Procedure used to remove impurities from wool:

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Accepted Answer

The correct option is 1:

Raw wool, straight from the sheep (known as greasy wool), contains a significant percentage of natural contaminants. These impurities, typically making up 30-40% of the total fleece weight, include wool grease (lanolin), suint (dried perspiration salts), dirt, sand, and dust. The essential pre-processing stage for removing these natural impurities from the raw fiber is called **Scouring**. Scouring involves washing the wool, often continuously through a series of bowls (wash liquor tanks), using a warm aqueous solution that contains a detergent (surfactant) and sometimes a mild alkali, like sodium carbonate. The purpose of this controlled chemical and mechanical action is to emulsify and saponify the non-water-soluble lanolin and to wash away the water-soluble suint and dirt. The whole procedure must be meticulously managed—especially regarding water temperature and alkalinity (pH must be carefully controlled below 10)—because wool is a delicate protein fiber highly susceptible to damage, such as felting or degradation, from rough handling, excessive heat, or strong alkali. Successfully completing the scouring process yields clean, soft wool fiber ready for the subsequent stages of manufacturing like carding and spinning.

The incorrect option is 2:
Singeing is a surface finishing operation, not a deep cleaning process for raw wool impurities. This technique involves rapidly passing already-woven fabric or spun yarn over a gas flame or heated metal plates to burn off the tiny, protruding fiber ends known as 'fuzz' or 'hairiness.' The main objective of singeing is to create a smoother, cleaner surface appearance and to make the fabric's weave structure more visible, which is beneficial for processes like printing and dyeing. Unlike scouring, which removes the bulk of natural grease and dirt from the raw material, singeing is applied later in the textile sequence to improve the aesthetic quality of the manufactured cloth. It is a surface treatment and does not extract the core contaminants present in the greasy raw wool.

The incorrect option is 3:
Mercerizing is a specific chemical finishing treatment applied to **cellulose** fibers and fabrics, primarily cotton and sometimes linen. This process involves immersing the material in a concentrated solution of caustic soda (sodium hydroxide) while holding it under tension. The primary aims are to permanently increase the cotton fiber's lustre (giving it a silk-like sheen), improve its tensile strength, and significantly enhance its affinity for dyes. Applying this strong alkaline process to wool is fundamentally inappropriate; wool is a protein fiber highly sensitive to strong alkali, and this treatment would severely damage the fiber's chemical structure, leading to degradation, harshness, and irreparable damage. Therefore, mercerizing is a treatment for cotton, not the impurity removal procedure for wool.

The incorrect option is 4:
Tentering, also commonly referred to as Stentering, is a crucial mechanical finishing process applied to **fabric** (woven or knitted) toward the very end of textile production. It is not an initial cleaning step for raw fiber. The purpose of the tenter frame is to stretch the fabric to a uniform, specified width, remove wrinkles and creases, and stabilize its dimensions (often using heat-setting in the case of synthetics or wool). The fabric's edges are held by pins or clips as it is transported through a heated chamber to set the final width and straighten the grain. This procedure is performed after cleaning, dyeing, and printing to ensure the final product has the correct shape and dimensional stability, making it a shaping and setting process, not an impurity removal procedure.