What is scouring of wool?

Raw wool contains impurities in the form of waxes, suint, cellulosic material such as straw and dried grass, dirt, and proteinaceous material. Because of this purification of wool is very important prior to subsequent bleaching, dyeing, and finishing. Scouring of wool is done in the fiber form to ease the spinning process of wool. Scouring is also known as wool washing is done to remove soil, vegetable impurities, grease and other contaminants from fibers with the help of hot water and detergents. It is very difficult to saponify wool wax without damaging the wool fibers. At a temperature slightly higher than wool wax’s melting point which is 40°C–45°C, wool wax can be emulsified. The most common method of cleaning loose wool is to use soap in emulsion scouring.

To scour the wool 2%–4% soap and 2% sodium carbonate is used which is calculated on the weight of the wool. The most economic way to scour wool is to use nonionic detergents like octa/nona-ethoxylatednonylphenols. These non-ionic detergents are much better than soap as they increase the efficiency of the treatment under neutral conditions, are stable in hard water, have lower cost, and are more efficient in removal of grease. In different rinsing conditions, these ionic detergents are easily absorbed. But, in comparison to soap for the suspension of dirt, they are not much efficient. To preserve the neutrality of the medium, as a detergent builder instead of sodium carbonate, sodium sulphate may also be used.

The scouring process reduces the oil content in wool by 0.4% to 0.6%, hence during the spinning process, it is customary to add olive oil or specially prepared mineral oil. The scouring of wool yarns may be conducted in hank form or in packages such as cones and cheeses. Depending on the sensitivity of the wool, during the scouring process, the concentration of soap and soda is to be chosen very cautiously.