Evolution of the morphology and characterization of compatibilized PBT/EVA blends prepared by reactive extrusion

In this work, the possibility of preparing compatibilized blends of poly(butylene terephthalate) (PBT) and an ethylene vinyl acetate (EVA) copolymer by reactive extrusion in the presence of an ethylene acrylic acid copolymer (EAA) and a bisoxazoline compound (PBO) as compatibilization promoters has been studied. In addition, the evolution of the morphology of the blends under different annealing conditions in the presence and absence of the compatibilizing promoters has been studied. Binary blends of PBT and EVA showed behavior typical of incompatible blends with a gross morphology and bad mechanical performance. The situation was however different for ternary PBT/EVA/EAA and especially for quaternary PBT/EVA/EAA/PBO blends. In the latter case, the morphology was finer, the adhesion improved and the mechanical properties were enhanced, with values almost doubled with respect to those of uncompatibilized blends. These results can be explained by the formation of in situ EAA-g-(PBO)PBT copolymers which act as compatibilizers for the blends. While the binary and, to some extent, the ternary blend display coalescence under annealing with rapid coarsening of the morphology, the quaternary cornpatibilized blends showed the best morphological stability as the particle dimensions remained practically unchanged. This phenomenon was interpreted considering the role of kinetic hindrance played by the compatibilizer formed in situ.