Transcrystallisation 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 glass-fibre 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 cold-drawn 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.

Dedicated to Prof. Dr. Wilhelm Ruland on the occasion of his 80th birthday