Rheology and morphology of compatibilized polyamide 6 blends containing liquid crystalline copolyesters

The rheology, mechanical properties and microstructural development during capillary flow of maleic anhydride compatibilized polyamide 6 [PA6(MAP)] blends containing liquid crystalline polymers (LCPs) were studied by means of the capillary rheometer, tensile test and scanning electron microscopy (SEM). The LCPs used were Vectra A950, and a copolyester consisting of 60 mole percent p-hydroxybenzoic acid (PHB) and 40 mole percent poly(ethyleneterephthalate) (PET). The rheological measurements showed that the viscosity ratio between the Vectra A950 and [PA6(MAP)] matrix is much larger than unity. This implied that the LCP fibrillation is unlikely to occur in the [PA6(MAP)] blends containing Vectra A950 additions. However, SEM observations revealed that long and fine fibrils are formed extensively in the matrix of [PA6(MAP)] polyblends containing Vectra A950 content greater than or equal to 20 wt%. Consequently, the tensile strength of these polyblends appeared to increase with increasing LCP content, and deviated from the predictions of the rule of mixtures. On the other hand, the viscosity ratio between the 60/40 PHB/PET and [PA6(MAP)] matrix is smaller than unity, thus favouring the formation of LCP fibrils. But, the SEM examinations showed that the LCP phase dispersed into porous and foamy structure in the matrix owing to the decomposition of 60/40 PHB/PET polymer and PA6(MAP) during processing. In this case, the tensile strength of the [PA6(MAP)] polyblends containing 60/40 PHB/PET polymer appeared to decrease sharply with increasing LCP content. The correlation between the flow properties and LCP morphology was discussed. (C) 1997 Elsevier Science Ltd.