DYNAMIC-MECHANICAL STUDY OF AMORPHOUS PHASES IN POLY(ETHYLENE TEREPHTHALATE) NYLON-6 BLENDS/

The changes in the thermomechanical behaviour of a poly(ethylene terep hthalate)/nylon-6 (PET/PA) blend (1:1 by weight) subjected to mechanic al and thermal treatments are examined by means of dynamic mechanical measurements. It is established from previous studies that PET/PA blen ds are incompatible in the isotropic state, but form so-called microfi brillar-reinforced composites upon extrusion, drawing and suitable ann ealing. This study focuses mainly on the amorphous component of these blends and thus complements that recently performed (Polymer 1993, 34, 4669) in which the crystalline phases were analysed. The orientation and crystallization of the homopolymers induced by drawing improve the dispersion of components and induce some compatibility as far as one glass transition temperature is observed. Yet, by annealing the drawn blend at temperatures below the melting temperatures of both component s (220 degrees C, for instance) the biphasic character of the composit e is enhanced in as much as the microstructures of both the crystallin e and amorphous phases are improved and the reorganization of species within separate phases is favoured. The components of the heterogeneou s blend become compatible provided that the annealing is performed at a sufficiently high temperature (240 degrees C). This temperature is i ntermediate between the melting temperature of the two components and allows for the isotropization of the low-melting component PA. The inc rease of compatibility is attributed to transreactions producing compa tibilizing layers of PET/PA copolymers at phase boundaries between mic rofibrils and the amorphous matrix. Prolonged annealing (25 h) leads t o the randomization of the original block copolymers and results in th e complete participation of PA in the copolymer, which is evidenced by the disappearance of the glass transition peak of PA.