SAMPE Journal - March/April 2023 - 40

FEATURE / HYBRID COMPOSITES
wrapped in aluminum foil.22
The fibers were
transferred to a microscopic slide and exposed to
a charge by a high frequency generator (ElectroTechni
Products, Chicago, IL) to disperse the fibers
so no fibers were overlapping. The fibers were
imaged utilizing a VHX-5000 digital microscope
(Keyence Corporation, Itasca, IL). From the images,
the fiber lengths were analyzed via ImageJ utilizing
a python script [2]. The accuracy of the fiber
lengths measured with the script were checked for
accuracy by manually measuring the fiber lengths.
At least 1000 fibers were measured for each sample
type.
(a)
RESULTS
Mechanical Property Characterization
Four different samples with various amounts of
recycled content (0 wt%, 33 wt%, 67 wt%, 100 wt%)
were mechanically characterized to determine the
tensile strength and tensile modulus to understand
how mechanical properties are affected by
mechanical recycling. The tensile strength was
determined by averaging the maximum stress
value from each trial and the tensile modulus was
determined by taking the slope of the elastic region
(linear portion) of the stress-strain curves (Figure
2a). The tensile strength and tensile modulus for
each sample type are shown in Figure 2b.
As the percent of recycled content increased
the tensile strength and elastic modulus decreased.
From 0% recycled content to 100% recycled content
the tensile strength and modulus decreased by
18% and 13%, respectively. The decrease in tensile
strength was more consistent than the decrease
in elastic modulus where the moduli for the 33%
and 67% recycled content samples were similar.
However, the overall decreases observed in the
tensile strength and modulus are not dramatic
which furthers the case for utilization of recycled
content in manufacturing for the specific recycling
pathway employed here.
The changes in mechanical performance are
dependent on the processing/recycling pathway
shown in Figure 1. While these results show how
mechanical performance is affected through this
specific recycling pathway, other manufacturing
and recycling techniques may yield different
results. Therefore, it is important to understand
the mechanisms causing the change in mechanical
properties rather than how much the mechanical
properties decreased for this specific recycling
pathway.
The potential contributors to the
decrease of the mechanical properties for this
recycling pathway are identified as loss in fiber
content, fiber length attrition, and degradation of
(b)
Figure 2. (a) Representative stress-strain curves and (b) the tensile strength
and modulus results of the samples with varied recycled content. The error
bars represent one standard deviation.
(a)
(b)
Figure 3. (a) representative percent weight vs temperature plots from TGA
and (b) fiber content of the PA66/30CF/10AltF material at different steps
along the recycling pathway.
the PA66, which are all explored in the following
section discussions.
Effect of Recycling Pathway on Fiber Content
The mechanical recycling process has the potential
to cause a decrease in fiber content of the samples
containing recycled content due to dust generation
during mechanical recycling. The fiber content in
the PA66/30CF/10AltF material along each step of
the recycling pathway was characterized through
TGA. The remaining weight percent at 600°C was
taken as the fiber content for each sample (Figure
3a). A neat PA66 pellet was also tested which
yielded a remaining weight percent near 0% to
show that the remaining weight percent of the fiber
filled samples was indeed the weight of the fibers.
40 | SAMPE JOURNAL | MARCH APRIL 2023
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SAMPE Journal - March/April 2023

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