Large-Scale Production of PMMA/SWCNT Composites Based on SWCNT Modified with PMMA Robin Anderson Fraser, † Karen Stoeffler,* ,‡ Behnam Ashrafi, § Yunfa Zhang, § and Benoit Simard † † Steacie Institute for Molecular Sciences, National Research Council Canada, 100 Sussex Drive, Ottawa, Ontario K1A 0R6, Canada ‡ Industrial Materials Institute, National Research Council Canada, 75 de Mortagne, Boucherville, Quebec J4B 6Y4, Canada § Institute for Aerospace Research, National Research Council Canada, 1200 Montreal Road, Building M-3, Ottawa, Ontario K1A 0R6, Canada ABSTRACT: In this work, a two-step method consisting of in situ polymerization of polymethyl methacrylate (PMMA) in the presence of single-walled carbon nanotubes (SWCNT), followed by the redispersion of the resulting compound in dimethylformamide (DMF), was used to fabricate SWCNT modified with PMMA (SWCNT-PMMA). Raman spectroscopy revealed that PMMA was merely wrapped around the SWCNT when raw SWCNT or purified SWCNT were used as the starting material. However, PMMA was covalently bonded to SWCNT when acid treated SWCNT (SWCNT-COOH) was used as the starting material. SWCNT- PMMA compounds were further diluted in pure PMMA by conventional melt compounding at large scale (several kilograms) to obtain transparent composites containing 0.09 wt % SWCNT. The micro- and nano-dispersion of the SWCNT in the composites were analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The thermal and mechanical properties of the composites were determined by thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), tensile testing, and Charpy impact testing. At the the low SWCNT loading studied, the tensile properties remain unchanged, whereas the impact strength improves by 20%. KEYWORDS: single-walled carbon nanotubes (SWCNT), polymethyl methacrylate (PMMA), covalent functionalization, dispersion ■ INTRODUCTION In the last several years, there has been significant progress in the field of polymer/single-walled carbon nanotube (SWCNT) nanocomposites. 1 Once properly developed, polymer/SWCNT nanocomposites could have applications in a variety of industries, from textiles 2 to aerospace. 3,4 To date, SWCNT have been incorporated into several polymers with mixed results. 5,6 The two major hurdles that need to be overcome before the promise of SWCNT based nanocomposites can be realized are (1) homogeneous dispersion of SWCNT in the matrix and (2) efficient load transfer between SWCNT and the matrix. 7-9 A homogeneous dispersion is paramount as it allows for full utilization of the amazing properties 10,11 of SWCNT. Indeed, when SWCNT are aggregated in a matrix, they can cause large stress concentrations, which weaken the compo- site. 12 A number of techniques, such as solution mixing or melt compounding, have been developed to incorporate SWCNT in solvents and polymer matrices. However, the poor compati- bility of SWCNT with common solvents and polymers usually leads to the production of composites with aggregated SWCNT. Non-covalent wrapping of the SWCNT with a polymer or surfactant that is both compatible with SWCNT and the matrix can enhance the dispersion of SWCNT in polymer matrices. This method relies on van der Waals or electrostatic interactions between the wrapping molecule and the SWCNT. Although no damage is done to the nanotube structure (thus preserving the electronic and mechanical properties) and well-dispersed nanocomposites can be achieved, these interacting forces are inherently weaker than a covalent bond and may not result in mechanical properties enhancement for the final nanocomposite. 1 Another method to aid integration of SWCNT into a polymer matrix is functionalizing the SWCNT surface. Proper choice of func- tional group(s) allows one to both impart solubility to the SWCNT (in a solvent, monomer, or polymer solution) and create a covalent bond with the polymer matrix. Toward the production of enhanced polymer/SWCNT nanocomposites, we have focused on incorporating SWCNT into polymethyl methacrylate (PMMA). PMMA-based materi- als are useful in practically all segments of the economy, from household to automotive products, because of their toughness, stiffness, and transparency. 13 Although less dense than the glass they usually replace, the weight of PMMA materials remains a drawback for several applications. Incorporation of reinforcing fillers, such as SWCNT, into a PMMA matrix could result in an enhanced material. The aim of the present work is to achieve a homogeneous dispersion of SWCNT covalently bonded to the matrix via a method that can be used to fabricate composites at the industrial scale (several kilograms). To accomplish this, we have used a two-steps method. In a first step, PMMA was in situ polymerized in presence of SWCNT (Figure 1b). In a second step, the compound obtained was redispersed in a solvent in Received: December 22, 2011 Accepted: March 15, 2012 Published: March 15, 2012 Research Article www.acsami.org © 2012 American Chemical Society 1990 dx.doi.org/10.1021/am201824k | ACS Appl. Mater. Interfaces 2012, 4, 1990-1997