Upending ultrasound
No sodium hydrosulfite, very little water. High frequency sound waves. This is the new recipe for indigo dyeing that Pure Denim and Sonovia are working on.
PureDenim’s Luigi Caccia is always on the lookout for innovative solutions that can help reduce the industry’s environmental impact. He is currently working with Israel-based start-up Sonovia to finalise a radical new method for dyeing using ultrasound.
“We have been dyeing fabrics indigo in pretty much the same way for ages,” says Luigi Caccia, co-founder and CEO of Pure Denim, a mill located close to Milan. D(y)enim, the name of the new solution he is working on with Sonovia, does not require indigo pigment to be reduced. This removes the need for sodium hydrosulfite, a hazardous chemistry to handle during manufacturing, difficult to manage in wastewater, and downright toxic if it ends up in waterways.
Mr Caccia had been looking into the possibility of washing denim fabrics with ultrasound waves when he was introduced to Sonovia, which specialises in this technology for the textile industry. It is a physical – that is non-chemical – process used in textile manufacturing for cleaning purposes that does not require much water. “It can reduce the amount of water consumed by up to 90%,” he says.
But Sonovia has upended this technology by using it not to remove impurities but as a carrier to embed colour, or a functional finish, into a textile. Its research, an evolution of a patent it purchased from Bar-Ilan University, has led to the development of a first industrial machine, SonoFIX. This device uses ultrasound waves to anchor a chemical additive deep inside a fabric. It is in advanced trials at Delta Galil, an apparel manufacturer based in Israel, to apply an anti-odour finish that is said to be nearly permanent.
The power of sound waves
For indigo dyeing, Sonovia is taking the same core technology, but has modified it so that it does not embed the pigment too deeply. The world of denim wants its dyed yarns to have a white core. “We needed to tweak the ultrasounds for indigo pigment and our main tool for this is to modify the frequency of the ultrasound waves,” says Sonovia CEO Igal Zeitun. The company also needed to devise a machine made to treat continuous warp yarns, not fabric rolls. The two partners are currently using a lab-scale device (pictured). A larger scale machine should be ready to be installed at Pure Denim later this year, they say.
Once ultrasound-dyed, a denim fabric also has to behave as does a traditionally processed fabric. The two partners are also focusing their efforts on achieving the same effect as the ‘real’ thing. A challenge, they admit. “If this process requires any change in the current supply chain, we know it won’t fly,” says Mr Caccia. Tests are currently underway to see how the ultrasound-dyed fabrics react to ozone and laser finishing.
Saving fresh water
Indigo is not soluble. Various substances have been used to made it soluble, urine back in the day, now sodium hydrosulfite. Indigo also needs to oxidise, which makes it blue again. These are the usual conditions of indigo dyeing. D(y)enim does not require indigo to be made soluble. “There is no oxy-reduction and this allows us to bypass all that harmful chemistry,” says Mr Zeitun.
“Sonovia is introducing a completely new method that removes the problem of salt and achieves exactly the same effect,” says Mr Caccia. This leads to significant savings at many levels of production, the two partners claim. “In traditional dyeing ranges, 800 metres of yarn are lost in between lots. Not only does Sonovia’s process reduce the water, chemicals and energy needed for indigo dyeing, it also saves the energy not used to remove hydrosulfite from wastewater,” he adds. Instead of 10 indigo dye bathes, our system requires only one or two, notes Mr Zeitun, this further reduces water consumption. Mr Caccia adds that there is no need for the water to have a special pH, which also makes the process easier and cheaper.
D(y)enim leads to significant savings during production, but it is expected that the machine itself will represent a substantial investment. Sonovia’s business model is to install the machine at mills and dyehouses and provide the specially formulated indigo pigment. “Our indigo is basically the same raw material, but it needs to be made compatible with ultrasound,” says Mr Zeitun.
Water is a critical issue that Mr Caccia feels very strongly about and why he sees in D(y)enim a game-changing solution for the industry. “It is possible to recycle water, and there are mills that can do this,” he remarks. “But the truth is, when you recycle water, all you are doing is moving the problem, that is the salt, from the water to the sludge.”
He insists that D(y)enim has the potential to revolutionise the industry like nothing else seen to date. “This revolution is at a scale of what digital printing has done to the traditional printing industry.” He adds that its greatest impact is not for a company like Pure Denim that produces in the north of Italy, but “rather for all the denim producers in water-stressed countries. Sonovia’s technology removes the problem of salinity in water, avoids creating ‘blue rivers’, and virtually eliminates pollution.”
View of the ultrasound dyeing machine that Pure Denim and ultrasound specialist Sonovia are working on.
Photo: PureDenim/Sonovia
