Page 312 - Handbook of Properties of Textile and Technical Fibres

286 Handbook of Properties of Textile and Technical Fibres

Consequently, the fiber morphology, cell wall composition, and yield of these
flax plants differ according to the stem location. Lefeuvre et al. (2015) have collected
fibers from five areas along the length of the technical fibers (Eden variety) and
studied the mechanical properties of elementary fibers. The Young’s modulus
(E fL )and thestress(s fLu ) show the same trend, with an increase in values
from the bottom (E fL ¼ 48.4 GPa; s fLu ¼ 590 MPa) to the middle (E fL ¼ 63.4 GPa;
s fLu ¼ 940 MPa), followed by a decrease at the top (E fL ¼ 50.8 GPa;
s fLu ¼ 760 MPa). The lowest values are obtained at the bottom extremity, whereas
the highest values are from the middle of the stem, corresponding to a stiffness
considered as high as (>55 GPa) according to Baley and Bourmaud (2014),work
presented later.

8.4.6 Average mechanical properties of flax fibers from middle
of the stem
Different flax fiber batches have been characterized following similar conditions and
protocol (Baley and Bourmaud, 2014). Tensile properties of elementary flax fiber,
harvested between 1993 and 2011, have been quantified (L. usitatissimum L.) This
represents a total of 2954 fibers divided into 50 batches of different fibers (37 batches
of textile flax and 13 batches of oleaginous) of 12 different varieties (7 variety of textile
flax and 5 variety of oleaginous). Nowadays, plant selection is not performed based on
the mechanical performance of fibers as textiles remain the first source of income.
Thus, selection of a novel variety depends on harvester’s requirements, scutchers
and yarn producers followings the present rules:

• Agronomic: adaptation to soil and climate sensitivity to diseases, vegetative precocity,
lodging sensitivity, etc.
• Economic: yields production per hectare and percentage of each components (fibers, shives,
seeds).
• Yarn production requirements: fiber finesse, regularity, strength, and fiber division.
Intellectual property is assured for 20 years, which leads inevitably to changes of
fiber variety. Fig. 8.5 presents mean tensile strengths as a function of mean tangent
modulus (see standard NF T25-501-2) of all the batches. It can be noticed that the
stiffest fibers are also those which exhibit the highest tensile strength. Fig. 8.6 shows
the strain at break as a function of tangent modulus.
Mean mechanical properties are E fL ¼ 52.47 8.57 GPa (maximum: 75 GPa
and minimum: 36 GPa), tensile strength sfL ¼ 945 200 MPa (maximum: 1454
and minimum: 588 MPa), and strain at break A% ¼ 2.07 0.45% (maximum:
3.5% and minimum: 1.6%). Mean fiber diameter is 16.8 2.7 mm. Analysis of
the results does not reveal the influence of varieties and harvesting conditions. In
addition, there are no batches that present very low performance, which is very
promising for industrial applications. Nevertheless, oleaginous flax fibers have
slightly lower mechanical properties than their textile counterparts. However, they
represent a promising source of material reinforcement as well (E fL ¼ 52.8 GPa,
s fL ¼ 855 MPa at A% ¼ 1.82%).