Distribution and alignment of carbon nanotubes and nanofibrils in a polymer matrix

Composites consisting of different quantities of carbon nanotubes and nanofibrils in a poly(methyl methacrylate) (PMMA) matrix have been prepared using a polymer extrusion technique. The nanotubes or nanofibrils were first dispersed over the polymer matrix particles using a dry powder mixing method. The final composite specimens contained well-dispersed and aligned nanofibrils and nanotubes. The orientation distribution of carbon fibrils and nanotubes in the composite was determined by image analysis and found to be maximized in the extrusion flow direction. The Knoop hardness data confirmed this observation, as a maximum was observed at 90degrees to the orientation of the reinforcement. When the initial PMMA particle diameter was under 200 mum, considerable improvements were observed in the mechanical properties of the nanofibril/PMMA composites. The interpretation of the mechanical data for nanotube/PMMA composites was more complex. Indeed, the tensile modulus was almost insensitive to the presence of either single-wall or multi-wall nanotubes, whereas the impact strength (thus, indirectly, the fracture toughness) was significantly improved by even small amounts of single-wall nanotubes. The method proposed here for the dispersion and orientation of carbon nanotubes and nanofibrils in a polymer matrix show promise for the preparation of improved engineering composites. (C) 2002 Elsevier Science Ltd. All rights reserved.