Graphene nanoplatelets (GN) produced on a large scale by mechanochemical exfoliation of graphite are incorporated in a co‐continuous ethylene‐vinyl acetate/linear low‐density polyethylene (EVA/LLDPE) blend. Two different processing routes are chosen to selectively place GN in the EVA phase or force its migration to the EVA/LLDPE interface. The results show a drastic decrease in the electrical percolation threshold when the blends are compared to the respective single‐polymer composites. Even with the presence of agglomerates, GN particles are able to migrate to the blend interface and stabilize the morphology and hence the electrical properties. Annealing the insulating samples at processing temperatures causes a drastic increase in conductivity due to continued GN migration and blend morphology coarsening. Semi‐conductive samples, in which a more robust GN network is already established during processing, present no change in morphology but a slight increase in conductivity during annealing. The mechanical performance of the materials is also evaluated and some of the blends with GN present similar elongation at break as pure EVA, but with increased tensile modulus and tensile strength. The electrical performance at different working temperatures shows that the EVA/LLDPE/GN composites are good candidates to act as a semi‐conductive screen material in power cables or as anti‐static materials in electronic devices.

Economically viable high‐density polyethylene (HDPE)/graphene nanocomposites were produced using mass produced graphene powder and an industrial twin‐screw melt‐compounding machine. Rheological and electrical properties were investigated and scanning electron microscopy was carried out to investigate graphene dispersion and its network formation in the matrix. Mechanical properties of the nanocomposites were evaluated using tensile, flexural and impact tests. Differential scanning calorimetry analysis indicated that the crystalline structure of the polymer might be affected by high loadings of graphene. SEM evaluation revealed reasonable graphene dispersion in the matrix. In addition, the amount of graphene required to form a percolated network was similar for both rheological and electrical networks. The nanocomposites exhibited a significant increase in Young's and flexural moduli without a notable reduction in impact strength up to 14 wt% graphene loading. In these experiments, compounding graphene powder with HDPE produced a clear and distinct improvement in mechanical properties at an industrially suitable low cost. POLYM. ENG. SCI., 59:675–682, 2019. © 2018 Society of Plastics Engineers

The dielectric properties of nanocomposites of polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) triblock copolymers containing organically modified clay nanoparticles featuring controlled spatial orientation at the nanoscale: isotropic, totally oriented and partially oriented, have been investigated and correlated with the nanocomposite morphologies. A slow dielectric relaxation process attributed to elastomer chains with reduced mobility confined at nanoparticle/polymer interphase was observed in all the nanocomposites and was found to be dependent on the orientation of nanoclay and polystyrene (PS) domains, the location of clay tactoids as well as the PS block fraction. A dielectric "interfacial" glass transition temperature T gi assigned to this characteristic relaxation was estimated to occur at temperatures ranging between 6 °C and 35 °C depending on the nanocomposite, which is much higher than the bulk rubber phase glass transition temperature, normally lower than -40 °C for the studied block copolymers. Interestingly, the highest T gi were associated with the nanocomposites featuring random or partial orientation and/or selective location of nanoparticles in the rubber phase. I) IntroductionIn nanocomposite materials, controlled orientation of certain anisotropic nanoparticles such as nanoclay 1,2 , carbon nanotubes 3 and recently boron nitride nanotubes and nanosheets 4,5 is very beneficial for a wide spectrum of applications requiring excellent mechanical, electrical and/or thermal properties.For example, in the case of mechanical reinforcement, the alignment of nanoclay was reported in several publications to induce an improved mechanical strength in the alignment direction 6 . In the specific case of nanodielectrics, more efficient electron scattering and consequently higher breakdown strength perpendicular to the nanoparticles alignment direction were reported 2,7,8,9 . Simultaneously, nanoparticle alignment was shown to reduce dielectric losses in the direction perpendicular to the main plane of the M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT3 aligned nanoparticles 2 . This controlled orientation can be obtained using a wide range of techniques 3 although spatial alignment of nanoparticles according to 2D and 3D patterns is still a challenging field of study 10 .In applications requiring tuned spatial distribution of nanoparticles, the use of block copolymers can be really an asset due to the different nanoscale morphologies these materials present 11,12,13,14,15,16 . To probe the effect of tailored morphology and orientation of such designed nanocomposites on their polymer-filler interactions and implicitly on their final performance, techniques such as broadband dielectric spectroscopy (BDS) are often required 17 .In fact, the performance of polymer nanocomposites in general is governed by the interphase region 18,19 which consists mainly of a bound layer where the motion of macromolecular chains is strongly restricted affecting several properties including dielectric and m...

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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.