Mechanochemical Routes to Functionalized Graphene Nanofillers Tuned for Lightweight Carbon/Hydrocarbon Composites

Abstract

Graphite exfoliation by shear-induced dry and wet processes and especially mechanochemistry represent attractive routes to carbon nanofillers. Dry ball-milling of graphite in a planetary mill under gas pressure is a scalable and environmentally benign one-step process, which requires neither hazardous solvents nor tedious separate functionalization and purification steps. Gas type, pressure, and milling duration govern average particle size, shape, and functionalization. Ball-milling under Ar yields hydroxylated spherical carbon particle agglomerates, whereas ball-milling under CO2 affords functionalized nanoplatelets without encountering agglomeration problems and highly exothermic post-milling reactions with air. The carboxylation of graphene nanoplatelets enhances their dispersibility in various media including polypropylene (PP) even in the absence of compatibilizers. Large amounts of carboxylated nanoplatelets are dispersed in PP without massive viscosity build-up. Functionalized carbon nanoplatelet fillers enable tailoring of recyclable lightweight carbon/hydrocarbon composites exhibiting an improved balance of stiffness, strength, toughness, electrical, and thermal conductivity.