Macromolecular Nanotechnology Polyamide 6/Graphene composites: The effect of in situ polymerisation on the structure and properties of graphene oxide and reduced graphene oxide Aidan O’Neill a , Dimitri Bakirtzis b , Dorian Dixon a,⇑ a Nanotechnology and Integrated BioEngineering Centre (NIBEC), University of Ulster, Belfast, NI BT370QB, United Kingdom b Fire Safety Engineering Research and Technology (FireSERT), University of Ulster, Belfast, NI BT370QB, United Kingdom article info Article history: Received 28 April 2014 Received in revised form 19 July 2014 Accepted 27 July 2014 Available online 8 August 2014 Keywords: Graphene oxide Reduced graphene oxide Polyamide 6 In situ polymerisation abstract Nanocomposites were prepared via in situ, ring opening polymerisation of e-caprolactam in the presence of single layer graphene oxide (GO) and chemically reduced graphene oxide (rGO). The structure and properties of the graphene before and after polymerisation were investigated, alongside the properties of the composites, using Atomic Force Microscopy (AFM), Fourier Transform Infra-red spectroscopy (FTIR), Raman spectroscopy, X-ray Photo- electron Spectroscopy (XPS), X-ray Diffraction (XRD), Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). Reduction of the Graphene oxide (GO) during polymerisation was observed along with functionalisation of graphene flakes with polyam- ide 6 (PA6) chains. FTIR and XRD show the retention of some oxygen functionalities after reduction, specifically doubly bound oxygen species. The functionalised graphene sheets were analysed after centrifugal removal from composites using formic acid as a solvent. AFM imaging indicated a sheet height of 0.75 nm for single layer graphene oxide with an increase to 4 nm for graphene sheets after polymerisation. This suggests that the graphene acts as a base for polymerisation with polymer chains propagating from its surface, pro- moting interfacial interaction. More so in PA6/GO composites as there is a greater amount of PA6 bound to GO when compared to rGO. Raman data depicts a slight restoration of sp 2 hybrid for functionalised-GO (f-GO) which does not occur in functionalised-rGO (f-rGO). XRD suggests that no restacking of GO sheets occurred during the polymerisation process whilst graphitisation of rGO occurred. Thermal analysis measurements revealed that nano- composites are thermally stable and graphene inclusion influenced both crystallinity and the molecular weight of the polymer. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Graphene is a two dimensional sheet made up of carbon atoms arranged in a hexagonal lattice and is considered as the basic building block for all other sp 2 carbon structures [1]. Recently it has eclipsed fullerenes and carbon nano- tubes (CNTs) in terms of research publication output, potential applications under investigation and patents [2]. It has extraordinary mechanical properties with a reported Young’s modulus of 1 TPa and a tensile strength of 130 GPa [3]. A remarkable thermal conductivity of 5000 Watts per metre Kelvin W/(m k) has also been recorded [4]. Due to graphene’s 2D honeycomb structure low lying electrons can move freely over the flat surface of the material and act like Dirac fermions. Room temper- ature transport phenomenon in graphene can be observed via the quantum Hall effect [5]. The charge carriers in http://dx.doi.org/10.1016/j.eurpolymj.2014.07.038 0014-3057/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +44 2890366153. E-mail address: d.dixon@ulster.ac.uk (D. Dixon). European Polymer Journal 59 (2014) 353–362 Contents lists available at ScienceDirect European Polymer Journal journal homepage: www.elsevier.com/locate/europolj MACROMOLECULAR NANOTECHNOLOGY