JEC COMPOSITES MAGAZINE - Issue #103 - March 2016 - 65

Fig. 2: Evonik's innovation target: efficiency of
materials, process and parts

at temperatures above 170°C, and without
the disadvantages of current prepregs.
They are stable in storage, not sticky, and
do not have to be separated by films during storage and transport. Thanks to the
thermally reversible crosslinking of the
hybrid polymer, any scrap can be re-used
(figure 3).
In addition to materials for monolithic
composite structures, some materials
being developed can be combined with
metals. The combination of metals and
fibre-reinforced polymers (FRP) in a multi-material approach allows for optimized
and flexible lightweight design. These socalled hybrid structures combine the high
ductility and formability of metals with
the low fatigue and high specific strength
of FRP. The local reinforcement of a metal
part with FRP leads to considerable weight
savings compared to monolithic metal
structures, while maintaining conventional
processing steps (figure 4).
A polyurethane matrix tailor-made for use

Fig. 4: B-pillar as a demonstrator of PU-based
prepregs for FRP-metal hybrid structures
(courtesy of Benteler Automobiltechnik GmbH and
Germa Composites)

Fig. 3: Composite properties of a thermoreversible thermoplastic-thermoset hybrid material

in structural automotive hybrid structures
was developed within the Project House.
Like thermoplastics, prepregs based on
this matrix combine fast cycle times with
high storage stability and automated
handling at ambient temperatures. After
the final curing step, the prepreg achieves
high mechanical properties comparable
to conventional thermosets and exhibits
inherent toughness.
In addition to these outstanding properties, which are also met by the existing
Evonik product Vestanat® PP, the new
polyurethane matrix exhibits excellent
adhesion to metals. The resulting prepregs
exhibit lap shear strengths well above 10
MPa on conventional untreated automotive steel and aluminium grades. Since
no pre-treatment of the metal surfaces
or coating with a primer is needed, this
contributes to a lean and cost-efficient
production process for hybrid parts.

Fig. 5: Evonik's pilot plant for melt-impregnated
unidirectional thermoplastic tapes

Another focus of the Project House work
was the production of unidirectional
tapes, which have already proven themselves in the aviation industry and are
also becoming increasingly important in
the automotive and oil & gas industries.
Developments based on unidirectional
tapes enable manufacturers of offshore
projects to offer solutions that can overcome two of the great challenges of this
industry: increasingly great water depths
with the associated high external pressure,
and the extraction of very corrosive oils.
The good relationship between the rigidity
and weight of composite solutions makes
it possible to design long pipes with great
external pressure resistance in such a way
that they can still be spooled. Corrosion
can also be avoided by replacing steel with
composite solutions (figure 6).
The Project House developed a method
for producing these unidirectional tapes
that saves cost, time, and energy compared
to conventional production. This makes it
possible to manufacture the tapes directly
from melt (figure 5). In this process, the
polymer does not have to be ground into
powder and processed as a suspension,
as was the case until now. Instead, it is extruded as granulates right onto the fibres.
The process is already being implemented
in a mass-production-scale pilot system.
The automotive industry is also interested
in tapes manufactured in this way, which it
can use to build lighter vehicles. As part of
the Camisma research project, the Project

No103 March 2016 /

jec composites magazine 65

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #103 - March 2016