Graphene, the newest member of the carbon’s family, has proven its efficiency in improving polymers’ resistance against photodegradation, even at low loadings equal to 1 wt% or lower. This protective role involves a multitude of complementary mechanisms associated with graphene’s unique geometry and chemistry. In this review, these mechanisms, taking place during both the initiation and propagation steps of photodegradation, are discussed concerning graphene and graphene derivatives, i.e., graphene oxide (GO) and reduced graphene oxide (rGO). In particular, graphene displays important UV absorption, free radical scavenging, and quenching capabilities thanks to the abundant π-bonds and sp2 carbon sites in its hexagonal lattice structure. The free radical scavenging effect is also partially linked with functional hydroxyl groups on the surface. However, the sp2 sites remain the predominant player, which makes graphene’s antioxidant effect potentially stronger than rGO and GO. Besides, UV screening and oxygen barriers are active protective mechanisms attributed to graphene’s high surface area and 2D geometry. Moreover, the way that graphene, as a nucleating agent, can improve the photostability of polymers, have been explored as well. These include the potential effect of graphene on increasing polymer’s glass transition temperature and crystallinity.

In this work, co-continuous blends of linear low density polyethylene (LLDPE)/ Ethyl vinyl acetate (EVA) containing graphene (GN) have been studied. Although mass-produced GN grade prepared by mechanochemical exfoliation of graphite and a facile melt compounding technique were adopted, it was possible to lower the electrical percolation threshold significantly by controlling the localization of GN nanoplatelets in the blend and by applying an appropriate thermal annealing procedure. The electrical and rheological properties of the obtained nanocomposites were systematically investigated to get an insight on the composite morphology. During annealing, an alignment between time-dependent behaviors of viscoelastic moduli and electrical conductivity was observed. An increase of both quantities and a simultaneous coarsening of the blend's morphologies occurred during the first 30 minutes of annealing followed by a more stable behavior. This rise was attributed to the diffusion and flocculation of GN nanoplatelets and their migration to the interface. Furthermore, the electrical and rheological percolation threshold concentrations were evaluated using a scaling Power law. The electrical percolation threshold was reduced to 0.5 vol% upon thermal annealing and was close to the rheological percolation threshold. Finally, the viscoelastic response of the composites was well described by a two-phase model, indicating that the effect of the relaxation dynamics of the interfacial network does not depend on the blend's morphology, even though the latter affects the space arrangement of GN and consequently the strength of the formed network.

This work demonstrates how the addition of few-layer graphene (FLG) influences the processability and mechanical properties of the mixed polyolefin waste stream (R-(PE/PP)). Three different types of compounds were investigated: (1) R-(PE/PP) with FLG; (2) blends of R-(PE/PP) with prime polyethylene (PE) or polypropylene (PP) or PP copolymer; and (3) R-(PE/PP) with both the prime polymer and FLG. The processability was assessed by measuring the torque during melt extrusion, the melt flow index (MFI), and viscosity of the compounds. Investigations of the processability and mechanical properties of the composites indicate that the presence of FLG can reinforce the composites without hindering the processability, an unusual but desired feature of rigid fillers. A maximum increase in tensile strength by 9%, flexural strength by 23%, but a reduction in impact strength were observed for the compounds containing R-(PE/PP), 4 wt.% FLG, and 9 wt.% prime PP. The addition of FLG concentrations higher than 4 wt.% in R-(PE/PP), however, resulted in higher tensile and flexural properties while preserving the impact strength. Remarkably, the addition of 10 wt.% FLG increased the impact strength of the composite by 9%. This increase in impact strength is attributed to the dominant resistance of the rigid FLG particles to crack propagation.

No abstract

No abstract