Characterization of non-covalently, non-specifically functionalized multi-wall carbon nanotubes and their melt compounded composites with an ethylene–octene copolymer Osayuki Osazuwa a , Kyle Petrie a , Marianna Kontopoulou a,⇑ , Peng Xiang b , Zhibin Ye b , Aristides Docoslis a a Department of Chemical Engineering, Queen’s University, Kingston, Ontario, Canada K7L 3N6 b School of Engineering, Laurentian University, Sudbury, Ontario, Canada P3E 2C6 article info Article history: Received 17 April 2012 Received in revised form 17 July 2012 Accepted 23 August 2012 Available online 1 September 2012 Keywords: A. Carbon nanotubes A. Nanocomposites B. Electrical properties B. Mechanical properties E. Melt compounding abstract Multi-wall carbon nanotubes (MWCNTs) were functionalized with a hyperbranched polyethylene (HBPE) using a non-covalent, non-specific functionalization approach. The adsorption behavior of HBPE on MWCNTs was characterized by means of an adsorption isotherm. HBPE adsorption reached a plateau value of 0.3:1.0 (w/w) HBPE:MWCNT, corresponding to a surface coverage of approximately 30%. The functionalized MWCNTs were better dispersed in tetrahydrofuran (THF), forming smaller aggregates compared to their unmodified counterparts. Pristine and HBPE-functionalized MWCNTs were melt com- pounded with a low-viscosity ethylene–octene copolymer (EOC) matrix. Electrical and rheological perco- lation thresholds were observed at nanotube loadings of less than 1 wt%. Functionalization did not affect significantly the electrical conductivity and rheological properties. The improved dispersion of the func- tionalized MWCNTs within the EOC matrix resulted in improved ductility over the non-functionalized counterpart. This study demonstrates that this method of functionalization results in partial surface cov- erage of the nanotubes, therefore providing an efficient means for achieving good nanotube dispersion, without compromising their surface properties. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Polymer/carbon nanotube (CNT) composites have been widely studied, because of their superior mechanical, thermal and electri- cal properties [1–7]. The preparation of polymer/carbon nanotube composites has been an area of active scientific research, since the exceptional properties of CNTs may extend the end-use applica- tions of polymeric materials. Owing to their low density, improved mechanical properties and electrical conductivity, these compos- ites can find applications in structural materials, antistatic films, electromagnetic interference (EMI) shielding, and coatings for elec- trostatic painting, hydrogen storage media and nanometer-sized semiconductor devices, probes and interconnects [8], automotive parts, reinforced aerospace materials, and sporting goods [9]. The use of CNTs in polymer composites has been greatly hin- dered due to their incompatibility with polymers and conse- quently, their poor dispersion in polymer matrices, especially in melt compounding operations. CNTs tend to exist as bundles of single wall carbon nanotubes (SWCNTs), or aggregates of multi- wall carbon nanotubes (MWCNTs) held together by van der Waals forces and p–p interactions, which make their separation and suc- cessful dispersion into polymers a very difficult task. Other factors influencing the dispersion of CNT include the viscosity of the poly- mer matrix, the melt compounding procedure, etc. [10,11]. Melt compounded thermoplastic composites containing MWCNTs have the potential of producing composite systems, with electrical conductivity higher than 10 4 S/m [12], at relatively low nanotube loadings, suitable for applications such as electrostatic painting, electromagnetic interference (EMI) shielding, electro- static discharge and conductive coatings, and other injection molded parts. However, in order to broaden the field of application of these composites to include large structural components, the mechanical properties must also remain at an acceptable level, and not be compromised by excessive aggregation. A number of surface functionalization methods have been developed in order to either render MWCNTs dispersible in sol- vents, or improve their dispersibility in polymers. Local strain in carbon nanotubes, arising from pyramidalization and misalign- ment of the p-orbitals of the sp 2 -hybridized carbon atoms, makes nanotubes more reactive than a flat graphene sheet, thus more amenable to chemical functionalization [13]. Covalent functionali- zation of nanotubes can improve the properties of the resulting composites through better nanotube dispersion in the matrix and enhanced nanotube/polymer interfacial binding [14]. Covalent 0266-3538/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.compscitech.2012.08.015 ⇑ Corresponding author. Tel.: +1 613 533 3079; fax: +1 613 533 6637. E-mail address: marianna.kontopoulou@chee.queensu.ca (M. Kontopoulou). Composites Science and Technology 73 (2012) 27–33 Contents lists available at SciVerse ScienceDirect Composites Science and Technology journal homepage: www.elsevier.com/locate/compscitech