How to know the fabric is properly mercerized or not?

There are various methods to to test the quality of mercerization. These are:

i) Lustre, %

ii) Microscopic examination

iii) Deconvolution count

iv) Barium activity number

i) Lustre, %: The mercerized sample is illuminated at an angle of incidence of 45 degree with the help of filament lamp. Light reflected at 45 degree and 90 degree is measured by photo electric cell. Lustre is defind by the contrast ratio of specular to diffuse reflectance. The specular reflectance measurement method is considered as an accurate evaluation of lustre. 

Lustre = contrast ratio of specular to diffuse reflectance

Lustre= Light reflected at 45 degree/ light reflected at 90 degree

ii) Microscopic examination:The test involves the assessment of degree of mercerization by counting the number of twisted and untwisted fibres (deconvolution count) while viewing through the microscope. If the sample under investigation is immersed in a solution containing 20 g iodine in 100 ml potassium iodide for 3 seconds and then wash off well, mercerized cotton will be stained bluish black and unmercerised cotton will be white.

iii) Deconvolution count: Under this mercerised fibres are cut down and examine under microscope and fibre with and without convolution are counted. The numbers of fibres without convolution per 100 fibres is called "Deconvolution Count" Generally percent unconvoluted fibres are measured. Generally the unconvoluted fibre(%) in the unmercerized cotton is around 5 to 15 %, while in fully mercerized it become upto 80%.

iv Barium Activity Number: The degree of mercerization can be measured by this test. In increase in absorption properties are shown by alkali's, the ratio of soda absorbed by mercerized to that by the unmercerized cotton may be used as a parameter of the degree to which the cellulose has been swollen. From the practical point of view, Barium hydroxide number is very easy to estimate, and the ratio of uptakes for this reagent is referred to as the barium activity number. In the test, the mercerized and unmerserized samples weighing 1 g were treated with 30 ml of 0.25 N Barium hydroxide solution for 2 hours. Then 10 ml of solution (with few drops of phenolphthalein indicator) from that was titrated against 0.1 N hydrochloric acid (pink colour to colourless). A blank was also run without any fibre sample. The barium activity number is measured by using following formula:

Barium activity number = {(B-M)X100}/ (B-U)

Where B is the titration reading for blank, M for mercerised and U for unmercerized. While unmercerized cotton gives a barium activity number of 100, it ranges between 115 to 130 for mercerized fabric and 150-160 for mercerised yarns.