Page 307 - Handbook of Properties of Textile and Technical Fibres

Tensile properties of flax fibers 281

prior to spinning. Tows are considered today to be undesirable and unavoidable by-
products. These fibers are sold at about half the price of scutched flax.
The mechanical properties of elementary fibers sampled either from scutched
fibers or from tows have been found to be similar (Martin et al., 2014). Usually, the
scutched fibers are organoleptically evaluated as a function of their length, color, soft-
ness, fineness, and tenacity (Bert, 2013). The variety, soil, cultural practices, climate,
on the one hand, and plant maturity, retting degree, stocking conditions, and strength
of scutching, on the other, are among the important parameters which contribute to the
technical fiber quality.

8.3 Single flax fiber description

8.3.1 Presentation
Within the stem, flax fibers generally exhibit a polygonal shape with 5e7
sides (Fig. 8.2) while they appear rather round or oval when free, as seen in scanning
electron microscopy (Fig. 8.3).
The longitudinal view of a fiber reveals a nonconstant transverse dimension
(Charlet et al., 2010). The fibers are larger near the root and become thinner nearer
the tip. It is, however, important to note the scatter in the geometrical dimensions.
The transverse and the longitudinal dimensions lie in the range of 5e30 mm and
5e80 mm, respectively (van Dam and Gorshkova, 2003; Batra, 1998; Wang et al.,
2001; Mukherjee and Satyanarayana, 1984). Fig. 8.3 shows examples of cross-
marks (deformed zones), presumably kink bands, called “nodes” or “dislocations.”
Such defaults are also observed in nettle and hemp fibers (Bergfjord and Holst, 2010).
Within a composite, the aspect ratio (length/diameter) is an important parameter to
optimize the charge transfer between fibers. Its average has been estimated to 2500
(Baley et al., 2017), a value similar to those of ramie (van Dam and Gorshkova,
2003; Mukherjee and Satyanarayana, 1984). Another parameter, mainly linked to

Figure 8.3 Elementary flax fibers.