Page 302 - Handbook of Properties of Textile and Technical Fibres

276 Handbook of Properties of Textile and Technical Fibres

The interest in this culture is explained by various advantages of flax fibers:

• Flax fibers are available in Europe, therefore it is possible to locally create new products that,
tomorrow, will be in industrially production.
• The presence of a lot of actors: an active variety selection, many farmers with real
know-how, specialists of the fiber extraction step and their marketing, manufacturers
of specific machines for this plant (seeder; harvester; turner binder; machines for
scutching, combing, and carding, etc.).
• Elementary flax fibers, in the field of plant fibers, can be considered as a very long fiber
(Eder and Burgert, 2010).
• Diameter of an average fiber (df ¼ 16.8 2.7 mm) is close to that of E glass fibers
(conventionally used for polymer reinforcement) (Baley and Bourmaud, 2014).
• Good mechanical properties in tension (Baley and Bourmaud, 2014) and a low specific
gravity (about 1.5) (Batra, 1998), which will be detailed below.
Textile use is the main market, but new fields, such as polymer reinforcement,
are developing. This explains why currently the properties of flax fibers are the
subject of much scientific research. However, the use of flax fibers as reinforcement
is not a recent innovation. Indeed, in 1937, de Bruyne developed Gordon Aerolite, a
composite made of flax rovings impregnated with a phenolic resin matrix (Bakelite).
This material was used for aircraft applications during World War II (Cotterell,
2010).
The aim of this chapter is to present the properties of flax fibers generally. In the first
part, the plant will be presented, then the fibers and their mechanical properties.
Finally, the chapter will be completed by remarks on the use of these fibers as polymer
reinforcements.

8.2 From plant to fibers

8.2.1 Stem organization/stem cross section description, role of
each component and especially fibers

The fibers within a stem are supporting elements (they reinforce the stem) located
around the exterior and are assembled in groups in the form of bundles (about 40
bundles of 30 fibers) (Fig. 8.1).
The mean diameter of a flax fiber is between 15 and 20 mm and its length is be-
tween 5 and 80 mm. An individual flax plant produces 15,000 to 50,000 fibers
(van Dam and Gorshkova, 2003), yielding 0.3e0.5 g dry fibers. Flax bast fiber cells
are an ideal example of the type, with extraordinary cell wall thickness and length.
Their major function is to provide strength to the long (1 m) and thin (2 mm) flax
stem. Examination of the structure of a flax stem provides much information. The
stem has the structure of a composite material reinforced by continuous vessels
(wood part: phloem and xylem) and discontinuous fibers (in the cortex) (Fig. 8.2).
The wind subjects the plant to flexural and torsion loads. A bending moment results
in tensile and compression strains in the stem. Behavior in compression is the weak
point of plant support elements. The presence of cohesive bundles of fibers, regularly