Efeito da incorporação de nanocargas em compósito laminado de tecido de aramida e filme de polietileno

Abstract

The advancement of tactical and military technologies makes enhancing armor systems such as vests and helmets essential, aiming for improved functionality, lower density, and increased flexibility. One strategy to enhance these properties involves replacing conventional materials with alternatives, such as commodity polymers, which are cost-effective and exhibit attractive mechanical, chemical, and thermal properties. The addition of nanofillers to polymeric matrices has gained prominence, enhancing the properties of materials known as nanocomposites, particularly in terms of mechanical and thermal properties. Notable nanofillers include calcium carbonate nanoparticles (NCC), montmorillonite clay (MMT), and graphene nanoplatelets (GNP), each with distinct morphology and characteristics. The use of calcium carbonate nanoparticles combined with thermoplastic polymers in ballistic applications was not found in the literature. The aim of this study was to evaluate the influence of different nanofillers (NCC, MMT and GNP) in high-density polyethylene (HDPE) films, and in laminated composites obtained with aramid fabric interleaved with reinforced HDPE films, through their potential for application in ballistic protection. The nanofillers and HDPE were mixed in twin-screw extrusion, followed by blown film extrusion to obtain a film with a thickness of ~50 µm. The aramid fabric and films were cut and arranged in interleaved layers and hot pressed to produce the plates. The first multilayer plates, with HDPE films containing NCC in concentrations of 0, 0,5, 1, and 2% by mass, were evaluated in step 1. With the most effective concentration, new films with MMT and GNP were produced, including an evaluation of the addition of maleic anhydride. All nanostructured films were characterized in step 2. In step 3, laminated composites with aramid fabric and nanostructured films were manufactured and tested. In the first stage, dynamic compression testing using the Hopkinson bar (SHPB) revealed that the sample containing 1% of NCC exhibited superior energy dissipation behavior compared to others. The concentration 1% was predefined for subsequent film production. All samples in the first stage met ballistic protection level III-A. Hybrid films containing 0.5% of each filler were also produced in the second stage. The films exhibited a homogeneous surface, except for those containing GNP, an increase in viscosity with the addition of nanofillers, and a single thermal mass loss event at around 475 °C. Tensile strength results indicated that NCC and MMT reinforced the film, whereas the GNP-containing sample, with higher crystallinity (62%), exhibited values lower than pure HDPE. In the Hopkinson bar dynamic compression test, samples containing 1% NCC with maleic anhydride, 1% MMT, and 1% GNP resulted in higher stress and toughness values. In contrast, hybrid samples did not yield satisfactory results. In the third stage, multilayered plates were evaluated by SHPB, and besides samples with NCC, MMT, and GNP, hybrid samples were created by interleaving one film of each nanofiller. Samples that stood out and exhibited superior stress and toughness behavior at high deformation rates, contributing to better energy dissipation in these composites, were those containing HDPE film with 1% GNP and the hybrid sample containing HDPE films with 1% GNP and HDPE with 1% NCC alternating interleaved. [resumo fornecido pelo autor]