The Role of Selectively Located Commercial Graphene Nanoplatelets in the Electrical Properties, Morphology, and Stability of EVA/LLDPE Blends

Abstract

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.

Correlation between morphology, rheological behavior, and electrical behavior of conductive cocontinuous LLDPE/EVA blends containing commercial graphene nanoplatelets

“…Furthermore, in many cases, the incorporation of particles in the blends and their selective localization often induces changes in the blend's morphology. In particular, their localization at the interface effectively suppresses coarsening and promotes refined and stable blend morphologies [27,29,[41][42][43][44][45]. In the same context, it was found that plate-like fillers, among them graphene, can adapt better to polymer-polymer interfaces and are subsequently more efficient in suppressing coarsening [42].…”

“…The nanoplatelets surface is functionalized with hydroxyl and carboxyl groups. They have a mean thickness of 20 nm and average agglomerate flake size of 50 μm [29,60]. Linear low density polyethylene (LLDPE) NOVAPOL PI-2024-A grade of density 0.924 g/cm 3 was purchased from Nova Chemicals and Ethylene vinyl acetate copolymer (EVA) Alcudia PA-540 grade of density 0.937 g/cm 3 was supplied from Repsol.…”

“…In addition, LLDPE/EVA/GN blends were also prepared with the ratio of PE/EVA resins equal to 50wt%/50wt%. This composition was selected to achieve a co-continuous morphology, based on the ratio of viscosities measured by capillary rheometer as discussed in our previous manuscript [29]. The viscosity data are also reported in Figure S1 of the electronic supporting information (ESI) file.…”

“…The blend nanocomposites have been prepared by a facile melt compounding technique. In our previous studies on these materials [29,62], we demonstrated that controlling the processing sequence and in a second step doing a thermal annealing treatment for 2 hours were both effective to tune the localization of GN nanoplatelets in the blend and to lower the percolation threshold concentration. From a practical point of view, the obtained range of electrical conductivity at different working temperatures confirmed that the as-obtained LLDPE/EVA/GN composites can be considered as potential candidates for semi-conductive screen materials and electrostatic dissipation materials.…”

“…Regarding the option of using multiphase polymer matrices, immiscible polymer blends with co-continuous morphology were found to be a powerful tool to achieve not only the double percolation of the polymer phases and conductive particles, but also the selective localization of the particles in one phase or at the interface; thus reducing considerably the onset of the percolation threshold. This concept was demonstrated for different conductive particles [3,4,[27][28][29][30][31][32][33][34][35][36][37][38][39][40]. Furthermore, in many cases, the incorporation of particles in the blends and their selective localization often induces changes in the blend's morphology.…”