JEC COMPOSITES MAGAZINE - Issue #95 - Special JEC Europe - March 2015 - 80

short natural fibres

very different for the two materials under analysis, as shown in
Figure 5.
Large particles
The analyser software also makes it possible to individually
examine or eliminate very large particles that are not considered
to be fibres (e.g. with widths greater than 100 µm).

Fig. 5: Dust content - Proportion of fibres < 200mm

are generally the most numerous, which pulls the mean value
downwards. Figure 4 shows the very low values for this parameter.
Geodesic length by volume
The average length by volume is a weighted mean, where the
length of each fibre is weighted by the fibre's estimated volume.
This method corresponds roughly to what is obtained by sorting the particles through a sieve. In this type of calculation, the
result is heavily influenced by the longest fibres, which also have
the greatest volume, even if there are fewer of these fibres. This
pulls the mean value upwards (Figure 4).
Geodesic width
Of course, the equivalent parameter values for number and
volume are also available for the geodesic width, which indicates
fibre fineness. These parameters also serve to calculate what is called the aspect ratio, i.e. the ratio between fibre width and length.
Dust content
It can be decided by convention that fibres shorter than 200 µm
(or another value) play the role more of a filler than of a reinforcement, or that these very short particles are to be considered
as dust content. The proportion in volume of these fibres is

Fig. 6: Tensile and flexural modulus

80 jec composites magazine / No95 March 2015

Reproducibility
Reproducibility is one of the greatest unknowns when it comes
to natural products. Does this delivery contain the same type
of fibres as the ones I received in the last delivery? The way to
answer this question is to divide the distribution for any one
parameter (e.g. the geodesic length) into a certain number of
classes. If we know the quantity of fibres present in each class
for the benchmark material and for the material to be validated,
we can calculate a particular statistical parameter. If it is lower
than a particular theoretical value, then we can consider that
both samples come from the same population, and accept the
delivery. In this case, we would work on volume distribution.

Results of mechanical tests on composite specimens
The two types of fibres analysed were first processed into pellets
about 4 mm in diameter, then fed into a compounding machine
where they were mixed with polyamide 11, the proportion in
fibre weight being 30%. The pellets thus obtained were fed into
an injection machine to make standard specimens to be subjected to standardized mechanical tests. The results of these tests
are shown below.
Tensile and flexural tests
We observe that the tensile and flexural performance of the X
fibres is higher than that of the Y fibres (Figures 6).
Impact tests
Here, we observe that the performance of both materials is quite
comparable (Figure 7).

JEC COMPOSITES MAGAZINE - Issue #95 - Special JEC Europe - March 2015

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