Scouring is a cleaning process that removes impurities such as waxes, pectins, hemicelluloses, and mineral salts from cotton yarns and fabric before dyeing. Traditionally, scouring involves several high-temperature processes with a large consumption of chemicals such as sodium hydroxide, sodium carbonate, and hydrogen peroxide. Scourzyme 301 L provides a biological alternative. It is a liquid enzyme product developed by Novozymes with high specificity towards difficult-to-remove pectin compounds on the raw cotton. It enables a faster and gentler scouring process with lower energy and chemical consumption and less harm to the cotton. The process is known as BioScouring and was first launched by Novozymes in April 1999.

Cotton goes through scouring to remove noncellulosic components such as wax. The trouble is that chemicals do not just remove the impurities, they attack the cellulose too.

It might seem obvious to assume that Bio­Scouring contributes to the sustainable development of cotton-based products in comparison to conventional scouring with chemicals. To discover the facts, Novozymes performed a life cycle assessment (LCA) at a textile mill in China, one of the prime markets for BioScouring. This kind of environmental assessment is used to compare the environmental impact of producing the enzyme on the one hand with the savings in yarn, chemicals, energy, and water on the other (see box on the next page). The study was based on the principles of the ISO 14040 series, where all significant processes “from cradle to grave” are included.

No investments needed
The study took place at the Zhejiang Rongxin Fibre Co. Ltd. yarn dyeing mill located in Haining industrial park where conventional scouring was replaced by BioScouring in October 2006. Rongxin is located 90 km from Shanghai and has more than 800 employees. The study was based on a full-scale commercial yarn dyeing line in Haining with an output of 50,000 kg of dyed yarn per day. As conventional scouring and BioScouring can be performed on the same production line with the same equipment, there was no need for Rongxin to make any significant capital investment in order to switch between the two scouring methods.

One step, not three
Scouring is performed in a bath where a mixture of water and chemicals or enzymes is pumped through yarn wound onto a perforated cylinder.

Before Rongxin began using Scourzyme 301 L in 2006, conventional scouring was performed in a three-step procedure: a scouring process followed by two rinsing steps. The scouring process was performed at 100 °C with the addition of a penetration agent (a surfactant), sodium hydroxide, and hydrogen peroxide. Sodium hydroxide was used to remove the unwanted impurities but it also attacked other substances in the yarn, including the cellulose.

The impurities were washed out of the yarn in the two rinsing steps. The first rinsing step was performed at 95 °C whereas the second was performed at 50 °C, and acetic acid was added to reduce pH. The entire scouring process took 3 hours, and included both filling and emptying the bath.

In comparison, BioScouring is performed in a single process at 60 °C with the addition of a penetration agent and Scourzyme 301 L. Scourzyme 301 L contains one specific enzyme – a pectate lyase which degrades pectins into soluble compounds. No rinsing steps or neutralizing steps are required before dyeing the yarn. BioScouring takes 1.5 hours including the filling and emptying of the bath. That is half the time of conventional scouring.

BioScouring with Scourzyme® 301 L is being used in full-scale production at Rongxin in Haining.

The time saving is important for the Rongxin mill from an economical point of view as it means they can increase their production capacity. From an environmental point of view, there are also savings. BioScouring uses industrially produced enzymes but saves a range of conventional organic and inorganic chemicals. Furthermore, water, steam, and electricity are saved because less water is needed for the single-step process than the three-step process­es. Consequently less water needs to be heated and pumped through the yarn. Savings of water, electricity, and steam are quite high because the liquor ratio is rather high (10 tons of water per ton of yarn) and because the liquor has to be pumped through the yarn. The quantities of saved materials and utilities when switching from conventional scouring to BioScouring are shown in the box on the next page.

Less weight loss
Conventional scouring is a relatively harsh treatment and the yarn weight loss during the process can be 4% or more. BioScouring is gentler and yarn weight loss is less. Scouring trials under nearly the same conditions as in Rongxin have shown yarn weight loss to be 5.7% with conventional scouring and 3.3% with BioScouring.

Dye uptake is often higher with BioScouring than with conventional scouring and a saving in dyestuffs can be expected. Furthermore, BioScouring maintains more of the natural softness of the yarn than conventional scouring and less softener needs to be applied at the end of the dyeing process.

“The BioScouring process enhances the competitiveness of our enterprise, and the mill can provide higher-­quality products for its customers. The application of Scourzyme has a very good effect on decreasing the overall production cost and the level of pollution,” says Zhangrong Ge, Chairman of Zhejiang Rongxin Fibre Co. Ltd.

Saved!
Hydrogen peroxide (27%): 40 kg Sodium hydroxide (100%): 15 kg Acetic acid (98%): 5 kg Yarn: 25 kg Steam: 2,500 kg Electricity: 150 kWh Water: 20 m3 (20,000 L)	Saved at the Rongxin mill through the use of Scourzyme® 301 L in comparison to conventional scouring. All quantities are per ton of scoured yarn (dry weight), and the enzyme dose was 10 liters per ton.

Impact assessment
A small dose of the enzyme Scourzyme 301 L saves large amounts of raw materials (yarn), chemicals, energy, and water in the scouring process.

“In all the LCAs that I have conducted at Novozymes, I have never seen such a dramatic water saving as this,” comments Per H. Nielsen, an LCA specialist and Manager in Sustainable Development at Novozymes. “The reduction in the contributions to global warming is also an important benefit. There is a lot of focus on CO2 emissions in China these days.”

The study shows that CO2 emissions are reduced by around 1,000 kg per ton of yarn. If all the Chinese mills dyeing yarn to dark shades switched from conventional scouring to BioScouring, the total CO2 reduction in China would be around 200,000 tons annually, which corresponds to the emissions from 50,000 cars. These figures are based on the use of electricity from coal-fired power stations in China. However, even if another fuel was used to generate electricity such as oil, natural gas, or wood pellets, there would still be a clear advantage by using enzymes for BioScouring.

Increasing awareness of climate change has started a global search for ways to reduce CO2 emissions and BioScouring presents an opportunity for mills to do this. At the same time, they save energy, time, chemicals, and huge amounts of rinsing water.