No abstract

Isotactic polypropylene (PP) composite drawn fibers were prepared using melt extrusion and high-temperature solid-state drawing at a draw ratio of 7. Five different fillers were used as reinforcement agents (microtalc, ultrafine talc, wollastonite, attapulgite and single-wall carbon nanotubes). In all the prepared samples, antioxidant was added, while all samples were prepared with and without using PP grafted with maleic anhydride as compatibilizer. Material characterization was performed by tensile tests, differential scanning calorimetry, thermogravimetric analysis and Fourier transform infrared spectroscopy. Attapulgite composite fibers exhibited poor results in terms of tensile strength and thermal stability. The use of ultrafine talc particles yields better results, in terms of thermal stability and tensile strength, compared to microtalc. Better results were observed using needle-like fillers, such as wollastonite and single-wall carbon nanotubes, since, as was previously observed, high aspect ratio particles tend to align during the drawing process and, thus, contribute to a more symmetrical distribution of stresses. Competitive and synergistic effects were recognized to occur among the additives and fillers, such as the antioxidant effect being enhanced by the addition of the compatibilizer, while the antioxidant itself acts as a compatibilizing agent.

No abstract

Emerging energy and insulation applications require dielectric materials that can operate at high electric fields and meanwhile possess low leakage currents. For dielectric polymer nanocomposites, beyond filler dispersion, tailoring hierarchical structures offers a promising, yet largely untapped, approach to reach this goal. Here, we demonstrate that the controlled arrangement of pseudo-2D nanofillers and polymer crystals in polyethylene/montmorillonite nanocomposites can be used as an effective approach to achieve nontrivial highly enhanced dielectric performances, far beyond what is feasible with conventional (macroscopic, isotropic) composites. In particular, it is shown that aligned nanofillers can increase the breakdown strength, while, at the same time, reducing the leakage current, in these dielectric nanostructured composites. The orientation of the nanosized pseudo-2D fillers increases the path tortuosity for charge transport, acting as an effective geometric barrier, in the same way and in addition to the oriented polymer crystals of the polymer matrix. Thus, incorporation of aligned nanoplatelet fillers provides an independent and complementary increase to breakdown strength, in excess of any improvements due to the crystal orientation. In this manner, a substantially improved breakdown strength can be realized in the nanostructured composite, with the aligned fillers and aligned polymer crystals acting as a macroscopic barrier established across the sample.