Carbon nanotubes for reinforcement of plastics? A case study with poly(vinyl alcohol)

This paper reports a 4.5 fold increase in the Young's modulus of a semi-crystalline polymer, poly(vinyl alcohol), with the addition of carbon nanotubes. The importance of nanotube diameter is addressed with the production of four composite solutions with each solution containing carbon nanotubes of a specific diameter. Thin films were cast for tensile tests while Differential Scanning Calorimetry (DSC) measured the crystallinity of the composite material. Nanotubes were observed to increase polymer crystallinity such that the Young's modulus of the composite also increased. Thus it is suggested here that in semi-crystalline polymer/nanotube systems, with non-covalent bonding between the filler and matrix, the formation of nanotube induced crystalline polymer domains is the dominant reinforcement mechanism and not stress transfer to the nanotube: the role of the nanotube lies in nucleating crystallization. In addition, the calorimetry data indicates that nanotube diameter and quality of dispersion determines the increase in crystallinity which in turn determines the mechanical properties of the composite. Furthermore, Transmission Electron Microscopy (TEM) images confirm an excellent dispersion and wetting of the various nanotube types in the polymer solution. (c) 2006 Elsevier Ltd. All rights reserved.