The main
principle is electrometric measurement of the pH value of the aqueous extract
of textiles at room temperature by means of a glass electrode. The method is
applicable to textiles in any form provided that a representative sample may be
obtained which is in a form that permits a ready exchange of liquid between the
interior of the material and the solution used in preparing the extract. The
result shows the acidity or alkalinity of the textile.
EQUIPMENT
• Distilled
water, of at least grade 3, pH 5.0-7.5, conductivity 5 μS/cm
• Standard
reference materials buffer (SRM) solutions: pH 6 and 10 or Commercial grade
buffer solution: pH 4, pH 7 and pH 10.
• 3 M Potassium
Chloride (KCl) solution
• Glass or
polypropylene flasks with stopper, 150 ml. The flasks used for this test should
be set aside for this purpose only.
• Funnel
• Volumetric
flask with stopper, 1000 ml
• Measuring
cylinder
• Gloves
• Mechanical
shaker, providing rotational or reciprocating movement. A to-and-fro movement
at a rate of 60 per minute or a rotational frequency of 30 per minute have been
found satisfactory.
• pH-meter,
with a glass electrode, capable of measuring to at least 0,1 pH-units
• Balance,
accuracy 0.01 g
REAGENTS
•
Distilled or deionised water, of at least grade 3, having a pH value between
5.0 and 7.5 and a maximum conductivity of 5 μS/cm.
•
Buffer solutions: Either SRM with pH values 6 and 10 or Commercial grade
buffer: pH 4, pH 7 and pH 10.
• Potassium
chloride solution (KCl) in concentration 0.1 M (mol/litre) prepared using 3 M
KCl and distilled water. Below table shows how to prepare 1, 2, 3, 4 or 5 litre
of 0.1 M KCl:. To make 1 litre 0.1 M KCl: Take 33 ml of 3 M KCl solution to a 1
litre volumetric flask. Add distilled water up to 1 litre and shake the
solution.
Take this
volume of 3 M KCl
|
Take this
volume of distilled water
|
It will
give this volume 0.1 M KCl
|
33 ml
|
967 ml
|
1000 ml
|
67 ml
|
1933 ml
|
2000 ml
|
100 ml
|
2900 ml
|
3000 ml
|
133 ml
|
3867 ml
|
4000 ml
|
167 ml
|
4833 ml
|
5000 ml
|
TEST
SPECIMEN
•
Each colour on the fabric test specimen shall be tested separately.
• If there are
prints, the fabric and print shall be tested together and the colours shall not
be separated.
Each test
specimen is 2.0 g (±0.05 g).
METHOD
Preparation
of samples with mechanical shaker
a)
Prepare triplicate samples. Cut (2±0.05)g of the sample that is representative
for the bulk production into small pieces having approximately 5 mm sides or of
such a size and place them in the flasks. Use gloves.
b)
Add 100 ml of 0.1 M KCl solution to each flask.
c) Shake the
flasks until the fabric is wet, and then shake it mechanically for 2 hours ± 5
min according to section 5.2.
Preparation
of samples without mechanical shaker
a)
Prepare triplicate samples. Cut (2±0.05)g of the sample that is representative
for the bulk production in small pieces and place them in the flasks. Use
gloves.
b)
Add 100 ml of 0.1 M KCl solution to each flask.
c)
Shake the flasks until the fabric is wet.
d) Let the samples
stand for about 15 hours in room temperature. Shake the flasks from time to
time.
Calibration
of pH meter- with standard reference materials buffer solution
1. Open the
fill hole on the electrode; add KCl solutions (3M) if necessary.
2. Switch on
the pH meter by pressing [On/Off] key.
3. Rinse the
electrode with distilled water and immerse it in the pH 6 buffer solution.
4. Press the
[pH cal] key (twice) to measure the temperature.
5. When the
display shows “pH 6.00”, press [Enter] to measure the first buffer solution.
6. When the
display shows “bu 2”, rinse the electrode, immerse it in the pH 10 buffer
solution and press [Enter] to measure the temperature.
7. When the
display shows “pH 10.00”, press [Enter] to measure the second buffer solution.
8. When the
display shows a slope, the calibration is completed. Note the calibration % on
the report sheet. If it is below 93%, calibrate once more with fresh buffer
solutions.
Calibration
of pH meter - with commercial grade buffer solution (three calibration points)
1. Open the
fill hole on the electrode; add KCl solutions (3M) if necessary.
2. Switch on
the pH meter by pressing [On/Off] key.
3. Rinse the
electrode with distilled water before individual buffer reading.
4. Calibrate
with buffer pH 4, pH 7 and pH 10 as per respective pH meter manual.
5. Measure and
record the temperature during calibration.
6. When the
display shows a slope, the calibration is completed. Note the calibration % on
the report sheet. If it is below 93%, calibrate once more with fresh buffer
solutions.
Measuring
the pH value of the samples
1.
Rinse the electrode in distilled water.
2.
Place it in flask 1:1 and stir during measuring. Wait for the pH value to
stabilize and note the result on the report sheet.
3.
Place the electrode in flask 1:2 without rinsing and leave it still. Wait for
the triangle in the display to disappear and note the result.
4. Place the
electrode in flask 1:3 without rinsing and leave it still. Wait for the
triangle in the display to disappear and note the result. The difference
between pH values of samples 1:2 and 1:3 should not be greater than 0.3 pH
units, if it is the samples need to be measured again.
5.
Repeat point 1-4 for all samples.
6. Finally the
buffer solutions shall be measured. Rinse the electrode between the two
solutions and note the values. If the buffer values differ more than ± 0.05,
the calibration and measurement of the samples needs to be re-made.
RESULTS
The average
value of second and third measures of one sample is calculated according to the
formula below: 𝐴𝑣𝑒𝑟𝑎𝑔𝑒=1:2+1:32
The result
shall be reported with one decimal only.
NOTE
Note! If there
should be a garment wash on the order, the pH value should be measured after
the final treatment is made.
Note! The
buffer solutions shall have the same temperature as the samples (room
temperature
Note! Sample
1:1 shall not be included in the calculation of the result.
