Page 335 - Handbook of Properties of Textile and Technical Fibres

308 Handbook of Properties of Textile and Technical Fibres

potassium hydroxide, and soda ash to dissolve the pectin component. The surface
active agents could be used in retting to remove the unwanted noncellulosic compo-
nents adhering to the fibers (dispersion and emulsion forming process). Chemical
and surfactant retting produces high-quality fibers but the cost is higher than that of
traditional methods (Natural fibers, biopolymers, and biocomposites, 2005). There
are other processes such as Duralin and tuxying used to separate the fibers. The Duralin
process is used with deseeded flax, called flax straw, and eliminates the need for tradi-
tional dew retting. Bundles of flax straw are heated in water under pressure at between

160 and 180 C for 15 min. The flax straw is then dried for 30 min at temperatures up to

180 C. This allows easy separation of the fibers from the stalks. Tuxying is the process
of extracting the fiber from the leaf sheaths of the abaca plant, related to the banana
plant, produced mainly in the Philippines and used for cordage and paper making.
A specially made tuxying knife is used to make an incision through the inner and mid-
dle layer of each sheath, close to the base or butt end to remove the outer layer. The
fiber extraction and cleaning takes place after the retting process where the nonfibrous
materials are removed entirely. The extraction can take place in one step or in several
steps such as breaking, milling, scutching, and decortication. The fibers are cleaned
after extraction to be used in several applications.

9.4 Treatment and modification of plant fibers

To obtain reliable composite materials for industrial applications and to utilize fully the
potential of reinforcing fibers, both perfect reinforcement and strong interfacial bond
formation have to be guaranteed (de Albuquerque et al., 2000). The properties of plant
fibers can be improved by suitable treatment methods, particularly considering woven
fibers in fabric forms, for composite fabrication (Barreto et al., 2011; John and
Thomas, 2008; Trdine et al., November 2010; Kaewkuk et al., 2010; Kabir et al.,
2011; Milanese et al., 2011; Campos et al., 2012). However, the application of plant
fibers has some drawbacks, e.g., the hydrophobicity of the fibers, the relatively poor
thermal stability of the plant fiber composites, and especially the poor compatibility
with a hydrophobic polymer matrix, resulting in weak interfaces and poor mechanical
properties of the composites. Most of these drawbacks may be overcome by the use of
surface modification of the fibers (Mohanty et al., 2001; Li et al., 2007; Scarponi and
Pizzinelli, 2009). On the other hand, being an organic material, the plant fibers are
vulnerable to biological attacks; they are affected by the moisture condition and are
sensitive to alkali attack that can decompose lignin and the other constituents. The
weaknesses of plant fiberereinforced composites can be improved by treating the fi-
bers by chemical or physical methods or by the use of coupling agents (Joseph
et al., 1996, 2002a; Mwaikambo and Ansell, 2002). Plant fibers contain highly reactive
hydroxyl groups (eOH) groups, which cause them to be susceptible to moisture and
directly impair the properties of composites, especially dimensional stability. These fi-
bers do not efficiently adhere to nonpolar matrices due to this polar group. To over-
come this difficulty, these fibers need to be modified chemically or physically
(Corrales et al., 2007).