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 degrees C and 25 h, respectively, results in a strong decrease of the solubility of the PA 6 fraction in formic acid (by 5x) 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.