Transcrystallisation with reorientation of polypropylene in drawn PET/PP and PA66/PP blends. Part 2. Electron microscopic observations on the PET/PP blend

Abstract

In the present second part of the study it is shown that polymer microfibrils are able to promote transcrystallisation of the surrounding polymer matrix in agreement with the results of an X-ray study reported in the first part. Polymer blends (microfibrillar-reinforced composites, MFC) containing microfibrils of poly(ethylene terephthalate) (PET) in a matrix phase consisting of polypropylene (PP) were studied by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM) and environmental scanning electron microscopy (ESEM) after melting and crystallisation of only the matrix phase polymer in an injection moulding process. Collective preferred orientation of layers was observed in the PP matrix in transcrystalline zones grown epitaxially from the PET microfibrils. With respect to these microfibrils the lamellar stacks are oriented in perpendicular direction. The range of collective layer orientation along the longitudinal direction of a microfibril was found to be very long. ESEM exhibits layers which appear to be stacked, two-dimensional spherulites with a diameter of several microns. TEM micrographs show a transcrystalline zone around the PET microfibrils containing stacked crystalline PP layers. The lateral extension of these zones is restricted to a region narrower (100–200 nm) than that observed in respective MFC fibre materials (cf. Part 1) in which the matrix phase polymer was molten and crystallised more slowly and under quiescent conditions. The differing results of ESEM and TEM concerning the extension of the transcrystalline zone can be explained on the basis of a complex model by Bassett (dominant crystallites close to the nucleating microfibril and subsidiary crystallites farther out). The addition of a compatibiliser to the PET/PP blend completely inhibits the formation of transcrystalline layers in samples with MFC structure.

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