Page 337 - Handbook of Properties of Textile and Technical Fibres

310 Handbook of Properties of Textile and Technical Fibres

9.5 Plant fibers

Fibers from plants can be in the form of hairs (cotton, kapok), hard fibers (coir, sisal),
and fiber sheaves (flax, hemp, jute). The plant fibers are classified depending on their
utility such as primary and secondary. Plants to be used as fibers for primary utilities
include hemp, jute, kenaf, etc., while the by-products of plants such as coir, pineapple,
etc., belong to the secondary group (Faruk et al., 2012). Fibers extracted from plants
are a type of renewable sources and a new generation of reinforcements and supple-
ments for polymer-based materials. These fibers are renewable, cheap, completely
or partially recyclable, biodegradable, and environmentally-friendly materials. Their
availability, low density, price, and satisfactory mechanical properties make them
attractive alternative reinforcements to glass, carbon, and other artificial fibers (Palani-
kumar et al., 2016; Vimal et al., 2015; Ramesh et al., 2016a; Jakubowska et al., 2012).

9.5.1 Hemp fiber

Hemp (Cannabis sativa) is a bast fiber crop cultivated mainly in China and France for
fiber, oil, and seed. The family of cannabis plants was indigenous to central Asia and
was believed to have reached Europe in the Iron Age (Barber, 1991). Today, it is also
widely grown in countries, which experience moderate weather conditions such as
Chile, North Korea, India, Japan, and many European countries. The European Union
considers promoting hemp cultivation in member countries by subsidies and is looking
forward for further developments. Nowadays, hemp is used in several applications
such as textile fibers, paper, fibers for composites, seed food, oil, wax, resin, pulp, bio-
fuel, etc., and its usage mainly depends on the grade/quality of the hemp plant
(Shahzad, 2012). The hemp plant secretes small amounts of tetrahydrocannabinol
(THC), which is famous for the narcotic substance marijuana. Because the amount
of THC present in hemp is lower than 0.2%, it cannot be used as a drug like other
varieties of C. sativa. Hemp fiber cultivation was briefly banned between 1971 and
1993 to avoid misuse and on lifting of the ban, production increased exponentially
but still hemp fiber accounts for less than 0.5% of total plant fiber production. The
average height of industrial hemp is 10 ft and the width is normally very narrow as
the plants are grown closely together. Hierarchical organization of hemp fiber and fiber
bundle size has been analyzed by several authors (Catling and Grayson, 1982; Olesen
and Plackett, May 27e28, 1999). It has been reported that the diameter of the average
fiber bundle is 25 mm and the length of the average fiber bundle is 25 mm (Olesen and
Plackett, May 27e28, 1999). The cellulose content of the hemp fiber has been shown
to vary from 70.2% to 74.4%. It has several applications and owing to its high strength
and stiffness hemp fiber is also used as reinforcement in biocomposites (Kandachar
and Brouwer, 2001). The variation in the chemical composition is due to several fac-
tors which lead to variability in the mechanical properties of the hemp fibers (Nishino,
2004). Plant populations, produced under varying growing conditions, were shown to
result in different hemp fiber morphologies and physical properties (Amaducci et al.,
2002; Svennerstedt and Sevenson, 2006).