O o d h e a d p u b L i s h I n g L i m I t e d

W
Ganz
 = Y + Px + Qy + C
where x = X/(X + Y + Z), y = Y/(X + Y + Z) and P, Q and C are constants that
are specific to the spectrophotometer and its light source (particularly its UV
content) and are set during calibration of the instrument.
Table 9.2 again highlights one of the major challenges for wool, the
development of a more effective bleaching process capable of achieving
whiteness values similar to cotton and synthetics. The other major challenge
for wool is to maintain a comparable level of photostability after application
of the FWA. This is discussed in the following section.
Table 9.2 Comparison of brightness (Y), yellowness (Y–Z) and CIE Ganz 82
whiteness index (
W) for wool, cotton and polyester fabrics
Fibre
D65/10
D65/10
CIE Ganz 82
Brightness
Yellowness
Whiteness
(
Y)
(
Y–Z)
(
W)
Natural wool
68.8
8.2
17.0
H
2
O
2
-bleached wool
74.4
6.0
31.0
Double-bleached wool
76.9
2.7
48.7
Double-bleached/FWA-treated
81.7
–15.4
104.6
wool
Greige (scoured) cotton
76.9
1.7
50.3
H
2
O
2
-bleached cotton
85.3
–3.3
75.5
Bleached/FWA-treated cotton
85.3
–20.0
122.2
PET
80.8
–3.7
104.4
FWA-treated PET
86.2
–27.2
138.5
© 2009 Woodhead Publishing Limited

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Advances in wool technology
226