtually no waste-water.
If only a quarter of the world’s jeans were dyed using the advanced denim process, around 2.5 billion gallons (9.46 billion liters) of water would be saved every year – enough to cover the needs of 1.7 million people annually. It would also prevent the release of 8.3 million cubic meters of wastewater, and save up to 220 million kilowatt-hours of electricity.