Garments & Apparel “pH Value” Test Procedure

Scope and Principle

This method is intended to determine the pH value of the aqueous extract of textiles:

a) for information of processing history.
b) to ascertain the conformity of acidity and alkalinity on fabrics.

Apparatus

Glass Flasks or Bottles, Chemically Resistant
Glass or Polypropylene Stoppers/Screw Caps, Chemically Resistant
150ml Glass Beakers, Chemically Resistant
Rods, Chemically Resistant
Mechanical Shaker
pH Meter, with glass electrode, accurate to 0.1 unit of pH
Balance, Accurate to 0.01g
100ml Glass Measuring Cylinder
Rubber Gloves

Reagents

Distilled/De-ionised, grade 3 water (see Testing Guidelines)
Hydrochloric Acid 0.1 mol/l (AR Grade)
Buffer solutions for calibration of the pH meter

NB. The flasks or bottles and beakers should be filled with 0.1mol/l hydrochloric acid solution two days before use, then washed with distilled water. This glassware should be used for this test only and filled with distilled water between tests.
Specimen Preparation

Rubber gloves should be worn throughout the preparation procedure to avoid contamination.

A sample, which is representative of the bulk and sufficient for 3 specimens, should be cut into small pieces, approximately 5mm square.

From the cut sample, take three specimens weighing 2g ± 0.05g.

Test Procedure

Three extracts should be prepared at room temperature.

a) Place the 2g of cut specimen and 100ml of distilled/de-ionised water into a stoppered flask or bottle.

b) Shake the flask/bottle vigorously by hand to thoroughly wet out the fabric.

c) Mechanically shake the three prepared test solutions for 2 hours ± 5 mins.

d) Using the two buffer solutions calibrate the pH meter at the same temperature as the aqueous extract.

e) Immerse the glass electrode into distilled/de ionised water several times until the indicated pH value stabilizes.

f) Decant the first extract into a beaker and immediately immerse the glass electrode to a depth of at least 10mm. Stir with a glass rod until the pH stabilizes.
Do not record this reading.

g) Decant the second extract into a beaker and immediately immerse the electrode, without washing, to a depth of at least 10mm. Allow to stand without stirring until the pH value stabilizes.
Record this value.

h) Decant the third extract into a separate beaker and test for pH as above.
Record this value.
Calculation of Results

Repeat the Test Procedure if the difference between the two recorded pH values, expressed to the nearest 0.1 unit, is greater than 0.2.

Calculate the mean of the two recorded values.
Test Report

Report the test method number and title.

Report the mean of the pH value of the second and third extracts only to the nearest 0.1.

Report the pH of the distilled/deionised water.

Report the temperature of the test solution.

Report any factors which may have affected the result, e.g. difficulty in wetting out.

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