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What is carbonizing process of wool?

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Carbonizing is a continuous process along with scouring. Carbonization is a chemical process done to remove the wool, grease and vegetable matter such as seeds, burs and grass from wool fibers. In this process, the wool fibers are treated with acid or acid-producing salts. This process makes the wool porous in nature hence increasing the dye uptake of fibers.

The vegetable matter which is present in the wool fibers are cellulosic in nature. Hence the first step in carbonizing is immersing the wool in a strong solution (6% to 7% weight for volume) of sulfuric acid (H2SO4) containing acid stable wetting agent and hydroextracted. Magnesium chloride, aluminium chloride or gaseous hydrochloric acid are also used sometimes for carbonising of wool. To minimise degradation by sulphuric acid the treated wool substance is then dried at low temperature.

Then the dried wool is baked or heated in a dryer at a temperature between 95° C to 120° C. This breaks down the vegetable matter present in wool substance into carbon. After this, the wool is passed through a series of heavy metal fluted rollers or a milling machine to crush the charred vegetable matter into dust. Apart from cellulose, this wool burn contains hemi-cellulose and lignin. Although the lignin is not affected by the carbonizing process on acid hydrolysis.

The treated wool is then passed through a dedusting unit where through the help of mechanical action the dust is separated from the wool. At this stage, since the wool was immersed in sulphuric acid hence the wool is acidic in nature. To neutralize the wool, the wool is passed through an alkali solution. This alkali solution is made from different chemicals such as Sodium Carbonate (Na2Co4), ammonia or ammonia/ammonium acetate mixtures. And in the last step before the wool is dried, it is passed through a liquid bath containing a solution of Hydrogen Peroxide bleach (H2O2). This is done to improve the color of wool.

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