Page 334 - Handbook of Properties of Textile and Technical Fibres

Hemp, jute, banana, kenaf, ramie, sisal fibers 307

limitations are similar to that of cold water retting; however, this process has been aban-
doned in most parts of Europe (Natural fibers, biopolymers, and biocomposites, 2005).
The waste water can be used as liquid fertilizer if it is treated to remove toxic elements.

9.3.5 Mechanical retting
Mechanical retting, also known as green retting, is a simple and cost-effective process
to separate the fibers. Mechanical retting is performed after field or technical drying.
Field drying normally takes about 2e3 days. The fibers are separated from woody tis-
sues mechanically. Fibers produced by mechanical retting are coarser than those ob-
tained by the field or water retting processes (Natural fibers, biopolymers, and
biocomposites, 2005).

9.3.6 Ultrasound retting

In this process, crushed and washed fibers from the plants are fed into a hot water bath

to separate the fiber. The water bath is kept at 70 C with additions of small amounts of
alkali and surfactants, and subjected to high intensity ultrasound agitation at 40 kHz. In
this continuous process the fibers are separated from the hurds, which is the name
given to the coarse parts of flax or hemp that adhere to the fiber after it is separated.
The advantage of this process is that it does not need field drying as the raw fibrous
part of the plant is used (Sharma, 1987).

9.3.7 Steam explosion

Steam explosion is a good alternative to the conventional retting process. The steam and
the additives penetrate the fiber interspaces of the fiber bundles under pressure and high
temperature so as to remove the central lamella under optimum conditions. The resulting
relaxation leads to the breaking up of the fibers and results in decomposition into fine
fibers. The fibers produced by this method are fine and have good mechanical and phys-
ical properties (Natural fibers, biopolymers, and biocomposites, 2005).

9.3.8 Enzyme retting
Pectin degrading enzymes are used to separate the fibers from the woody tissue of the
plant. This gives controlled retting of the fiber crops through selective biodegradation
of the pectinaceous substances. The enzyme activity increases with increasing temper-
ature up to an optimum temperature above which the enzyme starts to denature. The
fibers produced by this process are of high and consistent quality (Natural fibers, bio-
polymers, and biocomposites, 2005).

9.3.9 Chemical and surfactant retting

This refers to all retting processes in which the fiber section of the plant is submerged
in heated tanks with water solutions of sulfuric acid, chlorinated lime, sodium or