SAMPE Journal - March/April 2023 - 41

The fiber contents of the virgin pellets shredded
granulate and 0%, 33%, 67%, and 100% recycled
content injection molded samples are shown in
Figure 3b. The virgin pellets had an average fiber
content of ~ 39% also indicating that the remaining
weight percent from TGA can determine the fiber
content as the composites had a total fiber weight
percent of 40. The fiber content remained relatively
consistent in the PA66/30CF/10AltF composites
along each step of the recycling pathway. Although
the 33% recycled content sample may appear
to have a decrease, it is within error of the other
samples containing recycled content. From the
consistency in the fiber content among all the
samples, it is unlikely that a decrease in fiber
content was a contributor to the decrease in
mechanical properties shown in Figure 2b.
Recycling Pathway Effects on Fiber Length
Fiber length attrition is common when fiber
reinforced composites are exposed to high shear
force environments during processing.23,24
Figure 4. The fiber length distributions of the PA66/30CF/10AltF material
at different steps along the recycling pathway.
For
reinforcing fibers, typically higher aspect ratio
fibers (longer fibers) lead to higher mechanical
properties than shorter aspect ratio fibers (shorter
fibers) of the same type. Therefore, as the fibers
break, the fiber length decreases and the aspect ratio
decreases resulting in lower mechanical properties.
Additionally, As the fiber length decreases, more
fiber ends are created causing less efficient load
transfer and more sites for stress concentrations
to develop.25
The fiber length distributions in the
PA66/30CF/10AltF composites along the recycling
pathway are shown in Figure 4.
Across all the samples the majority of the fiber
lengths were less than 500µm with the exception of
the virgin pellets. The virgin pellets had a broader
fiber length distribution while the 0% recycled,
shredded granulate, 33% recycled, 67% recycled,
and 100% recycled had a relatively similar and
more narrow distribution.
The processing step between the virgin pellets
and the 0% recycled content samples was injection
molding. During injection molding, the virgin
pellets are exposed to a high shear environment
when the melt is plasticized to create the shot at
the bottom of the barrel. After the first injection
molding step, the fiber length distribution
remained relatively constant even after mechanical
recycling and the second injection molding step
indicating a stable fiber length has been reached. A
critical fiber length is reached when the fiber length
distribution no longer changes as a result of further
material processing. From Figure 4, the fiber
lengths decreased from the first injection molding
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(b)
(a)
(c)
Figure 5. 13
(a) low PPM and (b) high PPM and (c) 1
the 100% recycled sample.
MARCH APRIL 2023
C NMR spectra for neat PA66 and the 100% recycled sample at
H NMR spectra for neat PA66 and
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41
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SAMPE Journal - March/April 2023

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