Mechanochemically modified graphene nanoplatelets for high-performance polycarbonate composites

Abstract

The exceptional mechanical, electrical and thermal properties of graphene and its derivative have established their vital role in developing novel polymer nanocomposites. However, it is a great challenge to achieve uniform dispersion of graphene and strong interfacial bonding within polymer matrices, especially by industry-compatible methods such as melt compounding. Different to traditional solvent-based modification methods, our mechanochemical approach involves the surface modification of graphene nanoplatelets (GNPs) with a long-chain surfactant – Jeffamine M2070. The process is scalable, environmentally friendly and solvent-free. GNPs, ball-milled GNPs (BMGNPs) and M2070-modified GNPs (MmGNPs) were respectively incorporated into a polycarbonate matrix using twin-screw extrusion, to produce three groups of nanocomposites. GNPs exhibited aggregation due to unideal compatibility with the matrix, whereas BMGNPs showed reduced aggregation owing to mechanical exfoliation. MmGNPs demonstrated the best compatibility with polycarbonate and thus exhibited the most uniform dispersion and significant improvements in mechanical performance, e.g., 16.9 % in tensile strength and 36.4 % in Young's modulus. Despite the defects caused by the mechanochemical modification, MmGNPs in the matrix resulted in an increment of 50 % in thermal conductivity, reaching 0.32 W m⁻¹ K⁻¹ in comparison with ∼0.18 W m⁻¹ K⁻¹ for polycarbonate. This study highlights the importance of surface modification by mechanochemical processing techniques in enhancing the exfoliation and dispersion of graphene and thus the properties of thermoplastics.