The Effects of Geometry and Chemical Composition of Nanoparticles on The Fracture Toughness of iPP Nanocomposites

Abstract

This research deals with possible hybrid effects in the fracture energy of hybrid nanocomposites while taking a critical approach toward the currently-prevailing engineering practice of applying classical composite micromechanics to nanocomposites. For this purpose, different nanoparticles were embedded in an isotactic polypropylene matrix. The particles had different geometries (fibrous and platelets) and different chemical structures (organic vapor grown carbon nanofibers (VGCF); graphene nanoplatelets (GNP); and inorganic nanoclays, SiO 2 nanofibers, and ZrO 2 nanofibers). Almost all the composite systems presented improvements in the fracture energy, whereas the iPP/VGCF/GNP presented a positive hybrid effect. The main conclusion was that each nanocomposite system should be analyzed individually according to the constituent properties; the quality of the dispersion; and, primarily, by the type of interaction between the particles and the matrix.(CNCs) and organically modified montmorillonite (OMMT). The total filler composition was 4%, with a ratio of 1:1 among the fillers. This led to the highest tensile strength and Young's modulus [5].Another property that can present a hybrid effect is toughness, as was demonstrated in our previous work; here, the PVB (polyvinyl butyral) that contained both surface-treated CNT and nanoclay introduced an improvement of 181% versus neat PVB [6]. El Miri et al. produced a system of PVA with cellulose nanocrystals (CNC) and graphene oxide nanosheets (GON). The sample that contained 5% filler in the ratio of 1:2 CNC:GON presented an improvement of 159% in toughness, 124% in tensile test, and 320% in Young's modulus [7]. Valentini et al. studied ethylene-propylene-diene terpolymer rubber (EPDM) with carbon black (CB) and graphite nanoplatelets (GNPs). The presence of both fillers enhanced the Young's modulus, maximum strength, damping, and thermal conductivity [8]. Saharudin et al. analyzed a composition of halloysite nanotubes (HNTs) and CNT embedded in epoxy. The hybrid set demonstrated the highest percentage of improvement: 45% for tensile strength, 49% for Young's modulus, 46% for flexural strength, 17% for flexural modulus, and 125% for fracture toughness [9].Despite these significant improvements achieved by nanofillers, we found that the nanocomposite systems failed to reach their theoretical values of mechanical properties as predicted by the models of micromechanics. This finding reflects mainly the tensile strength and Young's modulus, where nanosystems suffer from aggregation, which impairs load transfer. This state may be different for the fracture toughness, which increases through mechanisms other than load transfer, e.g., crack front bowing and pull out [10,11]. Based on these findings, we examined the effect of geometry and chemical structure of the nanofillers on the fracture energy, and possible hybrid effects of hybrid systems comprised of isotactic polypropylene with different nanofillers. We divided the fillers into two groups: The first group comprised par...

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