Agriculture Reference
In-Depth Information
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The desirable qualities for thread produc-
correlation exists between the size of the fibre
bundles and the size of the stem. Knowing that
the mechanical preparation of textile fibres
(essentially carding operations) will break up
the bundles without going as far as to isolate
individual fibres, it is recommended that bun-
dles of small diameter are produced. It is also
true that retting is more efficient if stems are
thin. In practice, it is very difficult to exceed
300 plants/m
2
, which would allow stems of
5 mm diameter to be produced. Producers of
hemp for the textile industry sow at around
80 kg of hemp seed/ha.
Harvesting is undertaken before maturity,
at the end of flowering. Dioecious varieties are
late and the optimal stage is reached during the
second fortnight in August. Taking into account
the time of reaping, it is not possible to harvest
the hemp seed. The stems are bundled into
sheafs and tied with stems. These sheafs are
loaded into the trailer and taken to retting baths.
Two techniques are used for retting: either the
trailers are submerged in the retting baths or
they are emptied into the baths. Retting lasts
for 8-10 days for a water temperature of 20°C.
At the end of this period of immersion, the
sheafs are dried and then stored under shelter
or in stacks.
An alternative to the traditional method is
being developed in Italy, where hemp produc-
tion seeks to produce plant stands of a similar
height to those of flax. This allows the hemp to
be harvested and fibres extracted using the same
techniques as are used for flax. A shortener (a
mix of chlorocholine chloride and ethephon) is
sprayed over the crop at the start of the rapid
growth phase, thus limiting growth. A total
weedkiller (glyphosphate or sulfosphate) is then
used to stop the vegetative phase at the very
start of flowering. The harvesting, retting, baling
and fibre extraction are all then conducted in a
similar way to that practised for flax.
'Bench-top' or in-laboratory retting meth-
ods (using enzymatic or chemical processes, or
a combination of the two) were tested in France
approximately 15 years ago following fibre
extraction to try to find an alternative to the ret-
ting bath. No industrial applications resulted.
Traditionally, up until the middle of the
19th century, male stalks were torn out first as
early as the end of July. These were submerged
immediately in retting pools (known in French
tion are essentially its fineness, suppleness
and solidity.
The paper market is very concerned
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with contamination-related problems,
in particular, those posed by plastic
materials and weeds. The presence of
chlorophyll pigments in fibres can also
pose a problem: the pulped paper
requires bleaching and this results in the
production of chlorine-based waste that
must then be disposed of.
Fibres destined for the plastics industry
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must, depending on the industry, be virtu-
ally free of hurds for temperature-hardened
plastics. For thermoplastics, fibres must be
graded by length according to their use
and according to the technology.
The end uses of the fibres influence the pro-
duction techniques.
These techniques meet the need to pro-
duce first-class fibres for the companies that
are adapted to the use the extracted fibres will
be put to.
For hemp seed, the quality required
imposes precise specifications that take the
seeds' fragility into account.
Production of textile fibres
The standards for hemp cultivation for the tex-
tile industry essentially come from the Danube
valley, which is the last area in Europe where
this form of production is still in existence.
In order to obtain fine and supple fibres, it
is necessary to cultivate dioecious varieties to
benefit from fibres derived from the male plant.
These fibres are fine, comparing well with flax
fibres, whereas fibres from the female plants
(or from monoecious plants that present the
same characteristics) are eight to ten times
wider. Although the ratio of male to female
flowers is close to one, the total weight of
female fibres is double that obtained from male
plants. The male fibres, however, are fine and
can produce good-quality thread.
The sowing density aims to produce a
high density of plants and thereby limit stem
diameter. It should be noted, however, that
the diameter of the stems is independent of
the fineness of the fibres. That said, a close
