Agriculture Reference
In-Depth Information
A proportional amount of hurds and pow-
der is therefore also produced.
being undertaken to determine the optimal
amount of retting (cf. the work of the INRA
undertaken by Bernard Kurek).
The automobile and construction indus-
tries demand products that have constant
and reproducible characteristics. The plas-
tics industry therefore needs hemp fibres
that always present the same technical char-
acteristics, that is to say 'standard hemp'.
The technical processes and the varieties
need to be defined precisely according to
the final product. There is also a need for
traceability.
The interested reader is referred to the
explanations provided by Dr Joërg Müssig on
the subject of the desiderata of plastic techni-
cians (see Chapter 10) and how to qualify any
natural fibre easily.
9.3.3 Preparation of the
fibres for technical uses
'Technical fibres' is the professional term used
for fibres that are destined for technical or
industrial uses, as distinct from the fibres
discussed previously, which generally are des-
tined for use in paper manufacturing.
Their main uses are:
1. Non-woven products, including mats and
felts of different thicknesses;
2. Hemp wool;
3. Inclusion in compound plastics;
4. Geotextiles.
These different uses each have their own par-
ticular demands and requirements.
FIBRE QUALITY FOR NON
-
WOVEN TISSUES
:
LENGTH
AND DEGREE OF RETTING
.
Where non-woven
materials are concerned, manufacturers need
long fibres (optimum length 20 cm). These
must be very clean in order to avoid clogging
up the needles when the material is finally
carded.
A light retting improves the final quality of
the product by facilitating fibre extraction.
Degradation of long fibres into shorter fibres is
reduced.
Expected characteristics
of technical fibres
FIBRE QUALITY FOR USE IN THE PLASTICS INDUSTRY
:
CLEANLINESS AND DEGREE OF RETTING
.
Fibre
length is not an important criterion, the fibres
having been cut before they are processed. By
contrast, they must be totally clean (ideally with
0% hurds), because the presence of such con-
tamination of the fibre, and therefore of the
compound, can render the end product fragile
and increase the number of points at which it
is prone to break. Hurds can, however, be used
in plastics manufacturing where the intention is
to produce a particular aesthetic effect (in flow-
erpots, for example). In these cases, they are
added by the manufacturer according to a
selected percentage, and is therefore a matter
of choice.
The physical properties of the end prod-
uct are not as good if the fibres have been sub-
jected to a prolonged retting process. Fibres
that have been retted excessively are not
accepted by plastic manufacturers as they are
likely to cause problems, affecting both the col-
our and resistance of the final product. It is
therefore necessary to find the optimal degree
of retting in order to produce clean fibres and
materials with the right properties. Studies are
QUALITY OF FIBRES DESTINED FOR USE AS INSULATING
MATERIAL
(
HEMP WOOL
):
LENGTH
,
ABSENCE OF ALLER
-
GENIC SUBSTANCES AND COMPRESSION RESIS
-
TANCE
.
Here again, manufacturers need very
clean, long fibres. Two points are essential: the
hygiene aspect and the compression resistance
of the material.
These fibres are destined to be used in
the home and must therefore be free of any-
thing that could impact negatively on human
health. The extent of retting can have an
influence on this process and can introduce
potentially allergenic microorganisms into
the fibres. As an insulating material, the com-
pression resistance of this wool is also impor-
tant. Retting, and therefore the solidity of the
fibres, together with the date of harvesting
are two important factors. As with the fibres
destined for use in the plastics industry,
research is ongoing to determine the optimum
