Mercerisation Process Control Questions and Answers

Answer: A

Correct answer: concentrated sodium hydroxide under tension

Mercerisation swells the cotton in strong caustic soda - around 20 to 26 per cent, or about 50 degrees Twaddell - while the fabric is held stretched. Both parts are essential: the caustic swells and reorganises the cellulose, and the tension prevents the shrinkage that would otherwise accompany the swelling and would cost the lustre.

Answer: B

Correct answer: A-2, B-4, C-1, D-3

Four benefits from three structural changes. The convoluted, flattened cotton fibre swells into a round smooth cylinder that reflects light directionally, which gives the lustre. The swollen cellulose is more accessible to dye, which raises the uptake. The chains become better aligned along the fibre axis, which raises the strength. And the shrinkage is taken up under tension during the process, so the finished fabric is dimensionally stable afterwards.

Answer: C

Both are true and the reason gives the mechanism: slack mercerisation is a real process, used where bulk and stretch are wanted rather than lustre, so tension is what distinguishes the two outcomes. Slack goods are made deliberately in this way.

Answer: D

The same swelling occurs but the fibre is allowed to contract, which gives a fuller handle and elastic recovery. It is used for stretch fabrics and towelling rather than for lustrous goods. The chemistry is identical in both cases.

Answer: A

Twenty-eight degrees Baume is around two hundred and fifty grams per litre, and the range for mercerising is roughly twenty-four to thirty. Baume is the traditional mill unit and its conversion should always be to hand.

Answer: B

The first two are correct. The third is wrong, since above the working range the extra caustic adds cost and effluent without further benefit and can make the fabric harsh to handle. Baume is the traditional mill unit for the liquor.

Answer: C

Both are true and the reason gives the direction: the reaction is exothermic and the liquor must be cooled to hold the temperature, which is one of the larger utility loads on the range. Cooling water is a significant service on the plant.

Answer: D

Correct answer: True

Hot mercerising swells the fibre less, so the effect on lustre is smaller, but the hot caustic penetrates a fabric far faster and more evenly - particularly a heavy or tightly constructed one, and one that has not been fully prepared. Where uniformity matters more than maximum lustre, and where the range must run quickly, the trade is worth making.

Answer: A

Correct answer: increased water repellency

Mercerisation does the opposite: the swollen, more accessible cellulose absorbs water more readily, which is part of why it takes up dye better. Lustre, dye uptake and tensile strength all increase, and so does dimensional stability - but nothing about the process makes the fibre hydrophobic.

Answer: B

Dye yield can rise by a quarter or more for the same application, which is a real saving. It also means mercerised and unmercerised goods cannot be dyed in the same bath to the same shade. Yield can rise by a quarter or more.