NEW SCOURING METHOD
low carbon footprint synthetic fabric scouring
Background
In the search for textile processing technologies with low water- and carbon footprints, several novel, sustainable coloration technologies have been developed in the last decade, for both printing and dyeing operations. This can indeed lead to a significant sustainability improvement but the pre- and post-treatments have been largely left out of considerations until now, despite the fact that these have similar water consumptions and carbon footprints.
Scouring of fabrics of polyester and its blends with spandex in conventional jet machines, for instance, uses up to 18,000L water/ton fabric for scouring and subsequent neutralization and generates 1150kg CO2 equivalents per ton fabric.
An alternative is solvent scouring, which is on the market but suffers from the inherent disadvantage that organic solvents have a bad reputation for being flammable and toxic, preventing this method from becoming mainstream production technology.
Our solution
We have developed a solution for waterless, low-carbon footprint scouring, using compressed carbon dioxide (CO2) as non-toxic solvent. Fabric of polyester or polyester-spandex is rolled on a beam and perfused by the CO2, which dissolves and carries away all knitting and spinning oil from the fibers.
Gentle process
The fact that the fabric is not moving in the machine, means that even the most sensitive fabrics can be treated with this process. What is more, there will be no microfibers released from the fabric. Downstream of the scouring vessel, the oil is obtained from the machine pure and clean, offering the possibility of circularity by oil re-use.
The pressure and temperature inside the scouring vessel are 60 bar, 20 degC, so that no shrinking or fiber damage takes place. If dope-dyed fabric is scoured, no dye will be accidentally extracted, the colour remains unchanged. Relaxation and heat setting has to be done as usual after the scouring, e.g. in a stenter, if the fabric is to be subsequently dyed or printed.
Because of the low temperature of 20 degC, the energy consumption of this method is low. On top of this, a stenter treating the fabric after scouring does not need to dry the fabric and thus extra energy is saved. The total carbon footprint of the process is only 540 kg CO2 equivalents per ton of fabric, 50% lower than the typical 1150 kg CO2 eq/ton that is typical of scouring synthetics in a jet machine.
We have developed the process experimentally, on a 1-kg scale in their R&D machine designed by us and built by our business partner: machine builder Ozephius Stainless B.V., near the port of Rotterdam. It was found that the oil content of commercial fabric could be reduced in only an hour total process time, from 3% down to 0.2% or even 0%. A patent on the process and equipment is submitted and pending.
The machine
From the experimental results, we designed the commercial scale equipment needed to scour 1.6 million kg polyester per year or polyester-spandex in 140-kg batches on a beam. The machine cost is in the same order as a solvent scouring machine, the exact price depending on how much machines are manufactured in series and in which country this is done. The lower machine operating cost, especially the lower energy use, compensate for this relatively high investment cost, the nett effect being a lower total cost: 160 USD/ton fabric for CO2 scouring, versus 250 USD/ton for conventional jet scouring.
The CO2 scouring technology can be used for any factory that makes polyester or polyester-spandex, be it as dope dyed fabric, conventional water-based dyeing or printing. In all cases, the same combination of sustainability and cost saving is found. In some cases, it can even mean completely waterless production of fabrics.
Scouring in CO2 – summarized:
- Sustainable: no water and less energy
- Lower cost: 160 versus 250 USD/ton fabric (including machine depreciation)
- Lower carbon footprint: 540 versus 1150 kg CO2/ton fabric
- No chemicals, only pure CO2
- Gentle fabric treatment
- Oil is obtained clean, pure and can be re-used
- No microfibers are released
With the technical and economic feasibility proven, and the carbon footprint calculated, we are now looking for investors to fund the building of the first full-scale, commercial machine so that we can demonstrate the solution and its low carbon footprint to dyehouses and brands.
To see press publications on our sustainable scouring method: