Agriculture Reference
In-Depth Information
methods presented here. These methods are
adapted and optimized for bast fibre bundle
testing and even if testing only a small number
of collectives produces reliable tensile strength
data, assuming fineness (i.e. the number of
fibre bundles in the collective) is taken into
account. A collective consisting of many fine
fibre bundles has lower tensile strength than a
collective of a few coarse fibre bundles. To
obtain precise data for a numerical simulation
of the behaviour of a natural fibre reinforced
plastic, it is necessary to use the single-element
test. With the Dia-Stron system, it is possible to
obtain area-related strength and Young's mod-
ulus values.
For fine bast fibre bundles, testing fineness
is possible by the OFDA method or by
Laserscan. Coarser samples can cause errors,
because OFDA and Laserscan have been
developed for wool, where very coarse fibres
are not present. Complete analysis of fibre and
fibre bundle morphology (including fineness) is
best done by the Fibreshape system.
Knowledge of fineness is essential for the
selection of optimal fibre lots for special prod-
ucts. The tensile strength of, for example, nee-
dle felts is much higher if they are produced
from fine fibre bundles. This is due to greater
surface area and thus better sticking of the fine
fibre bundles to each other. Similar effects are
observed in the production of natural fibre
reinforced thermosets. If the felt structure is
penetrated completely by the monomer, the
mechanical properties are enhanced signifi-
cantly. On the other hand, the small intermedi-
ate spaces of fine fibre bundles can sometimes
prevent complete penetration by the mono-
mer. In such special cases, use of coarser fibre
bundles - obtained by less intensive mechanical
separation - can help. This pathway can also
be useful for the cheap production of low-
performance composites by spray technology.
In each case, the steps of harvesting and
retting have to be considered in a quality man-
agement system, because they have signifi-
cant influence on the fineness of the fibre
bundles. Decortication is possibly better and
separation leads to finer fibre bundles - if ret-
ting has been well controlled. Use of unretted
or badly retted stems increases fibre loss, pro-
duces shorter bundles and leaves more resid-
ual hurds in the subsequent separation and
carding processes.
In fibre bundle separation, the changes in
fineness and length are the most important
parameters to be controlled by a quality control
system. In normal production with fibre bun-
dles <250 mm, length distribution can be con-
trolled easily by an Almeter, combined with a
modified preparation unit. This is also valid for
the subsequent carding step, because fibre bun-
dle length influences the needle felt properties
directly.
The application of such a reliable quality
control system can be a big advantage for the
industry and enhance the use of domestic fibre
plants. This would be not only of ecological sig-
nificance but also economically advantageous,
as it would offer short transport distances in
the whole value-added chain, as well as the
possibility of making natural resources available
in constant qualities.
Note
1
Natural fibre reinforced polypropylene.
