Testing of common salt (for dyeing purpose)
Salt in textile dyeing is mainly for exhaustion of dyes from the dye liquor to the substrate. It is also used in the water softening process to regenerate the zeolite .The salt used must be good quality , with low water hardness causing salts, minimum insoluble material and free from metal salt impurities.
Following common tests are done to ensure the good salt quality,
2.Dust or insoluble impurities
3. Water hardness caused by water when used in dyeing.
4.% purity of salt.
Moisture content :-
is tested by using a moisture meter or by drying and pre weighed sample in hot air oven .
Dust or insoluble impurities :-
By taking about 100 gms of dried salt sample and dissolve it 250 ml distilled water , allow the insoluble to settle down and then filter it with whatman filter paper no.40. dry and weigh the residue to find out the percentage .
Water hardness :-
Since salt is used in large quantities in reactive dyeing , therefore water hardness caused by salt affect the overall dyeing quality , therefore salt must be tested for water hardness .
Make a solution of 100 gpl salt and test it for water hardness , by using standard EDTA solution.
Take about 6 gms of sample accurately weighed and dissolved in distilled water , made upto 1 ltr. Take 50 ml aliquot and titrate it with 0.1 N silver nitrate solution using 5 % potassium chromate solution as indicator till a reddish orange tinge is obtained.
1 ml of 0.1 N silver nitrate = 0.005845 gm of NaCl
Quality parameter of Salt for Dyeing
pH of aq. Solution = neutral
Calcium = maximum 100 mg /kg
Magnesium = maximum 50 mg/ kg
Iron = maximum 0.01 mg/kg
Copper = not detectable
Hardness of 80 gpl solution = maximum 50 ppm
Moisture content = maximum 0.25 %
Insoluble dust = maximum 0.25%