Analysis of damaged cotton by Fehling’s Solution

Objective

Cotton is a very long chain of glucose anhydride molecules linked together, when cellulose is attacked by acids, hydrolysis occurs at the junction points between the glucose residues, the reaction proceeding to product B.

Principles

Both hydrocellulose and oxycellulose contain aldehyde groups which reduce Fehling’s solution to give a precipitate of red cuprous oxide, when cotton is treated at or near the boil in the reagent. The amount of brown cuprous oxide deposited on the cloth indicates the extent to which the cellulose being oxidized.

Procedures

1. 3 different sample (1/4) – Unchanged, 20°C Bleached and 50°C Bleached cotton sample
2. Put 25ml each solution A & B into dyepot
3. Add 100ml water and wash 5 times, 100ml@/1 min*
4. Equal parts of solution A and B are mixed are brought to the boil
5. Rinsed in 70°C hot water
6. Immerse one set of cloths in this solution and continue boiling gently for 20 minutes
7. Neutralize with 100ml of 1% acetic acid and rinse again
8. Solution A – 60g of copper sulphate per litre of water
9. Solution B – 346g of potassium sodium tartrate
10. Sodium Hydroxide – 100g per litre of water
11. Examined visually or under the microscope

Wash 5 times, 100ml@/1 min*
1st - Deionized water, 100ml
2nd - Acetic Acid 1%, 100ml
3rd - Deionized water, 100ml
4th - Deionized water, 100ml
5th - Deionized water, 100ml

Photos in the experiment:

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The sample specimens as bellow:

Unchanged cotton sample

20°C Bleached cotton sample

50°C Bleached cotton sample

Comments

Fehling’s Solution test which is the places on the fibre carrying aldehyde groups will be coloured pink or red, and granules may often be seen under the microscope. Pink or red colour (bleached at 20°C), sometimes at the fringes of holes in fabric, suggests acid damage or possibly oxidation damage. Because oxycellulose frequently contains a preponderance of carboxyl groups instead of aldehyde groups, the test is much less sensitive to oxidation damage.