Morphology of microfibrillar reinforced composites PET/PA 6 blend

Abstract

Extruded isotropic films of a poly(ethylene terephthalate) (PET) and polyamide 6 (PA 6) blend are subjected to drawing and annealing at different temperatures and durations in order to produce microfibrillar reinforced composites (MFC). In conformity with previous X-ray studies of the same system, the present scanning electron microscopic (SEM) observations show that drawing results in the formation of a highly oriented fibrillar structure of PET which is preserved even after annealing above the melting point of PA 6. Further raising of both annealing temperature and duration up to 240°C and 25 h, respectively, results in a strong decrease of the solubility of the PA 6 fraction in formic acid (by 5×) as well as in a continuous increase of the intensity of the infra-red spectral band at 3300 cm−1 which is characteristic of the amide group. SEM observations of these samples reveal larger aggregates of fibrillized PET arising from the gradual incorporation of PET in a copolymer matrix, the latter being insoluble in formic acid. The observed changes are explained by the occurrence of chemical interactions between PET and PA 6 under these conditions, as concluded earlier from the complete loss of crystallinity of the PA 6 component. Starting from the present and previous results on MFC, a model is proposed, illustrating the morphological changes on the macro- and molecular levels, during their preparation.