Layers-to-layers assembled graphene-boron nitride for polymer composites with enhanced thermal stability and dielectric constant at low loss

Carbon-based percolative polymer nanocomposites have shown high capability of large dielectric constant (ε^I) output. However, such nanocomposites are associated with high dielectric loss (ε^II) and low voltage strength (E_b). These practically prevent their application as capacitive energy storage materials. This study addressed these hurdles by assembling graphene nanosheets (GNs) and boron nitride (BN) nanosheets. This was done by simple two steps; hydrothermal and self-assembly techniques. Prior to that, the nanosheets were surface functionalized to promote their wettability and dispersion in the polymer matrix. The assembled BN onto GNs surfaces (BN@GNs) was used in preparation of masterbatch via solvent-mixing with polypropylene grafted maleic anhydride (PPMA). Then, the concentrated masterbatch was diluted using pure polypropylene (PP) by melt compounding in preparation of the nanocomposites. PP/BN@GNs nanocomposites showed better thermal stability than that of PP/GNs, PP/BN and pure PP. Also, PP/1BN@GNs showed lower ε^II of about 0.09 at 1 kHz and higher E_b of 120.6 kV/mm compared to PP/1GNs with ε^II of 8.5 and E_b of 36.3 kV/mm. This was attributed to the insulative characteristic of the layered BN attached on the surfaces of the conductive GNs, which prevented their direct interconnection in the PP matrix. Although the ε^I of PP/BN@GNs was lower than that of PP/GNs nanocomposites, the PP/BN@GNs exhibited increase with increasing BN@GNs content with optimal of about 822.5% higher than the pure PP at 1 kHz.