Highly dispersed graphene nanoplatelets in polypropylene composites by employing high-shear stress for enhanced dielectric properties and frequency-selective electromagnetic interference shielding capability

Although graphene nanoplatelets (GNPs) are currently receiving significant interest as a filler for polymer composites, the issue of agglomeration is yet to be overcome for their wide applications. Herein, the high-shear extrusion technique was thoroughly investigated to effectively disperse GNPs in a polypropylene (PP) matrix with a content of 3 wt%. The screw rotation speed was controlled in the range of 1000–3000 rpm, which is extremely high corresponding to the shear rate of 733–2199 s⁻¹ that should be compared with 200 rpm and 99 s⁻¹ of a conventional extruder, respectively. As the shear rate increased, the size of GNP agglomerates decreased from several microns to ca. 250 nm. This size reduction resulted in the significant enhancement of dielectric loss, owing to the strong interfacial polarization at the interfaces between the GNPs and PP matrix. Furthermore, frequency-selective characteristics in electromagnetic interference shielding could be controlled in the wide frequency spectrum covering the X- and Ka-bands by adjusting the shear rates providing different aperture sizes specified by the interstitial distances of GNPs. Altogether, the developed GNP/PP nanocomposites and their methodology have remarkable potential as promising solutions for graphene-based polymer composites.