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Fiber-reinforced plastics are hybrid materials designed for the needs of the 21st century.
With their capability to form low weight structures, while preserving high stiffness
and excellent damping, these composites provide solutions for a broad range of markets.
Unfortunately, some of these advantages are not used in practice because there exist
no fast and automated manufacturing processes for efficient production. In the research
field of continuous-reinforced thermoplastic composites, industry is facing a
challenge of high viscose polymer melt and thereby an imperfect fiber wet-out. As a
result, synergy effects of fibers within a polymer could not be fully exploited.
The topic of this work is to adapt new processing technologies for reactive thermoplastic
polymers. On one hand, fast heating and cooling options offer processes with
shorter cycle time, and on the other hand, low viscosity of reactive polymers impregnates
the textile structures faster. This results in faster and cheaper manufacturing of
composites that are yet to be realized for the market.
All FRPCs were produced on a continuous compression molding press. As a noncontinuous
technology, an inductive heated CageSystem® from RocTool has been
selected. Entropically driven ring-opening cyclic oligomers form Cyclics with waterlike
melt viscosities are chosen as reactive matrix.
The viscosity of Cyclic Butylene Terephthalate (CBT*) was measured using a rheometer.
The rheological behavior is determined under isothermal conditions for various
temperatures. The chemical transformation from oligomer to macromolecule pCBT1
was assessed by size exclusion chromatography. Based on these studies, a kinetic
polymerization model was constructed which involved an Arrhenius-type equation. By
using the activation energy and pre-exponential factor, it was possible to offer an
exact mathematical solution for the prediction of isothermal conversion. A numerical
solution of the Arrhenius equation helped to predict the polymerization for any timetemperature
conditions. Furthermore, the polymerization model was extended to describe
the chemo-rheology. Inserting specific material parameters, the bipartite model
was able to provide a numerical prognosis for the viscosity with the input parameters
time-temperature. All models were calibrated and validated with the experimental
data. The continuous compression molding press was used to consolidate CBT-prepregs
and PBT-prepregs. As reinforcing phase, a multiaxial non-crimp-fabric from Ahlstrom
was used. This fabric contained glass fibers with a “CBT*-compatible” sizing. The
design of experiments was mainly focusing on the variation in the temperature distribution
in process direction with respect to process speeds. An extensive analysis,
from optical to energy absorption, was performed on the resulting FRPC-product,
called organic sheet. All test results showed a better performance for GF-pCBT
compared to GF-PBT. Even for much higher process speed, the material properties
of GF-pCBT did not deteriorate strongly in contrast to GF-PBT. The enhancement
was traced to a better fiber-matrix interface (e.g., ILSS values) and to an excellent
fiber wet-out with pCBT (e.g., SEM pictures).
Viscosity and impregnation are the main factors behind the transversal visco-elastic
impregnation model that was deduced. An arithmetic function that tracks the impregnation
process for the classical thermoplastic PBT and its reactive pendant CBT*
was derived. This was based on the dimensionless B-factor which was considered as
technology independent performance indicator. The model was able to link the fast
impregnation with CBT* - the viscosity of which is 10-5 magnitude lower than PBT - to
all temperature-time-conditions. An optimization method was used to find process
parameters to realize a minimum cycle time for the continuous process. This model
was adapted to the non-continuous pressing technology to find the minimum cycle
time.
To evaluate the economic potential, a transparent process analysis was set up in
form of a static cost calculation. In a first step, all monetary activities from each technology
were identified and rated. The cycle time - as main capacity indicator - was
based on the chemo-rheological model introduced above. Different break-even
analyses and production costs highlighted the techno-economic potential of the related
process-material-combination. A synergistic effect between innovative process
technologies and reactive thermoplastic polymer was found.
Faster and more efficient technologies for the production of fiber-reinforced plastics
have been systematically developed and evaluated. The results were achieved with
an intelligent combination of manufacturing technology and modern reactive thermoplastic
polymers. Moreover, the approach of this work can be transferred to the other
reactive thermoplastic matrix-based composites.