Dynamic mechanical study of amorphous phases in poly(ethylene terephthalate) /nylon-6 blends

The changes in the thermomechanical behaviour of a poly(ethylene terephthalate)/nylon-6 (PET/PA) blend (1:1 by weight) subjected to mechanical and thermal treatments are examined by means of dynamic mechanical measurements. It is established from previous studies that PET/PA blends are incompatible in the isotropic state, but form so-called microfibrillar-reinforced composites upon extrusion, drawing and suitable annealing. 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 components (220°C, for instance) the biphasic character of the composite is enhanced in as much as the microstructures of both the crystalline and amorphous phases are improved and the reorganization of species within separate phases is favoured. The components of the heterogeneous blend become compatible provided that the annealing is performed at a sufficiently high temperature (240°C). This temperature is intermediate between the melting temperature of the two components and allows for the isotropization of the low-melting component PA. The increase of compatibility is attributed to transreactions producing compatibilizing layers of PET/PA copolymers at phase boundaries between microfibrils and the amorphous matrix. Prolonged annealing (25 h) leads to the randomization of the original block copolymers and results in the complete participation of PA in the copolymer, which is evidenced by the disappearance of the glass transition peak of PA.