Nanostructure and mechanical properties studied during dynamical straining of microfibrillar reinforced HDPE/PA blends

Abstract

Oriented polymer blends based on high-density polyethylene (HDPE) are strained until failure. Twodimensional (2D) small-angle X-ray scattering patterns monitor the nanostructure evolution. Data evaluation methods for high-precision determination of macroscopic mechanical and nanoscopic structure parameters are presented. The hardest materials exhibit a very inhomogeneous nanodomain structure. During straining their domains appear to be wedged together and inhibit transverse contraction on the nanometer scale. Further components are polyamides (PA6, PA12) (20–30%) and as compatibilizer Yparex® 8102 (YP) (0–10%). Some HDPE/PA6 blends are additionally loaded with nanoclays (Nanomer® or Cloisite®). Blending of HDPE with PA12 causes no synergistic effect. In the absence of nanoclay, PA6 and HDPE form a heterogeneous nanostructure with high Young’s modulus. After addition of YP a more homogeneous scaffold structure is observed in which some of the PA6 microfibrils and HDPE crystallites appear to be rigidly connected, but the modulus has decreased. Both kinds of nanoclay induce a transition from a structure without transverse correlation among the microfibrils into a macrolattice with 3D correlations among HDPE domains from neighboring microfibrils. For extensions between 0.7% and 3.5% the scattering entities with 3D correlation exhibit transverse elongation instead of transverse contraction. The process is interpreted as overcoming a correlation barrier executed by the crystallites in an evasion-upon-approaching mechanism. During continued straining the 3D correlation is reduced or removed.