Accreditation Scheme
NEXT TEST METHOD 5
COLOUR FASTNESS TO CHLORINATED WATER (Swimming Pool Water)
Scope and Principle
This method is intended to determine the resistance of colour of textiles of all kinds and in all forms to the action of active chlorine in
concentrations such as that used to disinfect swimming pool water.
A specimen of the textile is treated with a weak chlorine solution and dried. The change in colour of the specimen is assessed with the grey scale.
Apparatus
Wash-wheel, with a thermostatically controlled water bath and rotating at 40 ± 2 rpm
Stainless Steel Cylinders, with chlorine resistant gaskets, 7.5cm diameter x 12.5cm depth and a capacity of 500ml + 50ml
Balance, accuracy of 0.01g
pH meter, accuracy of 0.01 units
Thermometer
1 x 25ml, 100ml, 250ml, 500ml Measuring Cylinders
0 - 50ml Burette
1 x 20ml and 25ml Pipette
4 x 1 litre Volumetric Flask
1 x 500 ml Volumetric Flask
3 x 250ml Conical Flasks
Digital Timer
Drying Screen (Non-Rusting)
Grey Scales Change (see Testing Guidelines, Part 2)
Colour Assessment Cabinet (see Testing Guidelines, Part 2
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Reagents
Distilled/De-ionised Water, Grade 3 (see Testing Guidelines, Part 1)
Sodium Hypochlorite Solution (NaOCl) contains 10% - 14% active chlorine
0.1N Sodium Thiosulphate Solution (Na2S2O3)
Potassium Di-Hydrogen Orthophosphate (KH2PO4)
Di-Sodium Hydrogen Orthophosphate Dihydrate (Na2HPO42H2O)
Potassium Iodide (Kl)
Starch - soluble
0.1N Hydrochloric Acid (HCl)
0.1N Sodium Hydroxide (NaOH)
0.1N Acetic Acid
Specimen Preparation
Fabrics:
Cut a specimen 10cm x 4cm from the main fabric. This is tested and mounted back into the original space, so that all colours are adjacent for
assessment.
For multi-coloured fabrics, prints or stripes, all the colours of the design should be included.
Avoid specimens within 5cm of the selvedge.
Yarns:
Specimens are wound onto a template 10cm in length, with the yarn parallel to this side, to form a hank. The weight of the specimen should
be 1.0g.
To secure the yarn, sandwich it in between a piece of polypropylene net 10cm x 8cm folded in half to give a specimen 10cm x 4cm.
Preparation of Starch Indicator (This must be freshly prepared):
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Weigh out 1.0g of starch. Pour into a beaker with a few drops of distilled/de-ionised water and mix to a paste.
Add 100ml of boiling distilled water and boil the solution for 1 minute, stirring initially to ensure the starch is mixed.
Allow the solution to cool until tepid (between 18°C and 30°C). Add 3.0g potassium iodide and stir.
Preparation of Solutions 2 and 3 (These can be stored in a fridge for up to six weeks):
Solution 2: Dissolve 14.35g of potassium di-hydrogen orthophosphate in a 1 litre volumetric flask with distilled or de-ionised water.
Solution 3: Dissolve 20.05g of di-sodium hydrogen orthophosphate di-hydrate in a 1 litre volumetric flask with distilled or
de-ionised water.
Preparation of Solution 1 (This must be made up after solutions 2 & 3 and used immediately as it degrades when made up in diluted form. It
can lose up to 50% of its strength within 1 hour):
Dilute 20ml sodium hypochlorite solution in 1 litre volumetric flask with distilled or de-ionised water.
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Titration Procedure
It is necessary to find the amount of available chlorine in the sodium hypochlorite as this decreases with time.
If the titre is less than 11.3ml the solution is considered to be too weak to be used.
a) Fill the burette with 0.1N sodium thiosulphate solution.
b) Into each conical flask add approximately 0.5g potassium iodide and approximately 25ml of hydrochloric acid.
c) Add 25ml of sodium hypochlorite (Solution 1) by pipette, at the beginning of each titration.
d) Titrate this brown solution (due to the liberated iodide) with the sodium thiosulphate solution from the burette until the solution becomes
straw coloured.
e) Add approximately 2.0ml starch indicator. The solution should become blue/black. If the solution just becomes colourless at this stage then
the titration has already exceeded the end point, and would need to be repeated.
f) Continue to slowly add the thiosulphate until the solution just becomes colourless. This is the titration end point.
g) Record the volume in the burette.
h) Repeat the titration twice more.
i) Take the average of the 3 titre readings.
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Calculate the volume of solution 1 to be used as follows:
Volume of solution 1 required to give 50mg/l active chlorine: 705ml ÷ 2
Titre
Note: Records must be kept of the titration end points.
Preparation of the Test Solution (This must be made up and used as soon after the completed titration as possible):
a) Add the calculated volume of solution 1 into a 1 litre volumetric flask.
b) Add 100ml of solution 2 and 500ml of solution 3 into the flask with Solution 1.
c) Dilute the test solution to 1litre with distilled or de-ionised water.
d) The pH of the test solution should be 7.5± 0.05 (between 7.45 and 7.55). If the solution is above 7.55 add 0.1N acetic acid until the correct
pH tolerance is obtained. Conversely if the solution is below 7.45 add 0.1N sodium hydroxide until the correct pH tolerance is obtained.
e) Keep a record of the pH values.
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Test Procedure
a) Adjust the wash-wheel to maintain a temperature 27 ±2°C.
b) When the temperature is reached, use a thermometer to check that it is within ±2°C of the set temperature.
c) Weigh the specimen. Calculate the amount of test solution according to a liquor ratio of 100:1 i.e. 100ml test solution per 1g of specimen.
d) Place the specimen into a container together with the test solution ensuring that the specimen is thoroughly wetted.
e) Clamp the cover and fasten the canister vertically into the holders on the rotor of the wash-wheel. Arrange the canisters to ensure there is
a balanced number on each side of the shaft.
f) Set the timer for 1 hour. Start the timer and the wash-wheel simultaneously.
g) On completion of the test cycle remove the containers from the wash-wheel.
h) Remove the specimen from the container, and hand squeeze to remove excess solution. Do not rinse the specimen.
Drying:
Lay fabrics on a screen in subdued lighting (avoid direct light sources).
For yarns open out the specimens by removing the stitching on all sides and dry separately.
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Evaluation of Results
All tested specimens must be assessed within a maximum of 24 hours after completion of the test.
After drying, position the specimen back into the original fabric and mount onto off-white card. Assess the specimen in a colour assessment
cabinet under D65 Artificial Daylight (see Testing Guidelines, Part 2).
Assess the change of shade using the grey scales for assessing change (see Testing Guidelines, Part 2).
Assess all colours individually, including the base.
Test Report
Report the test method number and title.
Report the numerical rating of the colour change of the specimen.
Report any change in hue.
State the concentration of active chlorine used.
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