Page 363 - Handbook of Properties of Textile and Technical Fibres

336 Handbook of Properties of Textile and Technical Fibres

fiber length to, the other end, a “parallel” model where the two domains alternate with
each other along the fiber width (Hearle, 2001; Young and Eichhorn, 2007). In the se-
ries model, both the crystalline and amorphous domains experience the same levels of
stress under tensile deformation, and in the parallel model, both domains experience
the same levels of strain. Thus, these models are also called the “uniform stress”
and “uniform strain” models, respectively. Fibers with a series arrangement are
characterized by an initial or elastic modulus that does not change with the degree
of crystallinity until it reaches high values, whereas in fibers with a parallel arrange-
ment, the modulus increases continuously with the degree of crystallinity (Kong
et al., 2008; Young and Eichhorn, 2007). Schematic illustrations of the two models
are shown in Fig. 10.7.
Among regenerated cellulosics, the stressestrain profiles of highly oriented fibers
are dominated by chain deformation and exhibit characteristics of a series distribution
(Kong et al., 2007). Examples include those produced from phosphoric acid solution
(also called “Fiber B”), the “Ioncell-F” fibers produced with the ionic liquid [DBNH]
[OAc], and the Cordenka extra high modulus (EHM) fibers (Northolt et al., 2001; Sixta
et al., 2015; Eichhorn et al., 2001, 2003). The stressestrain profiles of fibers with low
orientation are dominated by shear between crystals (Kong et al., 2007) and exhibit
characteristics of a hybrid structure comprised of crystalline and noncrystalline
domains arranged in series together with crystalline domains mixed with noncrystal-
line domains in both series and parallel arrangements. Examples include viscose
and lyocell fibers (Gindl et al., 2006; Kong et al., 2008; Kong and Eichhorn, 2005).
Representative values of tensile strength, elongation at break, and the elastic
modulus of various regenerated cellulosic fibers are shown in Table 10.1. Values of
glass, flax, and cotton are included for comparison.

A

A C

C

(a) (b)
Figure 10.7 Schematic illustration of the (a) parallel and (b) series arrangements of amorphous
(A) and crystalline (C) domains in fibers.
Redrawn from Young RJ, Eichhorn SJ: Deformation mechanisms in polymer fibres and
nanocomposites, Polymer 48:2e18, 2007.