Abstract
High-performance fibers made of poly-(p-phenylene terephthalamide) (PPTA) with high stiffness and high strength are widely used in body armor for protection due to their high degree of molecular chain alignment along the fiber direction. However, their poor mechanical properties in the transverse direction and low surface friction are undesirable for applications requiring resistance to ballistic impact. Here we provide a simple yet effective surface engineering strategy to improve both the transverse mechanical properties and the tribological property by coating PPTA fibers with ultra-high molecular weight polyethylene (UHMWPE) embedded with silica nanoparticles. The coated-PPTA fiber shows remarkable enhancement in transverse mechanical properties including ~127% increase of Young’s modulus, which is attributed to both the alignment of UHMWPE chains in the transverse direction and the embeded ceramic nanoparticles. Meanwhile, the surface friction of the coated fiber increases twofold as a result of the ceramic nanoparticles. In addition, the coated fibers exhibit an enhanced chemical resistance to external harsh environment. The improved transverse mechanical properties, surface frictional characteristics, and chemical resistance demonstrate that coating with UHMWPE and ceramic nanoparticles can be used as an effective approach to enhance the performance of PPTA and other high-performance polymer fibers for body armor applications.
Highlights
To date, a variety of methods or strategies are proposed to enhance either the transverse mechanical properties or the frictional characteristics
It is still a significant challenge to simultanously increase the transverse mechanical property and enhance the surface frictional characteristics of the PPTA fibers, which is highly desired for advanced ballistic applications
To achieve the above-mentioned objectives, here we propose a new polymer dip-coating strategy to coat the PPTA fibers with highly crystalliized ultra-high molecular weight polyethylene (UHMWPE) and ceramic nanoparticles to improve both the transverse properties and the surface friction
Summary
We found that coating of UHMWPE on PPTA fibers results in a remarkable enhancement in trasverse mechanical properties. In order to evaluate the protective effect of the UHMWPE/SiO2 nanoparticle coating, coated PPTA fibers along with uncoated fibers were immersed in either H2SO4 or NaOH, and the Young’s modulus of these fibers was monitored as a function of immersion time (Fig. 6). Furturemore, the effect of incorporating SiO2 nanoparticles into the UHMWPE phase has been explored, showing a remarkable increase of friction coefficient (nearly by 100%.) The Young’s modulus and the hardness of the PPTA fibers with the UHMWPE/SiO2 coating exhibit significant enhancement. This coating can shield the PPTA fibers from some chemical attacks and alleviate the loss in their mechanical performance. These results demonstrate the UHMWPE/SiO2 coating could simultaneously enhance multiple mechanical properties of PPTA fibers and extend their applicability in protective applications
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