Agriculture Reference
In-Depth Information
the threshold for injection be matched carefully
to the viscosity of the compound. The behaviour
of hemp-reinforced polymers is clearly pseudo-
plastic.
Natural fibres contain a certain amount of
pectin, which is degraded at temperatures in
excess of 160°C. This can confer a light brown-
ish colour to products without their properties
being affected. That said, a dark brown colora-
tion together with a strong-smelling product
indicates that the transformation conditions
are maladjusted.
When conducting initial tests, it is rec-
ommended that the compounds be diluted to
obtain a fibre concentration of approxi-
mately 20%. This approach allows materials
to be transformed without there being a risk
of degradation and allows operators to
familiarize themselves with the use of the
compound.
14.4 Applications
14.4.1 Plastics
Plastic materials reinforced with hemp fibres
are used in all the main plastic markets (Figs
14.13-14.17).
14.4.2 Unwoven felt
Natural fibres have been used by the automo-
bile industry for more than a decade in the
creation of car interior fittings. The products
are made of felt with a density of approximately
500-2000 g/m
2
. These felts are produced
from a 50:50 mix of natural fibres (hemp, flax,
sisal, jute, kenaf, abaca) and thermoplastic
fibres (typically, PP). The mix is carded and
needled to produce sheets with a thickness of
5-30 mm.
The felt is heated in flat presses to a
temperature approaching 200°C before
being placed in a cold mould. The end prod-
uct is light and rigid and is not brittle. The
manufacturing process only allows the pro-
duction of pieces with a constant thickness
and low stamping rate. The majority of
German and US car manufacturers use these
materials to produce door panels, parcel
shelves and boot panels.
The production of felts with a density of
400-1000 g/m
2
without the addition of syn-
thetic fibres allows sheets to be produced for
use in mulching and soilless cultivation.
MPa
7000
6000
5000
4000
3000
2000
1000
0
PEhd
PPh
PVCu
ABS
Fig. 14.11.
Section modulus for different polymers
reinforced with 30% hemp fibre.
MPa
35.0
30.0
25.0
20.0
15.0
10.0
5.0
0.0
Spruce
Flour
Spruce
Sawdust
Hemp
Sisal
Flax
Jute
Kenaf
Fig. 14.12.
Maximal tension resistance (compounds with 30% plant fibre reinforcement).
