(273f) Mechanochemical Functionalization Effects on the Percolation Behavior of Ultrahigh Aspect Ratio Multiwalled Carbon Nanotubes in Polycarbonate

Carbon nanotubes (CNTs) have been used as additives in polymer composites due to their unique morphology and outstanding properties. However, progress in these nanocomposites has stalled due to high costs associated with CNT production and purification. To reduce these costs, our group has recently developed a high yield synthesis process (30:1) for growing multiwalled carbon nanotube (MWCNTs) on multilayered supports as opposed to traditional monolayered supports. The MWCNTs synthesized by this method are approximately 100 µm in length and 15 nm in diameter (L/D ≈ 6,600). Because the volume percolation threshold of a filled system is inversely dependent on the aspect ratio of the filler, compounding these ultrahigh aspect ratio MWCNTs in polymers is promising for composites with extremely low carbon contents. However, preliminary work on the dispersibility of these MWCNTs has been disappointing due to severe agglomeration. In this work, we implement ball milling as a dry, scalable process for mechanochemical functionalization of MWCNTs toward enhanced wettability with a polycarbonate matrix. The energy of milling is carefully chosen to balance extent of functionalization and aspect ratio reduction. The functionalized MWCNTs are then compounded with polycarbonate in a conical twin-screw extruder and the resulting nanocomposites are characterized. The percolation behavior of pristine, ball milled, and mechanochemically functionalized MWCNTs are compared by electrical and rheological measurements. We also report the effects MWCNT functionalization on mechanical reinforcement and thermal stability of the composites. With this study, we hope to show that a simple ball milling process can be used to prepare deagglomerated functionalized MWCNTs for compounding in polymers at an industrial scale.