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

2.10
Latest developments in wool metrology
2.10.1 Fibre length
A new instrument, the OFDA4000, is now available which provides estimates
of length and length distribution parameters (including hauteur and barbe),
estimates of diameter parameters including MFD, SD, CVD, CF, the diameter
of fibre ends, curvature parameters, and an estimate of the diameter profile
of fibres in top.
23
 The instrument offers potential for measurements of fibre
length and length/diameter relationships which have not previously been
available. It is unclear how this new information will be applied in either the
trading or product/process development areas. There is the potential that
the extra information may improve processing prediction from greasy wool
to top, and from top to yarn, and may even enable selection of fibres
with particular along-fibre diameter profiles in top to spin yarns with
specialised characteristics, e.g. different combinations of surface softness
and stiffness.
The OFDA4000 has completed comparison trials with Almeter and
Laserscan instruments
25,26
 and IWTO has progressed a test specification for
this instrument to a DTM status.
2.10.2 Dark and medullated fibres
The introduction of exotic sheep breeds into Australia created an impetus to
developed improved instruments for measuring dark and medullated fibres
in raw wool and wool sliver. With funding provided by Australian Wool
Innovation and supported by AWTA Ltd an improved system based on the
balanced illumination method has been developed.
27
Wool fibres are semi-translucent, that is they both reflect and transmit
incident light. In the absence of any pigmentation (colour) they absorb little
of the incident white light and therefore appear white in colour.
Reflection of light occurs because the refractive index of wool fibres
(1.553) is different from air (1.00). Due to phenomenon of refraction, light
incident on the fibres is reflected from the exterior and interior air/fibre
interface. However, if normal white wool fibres are immersed in a solvent
with the same or very similar refractive index they become transparent and
very little reflection occurs. If the fibres are pigmented (e.g. dark fibres) then
some of the incident light will be absorbed and the pigmented fibres can be
© 2009 Woodhead Publishing Limited

---

Advances in wool technology
56
seen against a white background. Likewise, medullated fibres, due to their
internal medulla continue to reflect incident light so that against a black
background they appear white. Benzyl alcohol, a common industrial solvent,
has a refractive index of 1.540 and white wool fibres become virtually
transparent when immersed in this solvent.
The practical benefit of using this property in a test for dark and medullated
fibres is that it facilitates the examination of much larger samples. CSIRO
developed an efficient and safe process for immersing 5 grams of scoured
and carded core samples in benzyl alcohol. These packages can be examined
using a modified version of the existing dark fibre detector. This process,
enhanced by AWTA Ltd’s Research & Development Division, is the basis of
the new test. In recent further developments image analysis software is being
used to detect the dark and medullated fibres in scanned digital images of the
immersed wool fibres.
2.10.3 New staple measurements
Crimp frequency
Research by CSIRO into measuring style characteristics demonstrated that
crimp frequency could be measured by image analysis. When the style project
was terminated in 2001, AWTA Ltd proceeded to develop an image analysis
system for measuring crimp frequency only.
In 2003 AWTA Ltd advised IWTO that it had succeeded in developing a
prototype instrument that could be readily incorporated into the ATLAS
instrument to measure the crimp frequency of the same set of staples presented
to ATLAS for measurement of staple length, strength and POB.
AWTA Ltd is in the process of re-engineering the ATLAS instrument to
replace the electronics and software first engineered in the 1980s. The company
is considering introducing crimp frequency, initially as non-certified
information, with the roll-out of the re-engineered ATLAS instruments.
Staple extensibility
In 2003 AWTA Ltd also announced that it had designed modifications to the
ATLAS instrument that allow the measurement of extension of staples before
they break. Its scientists demonstrated that inclusion of this measurement in
processing prediction formulae, such as TEAM, improved these predictions
for certain wool types such as bellies, which tend to have a higher crimp
frequency and are more stretchy than the rest of the fleece. These measurements
will also become available as non-certified data with the rollout of the re-
engineered ATLAS instruments.
© 2009 Woodhead Publishing Limited

---

The objective measurement of wool fibre quality
57