Determination of Copper Numbers by Copper Number Test of Cellulosic Materials

Last Updated on 15/01/2021

Determination of Copper Numbers by Copper Number Test of Cellulosic Materials

Ahsanul Islam Shawn
Textile Engineer
Rahim Textile Mills Ltd.
University of South Asia, Bangladesh


Copper number:
We know that cotton is oxidized by H2O2 and oxycellulose is produced. Oxycellulose having aldehyde as functional group act as a reducing agent. Thus the traditional method of estimating the degree of degradation due to oxycellulose formation is to determine the copper number.

Copper number is the grams of copper, which are reduced from the cupric (Cu ++) to the cuprous (Cu+) state by 100gm of cellulose when it is boiled with Fehling’s solution or some equivalent reagent.

Copper number test:
A measured value used to determine the condition and stability of Cellulose. The copper number is determined as the amount of Copper reduced from the cupric to the cuprous state by 100 grams of cellulose pulp. A high copper number indicates that the cellulose is not pure and may have been degraded by bleaching. A low copper number indicates that the cellulose is not degraded. This test does not account for the presence of Lignin.

Determination of copper number:
Fehling’s solution is required for the estimation of copper number two different solutions is required which are mixed in equal volumes just before use.

Copper number test
Fig: Copper number test

Preparation of Fehling’s solutions:
Two different solutions were made as follows:

  1. 34.63 gm of crystalline copper sulphate is dissolved in 500 ml of water.
  2. 70 gm of sodium hydroxide and 173 gm of Rochelle salt are dissolved in 500 ml of water.

Procedure of determination of copper number:
Following procedures are followed for determination of copper number:

1. 3 gm of the sample of dry cellulose to be investigated was taken and cut into small pieces.

2. This was taken in flask together with 100 ml of Fehling’s solution (50 ml of each solution) and 200 ml of water.

3. It was then boiled for 15 minutes

4. After boiling the solution, containing the fiber and cuprous oxide was then filtered thorough a cintered crucible and residue is washed with boiling water.

5. Fibers together with the retained cuprous oxide on the crucible are transferred to beaker.

6. 1.5 gm of ferric alum was dissolved in dilute sulphuric acid (10%) solution and this was then added to the beaker. Thus ferrous sulphate, in an amount exactly equivalent to the cuprous oxide, will be formed in accordance with the following equations:

Fe2(SO24)3 + H2O = 2 FeSO4 + H2SO4 + O
Cu2O + 2 H2SO4 + O = 2 CuSO4 + 2H2O

7. The ferrous sulphate is determined by titration with 0.1N potassium permanganate. Preparation of 0.1N KMnO4 is describe in the 4.1.4 section.

8. The end point of titration is determined when the pink color retains for 30 seconds

Each ml of 0.1N potassium permanganate is equivalent to 0.0063 gm of copper.

Copper number = Z * 33.33 * 0.0063

Where Z is the titrate of 0.1N KMnO4 in ml.

Copper no ——————- ratting
Up to 0.3 ——————— standard
Up to 0.5 ——————— acceptable
Above 0.5 ——————– unacceptable

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  1. List of Chemical Testing Equipments for Dyeing Lab
  2. Typical List of Chemicals Used in Dyeing Mill

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