Agriculture Reference
In-Depth Information
In addition to hemp, all fibres of plant origin can
be considered for use in the reinforcing of plastics,
as the aim is to achieve certain technical charac-
teristics using an appropriate mix of fibres with
different characteristics. Additionally, natural
fibres that are not abrasive do not require treat-
ment of the surfaces of the transformed material.
These treatments can be expensive and have a
significant negative impact on the environment.
The use of hemp as a reinforcing material
in plastics does, however, require the close
control of the production and treatment of the
plant: cultivar, the nature of the soil, the method
of cultivation and of fibre separation can all
impact on the properties of the reinforced
products produced.
The originality of the procedure developed
by AFT Plasturgie (Brevet No W0 2004/071744)
lies in the use of a thermomechanical treatment
that creates a fibrillation on the surface of the
fibre (Fig. 14.4b). The single fibres thus freed up
can then anchor themselves to the parent fibre
within the polymer matrix.
The fibres incorporated after treatment
have a final average length of 4 mm.
Properties
MECHANICAL PROPERTIES
.
The procedure intro-
duced by AFT Plasturgie allows a reinforced
composite plastic to be obtained using hemp that
compares well with that obtained using the same
amount of glass fibre (Fig. 14.5 and Fig. 14.6).
With a content of 30% hemp, a PP com-
pound becomes extremely rigid, but also
increasingly easy to break. The ability to
withstand shock loading can be improved
significantly following treatment with a
compatibility agent. The pretreatment of
fibres with a lubricant does not improve per-
formance. By contrast, the use of both treat-
ments produces a synergistic effect that allows
the initial resistance to shock loading to be
doubled (Fig. 14.7).
14.3.3 Hemp/polymer compounds
The amount of reinforcement that can be
achieved using hemp exceeds 70% by weight.
That said, the transformation of compounds
can only proceed without problems where the
amount of hemp is less than 40%.
Procedure
Cellulose is a hydrophilic compound that is
incompatible with the majority of polymers,
which are generally hydrophobic. In order to
bind cellulose fibres with a polymer, it is neces-
sary, generally speaking. to incorporate a third
component. This additional component must
be compatible with both the fibre and the poly-
mer and is there as a binding agent.
THERMAL PROPERTIES
.
The thermal perform-
ance of polymers is improved significantly by
the incorporation of hemp fibres. A piece of
PP composite containing 30% hemp exposed
to 150°C for 400 h showed virtually no
deformation. By contrast, the same piece
Untreated fibre
Treated fibre
Fig. 14.4.
Untreated (a) and thermomechanically treated (b) hemp fibres.
