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Keywords:

  • crystallization;
  • drawing;
  • mechanical properties;
  • morphology;
  • nanocomposites;
  • nanoparticles;
  • polyamides;
  • uniaxial

Abstract

There is growing interest in the incorporation of nanoparticles into engineering polymers to improve various functional properties. However, ultimate properties of nanocomposites are affected by a large number of factors including the microstructural distributions that are generated during processing. In this work, polyamide-11 (PA-11) (also known as nylon-11) nanocomposites are generated with carbon nanostructures employing a solution crystallization technique at multiple polymer and nanoparticle concentrations, followed by drying, molding, uniaxial stretching and the analysis of the microstructural distributions and tensile properties of the nanocomposites. The morphology of crystals of PA-11 encapsulating the nanoparticles changed from nano-hybrid shish-kebabs at low polymer concentration (0.02 wt % PA-11 in solvent) to spherulites at high polymer concentration (10 wt % PA-11 in solvent). The drawing down of nanocomposite films at draw ratios ranging from 2 to 5 at 100 °C resulted in a shift of the PA-11 polymorph from the generally-encountered α phase to the technologically interesting γ phase (which is the crystal phase attributed to the piezoelectric and pyroelectric properties of PA-11). The drawing down also increased of the tensile modulus and yield stress of the nanocomposite films. In contrast, the α phase was conserved at a drawdown temperature of 150 °C, which was attributed to the resulting smaller normal force, i.e., the normal stress difference and the higher temperature allowing the partial relaxation of some of the macromolecules. These findings illustrate how PA-11 can be structured in the presence of carbon nanotubes and nanofibers to achieve enhanced functionality, which could broaden the application areas and utility of this polymer. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1311–1321, 2011