Trans-crystallisation with reorientation of polypropylene in drawn PET/PP and PA66/PP blends : part. 1 study with WAXS of synchrotron radiation

Abstract

Transcrystallisation induced by annealing in the polypropylene (PP) component of nanostructured polymer-polymer composites (NPC) was studied for two different polymeric fillers. In contrast to the typical narrow columnar transcrystalline regions around filler fibres in common glassfibre reinforced PP, volume-filling transcrystallisation was observed for both of the polymer fillers, thus resulting in reorientation of the PP matrix crystals instead of an expected isotropisation. Two colddrawn blends of PP with poly(ethylene terephthalate) (PET) or polyamide 66 (PA66), respectively, namely PET/PP and PA66/PP both in a ratio of 50/50 wt.% were investigated by means of wide-angle X-ray scattering (WAXS) of synchrotron radiation during heating, melting of only the low-melting component (PP) at 200 C yielding an isotropic melt, and subsequent crystallisation upon cooling. A strong epitaxial effect of the persistent embedded microfibrillar component (PET or PA66) on the non-isothermal crystallisation behaviour of PP during its cooling to room temperature was found. The composites obtained after such thermal treatment represented anisotropic semi-crystalline nanocomposites, in which the PP crystallites were reoriented. The ultimate structure for the PET/PP blend exhibited crystals with their molecular axis tilted at approx. 49 with respect to their initial orientation (parallel to the fibre axis). In the PA66/PP blends the ultimate structure returned to the initial orientation of the PP chains parallel to the fibre axis, but with a broadened orientation distribution. Results of similar studies on other blends are reviewed.