Desenvolvimento de compósitos nanomodificados utilizando fibras de aramida envelhecidas: uma alternativa para proteções balísticas

Abstract

This study portrays new destinations for aramid fabrics from discarded bulletproof vests and its application as ballistic shield. The new ballistic composite material is a hybrid laminate, in which expired aramid fibers are consolidated by epoxy resin and different nano-reinforcements, such as nanoparticles (nanosilica, nanoceramic and calcium carbonate nanocrystals), combined with ethylene glycol. The nanoparticles dispersed in ethylene glycol, has produced a new class of non-Newtonian fluid (shear thickening fluid - STF), which was incorporated into the aramid fibers. The STF incorporation process to aramid fibers has been accomplished through a combination of ultrasonic dispersion and airbrush, especially developed for this study. As this research deals with two different levels of analysis, i.e. the first one on nanoscale and the second one on macroscale, the experimental investigation must be divided in two different time frames. At nanoscale, the nanostructures were investigated with scanning electron microscope. At macroscale, ballistic tests were based on the NIJ Standard0101.04. Two types of ammunition were considered, i.e. 9mm Full Metal Jacket (FMJ) and .357 Magnum Jacketed Soft Point (JSP). The results demonstrated an enhancement close to 25% in ballistic penetration resistance, due combinated performance of aramid fabrics impregnated with STF and the epoxy system. Furthermore, considering only the addition of STF to the aramid fabrics through the improved dispersion technique, an enhacement close to 41% in ballistic performance was achieved. A normalized equation was proposed, which allows a comparative study between the effect of using non Newtonian fluids and the chest cavity trauma made by high speed projectiles, that has indicated that a combination between nanosilica and calcium carbonate could be a good option for a new type of STF even for expired aramid fibers, that can be used to design ballistic shields and vehicle protection systems