Fabrication of high performance carbon nanotubes-polyolefin nanocomposites using novel surface modification methods

Abstract

In this study, we report a novel method for preparing high performance conductive multi-walled carbon nanotubes (MWNTs) - polyolefins (e.g., polypropylene (PP) or polyethylene (PE)) nanocomposites by using covalently alkyl modified MWNTs or polyolefin-grafted MWNTs. The research objective of this study is to develop an effective modification method for enhancing the dispersion of MWNTs in a polyolefin matrix. The carbon nanotubes (CNTs) tend to form agglomerates during processing of composites due to strong van der Waals attraction such as $\pi-\pi$ interaction between nanotubes. The nanotubes agglomerates reduce the surface area and interrupt formation of the network structure of nanotubes. Therefore, improvement of interfacial bonding between polymer matrix and carbon nanotubes for uniform dispersion of nanotubes is needed to fabricate superior CNT composites. In order to achieve highly efficient interfacial interactions between nanotubes and hydrophobic polymers such as polyolefins, the introduction of hydrophobic organic molecules with long alkyl chains onto nanotube surfaces is reported to be one of the most effective ways. Previously, acid treatment of the nanotubes and subsequent reaction with aliphatic amines has been widely used to attach the alkyl chains to nanotubes. However, the acid treatment routes can be occurring CNTs damaging and take a long time to modify the CNTs. For ameliorating such problems, we successfully developed two types of new covalent modification method: highly alkylated MWNTs or polyethylene-grafted MWNTs prepared by $CF_4$ plasma technique assisted fluorination and subsequent alkylamination with octadecylamine (ODA) or amination of fluorinated MWNT (F-MWNT) with ehthylenediamine (EDA) followed by imidization of amine-modified MWNT with maleic anhydride-grafted polyethylene (MPE, PE-g-MAH), respectively. Then, we prepared modified MWNT/ polyolefin (PP or PE) nanocomposites and characterized their dispersion morphology, ele...