Page 89 - Handbook of Properties of Textile and Technical Fibres

70 Handbook of Properties of Textile and Technical Fibres

Figure 3.11 Transmission electron microscope images of a porcupine quill cross section
showing that the intermediate filaments have been sectioned transversely (T), longitudinally
(L), and obliquely (O), indicating they do not run exclusively parallel to the direction of quill
growth (Maxwell, 2002).
(Hearle, 2000, 2007) by Hearle. Popescu and H€ ocker (2009) also give a good overview
of the state of play in this area. In light of the emergence of new science technologies
that provide in-depth data on fiber hierarchical structure and morphology, subcellular
properties, protein composition and structure, scientists are starting to think about
more comprehensive computational modeling to understand and then to predict quan-
titatively the relation between the fiber structure and fiber properties (Hearle, 2003;
Bryson et al., 2005).

3.4 Methods of measurement

When measuring the tensile properties of wool fibers, two major issues need to be
addressed: in what form (single fiber, bundle, staple, yarn or fabric) should we test
the wool and how do we deal with the nonuniform diameter of the fiber? Wool fibers
start life on a sheep, nicely aligned and clumped together into staples. During scouring
to remove the wool grease, they become entangled. They are subsequently disen-
tangled and aligned during carding and combing before spinning into yarn. Finally
the yarn is woven or knitted into fabric. All stages along this pipeline are open to
testing; however, in this section we have concentrated on single fiber testing as the
only true measure of the fiber properties. Briefer mention is made of the testing of sta-
ple, yarn, and aligned bundles.

3.4.1 Staple

For wool, strength is often measured by testing whole staples. This is generally done
with a gauge length of 50e60 mm at a speed of 300 mm/s using either a standard