<p>High-performance fibers used for
ballistic protection are characterized by having outstanding mechanical properties
such high modulus and strength. These mechanical properties are granted by the
fiber’s chemical and physical structure as well as their high degree of
orientation. Twaron fibers are one of the most commonly used fibers on soft
body armors such as bulletproof vests. They are made from poly (p-phenylene
terephthalamide) (PPTA), a rigid-rod and highly crystalline polymer. Although
these fibers are crystalline and have great mechanical properties, their
performance can decrease when they are exposed to different degradation
factors. Free volume is the unoccupied space between the polymer molecules. It
is responsible for characteristics such as diffusion and viscosity. Hence, the
free volume changes as the polymer degrades.
This thesis focuses on the effects of sonication, pH changes, and sweat
on the free volume of PPTA fibers. </p><p><br></p>
<p>A non-destructive technique
known as positron annihilation lifetime spectroscopy (PALS) was used to measure
the free volume in PPTA. Changes in the free volume of fibers degraded under
different conditions were compared to their mechanical performance. Degradation
in DI water, pH 4 and pH 10 aqueous solutions was conducted for 10 weeks at 80<sup>o</sup>C. Sweat degradation of PPTA fibers was also
conducted for 10 weeks at 25<sup>o</sup>C, 50<sup>o</sup>C, and 100<sup>o</sup>C.
Fibers degraded in pH4 and sweat solutions had greater loss of mechanical
performance and changes in the free volume.
PALS was able to detect changes in the nanostructure of PPTA fibers at
early stages of degradation. This data was supported by mechanical tests and is
complementary to other characterization techniques such as small angle X-ray
scattering (SAXS). Results of this research are a steppingstone for future
studies on lifetime predictions of bulletproof vests and the development of the
next generation of soft body armors. </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/9037472 |
| Date | 14 August 2019 |
| Creators | Nelyan Lopez-Perez (7038068) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/Detection_of_Early_Stages_of_Degradation_on_PPTA_Fibers_Through_the_Use_of_Positron_Annihilation_Lifetime_Spectroscopy/9037472 |
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