Singeing and Desizing Questions and Answers

Answer: A

The projecting fibre ends make the surface hairy and scatter light, so removing them gives a smoother handle and a clearer print. Size removal is the quite separate operation that follows. A smoother surface also takes a print more cleanly.

Answer: B

Both are true and the reason gives the necessity: a hairy surface prevents the print paste from sitting cleanly on the cloth, and fine line work in particular suffers badly. Dyed grounds are less demanding in this respect.

Answer: C

Correct answer: rapidly over a row of gas flames

The fabric passes across a gas flame at high speed, so the protruding fibre ends - which have a large surface and little mass - burn away while the body of the cloth is barely heated. The result is a smooth surface that prints cleanly and dyes evenly, without the frosty appearance loose fibre ends give.

Answer: D

Correct answer: 1 and 2 only

Statements 1 and 2 are correct: the speed must be high enough that only the projecting ends are consumed, and the cloth is quenched immediately afterwards. Statement 3 confuses two operations - singeing removes surface fibre, and desizing removes the size from the warp. They are usually done on the same range, one after the other, which is why they are easily conflated.

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason is the hazard. Fibre ends can continue to smoulder after leaving the flame, and a roll of cloth wound up with a smouldering point in it can catch fire hours later. The quench box extinguishes them immediately, and it is convenient in another way: the desizing liquor is commonly applied in that same box, so the fabric goes straight from singeing into desizing.

Answer: B

Polyester melts rather than burning cleanly, and the beads pick up dye differently and feel harsh. Blends are often singed after dyeing for this reason. Speed and flame setting both need adjusting. Cotton burns to ash rather than melting.

Answer: C

The warp is subject to repeated abrasion and tension in the loom, and the size film protects it. Everything applied for that purpose must be taken off again before the fabric can be dyed. Size add-on is quoted on the weight of the yarn.

Answer: D

Starch is the one that needs a chemical or enzymatic attack, because it is insoluble and must be broken down before it will wash out. The synthetic sizes were developed partly to make removal easier. Solubility is what decides the route.

Answer: A

Correct answer: amylase, which hydrolyses the starch

Amylase hydrolyses the glycosidic bonds of starch into soluble dextrins and sugars, which are then washed away. The specificity is the point: cellulase would attack the cotton itself, and protease and lipase act on substrates that are not present here.

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason is the advantage. Acid desizing hydrolyses starch but also hydrolyses cellulose, so a slight excess of acid, time or temperature produces hydrocellulose and a measurable loss of strength. Amylase acts only on the starch, so the process has a wide safety margin - which is why enzymatic desizing displaced the acid route.