Singeing and Desizing Questions and Answers

Answer: C

Correct answer: 1 and 2 only

Statements 1 and 2 are correct: every enzyme has an optimum pH and temperature, and heating past it denatures the protein irreversibly, ending the activity for good. Statement 3 is wrong - hardness matters, and many bacterial amylases actually require calcium for stability, so the water must be controlled rather than merely supplied.

Answer: D

Correct answer: singeing over a gas flame

Singeing removes surface fibre and does nothing to the size, which lies within and around the warp yarns. The genuine desizing routes are all here: enzymatic hydrolysis with amylase, oxidative desizing with persulphate or peroxide, and rot steeping, in which the fabric is simply left damp and warm so that natural fermentation degrades the starch.

Answer: A

It is the oldest method, cheap but slow and uncontrolled, and it can damage the fabric if it is allowed to run too long. Enzymatic desizing is the controlled version of the same chemistry. Time and temperature are hard to hold steady.

Answer: B

The oxidant attacks size of any kind, which suits a commission finisher receiving cloth of unknown history. The risk is that it can attack the cellulose too if the conditions are not controlled. Commission finishers meet this situation often.

Answer: C

The same oxidising power that breaks down the size will attack the fibre if the pH, temperature or concentration drift. It is nonetheless valuable where the size is mixed or unknown. Stabilisers help to keep the attack selective.

Answer: D

Size must go before scouring or it would set on the fabric, and scouring must precede bleaching so the bleach is not wasted on waxes and pectins. The order is the standard preparation sequence. Reversing any pair causes trouble downstream.

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 of the order. Hot alkali can set a starch size, making it far harder to remove afterwards, and it wastes scouring chemicals on degrading size rather than on the natural impurities. Desizing first also removes a large part of the total load, so the scour is more effective for the same conditions.

Answer: B

Correct answer: 16 grams

\[ 200 \times 0.08 = 16\ \mathrm{g/m^2}. \] Six to twelve per cent add-on is normal for a woven cotton, and it is a substantial quantity - which is why desizing removes more material than any other preparation step and dominates the effluent load of a preparation range.

Answer: C

Correct answer: the Tegewa violet scale with iodine

A drop of iodine solution is applied to the fabric and the colour compared against the Tegewa standard scale, which runs from 1 for heavily sized to 9 for fully desized. Iodine gives the familiar blue-violet with starch, so the intensity reports directly how much starch remains. Grade 7 or 8 is usually required before the fabric goes forward.

Answer: D

The size film blocks the dye from reaching the fibre in the places where it remains, giving patchy or streaky results. It also interferes with the absorbency needed for the following processes. Both faults show up only after dyeing.