(186a) Transient Polymer Structure in Polyurethane Carbon Nanotube Nanocomposites Under Deformation
Nanocomposites were produced with addition of small amounts (0.5-10 vol%) of multiwall carbon nanotubes (CNT) to a thermoplastic elastomer polyurethane (PU). We obtained nanocomposites with high electrical conductivity (σ ~ 1-10 S/cm), low electrical percolation (Φ~ 0.005) and enhancement of mechanical properties including increased modulus and yield stress without the loss of the ability to stretch the elastomer above 1000% before rupture. In-situ WAX and SAX scattering during deformation indicated that these mechanical enhancements arise not only from the CNTs, but also from their impact on PU soft-segment crystallization. Yield and strain hardening characteristics of the nanocomposites correspond to deformation induced morphology changes depending on strain rate and CNT concentration. Deconvolution of X-ray data revealed details on alignment of CNTs, soft-segment crystallites and amorphous polymer, in addition to the extent of crystallinity. SAXS shows a peculiar transient morphological change of the PU crystalline phase at low deformations. The deformation behavior after yielding is similar for all nanocomposites, irrespective of CNT loading, and is mainly governed by the elastomer matrix. Flexibility of CNTs in addition to soft segment crystallization prove to be major factors on electrical and adaptive properties of CNT nanocomposites.