Three of the following are removed during cotton preparation. Which is the odd one out?
Answer: A
The cellulose is the fibre itself and any loss of it is damage rather than cleaning. The other three are all impurities that preparation is designed to remove. Losing fibre is damage, not cleaning. Preparation aims to leave the cellulose intact.
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Combined desizing, scouring and bleaching in a single stage is attractive because it
Answer: B
Correct answer: saves water, energy and time
Combining the three stages means one pass, one heating, one set of wash boxes and one lot of effluent instead of three, with the corresponding saving in range length and labour. The trade is control: with one set of conditions serving three purposes the risk of fibre damage rises and the whiteness achieved is usually a little below what separate optimised stages give.
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Consider the following statements about single stage preparation.
1. It reduces water and energy consumption considerably.
2. It demands closer process control than separate stages.
3. It is well suited to cloth of unknown or variable history.
Answer: C
The first two are correct. The third is the wrong way round, since a single stage process cannot be adjusted part way through and suits uniform cloth of known preparation. Variability is the enemy of a single stage route.
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The purpose of the wash boxes after a desizing range is to
Answer: D
Correct answer: carry the hydrolysed size away
Hydrolysis only breaks the size into soluble fragments; those fragments are still in the cloth and must be washed out. The wash boxes do that, in counter-current so that the cleanest water meets the cleanest fabric. Size left in the fabric would interfere with dyeing and finishing exactly as the original size did.
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Assertion (A): A desizing stage is always followed by thorough washing.
Reason (R): The size is only broken into soluble fragments and must still be washed out of the cloth.
Answer: A
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason gives the necessity. Desizing is a solubilisation rather than a removal - nothing leaves the cloth until it is washed out. Poor washing is a common source of unlevel dyeing, since the residual dextrins remain on the fibre and interfere with the dye reaching it.
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State whether the following is true or false.
A fabric that has been desized will always pass an absorbency test.
Answer: B
Natural waxes remain until scouring, so a desized but unscoured cotton is still water repellent. The two operations remove quite different materials and neither substitutes for the other. Absorbency is developed by the scour.
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