MORPHOLOGY OF TERNARY POLYMER BLENDS CONTAINING A LIQUID-CRYSTALLINE POLYMER

Morphology was studied in ternary polymer blends containing a polycarb onate (PC) matrix, a thermotropic HBA/HNA copolyester (LCP), and a pol y(ethyleneterephthalate) (PET) or a poly-epsilon-caprolactone (PCL) as the minor components. LCP is immiscible in the other three polymers, while PET and PC exhibit a partial mutual miscibility, and PC/PCL is a miscible blend in the studied composition range, as evidenced by T-g measurements. The melt rheology of the binary and ternary blends, stud ied using a capillary rheometer over a wide range of shear rates, show s unexpected dependency on the blend composition, which may partially stem from some degree of possible intermolecular reactions during melt blending, but is mainly due to morphological effects. The capillary e xtrudate morphology of the miscible blends (90PC/10PCL and 90PC/10PET) is that of a single-phase system. The morphology of the 85PC/15LCP an d 60PC/40PET blends consists of a dispersed fibrillar minor phase orie nted along the flow direction. However, no LCP fibrils, but rather par ticles, were observed in the [90/10]/15 [PC/PET or PCL]/LCP filaments. An intriguing morphology was observed in the [60/40]/15 [PC/PET]/LCP extrudates. As in the PC/LCP filaments, LCP particles, either spherica l, elongated, or fibrillar, depending on the filaments' preparation co nditions, were also observed in the ternary blends. However, they were engulfed by a PET-rich PET/PC layer. The preferred localization, engu lfing the LCP particles rather than separately dispersed, of the PET-r ich minor phase is expected by consideration of thermodynamic (interfa cial tensions and ''spreading coefficients'') and kinetic (viscosity r atios) parameters.