JEC COMPOSITES MAGAZINE - Issue #89 - May 2014 - 55

Tab. 1: Properties of BASF Acrodur® resin

Properties

Typical values

Solid content [approx.,%]

Raw materials
Flax tape: a green reinforcement
The new bio-based flax/Acrodur®
prepreg uses innovative, patented
flax tapes [4] (Figure 2) composed of
weight-controlled technical flax fibres
arranged unidirectionally without any
weft spinning (as observed in Figure
1). To maintain parallel cohesion of
the fibres, a new process based on reactivating the pectic cement by spray-

150-300

Density at 20°C
[approx., g/cm3]

cessing parameters of the sandwich
skins in order to optimize the quality
and properties of the final products.
The mechanical characteristics of the
flax laminates are governed by the
properties of both the fibres and the
resin matrix. In this paper, only the
specific tensile properties of flax tape
specimens and the Young's modulus
of derived flax/Acrodur® biocomposite are investigated, polyester acrylic
resins being largely used and wellknown in the industry. To this end, an
automotive part prototype was prepared and subjected to flexural tests
according to the customer's specifications. Its mechanical behaviour was
then modelled with the ABAQUS
finite element analysis software.

3.5

Viscosity at 23°C
[approx., mPa S]

Fig. 2: The LINEO flax tape (Flaxtape110) used as
composite reinforcement

50

pH [approx.,%]

1.2

Miscibility with water

Miscible in
all proportions

ing a water mist over the surface of
the fibre bundles is used. At first, flax
is scutched: the bundles forming the
flax stems are decorticated and separated, then the remaining shives and
woody core of the stem are removed.
Secondly, the scutched flax is hackled
to obtain long technical flax fibres.
These fibres are collected without any
particular selection and transported to
the flax tape processing line where the
bundles are stretched, maintained in
a unidirectional direction and sprayed
with a water mist. This guarantees the
cohesion of the flax tapes by binding
all the fibres. Then, the sprayed flax
tapes are dried in-line by an infrared
oven. Finally, the reinforcements are
air-cooled and ready for impregnation
and packaging. As shown in Figure
2, the semi-finished products are
completely free of twisting, crimping
or weft spinning. Flax tape weights
per unit area ranging from 50g/m² to
200g/m² are available.
BASF Acrodur® resin
A commercial polyester acrylic resin
was chosen as a relevant material for
a real industrial automotive process.
This resin offers good mechani-

cal properties, a short crosslinking
time, easy handling and cleaning,
combined with a good "open" time.
It is produced by dispersing a modified polycarboxylic acid and a polyol
(cross-linking agent) to create a
thermoset material (Figure 3). This
formaldehyde-free binder is suitable
for wood and vegetable fibres such as
flax, sisal or jute. The original water
content is 50% but the resin can
be diluted for easier impregnation.
Crosslinking at 160-180°C takes less
than two minutes.

Dry flax tape characterization
The properties of the flax tape reinforcement are influenced by several
processing factors such as the presence of tangle areas due to the flax
fibre length and content, organization
and distribution over the tape width.
Moreover, it has been shown in literature that the characteristics of flax
fibres also depend on their variable
morphology, biochemical composition and biodegradability, and on the
presence and location of defects in
the stem [4] [5] [6]. In addition, their
mechanical properties are affected by
the damage sustained during processing and thus have considerable
scatter [7]. Therefore, a simple and
efficient method is needed to evaluate the specific modulus of flax tape.
Conventional test methods are no
longer relevant for the mechanical
characterization of flax tape due to its
structure and section discontinuity.
To circumvent this issue, a new characterization protocol was established,
mainly based on a statistical study,
by analyzing the specific modulus

Fig. 3: Crosslinking reaction of Acrodur®

No89 May 2014

/ jec composites magazine 55
JEC COMPOSITES MAGAZINE - Issue #89 - May 2014

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