SAMPE Journal - March/April 2023 - 43

a both high temperature and shear environment
for processing could be selected. One such method
is compression molding because high shear is
not required for successful processing. Another
strategy would be to optimize high shear methods
to limit the polymer degradation during processing
by carefully selecting processing temperature,
screw speeds, and screw designs. Regardless,
understanding that high temperature and high
shear environments cause polymer degradation
and ultimately the mechanical properties is an
important consideration when aiming to utilize
mechanically recycled feedstocks.
CONCLUSIONS
The
selected
CF-based
hybrid
composite
(PA66/30CF/10AltF) was mechanically recycled
and blended with virgin material to understand
how mechanical recycling affects the mechanical
performance. The PA66/30CF/10AltF was injection
molded into test specimens (0% recycled content),
mechanically recycled, and re-injection using a
blend of granulate and virgin material to create
samples containing 33%, 67%, and 100% recycled
content. As the amount of recycled content
increased, the tensile strength and tensile modulus
decreased. While the percent decrease of both
tensile strength and modulus was less than 20%, the
effect of mechanical recycling on the mechanical
properties is dependent on the utilized processing/
recycling pathway.
The examined mechanisms of mechanical
property degradation were loss of fiber content,
fiber length attrition, and degradation of the PA66.
TGA was utilized to determine the fiber content of
the PA66/30CF/10AltF material, which remained
constant around 40 wt% throughout all steps in the
recycling pathway. After the first injection molding
step, the fibers reached a stable length causing a
relatively uniform fiber length distribution after
mechanical recycling and the second injection
molding step which would not affect the mechanical
properties as recycled content increases. Lastly,
PA66 degradation was found to likely occur via
NMR due to exposure to the high temperature
and high shear force environment created during
injection molding. Because the recycle material
has experienced additional exposure to a high
temperature and high shear environment it is likely
more degradation has taken place in the recycled
samples than the virgin samples causing a decrease
in mechanical properties as the recycle content
increases.
The loss of fiber content and decrease in fiber
length did not affect the mechanical properties
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MARCH APRIL 2023
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SAMPE JOURNAL | 43
as the recycled content increased. The PA66
degradation that occurred during injection
molding was the main contributor to the decrease
in tensile strength and modulus as the amount
of recycled content increased. While the percent
decrease in mechanical properties are expected
to be different for a specific recycling pathway,
exposing the material to a high temperature and
high shear environment will have the largest
effect on mechanical properties for short fiber
composites. However,
the
recycling
pathway
utilized here did not result in a dramatic decrease
in mechanical properties and could potentially
be employed by OEMs to help stabilize CF supply
chains as more CF composites are utilized. With
the substitution of a portion of the CF content and
utilization of recycled material, OEMs can stabilize
their CF supply chains while implementing
sustainable manufacturing practices allowing
more widespread adoption of CF composites in
industry.
ACKNOWLEDGEMENTS
This manuscript has been authored by UT-Battelle,
LLC, under contract DE-AC05-00OR22725 with
the US Department of Energy (DOE). The US
government retains and the publisher, by accepting
the article for publication, acknowledges that
the US government retains a nonexclusive, paidup,
irrevocable, worldwide license to publish or
reproduce the published form of this manuscript,
or allow others to do so, for US government
purposes. DOE will provide public access to
these results of federally sponsored research in
accordance with the DOE Public Access Plan
(http://energy.gov/downloads/doe-public-accessplan).
This material is based upon work supported
by the U.S. Department of Energy, Office of Vehicle
Technology. This research used resources of the
Oak Ridge Manufacturing Demonstration Facility,
which is a DOE Office of Science User Facility.
REFERENCES
1. Dong X, Lu C, Zhou P, Zhang S, Wang L, Li D.
Polyacrylonitrile/lignin sulfonate blend fiber for low-cost
carbon fiber. RSC Advances. 2015;5(42259). DOI: 10.1039/
c5ra01241d.
2. Friedrich K. Carbon Fiber Reinforced Thermoplastic
Composites for Future Automotive Applications 2016.
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Transit. Lancaster, PA: DEStech Publications, Inc.; 2011.
http://www.energy.gov/downloads/doe-public-access-plan http://www.energy.gov/downloads/doe-public-access-plan http://www.sampe.org
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