PURPOSE
To assess the
potential of white and light coloured fabrics to yellowing due to contamination
by sterically hindered phenols. This test is to be carried out on fabric which
has not yellowed.
Phenolic
yellowing is discolouration of textile materials caused by the action of oxides
of nitrogen and phenolic compounds (might be present in storage materials,
polyurethane foam, fabric finishes etc.), which lead to the production of a
yellow colour. This method is not intended to deal with other causes of
discolouration such as Optical Brightening Agents deposits, oxidation of fabric
lubricants etc.
EQUIPMENT
• Perspirometer
• 7
acrylic-resin or glass plates
• Incubator or
oven, to maintain (50±3)°C
• Test papers
75mm x 100mm (see ISO 105-X18 for definition)
• Control
fabric 30mm x 100mm (see ISO 105-X18 for definition)
• Butyl
hydroxytoluene (BHT)-free polyethylene film
• Light box
with light source D65
• Grey scale
for assessing change in colour (ISO 105-A02)
TEST
SPECIMEN
Two specimens for each colour and material measuring 3cm
x 10cm. For narrow fabrics a single strip of material measuring 10 cm in length
is enough. Products that contain polyurethane foam, such as padded bras are
especially risky, as they are products packed in plastic bags and/or stored
under polluted conditions (e.g. bad ventilation). Products subject to treatment
at high temperatures such as heat setting and moulding are also at higher risk.
METHOD
1.
Using a ruler and scissors and without marking the fabric, cut two single
layers of the fabric to be tested, each measuring 3cm x 10cm.
2.
Take one test paper for each sample. Fold it in half along the 10 cm axis and
place the sample inside, making a sandwich.
3.
Do the same with the control fabric
4.
Place each sandwich between two glass plates so that each sandwich is
separated.
5.
Place all glass plates on top of each other. One perspirometer can hold 5
samples + 1 control fabric (totally 7 glass plates). If less than 5 samples are
tested 7 plates should still be in the stack.
6.
Wrap the stack firmly in three layers of BHT free polyethylene film and seal
with adhesive tape to create an airtight package.
7. Place the
package in the perspirometer, apply a pressure of 12.5 kPa (=5 kg), lock it and
then remove the load.
8.
Place the test device on its side in the oven for 16 hours at (50±3)°C in
upright position.
9. Remove the
package and allow it to cool before unwrapping.
RESULTS
Assess the test
specimens within 30 minutes of unwrapping. Start the assessment with the
control fabric and make sure it has yellowed to at least a grade 3 using the
grey scale. If not, the test has not been carried out successfully, and needs
to be repeated.
