Carbonizing of Wool:

Wool Carbonizing Process:

Carbonizing is done to remove the cellulosic impurities from wool by treatment with acid or acid producing salts. Carbonizing may be carried out in loose wool or on piece goods after scouring. However, it is common practice to carbonise worsted
piece goods as well as woolens. The process begins by immersing the wool in a solution of sulfuric acid (H2SO4) that reacts with the cellulose impurities in the wool. 

Carbonizing process

Techniques of Carbonizing: 
The conventional carbonizing process comprises five main stages : scouring, acidizing, drying and baking, burr crushing and dedusting and neutralising. And recent development process includes: Acidising, Moisture removal, Drying/Baking, Burr crushing and dedusting, Neutralisation. 

The conventional technique of wool carbonizing has the following basic steps: 

1. Scouring of the raw wool with non-ionic detergent.
2. Rinsing.
3. Immersion in a long bowl containing 5-7% (w/v) sulphuric acid, 1-2 g/L detergent at 20-30oC.
4. Double squeezing and/or continuous centrifuging prior to drying.
5. Drying at 60-80oC to a low regain.
6. Baking at 95-120oC to carbonise the VM.
7. Pass through heavy fluted rollers to crush the embrittled VM.
8. Convey to a rotating shaker/de-duster to remove the charred VM dust.
9. Pass through a neutralising bowl usually containing sodium carbonate.
10. Rinsing with a small addition of detergent.
11. Bleaching wool with hydrogen peroxide at approximately pH 5 with formic acid.
12. Final drying.

The production rate through the process is usually low, typically 500-600 kg/h for an 1800 mm wide line, since sufficient time must elapse for the VM to adsorb the acid from the bowl and for subsequent baking to embrittle the acidified cellulose. 

Wool piece goods are treated with sulphuric acid (6-8 o Tw) containing acid stable wetting agent and hydroextracted. The treated wool substance is dried at low temperature (60-70~ very quickly to minimise degradation by sulphuric acid of intermediate critical concentration. The dried wool is then heated at 110~ for a short time. The goods are then neutralised immediately or run dry through a dolly or milling machine to remove the charred vegetable matter and then neutralised. 

Neutralisation of wool fabric can also be carried out in open-width scouring machine. Neutralisation with ammonia or ammonia/ammonium acetate mixtures removes acid from the fabric far more rapidly than either sodium carbonate and sodium acetate. 

In a rapid carbonising process wool is treated in up to 8% (w/v) sulphuric acid solution for 30 sec and time delay of about 10-15 min is introduced before drying. The locally damaged areas can greatly weaken the fibre if surface acid is not evenly distributed during drying. However, in the rapid carbonising method and total acid inside the wool changes. Free surface acid penetrate into the wool fibres and bonds to wool. Thus the amount of concentrated acid formed during drying and baking is minimised and as a consequence, less chemical attack occurs to wool in rapid carbonising. 

Magnesium chloride, aluminium chloride (8-10 ~ Tw) or gaseous hydrochloric acid may also be used for carbonising of wool. Rags are carbonised to remove cotton stitchings prior to use in shaddy by the 'dry carbonising' process by exposing to hydrochloric acid gas in an enclosed chamber. Metal acid salts liberate hydrochloric acid at high temperature and attack the cellulose in wool. But owing to their high cost and higher temperatures required which cause injury to dry wool, are rarely used. 

The wool burrs contain hemi-cellulose and lignin apart from cellulose. The lignin is not effected by carbonising process on acid hydrolysis, but can be split oxidatively. Salt ofpersulphuric acid accelerates degradation of wool burrs which enable shortening the time of reaction. 

Natural soiling of wool and vegetable matter and skin flakes, can also be enzymatically modified. The replacement ofcarbonisation by the use of enzymes, such as cellulases, ligninases, hydrolases, lyases, oxidoredulases etc. are reported. The main advantages of enzymatic carbonizing are reduced wool fibre damage, effluent load and energy consumption. 

Carbonised wool are more porous than scoured wool and hence the dye uptake is higher. Uneven dyeing may result due to faulty carbonising.